Any AUdio Amplifier Gurus in here ?

[dashpuppy]

I have a technical question for an audio amplifier / circuit type of person

I'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 see

I found this part http://ca.mouser.com/ProductDetail/Murata-Electronics/DK1E3EA102M86RBH01/?qs=sGAEpiMZZMve4%2fbfQkoj%252bBH4or657exy7LzcBHaXqYU%3d
Multiplayer 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 parts

I'm referring to cap  C8 connected to Q5 ( middle of schematic )

Schematic

[jaycee]

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 is http://www.kk-pcb.com/aleph-2.gif

I 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.

[cat87]

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%3d
Id 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.

[jaycee]

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.

It'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.

[dashpuppy]

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.

It'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.

Thanks for backing me on on that   I 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 blocks   it's enough power plus i love the sound of the alephs.

[dashpuppy]

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 is

Fixed.


Now to find the proper package in eagle & change them...

[cat87]

Quote from: cat87 on Today at 05:37:41 AM
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.

It'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.

Sorry, 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.

[oldway]

Output stage with Mosfets, that'is not a good choice for an audio amplifier....

[Alex Nikitin]

Output stage with Mosfets, that'is not a good choice for an audio amplifier....

Nothing 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  .

Cheers

Alex

[jaycee]

Hi Alex, nice to see you here... much better than the toxic environment of DIYAudio
Still love your VAS from the Cambridge A3i

[dashpuppy]

Output stage with Mosfets, that'is not a good choice for an audio amplifier....

Oh, 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....

[jaycee]

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.

[Kleinstein]

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.

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.

It'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.

I 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.

[dashpuppy]

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.

[retrolefty]

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.   

[dashpuppy]

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.   

I would NEVER spend 5k$ on an amplifier, i like DIY stuff all the way! Hence this project and many others