SOAP MKIII (Simple OpAmp Pre) With onboard PSU - diyAudio
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Old 7th May 2008, 09:24 AM   #1
zei is offline zei  Sweden
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Thumbs up 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


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Prototype

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Sche
Silk
Copper
Overview
BOM

Regards

/JZ
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Old 7th May 2008, 10:09 AM   #2
kmj is offline kmj  Sweden
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all-in-one. Me like
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Old 7th May 2008, 10:49 AM   #3
AndrewT is offline AndrewT  Scotland
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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.
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Old 7th May 2008, 12:00 PM   #4
zei is offline zei  Sweden
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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
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Old 7th May 2008, 12:30 PM   #5
Nuuk is offline Nuuk  United Kingdom
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Here are some other tweaks that you may like to try too.

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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.
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Old 7th May 2008, 12:40 PM   #6
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by zei 4,7uF ? The circuit is working fine without those caps as well...

How do you meen decoupling? Are you referring to C5, C6 ?[/B]
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.
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Old 7th May 2008, 12:42 PM   #7
zei is offline zei  Sweden
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Quote:
Here are some other tweaks that you may like to try too.
That,s the "ClassA" tweak i asume?

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




/JZ
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Old 7th May 2008, 12:47 PM   #8
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by Nuuk
Here are some other tweaks that you may like to try too.

Click the image to open in full size.

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.
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?
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Old 7th May 2008, 12:49 PM   #9
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by zei
That,s the "ClassA" tweak i assume?

It should very very easy to add that resistor under the board if someone wants to
or try a FET CCS rather than a resistor. Or even a cascoded FET CCS. It might sound better.
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Old 7th May 2008, 01:00 PM   #10
zei is offline zei  Sweden
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We are starting to leave the "Simple" out of SOAP

Thanx for all the trix and tweaks..


/JZ
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