Cheap as Chips OPA1688 Low-THD Muscle Amp

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X,

Extraordinary performance! Beautiful layout (congratulations JP!) and absolutely top class commercial work. I hope lots of people looking for a ultra-low THD HPA build this and that the pcb can be available from the DIY shop!

I think we can be very grateful for X and JP for their brilliant, restive work for our benefit. I am very grateful for X because he builds a lot of my prototype circuits at least 20 times quicker than I do it myself...... the ALPHA has been our work together, and the layout was brilliantly done by JP64.

I'm hoping more and more of the ALPHAs are built. This is a superb 20W Class A amplifier based on a combination of the AKSA/Lender preamp and the Aleph J active current source from Nelson Pass. It is a very good amplifier, one of the best - and thanks to X and JP64 who brought it into the world.

Cheers,

Hugh
 
Founder of XSA-Labs
Joined 2012
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If there is enough interest JPS64 and will probably do a group buy, but in general, JP does not release the layout files. This board has small WSON8 SMT parts (with underside thermal pad and no legs) that are not trivial to solder without proper equipment like a hot air gun. I may have to offer a prepopulated SMT board to reduce the level of difficulty on this amp.

692045d1531690873-cheap-chips-opa1688-low-thd-muscle-amp-5e24d06e-7530-4a3c-b2cf-05eff05f9983-jpeg
 
I made a similar amp earlier this year (when I realised the M2Tech dac I bought cheaply on impulse could not drive my headphones)

I used 2xOPA2172 per channel i.e four opamps per channel (however with all contributing output current) I also added some low IDSS 2sk170 for biasing and included regulation (simple Zener followers) +/- 5V

The measurement shows 1Vrms into 50ohm.
 

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Founder of XSA-Labs
Joined 2012
Paid Member
I made a similar amp earlier this year (when I realised the M2Tech dac I bought cheaply on impulse could not drive my headphones)

I used 2xOPA2172 per channel i.e four opamps per channel (however with all contributing output current) I also added some low IDSS 2sk170 for biasing and included regulation (simple Zener followers) +/- 5V

The measurement shows 1Vrms into 50ohm.

Nice design! Did you use the 2SK170’s to bias the rails into Class A?
 
Founder of XSA-Labs
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Ah ok, just through your Etsy then?

Also, any details on the power supply in the new renders?

Still under development but probably use a wallwart 12vdc Class 2 transformer or SMPS to power a +/-24v DC-DC step up followed by some low noise linear regulators for +/-18v and maybe 20mV rms at 2amps. Looking for a low noise option capable of 2A. The TPS7Axxx are only good for 1A.
 
>> lineup

It's a very nicely sounding opamp and is easy to work with, it has FET inputs and low offset I usually use it for servos but in this case its specs allowed for not needing AC coupling.




>> xrk71

Thanks! I couln't resist adding some bias about 7mA on each opamp, simply beause I have lots of spare fets in that IDSS range, also it is nice to have some current through the emitter followers.

I attached some measurments with and without bias to this post but the without measurements may contain some measurment error as some BNC connectors where difficult to mate properly. I did not notice at first as I found the measurements to be resonable. When I remeasured with the bias added I noticed the offending connector and was more carefull to make sure it was mated as good as it could.
 

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Nice job. Can you put near smd opamp pins also pads for dil8 opamp? That later also dil8 opamp can be tested.

That's a big of footprint change and would require major redesign of the layout - let's ask JPS64. SOIC-8, as SMT goes is easy to solder - just look for your favorite SOIC-8. All of the best opamps now are available in that format whereas DIL-8 is for legacy parts that are not so state of the art.
 
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