Any AUdio Amplifier Gurus in here ? - Page 1
Forum section: electronics / projects

author: dashpuppy
author_rank: Regular Contributor
timestamp: October 15, 2017, 05:48:47 pm
content: I have a technical question for an audio amplifier / circuit type of personI'm building a amplifier from a schematic Pass Labs Aleph 2. My goal is to do everything SMD except a few parts, obvisly the Output transistors and 2 other parts.I will attach the schematic i have drawn up, my issue is fining a 1nf-50V capacitor that is big enough to seeI found this parthttp://ca.mouser.com/ProductDetail/Murata-Electronics/DK1E3EA102M86RBH01/?qs=sGAEpiMZZMve4%2fbfQkoj%252bBH4or657exy7LzcBHaXqYU%3dMultiplayer Ceramic Capacitors MLCC - SMD/SMT 1000pF 300V 20% 11.4x6x2.5mm SMD That should work, now the cap is not in the audio path. Do we think this will be ok ?Just so people don't just start jumping on me to say i'm making this to make money "IM NOT" this is MY self project and this amplifier was discontinued years and years ago. Next this has been a 10 year goal to make a SMD version so i'm finally able to find all the parts and do it( I love SMD partsI'm referring to cap C8 connected to Q5 ( middle of schematic )Schematic

author: jaycee
author_rank: Regular Contributor
timestamp: October 15, 2017, 06:08:04 pm
content: Your schematic does not look correct - I think the base of Q5 should be connected to the other end of R8. edit: no that's not right either. The correct schematic ishttp://www.kk-pcb.com/aleph-2.gifI suspect C8 should be forming a compensation capacitor. If so, MLCC ceramics is the wrong dielectric for the job, as it tends to be voltage dependant. Look for something with a NP0/C0G type dielectric e.g. Mouser part 581-12061A102GAT2A. This is in a 1206 (inches) package and is very solderable by hand.edit: Try and manage 0805 parts if you can. They're not that hard to hand solder. Also C6 (100pF) should similarly be an NP0/C0G dielectric type. C1 and C3 are decoupling capacitors and can be X7R/Y5V dielectric types.

author: cat87
author_rank: Regular Contributor
timestamp: October 15, 2017, 06:37:41 pm
content: The amp itself doesn't look that impressive... I mean it's got a metric ton of distortion, all of which can be substantially diminished, but that's not the topic here.If you want to do it all in SMD, and as cheap as possible, then one option is NP0/C0G dielectric SMD caps. The C8 cap is part of the feedback path, so ideally, you'd want all the caps connected to this path to introduce little to no additional distortion. I'd avoid any X7 or Y5 dielctric caps. Those are really horrible for this kind of job. Besides the fact that their capacitance will be all over the place, you might finnd that they can mess with your feedback network.Ideally, the caps like C4, C6, C8 would be something like polypropylene or polystyrene ones, but those only come in THT versions. The nearest SMD version would be metalyzed PPS caps. Something like this perhaps:http://ro.mouser.com/ProductDetail/Panasonic/ECH-U1H102GX5/?qs=sGAEpiMZZMv1cc3ydrPrF%252bfZ13WJ%2fr1%2f%252bZfA9jFk2cU%3dId higher voltage ratings are needed, you'd have to do a parametric search and see if there's any in stock.These, I think, are better that the C0G caps and at little additional cost.

author: jaycee
author_rank: Regular Contributor
timestamp: October 15, 2017, 06:52:29 pm
content: Quote from: cat87 on October 15, 2017, 06:37:41 pmIt's one of Nelson Pass's designs, and he loves class A. His amps do have a tube-like quality apparently.. but the Aleph range are very highly regarded.

author: dashpuppy
author_rank: Regular Contributor
timestamp: October 15, 2017, 07:07:30 pm
content: Quote from: jaycee on October 15, 2017, 06:52:29 pmThanks for backing me on on thatI am a HUGE HUGE HUGE! Nelson Pass Aleph lover, i helped design the first SMD mini aleph ( suggestions and playout) back 14 years ago. The goal for this project is to build the 100watt class a aleph mono blocksit's enough power plus i love the sound of the alephs.

author: dashpuppy
author_rank: Regular Contributor
timestamp: October 15, 2017, 07:33:16 pm
content: Quote from: jaycee on October 15, 2017, 06:08:04 pm

author: cat87
author_rank: Regular Contributor
timestamp: October 16, 2017, 07:54:52 am
content: QuoteSorry, didn't want to offend anyone. I meant that strictly from an engineering point of view. I mean, there are other class A design with much lower distortion.

author: oldway
author_rank: Super Contributor
timestamp: October 16, 2017, 08:09:04 am
content: Output stage with Mosfets, that'is not a good choice for an audio amplifier....

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 16, 2017, 09:30:16 am
content: Quote from: oldway on October 16, 2017, 08:09:04 amNothing wrong with MOSFETs in an audio amplifier, it is just a question of correct implementation. I did design many amps with N-channel MOSFET outputs (Class AB though) and with good results. Nelson knows how to design good amps too, so I wouldn't be quick to dismiss his design.CheersAlex

author: jaycee
author_rank: Regular Contributor
timestamp: October 16, 2017, 10:54:08 am
content: Hi Alex, nice to see you here... much better than the toxic environment of DIYAudioStill love your VAS from the Cambridge A3i

author: dashpuppy
author_rank: Regular Contributor
timestamp: October 16, 2017, 02:46:06 pm
content: Quote from: oldway on October 16, 2017, 08:09:04 amOh, and whats a better class a 100watt rms amplifier schematic ? Krell, those make 5x more heat than this Class a. I like the Nelson stuff, they work very very well. AND BTW the new passlabs stuff still uses "FETS" so....

author: jaycee
author_rank: Regular Contributor
timestamp: October 16, 2017, 03:40:58 pm
content: Lateral FETs are better for Class AB but you dont really get those any more, and they're expensive when you do.Vertical FETs can work well for audio but usually only with a lot of bias, or in class A. Or in Class D of course.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 16, 2017, 07:38:59 pm
content: For the small caps NP0 or COG ceramics is perfectly fine. Film caps are usually not better for audio. So film caps would only be needed for the larger ones, like >5 nF.1 nF should be no problem to get as a NP0 version, though not super small size.Quote from: jaycee on October 15, 2017, 06:52:29 pmI would hope to get much better than tube-like quality. Even Hung low caps tend to have better MTBF and it might X7R caps to reach the THD level.

author: dashpuppy
author_rank: Regular Contributor
timestamp: October 16, 2017, 09:47:49 pm
content: SO far this is what i have been working on. Comments welcome. I haven't used Eagle in years so this is bringing back memories. I need to figure a few things out like a VIA from top to bottom and few other small things.

author: retrolefty
author_rank: Super Contributor
timestamp: October 17, 2017, 12:37:39 am
content: Interesting discussion. However I have to admit when I read the phrase "a tube-like quality" I cringe from the close association to the golden ear crowd that worships $5K+, 7 watt class A triode power amps.

author: dashpuppy
author_rank: Regular Contributor
timestamp: October 17, 2017, 02:29:33 am
content: Quote from: retrolefty on October 17, 2017, 12:37:39 amI would NEVER spend 5k$ on an amplifier, i like DIY stuff all the way! Hence this project and many others