SOAP MKIII (Simple OpAmp Pre) With onboard PSU
 

Just thought i should share this with you guys.

Made a new layout for the "SOAP" preamp and added a regulated (LM3x7) supply onboard.

Another difference is that In and Out is on the same sid of the PCB and that should make it a little easier when putting it in a chassi.

It has been tested with very good result.! :)

No hum, hiss or noise. Completly deadsilent background.
Sound is powerful and clean and it does a very good job.


If you want to etch yourself, Be my guest ;)


http://bildarkiv.hififorum.nu/Zei/SO...III_PSU_3D.JPG

Prototype

http://bildarkiv.hififorum.nu/Zei/SO...KIII_proto.JPG

Sche
Silk
Copper
Overview
BOM

Regards

/JZ

all-in-one. Me like :D

Hi,
are the input and output caps 1uF?
These are far too low for your typical impedances.
I would investigate adding decoupling to the opamp supply pins.

Thanx for the comments!

How much would you recommend then AndrewT? 4,7uF ? The circuit is working fine without those caps as well...

How do you meen decoupling? Are you referring to C5, C6 ?




/JZ

Here are some other tweaks that you may like to try too.

http://myweb.tiscali.co.uk/nuukspot/...opod%20pre.gif

Yes, it's the single version of the 2134 but the same applies.

I used 100uF/35v Panasonic for audio types on each power supply pin. The DC blocking was taken care of by caps in the DAC and the power amp.

yes C5 & C6 for decoupling. but do they need to be snubbed or electro//film or +ve to -ve or are ceramic OK?

For Zin=15k, 10uF film @ input is more suitable for preamp bass response.
For Zin=50k & 2u2F at the power amp, 10uF is better on the output, or if the power amp has no DC blocking, then 4u7F suits Zin>=20k.

Take care to avoid DC being sent and/or amplified through the pre and power amps.

That,s the "ClassA" tweak i asume?

It should very very easy to add that resistor under the board if someone wants to :)




/JZ

Hi Nuuk,
is R4 sourcing 10mA through the 134? That seems mighty high.
How hot will it run and will a 2134 survive with 10+10mA passing the output stage?

Do we really need a gain of 8times (+18.3dB) through the pre-amp?

What is the minimum load impedance and maximum cable capacitance that the ClassA output stage can feed?

or try a FET CCS rather than a resistor. Or even a cascoded FET CCS. It might sound better.

;) We are starting to leave the "Simple" out of SOAP ;)

Thanx for all the trix and tweaks.. :)


/JZ