Old School!!! - DIY Tube amp - Page 1
Forum section: electronics / projects

author: MTron
author_rank: Regular Contributor
timestamp: June 11, 2010, 01:48:29 pm
content: I have been into HiFi audio for a while, and i have toyed around with modding/assembling amps and the like....but i always wanted to built a tube amp....so i did!The amp is all finished, and it works awesome!Details - its a self inverting Push-Pull Class A amplifier, using EL84 power tubes and 5751 driver tubesThe output transformers are Hammond 125D's 9600 ohm input impedance, 6ohm output impedanceThe power transformers - the filament heater is 12.4v 4A, the input tranny is 180-0-180 250ma, both HammondIts all DC rectified (even the heaters) and extensively filtered. I get practically no hum whatsoever.Power output is about 8 watts per channelHere are some pics (click on thumbs for bigger pic)...excuse the messy wiring inside, its my first time! I'm planning a more powerful project and ill spend more time on the case and wiringP.s its not completely old school...for anyone familiar with push-pull class A tube design, class A must be forced in the circuit design i have used. Full class A operation is forced by the use of 2 LM317 voltage regulators (1 for each channel) wired up to supply constant current which is used to set the bias on the tubes...

author: KTP
author_rank: Frequent Contributor
timestamp: June 11, 2010, 02:48:56 pm
content: Nice job!One day semiconductors will be "old school" and people will post about how they built an amplifier using mosfets instead of quantum cheerios or whatever we will have in the future.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: June 11, 2010, 03:19:31 pm
content: EL84 ?Years ago , the 6C4 and the 5763 , was the heroes about clear modulation.You did a nice job down there , congrats ..

author: Time
author_rank: Frequent Contributor
timestamp: June 11, 2010, 03:25:07 pm
content: Wow, the final unit looks very nice. I think you just inspired a new personal project for me.sorry for the double post.

author: KTP
author_rank: Frequent Contributor
timestamp: June 11, 2010, 03:36:15 pm
content: Quote from: Time on June 11, 2010, 03:10:24 pmhttp://shopper.cnet.com/car-audio/scosche-1200w-class-a/4014-3425_9-33411308.html

author: saturation
author_rank: Super Contributor
timestamp: June 11, 2010, 03:43:57 pm
content: Nice. Was it a kit or did you design it from scratch?

author: KTP
author_rank: Frequent Contributor
timestamp: June 11, 2010, 04:08:22 pm
content: QuoteWell I know bjt has a greater voltage gain, but my point in saying mosfets was mostly because that is the newest technology (and mosfets are getting better)...hmm well actually maybe IGBT are newer technology.I think in history it went something like this:Early audio amplifier constisting of large horn shaped object usually decorated with floral patternVacuum tube amplifierBJT solid state amplifierMOSFET solid state amplifier

author: A-sic Enginerd
author_rank: Regular Contributor
timestamp: June 11, 2010, 04:21:51 pm
content: Yeah, but does it go to 11?nice handywork.

author: MTron
author_rank: Regular Contributor
timestamp: June 11, 2010, 04:55:20 pm
content: Quote from: saturation on June 11, 2010, 03:43:57 pmAll i had to start with was a circuit diagram, and some pics from people who built similar units, so no not a kit..lolAs well, i couldn't match the same components (namely the output transformers) that were spec'd in the circuit diagram, so it required some research and modification.As for the circuit board layout, case layout and wiring...thats all meI have over 100 pics...lol...a lot of them were me just laying out the components on the top of the case to get the look right. Took me about 2 days to plan out where everything would go up top, mark with pencil, get the angles and distances just right..ect, and drillIt was my biggest project to date....no templates, no drill guide, nothing pre-assembled....it was truly from scratch!Though i did receive a lot of help from sites like diyaudio and diyaudioprojects. The basis for my amp, as well as the circuit diagram is from diyaudioprojects from a design done by Bruce Heran

author: Strube09
author_rank: Regular Contributor
timestamp: June 11, 2010, 05:28:50 pm
content: How about a schematic?Wouldn't mind considering a tube amp project.Thanks

author: MTron
author_rank: Regular Contributor
timestamp: June 11, 2010, 05:36:56 pm
content: As in layout....dont have one..lolIf you want the circuit diagram and the designers notes, its on this page.http://diyaudioprojects.com/Tubes/EL84-Push-Pull-Tube-Amp/There isnt much there about assembly, layout or construction. More on the lines of "keep this away from that" etc as well as info on how to set it up (bias). As i said, its not quite the same as mine, as i had to modify the circuit to suit my output transformers, as i couldnt find the ones he suggested locally (shipping on transformers is a b!t@h) so i am using a configuration called Pentode mode. I also built in a switch to set it to Triode strap if i feel like a diff sound. As that diagram is set it is in an Ultra Linear config (mix between the two)enjoy!

author: Time
author_rank: Frequent Contributor
timestamp: June 11, 2010, 06:07:28 pm
content: For alot of good audio projects:http://sound.westhost.com/projects.htm

author: MTron
author_rank: Regular Contributor
timestamp: June 11, 2010, 06:09:18 pm
content: Quote from: Time on June 11, 2010, 06:07:28 pmYea, im working on a couple of his projects ATM. The hifi preamp and the phono stage to be exact. But im not going to purchase his PCB's...gona go the whole perf board route again

author: Time
author_rank: Frequent Contributor
timestamp: June 11, 2010, 06:12:14 pm
content: Quote from: MTron on June 11, 2010, 06:09:18 pmYeah, I agree. Honestly, wheres the fun in just populating someone elses PCB?

author: saturation
author_rank: Super Contributor
timestamp: June 11, 2010, 06:41:31 pm
content: Great, that's where all the fun is.Quote from: MTron on June 11, 2010, 04:55:20 pm

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 12, 2010, 04:59:16 am
content: QuotePretty much every modern design I have seen uses MOSFETs for the output. What's amazing is how it's possible to put power MOSFETs capable of 600W on the same silicon as a low voltage Delta Sigma modulator. (http://focus.ti.com/docs/prod/folders/print/tas5630.html) I would think that process differences would make that very tricky!And here's my new amplifier design:http://ecorenovator.org/forum/appliances-gadgets/984-allie-moore-ihybrid-40-next-generation-ti-hybrid-digital.html. I bet that in 10-20 years, that technology would be considered ancient and I'll have a nice story to tell by then.EDIT: I have experimented using display tubes as amplifiers. They are cool to look at and quite interesting to play with, but I'll stick to semiconductors for actual use.

author: saturation
author_rank: Super Contributor
timestamp: June 12, 2010, 11:01:12 am
content: I like your design NiHaoMike, that's how I build these days, use discarded parts except for the main drive elements, why pay for support electronics when much is free and in the trash?For your design 'Allie Moore', have you tried to check its specs? Its frequency response? Its distortion? At its rated output?Quote from: NiHaoMike on June 12, 2010, 04:59:16 am

author: Zed
author_rank: Contributor
timestamp: June 12, 2010, 03:53:04 pm
content: I love valve gear, even my CD player is valve, a Musical Fidelity CDT ''Frog Eye'' Class A Single Ended Triode. One of my future projects is to design an build a custom guitar amp. This site is a good starting point and the kits are pretty well priced as well.http://www.ampmaker.com/

author: cybergibbons
author_rank: Frequent Contributor
timestamp: June 12, 2010, 04:35:22 pm
content: Quote from: Zed on June 12, 2010, 03:53:04 pmWhen I first read that, I entertained the idea of the entire thing being valve, DAC and allI bet we see that someday on makezine/hackaday on a steampunk hifi.

author: Zed
author_rank: Contributor
timestamp: June 13, 2010, 04:02:35 pm
content: Quote from: cybergibbons on June 12, 2010, 04:35:22 pmNow that is something I would love to see, if I remember rightly the very first digital computer was valve and used to decode Nazi cyphered messages during the 2nd world war.Vinyl beats any CD player hands down in my opinion though, I think CD is a step backwards as far as sound quality is concerned and I fart in the general direction of MP3.

author: Unknown
author_rank: Unknown
timestamp: June 13, 2010, 04:21:48 pm
content: Quote from: Zed on June 13, 2010, 04:02:35 pmThe Bombe was mechanical, and used for cracking Enigma messages. The first digital computer was the ENIAC I think, and was indeed all tubes.Quote from: Zed on June 13, 2010, 04:02:35 pmHow about an all tubes MP3 player? The tubes might compensate for the digital crap. It might need something more complex than the ENIAC, though, to do real-time MP3 decoding.

author: Zed
author_rank: Contributor
timestamp: June 13, 2010, 04:40:23 pm
content: Quote from: alm on June 13, 2010, 04:21:48 pmThe thing about MP3 is that it is ''lossy'' compression, you lose dynamics. I got turned back onto vinyl because I wanted to buy an album and it was only available on vinyl (Andy Summers-XYZ) so I needed something to play it on and rip it to my PC, a friend gave me a Technics Hi-Fi system complete with turntable and when that needle hit the vinyl it was like an angel sticking its tongue in my ear. I hadn't listened to vinyl for over 20 years and now I understand why DJs use vinyl, the dynamics are awesome and the warm musical sound pisses on any CD player.

author: mlaargh
author_rank: Contributor
timestamp: June 14, 2010, 12:57:08 am
content: Looks fantastic!I've been meaning to make one of these for years. Did you fabricate the enclosure, or get it ready made from somewhere? If so, where?

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 14, 2010, 04:00:41 am
content: QuoteThe frequency response is pretty flat over the 20Hz-20kHz band, not sure exactly since I don't have an oscilloscope yet. ("She sounds great to me, but I'll check her out with a Rigol to be sure.") As for distortion, I had to alter the inductors during design. The "black" cores (from some old DC/DC converters) performed extremely well for efficiency but were much too nonlinear for general use. The "white/yellow" cores (from some old computer speakers) is slightly worse for efficiency but were much more linear. I haven't done much testing at full rated output except with some dummy load resistors.QuoteUse FLAC instead. It is mathematically indistinguishable from uncompressed PCM. I think of records like AM radio: although they are poor quality in most real world situations, it is theoretically possible for them to be very good. The main problem with records, of course, is that they'll eventually wear out with no way to make a perfect backup. With digital, there is no limit to how many times it can be perfectly backed up given a bit-for-bit copy.

author: Unknown
author_rank: Unknown
timestamp: June 14, 2010, 02:44:14 pm
content: Quote from: NiHaoMike on June 14, 2010, 04:00:41 amNot sure if a scope is the ideal tool to measure frequency response and distortion, typically the accuracy is only 1% or so, and the resolution is only 8-bit. Any competent amplifier should meet that spec without even trying. For audio, dedicated equipment like an audio oscillator, distortion analyzer or spectrum analyzer is often used. A good multi-meter with an AC range that includes 20-20kHz might also work. But you can probably make do with a scope, if you have a good signal source. You might be able to measure distortion by analog subtraction (Bob Pease did a piece about that once). If you do the subtraction of the fundamental frequency in the analog domain, it doesn't decrease the 8-bit dynamic range of your scope.You might be able to calibrate a good sound card with a loopback cable, and use it both as signal source and analyzer. Pretty sure that's how software like Rightmark Audio Analyzer works. You'd have to divide the output voltage down to get it down to line level. Not sure what the accuracy would be, probably not great, but at least the average soundcard has a 16-24 bit dynamic range.

author: ThunderSqueak
author_rank: Unknown
timestamp: July 01, 2010, 03:06:00 am
content: I love tube ampsI have designed and build a few now, always fun to play with and even better when I plug one of my guitars in ^^This is a fun place to start if you are looking at a guitar amphttp://www.ax84.com/My personal favorite build from that site is a firefly type. Awesome size for an apartmenthttp://www.ax84.com/index.php/oldprojects.html?project_id=fireflySample of said amp:http://ax84.com/media/ax84_m277.mp3I love mine (shown below)

author: Time
author_rank: Frequent Contributor
timestamp: July 01, 2010, 03:33:51 am
content: Quote from: ThunderSqueak on July 01, 2010, 03:06:00 amOOoo, pretty.