Krell phone stage - just in time - Page 1
Forum section: electronics / repair

author: cncjerry
author_rank: Unknown
timestamp: April 29, 2024, 05:31:44 pm
content: I've had this Krell KPE powered on for 28yrs continuously. I was cleaning around the phono and lifted the lid on the phono preamp stage and found this mess. I'm surprised it was still working! Also surprised the brown caps in the power supply stage are fine (will be replaced anyway) and these Spragues are all exploding and leaking.I ordered vishay beyschlag/draloric/bc caps from Digikey. I was just going to replace them with Spragues but you can't get the 30D types for a reasonable cost. People are trying to sell them for $20 per.Jerry

author: Bud
author_rank: Super Contributor
timestamp: April 29, 2024, 10:52:38 pm
content: What is KPE?

author: cncjerry
author_rank: Unknown
timestamp: April 30, 2024, 03:50:10 am
content: Krell reference phonograph pre-preamp. It is used with low-output moving coil phonograph cartridges. This one allows you to set the gain as well as the loading. I'm glad I had the top loose for access to the switches otherwise in the near future, I'd have a real mess.Jerry

author: wasedadoc
author_rank: Super Contributor
timestamp: April 30, 2024, 08:45:35 am
content: phononot phone.

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: April 30, 2024, 12:20:13 pm
content: Quote from: cncjerry on April 29, 2024, 05:31:44 pmHi Jerry,wow, 28 Years, you must be pleased with it (and loaded).What Transistors/OpAmps are used?Could you please post a picture of the whole unit?Ciao4now

author: coromonadalix
author_rank: Super Contributor
timestamp: April 30, 2024, 02:02:54 pm
content: yeah a good job of "recapping" all theses juicy capacitors ....

author: Haenk
author_rank: Super Contributor
timestamp: April 30, 2024, 02:12:42 pm
content: Quote from: cncjerry on April 29, 2024, 05:31:44 pmI'd say the leakage/corrosion is the worst thing happening there.From a technical point of view, I doubt all the caps are needed - that's a "show the buyer we used a lot of parts for this expensive HiFi device" thing. On the other hand, if they only used one electrolytic cap (which should be plenty enough), it likely would not work any more.Still nice to own, and certainly worth to be fixed.

author: cncjerry
author_rank: Unknown
timestamp: April 30, 2024, 06:32:52 pm
content: Couple things, blame auto spelling for phone vs phono and bad eyes. Also, This is not the "reference". I never knew the difference and thought the reference had the two cartridge types but it is the other way around. On the "standard" you can support both moving magnet and moving coil; on the reference, only moving coil and the power supply seems lighter. But then again, many of these have probably been recapped, as mine should have been, and maybe people skimped on the caps before taking internal pictures. I use a high output moving coil. So on the "reference" they took out the moving magnet stage, switching, etc and charged more. A case of less is more? Or audiophile foolery? I do use decent cables for the phone stage (MIT) as I had RFI from a local FM station - nothing to do with the sound of them. No "sweet sounding, pure copper, etc, etc., just no "American Top 40."I'm concerned about the other Krell equipment I have as the preamp is the same vintage. I need to open that up as well as see what is going on, if anything. That has not been powered on all that time.As far as the components, what I can see are J309 JFETs and MPS8099 NPN and MPS8599 PNP transistors. A bunch of them. No opamps.The KPE phone stage doesn't have balanced outputs and I always thought that was lame. The Krell preamp has balanced inputs. The preamp drives a DBX crossover (yes, weak link) and then into two amps; a Krell 160B for the lows and a Krell KSA-50S for the highs. Turntable is a TNT MKII with some upgrades. The cleaning people broke two needles over the years so I machined the white plastic cover of the cartridge. I was thinking of 3D printing something better lately. The amps are massive. The 160B runs class A bias all the time and heats up the room. The KSA-50S has a three step bias but between the two of them, no fireplace is needed.I also use a TASCAM mastering two-channel R2R with Dolby SR noise reduction. That setup has claimed very high dynamic range, supposedly 2db or so higher than 16bit LPCM . But tapes are flaking off now and getting harder to find any that dont. I changed the capstan belt in the deck recently, you can't even see it with the covers off, but I got it working, lots of Band-Aids from sharp metal.Parts should be here Friday, I'll open the preamp and post some pictures. Funny thing is, everything sounds great. Watch, when I put the new caps in, I'll get that "sweet Vishay cap sound"and have to wax lyrical as I listen to Black Sabbath and Led Zep and full volume.

author: themadhippy
author_rank: Super Contributor
timestamp: April 30, 2024, 06:48:58 pm
content: Quoteyou could always upgrade to a dolby lake

author: cncjerry
author_rank: Unknown
timestamp: May 01, 2024, 12:36:37 pm
content: The lake is digital. I keep that setup all analog, except for a crystal semi DAC that is on an input for background music. I remember looking around for a crossover, not finding anything, need to do it again. I used to just drive both speakers without it using a Y cable, letting the speaker crossovers, that are split, handle the frequency distribution. The DBX crossover has separate gains so I can boost the lows a little when listening at low levels. I should just get a passive crossover that has switchable caps or inductors, must be somethIng out there. B&W 801s had an external box for this, I use 802s and whomever made it never offered it for those, but maybe I could use the one Fabio used on his setup. He biamped his 801s. I almost bought the 801F setup not that long ago but you dont realize how big those speakers are until you mock them up in cardboard. My wife went nuts.

author: themadhippy
author_rank: Super Contributor
timestamp: May 01, 2024, 03:27:01 pm
content: QuoteFair enough wanting to keep the signal chain entirely anolougeQuotewhy not build something? its only a few filters,unless of course you want to start time alining individual outputs

author: floobydust
author_rank: Super Contributor
timestamp: May 01, 2024, 06:54:01 pm
content: OP, did you check the power supply voltages are good, that they are not over 25VDC? In case the regulator(s) have failed, I can see rework there.

author: cncjerry
author_rank: Unknown
timestamp: May 01, 2024, 09:50:14 pm
content: Quote from: themadhippy on May 01, 2024, 03:27:01 pmI was thinking about taking one of the DSP's I have, tweaking the crossover to match the speakers as I have the charts from when they were originally sold, and then once that sounds right, realize the DSP crossover in either passive or high-performance, low noise, opamps. Then I can take the DBX unit out. I thought about just taking the crossovers out of the speakers but the impedance is all wrong.