Can anyone explain the tech of £25,000 Audiophile Pre-Amp from Mend It Mark? - Page 1
Forum section: electronics / general

author: TimInCanada
author_rank: Regular Contributor
timestamp: December 13, 2024, 06:36:08 pm
content: I'll admit right off, I know squat about high-end audio, but did watch with curiosity the video by Mend It Mark, and perhaps more skilled people can help explain this thing.Backstory: Mend It Mark was given this pre-amp to fix and put a video on his Youtube channel. Tom Evans, the builder of the device, made a copyright claim and Youtube took down Mark's video. Of course, the video has now been reposted many times by others. Here's one copy:It's also at Archive.org athttps://archive.org/details/the-gbp-25-000-pre-amp-that-went-wrong-tom-evans-mastergroove-sr-mk-iii-rjbp-fsfzi-iTom Evans apparently wanted to charge the customer £6,000 to fix it, the customer said to send it to Mark, then Tom Evans told Mark he wouldn't be able to fix it. That worked about as well as you'd expect.The construction is awe-inspiring, as in "shock and awe":Mark reverse engineered it and made his own service manual. Each channel has this block diagram:Blocks 2,3,4,5 and 6 are dual rail power supplies. Blocks 7 and 8 are eight op-amps in parallel as a preamp and block 1 is a buffer amp for the line out. Power comes from a separate power supply:In the background is a HP 8566B or 8568B spectrum analyzer for scale. Mark initially thought this power supply contained a big transformer, but his reverse-engineered schematic (sorry, this was the best resolution I could grab) shows it's just a bridge rectifier and linear regulator:I'm thinking about the power budget. Just order of magnitude analysis. Starting at the output stage, there are two op-amps (with the part numbers sanded off) and two LM334 current sources with 10R setting resistors. From the TI datasheet, that looks like about 7 mA.(Interestingly, in this configuration the datasheet says "The LM134 makes an ideal remote temperature sensor because its current mode operation does not lose accuracy over long wire runs. Output current is directly proportional to absolute temperature in degrees Kelvin,")Let's say that IC2 in the output stage is a opa2134 dual audio op-amp and everything else is an op07, all with quiescent current (per amplifier) of 4 mA.In the output stage, line output on IC2a is of the order of 1.228 Vrms into 600R, so let's call that 2 mA out. Both IC2a and b have 7 mA current source loads, and let's say IC3 only draws quiescent current. That's 3 x 4 mA + 2 x 7 mA + 2 mA = 28 mA at +/-15 V.The preamp stage is 8 single op-amps with negligible load, so 32 mA. So we're up to 60 mA per rail to do the actual amplification.Mark isolated the Block 5 power supply board and powered it disconnected from the preamp board:That's 302 mA load on the negative rail and 211 mA on the positive. So let's call the quiescent load of each of the supply modules an average of 256 mA per rail.Now adding up by the blocks:Block 1, line amp, draw is 28 mA at +/- 15V => 0.84 WBlock 6, its supply, draw will be 28 + 256 = 284 mA at +/- 21.5V => 12.21 Wheat generation = 12.21 - 0.84 = 11.37 WBlocks 7,8, preamps, draw is 16 mA at +/- 15V => 0.48 W eachBlocks 4,5, their supplies, draw is 16 + 256 = 272 mA at +/- 21.5V => 11.70 W eachheat generation = 11.70 - 0.48 = 11.22 W eachBlock 2, feeds Block 6, draw will be 264 + 256 = 520 mA at +/- 28V => 29.12 Wheat generation = 29.12 - 12.21 = 16.91 WBlock 3, feeds Blocks 4,5, draw will be 2 x 272 + 256 = 800 mA at +/- 28V => 44.8 Wheat generation = 44.8 - 2 x 11.70 = 21.4 WThe +/- 28V external supply will deliver 520 + 800 = 1320 mA. Unfortunately I can't make out the values in the schematic, and there are three parallel resistive paths between the rails. Assume these create a negligible additional load. Someone check me on this, but for 1320 mA DC out, and this power supply being just a linear regulator, wouldn't that mean the mains load will be 1320 mA rms?Mains power will be 230 V x 1.32 A = 303.6 W, to provide about 1.8 W to the actual amplifiers.Heat generation would be 303.6 - 29.12 - 44.8 = 230 W. No wonder it's so massive even without a transformer -- that's a lot of heat to dissipate.Forgive me for being a little slow, but wouldn't a transformer isolate high frequency noise from the mains, then a low noise linear regulator bring the noise on the rails down to microvolts rms, which after the >100 db PSRR on the op-amps would make the effect of any power rail noise unmeasurable? All with a whole lot less heat thermocycling the actual audio components?I'll just throw out one more question: what's the deal with those pcb 'shields'? Some kind of capacitive coupling mechanism? Waste heat homogenizers? Solar flare reflectors? Antigravity dampeners?Maybe I'll sign off now....Tim

author: themadhippy
author_rank: Super Contributor
timestamp: December 13, 2024, 07:14:51 pm
content: Quotebut those 1.32A wont be at 230v,just because no transformer was shown it dosnt mean there isn't one

author: Gyro
author_rank: Super Contributor
timestamp: December 13, 2024, 07:31:48 pm
content: The power supply box (containing the transformer) is shown in the video. The supply to the pre-amp is already +/- DC rails. Mark indicates the pre and post repair voltages... something like +/-15V when working irrc.There's already a thread on this video take-down fiasco with several comments on the qualities (or lack of) of the secondary regulation scheme used...https://www.eevblog.com/forum/other-blog-specific/25-000-audiophile-pre-amp-repair-video-by-mend-it-mark/

author: magic
author_rank: Super Contributor
timestamp: December 13, 2024, 07:38:23 pm
content: It's a survival of the fittest thing.No one would drop £25k on a small box running on a few watts.You have to come up with something ludicrous to catch those rare big fish with deepest pockets.As for shielding, it doesn't seem to be doing jack shit besides demonstrating that it wasn't necessary in the first place, since the unit works and customers are happy. Effective shielding would need to enclose the whole circuitry and go all the way to the input jacks, that stuff here is just a gimmick like spoilers on a 1.2l car."Expensive end" audio is mostly cargo cult engineering.

author: daqq
author_rank: Super Contributor
timestamp: December 13, 2024, 09:01:20 pm
content: You know, it'll be quite hilarious when out of spite the Internet Residents completely reverse engineer, analyze and improve the design of a 25k$ Bullshit Containment Device.

author: TimInCanada
author_rank: Regular Contributor
timestamp: December 13, 2024, 10:28:32 pm
content: Quote from: themadhippy on December 13, 2024, 07:14:51 pmMark's schematics seem to be pretty thorough, and the one called External Power Supply shows a lot of components with values (unfortunately illegible in the video) and no transformer. As he created the service manual to expose Tom Evan's design, I'd expect any transformer would be shown.

author: themadhippy
author_rank: Super Contributor
timestamp: December 13, 2024, 11:08:19 pm
content: QuoteNo he didnt,he made the service manual to aid him in repairing the thing.You can see it use lm317/lm337 regulators ,if you shove more than around 37v up em they tend to get upset and stop working ,so what do you think there going to do with a few 100 volts chucked up em? and also look at the ground configuration ,without an isolating transformer all them grounds are going to be referenced to the mains, thats gonna give you a tingle every time you lift the tone arm.

author: tszaboo
author_rank: Super Contributor
timestamp: December 14, 2024, 12:58:00 am
content: Quote from: daqq on December 13, 2024, 09:01:20 pmWhen I saw that schematics, I seriously considered to make a better version with 4 opamp in parallel, and sell it at cost. Without Tantalum. Just to piss Tom off.OP: Those LM334s load the output of the opamp, and "put it into class A operation". At least that's the pseuodscience of it. Because opamps will have this built in already. But that's OK, you need to fill those PCBs with something.

author: Analog Kid
author_rank: Super Contributor
timestamp: December 14, 2024, 01:40:55 am
content: Quote from: tszaboo on December 14, 2024, 12:58:00 amDon't the output stages of all opamps operate in class B-ish (push-pull) mode?

author: langwadt
author_rank: Super Contributor
timestamp: December 14, 2024, 01:50:26 am
content: Quote from: tszaboo on December 14, 2024, 12:58:00 amdoes messing with parallel opamps offer any advantage over just using something like AD797, LT1115, AD8597 etc. ?

author: magic
author_rank: Super Contributor
timestamp: December 14, 2024, 10:19:07 am
content: Quote from: Analog Kid on December 14, 2024, 01:40:55 amOf course they do and you could likely see the difference on a THD analyzer, particularly at a sufficiently high gain.Plus it's also marketing: we run it class A, wow.Quote from: langwadt on December 14, 2024, 01:50:26 amParallel AD797 will still have advantage over one AD797, if source impedance is low enough.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 14, 2024, 11:09:13 am
content: With BJT based amplifiers, there is a limited advantage from parallel OP-amps unless there is no single 1 OP-amp with a similar noise.Already the AD797 / LT1115 need a really low impedance to get the lowest noise. There could still be some advantage when starting with super beta types as they can be better in the voltage noise times current noise metrics.There is a problem with the current noise specs in quite some data sheets - there are actually 2 parts for a correlated and non correlated part and single number can catch it all. Also some amplifier assume only one type and give too optimistic numbers this way. So one has to take the current noise numbers with a grain of salt.

author: Gyro
author_rank: Super Contributor
timestamp: December 14, 2024, 11:22:59 am
content: Quote from: TimInCanada on December 13, 2024, 10:28:32 pmThe still image of the PSU schematic is rather fuzzy and I can't see what it says above 'AC IN'. Mark clearly drew what heneededto draw - presumably the PCB components rather than the transformer and all the mains chassis wiring (yes you could regard it as an omission in afull'service manual'). The transformer is logically there because:1. The unit would not be electrically safe without one.2. The circuit would not work without one being present - remember this is UK/EU possibly a North American version too for a 120V outlet. Mains Neutral is tied to Earth in the supply infrastructure, either internal or external to the house. The circuit as shown will not be able produce symmetrical +/- output rails without being driven by a transformer with a center tapped secondary (AC IN, EARTH, AC IN). As shown in the video, it demonstrably does produce that symmetrical output.3. The component values shown, would not support direct mains voltage input without immediate catastrophic failure. This is rendered moot by the above two points. It would have been useful to include the transformer secondary voltage somewhere.QuoteYou're on the wrong track there. Mark did not create the service manual to"expose"Tom Evan's design (that would be uncharacteristically malicious), he did it so that he could understand and repair the unit, completely different.There is nothing inherently 'wrong' with the design - It uses grossly over duplicated basic linear regulator blocks (probably to the point that regulator noise contributes more supply rail noise than anything it is attenuating. Partly as a result of this over-duplication, it uses a vast number of Tantalum bead capacitors, which you could argue, affects reliability. You could also question the screening scheme for a sensitive low level input circuit.The circuit clearly functions, it is just, what I would describe a 'uninspired'. There is nothing innovative about it, no clever discrete input stages or cleverly optimized PSU filtering, just massive duplication. The idea of paralleling gain stages to statistically reduce output noise is many decades old (as is pushing opamp output stages into Class-A by loading them to a supply rail). Statistical noise reduction used in many places.This whole mess is nothing to do with "exposing" the design of the circuit as such. It is about Tom Evans's take-down of Mark's video for dubious and false 'violations' of his rights. Nothing more. Of course we can all discuss and pick holes in the design, construction etc, from our own perspective but Mark's intention, and achievement in the video is its successful repair.

author: magic
author_rank: Super Contributor
timestamp: December 14, 2024, 12:14:49 pm
content: Quote from: Kleinstein on December 14, 2024, 11:09:13 amAD797 has its lowest noise figure near 200Ω, LT1028 near 100Ω.Moving coil phono cartridges have output impedance from a few to tens of ohms.But it's quite possible that this product was designed to be more universal and probably uses FET opamps, or maybe indeed one of those few high GBW superbeta types which became available in the 21st century.Anyone with access to the hardware could quickly figure it out by desoldering the chips and running a few tests for input bias and noise.

author: iMo
author_rank: Super Contributor
timestamp: December 14, 2024, 12:21:15 pm
content: I saw the video couple of hours after Mark had published it and what came to my mind as the first thing was "..what Mr. Evans will do now.."Yep, there are sorts of customers who are ready to pay large money for goods and services because they think the more expensive the better. It is their lifestyle, you cannot change it. And where are those customers there are the clever sellers of goods and services, you cannot change it too..Mark's video is not about the technicalities, but about those customers, imho..

author: tszaboo
author_rank: Super Contributor
timestamp: December 14, 2024, 01:52:25 pm
content: Quote from: magic on December 14, 2024, 12:14:49 pmIt's probably a NE5532 or a Tl072 or some other 1980 opamp he uses.Just look at the regulators. The supposedly "ultra low noise" amplifier uses an LM317, not any of the improved versions of it.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: December 14, 2024, 02:09:09 pm
content: At that price level, I'd expect MIL spec components thoughout.

author: magic
author_rank: Super Contributor
timestamp: December 14, 2024, 02:13:54 pm
content: Quote from: tszaboo on December 14, 2024, 01:52:25 pmDoubt it. Bipolar only has good noise figure over maybe one decade of source resistance, and vintage JFET opamps are a complete joke. About the only things noisier than TL072 is LM358 and many CMOS opamps such as TI's "improved" TL072H.

author: Gyro
author_rank: Super Contributor
timestamp: December 14, 2024, 05:31:44 pm
content: Quote from: Messtechniker on December 14, 2024, 02:09:09 pmWhy? Unless you need operation over the full MIL temperature range, it's not going to buy you anything. Because of the way some parameters of analogue ICs are measured (the box method), MIL parts can actually exhibit more thermal drift over the normal ambient temperature range than commercial spec parts. This is normally more of an issue for things like precision references, but given the amount of time the manufacturer apparently spends matching Opamps...

author: TimInCanada
author_rank: Regular Contributor
timestamp: December 14, 2024, 06:02:59 pm
content: Quote from: themadhippy on December 13, 2024, 11:08:19 pmYeah, he said he needed a service manual, but doesn't it seem like rather a lot of work to trace every net on every board, including the external psu, draw it all up in CAD, include the values of every part that hadn't had its markings sanded off, even make board layout diagrams (at 11:43), all after he identified the external psu was operating correctly and the problem was a voltage rail on one channel was being pulled low? I mean, dozens of dipped tantalum capacitors. Perhaps the customer wanted to pay all that labour to get the service manual?On the other hand, Tom Evans did tell Mark he'd never be able to fix it.QuoteI agree no transformer would be suboptimal, but given the load being essentially constant, the series resistors after the rectifier could be sized to drop enough voltage. However, at about 9:20, Mark measures the output of the unloaded psu, so I concede there must be a transformer. Gyro also makes a great point that UK 230V power has one neutral conductor referenced to earth, so the DC ground would end up at 28V to earth. (Here in North America, 230V is two lines at 115V to earth.)I also made a mistake on my estimate of the preamp drawing 1320 mA at +/- 28V. That's for each channel, not both. Which points to about 150W going into the unit.

author: fzabkar
author_rank: Super Contributor
timestamp: December 14, 2024, 07:37:31 pm
content: Who are these audiophools who can stump up $25K for a box of BS? Most young people are flat out paying off their mortgage. In any case, how much fidelity does one need for a music source that goes "doof doof"? By the time a person acquires enough spare wealth to splurge on audiophoolery, presbycusis has already taken its toll on their hearing.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 14, 2024, 08:13:01 pm
content: This seems to be an amplifier mainly for a turn table. So no matter how good the amplifier one is still limited by the old style media.Chances are this is mainly a thing for older guys having earned big money and getting nostalgic with a collection of old LPs. It is not really about actual performance, more about a good feeling.

author: fzabkar
author_rank: Super Contributor
timestamp: December 14, 2024, 08:29:11 pm
content: Nostalgia makes sense, but in order for it to be authentic, you would need to dig out the old "hi-fi" equipment from that era. As for me, when I look at a turntable, I see Flintstones technology. The idea of a needle riding up and down, and side to side, in a plastic groove, producing predistorted sound that needs to be subsequently massaged by an RIAA equalised preamp, is just absurd.

author: armandine2
author_rank: Frequent Contributor
timestamp: December 14, 2024, 08:39:12 pm
content: Quote from: fzabkar on December 14, 2024, 08:29:11 pm.. absurd yes but some see analog technology more sympathetically

author: magic
author_rank: Super Contributor
timestamp: December 14, 2024, 09:10:54 pm
content: Quote from: fzabkar on December 14, 2024, 08:29:11 pm

author: Analog Kid
author_rank: Super Contributor
timestamp: December 14, 2024, 09:25:40 pm
content: Quote from: armandine2 on December 14, 2024, 08:39:12 pmAs do I.No, I'm not an audiophool; no oxygen-free gold-plated cables here, none of that voodoo.I do love vinyl and its technology, and the resulting sound.No, I'm not making any claims as to its quality relative to, say, CD (44.1 KHz). But I do loves the sound.I have some LPs that are absolutely pristine: not a click or pop to be heard, just luscious sound.And no, I'm not talking about what someone here brilliantly described as "doof doof" sounds; these are orchestral recordings.Thorens turntable and Signet cartridge here, otherwise nothing exceptional in the chain (including some decidedly cheap but effective speakers).I still think the stylus riding in a groove is an amazing technology.Just to clear one thing up: it's not riding up and down and side to side, really: the two channels are cut at 90° to each other diagonally. The "hill-and-dale" method was tried early in the 20th century but never really used.Also, the idea that RIAA equalization is there to get rid of "predistortion" is just wrong: it's simply a frequency-dependent attenuation network necessary to accommodate the physical requirements of the master-cutting process (limiting groove excursion). A decent RIAA network introduces no noticeable distortion to the signal.A friend of mine has a vinyl store here in town, and he's doing a booming business. Mostly 60s-80s rock/punk, etc., but other stuff too. People are just eating it up.

author: coppercone2
author_rank: Super Contributor
timestamp: December 14, 2024, 09:28:22 pm
content: equally absurd is DSP mathematics and GHz processors running crap meant to find submarines to play a sound made by a piece of woodAll those modern techniques are made with the goal of identifying (targeting) something accurately, not replicating it. Its like writing down the name of something, not showing you something. I think thats why people are still interested. The biggest drivers for the technology development are like voice controlled machinery and record keeping of discourse. It's like exceedingly rupe goldberg if you think about digital audio processing.

author: Analog Kid
author_rank: Super Contributor
timestamp: December 14, 2024, 09:35:48 pm
content: Quote from: coppercone2 on December 14, 2024, 09:28:22 pmWait, wut?

author: fzabkar
author_rank: Super Contributor
timestamp: December 14, 2024, 09:53:44 pm
content: The Model T Ford was brilliant technology for its time, but you don't see a legion of motophools proclaiming that it produces a ride that is superior to the vehicles of today.

author: Analog Kid
author_rank: Super Contributor
timestamp: December 14, 2024, 09:57:28 pm
content: To me, that's missing the point.Not superior, necessarily, but worth preserving.Like steam locomotives.Typewriters.Old Z80 computers.Old "heavy iron" computers.Old non-electronic computers.I'm sure you can think of a dozen more things.

author: Gyro
author_rank: Super Contributor
timestamp: December 14, 2024, 10:03:20 pm
content: Quote from: fzabkar on December 14, 2024, 09:53:44 pmWeren't Model T Fords renowned for being able to handle heavily rutted tracks? They might have been better at handling conditions that modern cars would really struggle with. Just saying.Edit: One was driven to the top of Ben Nevis in Scotland in 1911...https://www.history.com/topics/inventions/model-t

author: fzabkar
author_rank: Super Contributor
timestamp: December 14, 2024, 10:07:02 pm
content: Quote from: Analog Kid on December 14, 2024, 09:25:40 pmTo my mind, anything that alters the original recording, for whatever reason, "distorts" the sound. The sound that is reproduced at the output of the preamp is necessarily an imperfect copy of the original. Digital's detractors point to the A-to-D and D-to-A conversions as a limitation of digital audio, but I see the two stages of RIAA manipulation as even less desirable. And I'm not even considering wow, flutter, pop, crackle and hiss. Similarly, the rivalry between valve and solid state amps can be boiled down to one group preferring the "warm" distortion produced by a valve amp to the distortion produced by a solid state amp. The idea that one form of distortion sounds better than another misses the whole point of high fidelity.

author: Analog Kid
author_rank: Super Contributor
timestamp: December 14, 2024, 10:10:08 pm
content: Quote from: fzabkar on December 14, 2024, 10:07:02 pmBut isn't that the quintessential audiophool argument? The reason we should all be using capacitor-less Class A amps?Not accusing you of being one, just sayin'.

author: themadhippy
author_rank: Super Contributor
timestamp: December 14, 2024, 10:20:12 pm
content: Quoteyou mean the sound thats been altered multiple times from the moment its left the noise maker to landing on whatever media your storing the master recording

author: fzabkar
author_rank: Super Contributor
timestamp: December 14, 2024, 10:20:39 pm
content: Quote from: Analog Kid on December 14, 2024, 10:10:08 pmI admit that as a young guy, I was a spec hunter. However, nowadays I like to think of myself as a realist. I hate snap, crackle and pop, except on my cereal. I can't hear any of the claimed imperfections in digital audio, and I believe that 99% of the population can't either. For me, the choice is easy.

author: Analog Kid
author_rank: Super Contributor
timestamp: December 14, 2024, 10:51:18 pm
content: Quote from: fzabkar on December 14, 2024, 10:20:39 pmI have many LPs that are as quiet as any CD. Good record care, dontcha know. Not hard to do.Of course, I also have discs bought at secondhand stores, yard sales, etc., that are pretty noisy.When I listen to those I think of it as sitting around an audio campfire.

author: tszaboo
author_rank: Super Contributor
timestamp: December 14, 2024, 11:07:00 pm
content: Quote from: magic on December 14, 2024, 02:13:54 pmYou assume that it would measure good. That's not how this works.It's mostly voodoo, and pseudoscience. It's expensive, because knowing it's expensive makes it sound better. Distortions, and wave-y bode plot makes it "open up the midrange" and all kinds of other colorful description. If you make something that's flat, and measures good, that's actually bad.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 14, 2024, 11:11:53 pm
content: Errors in the RIAA network can cause changes to the frequency response and may introduce phase shifts. To a large part the ear can not really detect phase shifts and is not very sensitive to small amplitude changes. Usually the speakers are the way larger cause for a non ideal frequency response.

author: coppice
author_rank: Super Contributor
timestamp: December 14, 2024, 11:14:14 pm
content: Quote from: Kleinstein on December 14, 2024, 11:11:53 pmThe ear cannot detect phase shifts above about 2-3kHz. Most audio compression algorithms get a lot from that fact.

author: fzabkar
author_rank: Super Contributor
timestamp: December 14, 2024, 11:15:11 pm
content: Rather than testing direct coupled amplifier stages (is that what is meant by "capacitor-less"?), I'd like to see someone put an audiophile to the test by replacing signal cables with a length of wet string. :-)

author: tszaboo
author_rank: Super Contributor
timestamp: December 14, 2024, 11:21:45 pm
content: Quote from: fzabkar on December 14, 2024, 11:15:11 pmLook up: Coat hanger ABX tests.

author: fzabkar
author_rank: Super Contributor
timestamp: December 14, 2024, 11:30:00 pm
content: Quote from: tszaboo on December 14, 2024, 11:21:45 pmhttps://consumerist.com/2008/03/03/do-coat-hangers-sound-as-good-monster-cables/Quote

author: fzabkar
author_rank: Super Contributor
timestamp: December 14, 2024, 11:37:57 pm
content: Quote from: Analog Kid on December 14, 2024, 10:51:18 pmHere's a challenge. Make a high quality digital recording of a noisy LP source and then play it back through a cheap MP3 player. Will you be able to tell the difference? You won't be influenced by the obvious analogue imperfections because they will be present in both cases.

author: tom66
author_rank: Super Contributor
timestamp: December 14, 2024, 11:42:58 pm
content: I don't really get this obsession with very low THD+N which is common in audiophile circles. I kind of understand you don't want clipping because that does sound pretty bad, but I'd be shocked if an average person could tell the difference between 0.1% THD+N and 1% THD+N if it wasn't indicated in advance.

author: coppice
author_rank: Super Contributor
timestamp: December 14, 2024, 11:43:47 pm
content: Quote from: Analog Kid on December 14, 2024, 10:51:18 pmRecord care is important, but most LPs came from the factory with plenty of snap crackle and pop. If you took them back to complain you got another copy the same.

author: wilfred
author_rank: Super Contributor
timestamp: December 14, 2024, 11:43:57 pm
content: Quote from: Analog Kid on December 14, 2024, 10:51:18 pmNot to want to be overly critical of you personally but I found it interesting that you said the noisy discs were bought at secondhand stores and yard-sales. If you bought discs also lovingly cared for as you presumably care for yours there should be no reason they aren't as good as yours. Being secondhand isn't of itself necessarily the reason they were noisy. I buy DVDs from time to time at the local Salvation Army thrift store and they are generally fingerprinted and scratched but some are as clean as mine are.The point I make is you choose to associate them being secondhand and cheap with various degrees of past care and because they are noisy to boot it is likely that is the cause in your mind. Everyone does this at some time, whether they realise it or admit it to themselves.Whether it is test equipment, Audio gear, cameras, cars, fishing gear, golf clubs, tools or any of a hundred other things, unless you deliberately choose the cheapest technically suitable we're all likely to conflate a greater sense of self with more widely better regarded name brand stuff. The bigger your wallet the more expensive is the stuff you buy. Absolutely everybody is capable of seeking status and esteem through their stuff and I'm ok with it even though I must be more satisfied with getting something for much less than most would be willing to pay.With the pre-amp on Mend It Mark you just have to listen to the website blurb Louis Rossmann read out in his video to realise buyers are as interested in getting the exclusivity of something that is produced in small numbers of 10 per year as they are in the hand selected precision matched chips etc.

author: coppice
author_rank: Super Contributor
timestamp: December 14, 2024, 11:45:06 pm
content: Quote from: tom66 on December 14, 2024, 11:42:58 pmActually most audiophiles LOVE distortion. They crave tube amps because they feel they distort the sound in ways that sound better than the original.

author: tom66
author_rank: Super Contributor
timestamp: December 14, 2024, 11:48:11 pm
content: Quote from: coppice on December 14, 2024, 11:45:06 pmDepends on the audiophile. The tube nuts, sure, they love that third harmonic distortion that tubes typically introduce. I'm sure that can be created by DSP but I can kinda understand why they want the real deal, and it is actually *there*, so if they like it then fair do's.On the other hand, many audiophiles seem to like to have the lowest distortion in their system. These are the, err... fools (there's really no other word is there?) who buy stands for their cables because they are convinced that they can resonate excessively with the ground and that can impact sound quality. Or the fools who get special filtering power cables for that all-important last two metres of the power distribution to their amplifier, ignoring the power grid on the other side of that cable. Or the fools who spend extra on high performance LAN cables to lower jitter when playing audio files off a NAS drive.

author: Analog Kid
author_rank: Super Contributor
timestamp: December 14, 2024, 11:54:25 pm
content: Quote from: fzabkar on December 14, 2024, 11:37:57 pmProbly wouldn't be fair in my case: I'm 72 years old. My hearing is still pretty good (at least it seems so to me), but certainly not what it was 30 years ago.

author: magic
author_rank: Super Contributor
timestamp: December 14, 2024, 11:58:56 pm
content: Quote from: tszaboo on December 14, 2024, 11:07:00 pmHiss "doesn't open up the midrange".Go attenuate any audio signal to a few mV RMS or less and try to restore it with jellybean chips.You could maybe do it with NE5534, or probably a few in parallel, if source impedance permits it.Today some JFET opamps almost match voltage noise of NE5534 with much less current noise.(BTW, I specifically mention the 5534 because it has less noise and more GBW than the 5532.)

author: tszaboo
author_rank: Super Contributor
timestamp: December 15, 2024, 12:00:35 am
content: Quote from: tom66 on December 14, 2024, 11:48:11 pmSecond harmonic. Tubes are quadratic.Transistors are exponential, that make 3rd order distortion. Just write out the Taylor series.There is some science, that most instruments will also make much more 2nd harmonic frequencies.

author: Analog Kid
author_rank: Super Contributor
timestamp: December 15, 2024, 12:01:58 am
content: Quote from: wilfred on December 14, 2024, 11:43:57 pmSame here; records at secondhand stores (around here, Goodwill and some local charity stores) vary all over the place, and some of my pristine albums have been bought there, protected by the original inner sleeve with vinyl liner. Others are scratched to hell. Why would I even want to own such records? Because of the content, which I wouldn't otherwise have.QuoteNo; I realize that records are taken care of (or not) in all kinds of ways.BTW, something someone said up-thread just isn't true, that even new records are going to be full of clicks and pops.It's true that even high-quality discs can have some dirt on them when new; probably inevitable for anything that's the result of a manufacturing process. Which is why it's essential to have a good record-cleaning device.I use a carbon-fiber brush which works very well.For dirty, filthy records, I wash them carefully with dish detergent or Simple Green and a soft brush, spin them dry with an electric drill, then use the carbon fiber brush before playing.

author: pardo-bsso
author_rank: Frequent Contributor
timestamp: December 16, 2024, 08:32:12 pm
content: Quote from: fzabkar on December 14, 2024, 09:53:44 pmOf course not.We all phools know that the best rides of the 20th Century come from the Citroën DS & CX and the Peugeot 504 (403 and 404 too).In any order.(joke)

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 16, 2024, 10:10:07 pm
content: Nope, the Citroen SM.

author: Analog Kid
author_rank: Super Contributor
timestamp: December 16, 2024, 10:20:56 pm
content: Nah, gotta be the Sunbeam Alpine.Or the Minx. (I actually owned one of those once. Cutest car in the world. Wish I still had it.)Rootes Group foreva!

author: langwadt
author_rank: Super Contributor
timestamp: December 16, 2024, 10:23:11 pm
content: https://en.wikipedia.org/wiki/Rosy_retrospection

author: Analog Kid
author_rank: Super Contributor
timestamp: December 16, 2024, 10:31:37 pm
content: Quote from: langwadt on December 16, 2024, 10:23:11 pmHey man, don't harsh our buzz!

author: Zero999
author_rank: Super Contributor
timestamp: December 16, 2024, 11:03:19 pm
content: Mark talks about how it's important to have a low offset op-amp, but why not just AC couple it, so it's not a problem?

author: magic
author_rank: Super Contributor
timestamp: December 16, 2024, 11:04:45 pm
content: It's not a problem until you realize that it requires capacitors, then it's a problem

author: Zero999
author_rank: Super Contributor
timestamp: December 16, 2024, 11:16:36 pm
content: Quote from: magic on December 16, 2024, 11:04:45 pmWhy is it a problem? It isn't as though the extra cost is an issue.

author: temperance
author_rank: Super Contributor
timestamp: December 16, 2024, 11:24:47 pm
content: Quote from: Zero999 on December 16, 2024, 11:03:19 pmA few things being stated about the offset are not correct. The amplifiers are tied together with 100 resistors. The offset will only cause some power loss in the 100 R resistors. No big deal, or 10 mW with 1 V offset. Also, in his explanation about the noise reduction he states the signal doubles while the noise is reduced. That's also not correct. He also states that the offset has an impact on the signal being amplified by comparing the offset with the signal level being amplified.

author: Analog Kid
author_rank: Super Contributor
timestamp: December 16, 2024, 11:50:41 pm
content: Quote from: Zero999 on December 16, 2024, 11:16:36 pmBecause don't you know that capacitors--at least coupling caps--are the work of the Devil himself? That they are the worst offenders of all the distortion-producing, soundstage-corrupting components?

author: temperance
author_rank: Super Contributor
timestamp: December 17, 2024, 12:10:27 am
content: Quote from: Analog Kid on December 16, 2024, 11:50:41 pmSome real measurements:https://linearaudio.net/cyril-batemans-capacitor-sound-articles

author: fzabkar
author_rank: Super Contributor
timestamp: December 17, 2024, 12:54:05 am
content: Quote from: temperance on December 16, 2024, 11:24:47 pmHe states that the combined noise outputs of two parallel op amps "cancel each other out" somewhat. I think this is a loose explanation because two random sources can't "cancel" each other. As I see it, if these two amps have a gain of 100, and if each has a noise level of 1mV, then the noise voltage at the summing junction would be 141mV. That's because the noise power doubles, but the voltage only increases by sqrt(2). Moreover, since the noise power is what we hear, how can this gizmo provide any measurable or detectable benefit?

author: themadhippy
author_rank: Super Contributor
timestamp: December 17, 2024, 01:30:53 am
content: Quotethe noise would be double the input signal

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 17, 2024, 04:02:30 am
content: If the noises of the two channels are uncorrelated then the noise of a parallel combination (assuming the method of paralleling doesn't add significant) noise will be the square root of the sums of the square of each amplifiers noise. Or if the noise levels are the same, which would normally be the case the noise is 1.414 times a single units noise.The condition of the noises being uncorrelated is probably a good approximation in this case. But care should be taken when generalizing. For example if both amplifiers were powered by the same noisy power supply, and the PSRR was poor enough that supply noise was a significant part of the output noise you wouldn't see as much reduction from paralleling.Saying the noises partially cancel each other (especially with the qualifier that Mark gives that this is a rough simplification) is not terribly wrong.

author: fzabkar
author_rank: Super Contributor
timestamp: December 17, 2024, 05:23:41 am
content: Quote from: CatalinaWOW on December 17, 2024, 04:02:30 amI forgot that the signal power would be quadrupled. This more than offsets the doubling of the noise power. <brain fart>

author: hwasti
author_rank: Contributor
timestamp: December 17, 2024, 09:15:25 am
content: Quote from: fzabkar on December 17, 2024, 12:54:05 amBecause you don't understand the science behind it.When you spend all your money on this gizmo, you do not have enough money to eat, so your calorie intake decreased, which causes your brain function to decline, which leads to your brain not being able to process the noise which has actually increased, so you think there is an improvement.See, this all scientifically based, and the outrageous price is the real reason it works!!!!!

author: Zero999
author_rank: Super Contributor
timestamp: December 17, 2024, 09:57:40 am
content: Quote from: Analog Kid on December 16, 2024, 11:50:41 pmI can't tell whether this is sarcasm.Assuming you're being serious. It already has capacitors in the filters and for £25k, there's no reason no to use polypropylene or C0G capacitors. It's much easier than wasting time finding op-amps with the lowest offset or trimming.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 17, 2024, 10:17:54 am
content: Coupling capacitors are not that bad. They may cause some phase shift at the very low frequency end (and most of it below the audio band). This may change the signal, but there is usually no real information in the phase relation - it corresponds to a distance from the audia source. For the capacitors PP is closer to an ideal capacitor than lets say PEN / PET type capacitors with a little more loss. Still the difference is only in the phase angle and thus minor phase and amplitude changes at the low end. So the least relevant change to the signal. Electrolytic capacitors may be a slight issue as couling capacitors, but even there if the capacitors are large enough the main effects would be well below the audio frequencies. If you don't see them one could probably not hear the difference even with X7R or similar if used in the right way.With modern OP-amps it is not that difficult to also get low offset parts. The cheap parts tend to have a bit more offset though.The circuit part shown in the schematics near the start of the tread looks odd - either in error in reverse engeniering or a rather odd circuit that looks complicated but does not achieve much for actual performance. The more standard 2 OP-amp compound amplifier should work better.

author: magic
author_rank: Super Contributor
timestamp: December 17, 2024, 10:24:36 am
content: Quote from: Zero999 on December 17, 2024, 09:57:40 amFor £25k one would expect something better than unnecessary coupling capacitors.Wasn't it you who just argued that price should be adequate to quality?

author: Someone
author_rank: Super Contributor
timestamp: December 17, 2024, 10:37:32 am
content: Quote from: Zero999 on December 17, 2024, 09:57:40 amTrouble is a bunch of Audio paths use relatively low impedances to get noise down, so x00 ohms or 2k ohm with a corner frequency of less than 20Hz and the golden material capacitances end up more expensive than low offset (or hand trimmed) opamps.

author: Zero999
author_rank: Super Contributor
timestamp: December 17, 2024, 10:47:00 am
content: Quote from: Someone on December 17, 2024, 10:37:32 amWhere? I thought the first stage which has the most gain, is a load of non-inverting amplifiers which have a very high impedance. The summing amplifier can be DC coupled because it doesn't have much gain. Then all you need is a some big polypropylene capacitors on the outtput and you're done.

author: tszaboo
author_rank: Super Contributor
timestamp: December 17, 2024, 11:07:42 am
content: Quote from: Zero999 on December 16, 2024, 11:16:36 pmWhen you have a gain that's 1000x than a few mv offset can drive the output to the rail. Even if it doesn't your offset can change with temperature, time, humidity. Overall, it can even produce audible noise.Also, Elko can be noisy, at least I measured them to have more noise than not having them.

author: tom66
author_rank: Super Contributor
timestamp: December 17, 2024, 11:09:03 am
content: Quote from: fzabkar on December 17, 2024, 12:54:05 amI think the advantage here is that you can have four opamps at a gain of 25 summed together using resistors, so the noise gain (at the differential stage in the opamp) is lower.

author: Zero999
author_rank: Super Contributor
timestamp: December 17, 2024, 11:11:28 am
content: Quote from: tszaboo on December 17, 2024, 11:07:42 amAC coupling eliminates that, because the gain at DC is one.QuoteThen use polypropylene or C0G.EDIT:I had another look through the video. I can now see why the offset voltage needs to be low. I missed the fact the resistor values used in the non-inverting amplifiers are very low, just 1k33 and 2R2, which is presumably to keep the noise as low as possible, so 4700µF capacitors would have to be used to get a lower cut-off of 16Hz.https://youtu.be/uJ35ufUh2Tw?t=711

author: tszaboo
author_rank: Super Contributor
timestamp: December 17, 2024, 11:23:49 am
content: Quote from: Zero999 on December 17, 2024, 11:11:28 amUnless you have capacitors in the feedback of the opamp, turning it into a BPF with gain, the DC offset will have the same sort of gain as the AC signal. But this is not working with for example Sallen-key topology maybe with Multiple path filters. IDK, I usually don't use those as the gain is hard to adjust.And the topology used here definitely has the same offset gain as signal gain.

author: Stringwinder
author_rank: Contributor
timestamp: December 17, 2024, 12:00:13 pm
content: On old vinyl dynamic range was limited but no dramatic changes (improvements !?) was made to the music.Early digital media (CD's) kept the dynamics but got rid of the vinyl noise.Nowadays despite 24 bit/192 kHz lots of music is processed to death in mastering.Dynamic range is completly gone in some genres, illustration shows an example.Six decibels less dynamic range is A LOT if you are used to the full range."Remastered" is a foul swear word if you like the dynamics of live music.A useful tool to see what is left of the music after smothering (also called "mastering").https://www.lts.a.se/ljudteknik/masvis/So now in the digital era all music sounds so much better?(... or is it "Music in - Garbage out"?)

author: Zero999
author_rank: Super Contributor
timestamp: December 17, 2024, 12:10:04 pm
content: Quote from: tszaboo on December 17, 2024, 11:23:49 amRefer to my edit.Another way round this is to use a couple of op-amps as a capacitance multiplier.https://en.wikipedia.org/wiki/Capacitance_multiplier

author: themadhippy
author_rank: Super Contributor
timestamp: December 17, 2024, 12:11:27 pm
content: QuoteHallelujah brother .compress the crap out of everything, no one will care/notice.call it a remastered super enhanced version and even though they've already bought it on vinyl and cd we can flog it to them a third time.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 18, 2024, 01:28:06 am
content: Quote from: Stringwinder on December 17, 2024, 12:00:13 pmYes. This is all for market reasons. A large fraction of the listeners listen to music on small gear that requires heavy compression for music to be audible.So they do compress. A lot. And then, they add some. Like for processed food in which they add a lot of sugar and artificial sweeteners to make it taste "pleasing" when it actually just ruins food, but we still like it.

author: BrianHG
author_rank: Super Contributor
timestamp: December 18, 2024, 03:52:50 am
content: Quote from: SiliconWizard on December 18, 2024, 01:28:06 amThe problem is you just cant return an opened purchased CD if you find out the recording/mastering quality is crap. It almost makes it worth it to pirate the source in advance, then make sure it is good, then make sure the CD you buy is a matching pressing of the pirated version you have.I have a collection of my favorite music which were first generation CD recordings from before the mid 90's, before the loudness wars came into full bloom. By every measure, my versions of my old favorite prog. rock and classical albums roast all the remastered garbage which came after. In fact, way back on a private music community forum, when comparisons were done, I easily demonstrated those who purchased newly re-mastered versions of their music that all the new CD had were a +10db volume gain applied to them with a peak limiter. Digitally lowering the volume of the new CD by 10db basically made the new CD almost sound like the old one, but worse while since some audio equipment was still hiss filled in those days at higher volumes, I instructed those to rip their old CD and add a simple +6db gain to the album and burn a new CD. And wouldn't you know it, they were pissed beyond belief that they threw out +30$ for those remastered version which where revealed to be complete bullshit lower quality garbage.

author: SteveThackery
author_rank: Super Contributor
timestamp: December 18, 2024, 05:44:53 pm
content: Quote from: BrianHG on December 18, 2024, 03:52:50 amI don't get this. Digitally lowering the volume won't undo the damage done by that peak limiter.

author: coppice
author_rank: Super Contributor
timestamp: December 18, 2024, 05:47:40 pm
content: Quote from: BrianHG on December 18, 2024, 03:52:50 amWas that written as a joke? On the internet its often not clear.

author: BrianHG
author_rank: Super Contributor
timestamp: December 18, 2024, 06:27:13 pm
content: Quote from: SteveThackery on December 18, 2024, 05:44:53 pmNo it does not, but, it made my point to the one saying that their new +30$ version of their CD was bullshit when they lowered the volume and the sound between the original and new one with a matched volume could be compared side by side as being absurdly close except for when the limiter kept kicking in during the vocals mixed with bass drum. (Also, the waveform on the audio editor looked like some sort of puking blob compared to the original) The guy then realized that his audio equipment amp had an audio quality issue when turning up the volume knob for the original CD to match the new one's volume. Not that having a louder CD was actually better quality.

author: BrianHG
author_rank: Super Contributor
timestamp: December 18, 2024, 06:31:15 pm
content: Quote from: coppice on December 18, 2024, 05:47:40 pmWhat are you getting at?It is not a joke.This really happened back in ~2004.Such groups dealt exclusively with tracking CD revisions through perfect bit error free ripping tools, cheksum databases and almost exclusively using .flac file format released a few years earlier.Maybe read my response here:https://www.eevblog.com/forum/chat/can-anyone-explain-the-tech-of-25-000-audiophile-pre-amp-from-mend-it-mark/msg5752279/#msg5752279

author: Stringwinder
author_rank: Contributor
timestamp: December 18, 2024, 07:09:18 pm
content: If the volume control in an amplifier uses a "loudness" function to compensatefor the Fletcher Munson curves (equal loudness) there is a difference in thesound you hear. Low input signal level (higher volume setting) gives less bassand treble compared to higher signal level (and a lower volume control setting).Having the same level from all sources makes it easier to do other "audio tunings"to get a consistent result (according to your own taste)...so I sort of agree with BrianHG on this.

author: coppice
author_rank: Super Contributor
timestamp: December 18, 2024, 07:16:21 pm
content: Quote from: BrianHG on December 18, 2024, 06:31:15 pmThey recompressed a huge amount of music in the 1990s, cranked up the volume, and used soft clipping algorithms to minimise the effect of the overloads. You can turn down the volume control, but you can't get the dynamic range back, and the distortion from all the clipping is still there. Lately they've been going back to the old material, running it through Melodyne, and taking away all the pitch imperfections. They just can't stop taking the music we loved, and turning it into something fresh and new and bogus and unpleasant.

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: December 18, 2024, 07:31:57 pm
content: Quote from: Stringwinder on December 18, 2024, 07:09:18 pmIt works only if the loudness response of the loudspeaker is linear within all the frequency range (in the room at the listening position)... this is perhaps why it have disappeared

author: langwadt
author_rank: Super Contributor
timestamp: December 18, 2024, 07:41:23 pm
content: Quote from: coppice on December 18, 2024, 07:16:21 pma lot of music not only is pitch corrected and drums are aligned to a grid and sometimes replaced by samples

author: coppice
author_rank: Super Contributor
timestamp: December 18, 2024, 07:56:35 pm
content: Quote from: langwadt on December 18, 2024, 07:41:23 pmThe Wings of Pegasus channel on YouTube is making more and more videos bringing the extent of this to light. There doesn't seem to be anything they won't change. Even correcting singers famous for being naturally precise hitting the right pitch.That said, I don't know any DSP engineer who has not been deeply impressed by what Melodyne can achieve. Whoever is behind that is brilliant.

author: langwadt
author_rank: Super Contributor
timestamp: December 18, 2024, 11:16:37 pm
content: Quote from: coppice on December 18, 2024, 07:56:35 pmhttps://youtu.be/1bZ0OSEViyo?si=gzLwmwj2MlYDZkrZ

author: tszaboo
author_rank: Super Contributor
timestamp: December 18, 2024, 11:28:25 pm
content: Quote from: themadhippy on December 18, 2024, 07:48:22 pmYou mean the ones that were actually recorded, and not put together in someone's basement in the first place.Which I'm saying a bit tongue in a cheek. I started liking Electro-swing and Synthwave, most of that were never recorded, or some is only using ~100 year old music samples, and electronic stuff.

author: BrianHG
author_rank: Super Contributor
timestamp: December 19, 2024, 12:48:04 am
content: Quote from: tszaboo on December 18, 2024, 11:28:25 pmThe perfect example of progress in reverse.For the last 2, you might as well go right down to 8bit sound.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 19, 2024, 12:57:58 am
content: I was never much of an audiophile, and older ears have left hearing less and less. But this is way below even my standards. Fortunately I have older CDs and vinyl, all transcribed to mp3 for convenience. And I have the chance to clean up the pips and snaps while I am at it

author: wilfred
author_rank: Super Contributor
timestamp: December 19, 2024, 11:05:37 am
content: Will Mend it Mark ever have the video restored to his channel? It doesn't seem fair for him to be denied the full benefit of his creative work. All these other channels re-uploading the video may help him gain audience. I hope it does. I like his channel.I got the impression YT never actually told him what the copyright issue was.

author: Stringwinder
author_rank: Contributor
timestamp: December 19, 2024, 03:43:28 pm
content: After finding what "Audio Science Review" had to say about his design andcopyright claims (in over 200 posts) it is rumoured that production willbe moved to Llareggub, famous from Dylan Thomas drama "Under Milkwood".