An advice for a SS amp to suit a Pass3x ?

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yoplaboum

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#1
Hello to everybody 🙂 ,
I need an advice to use a Pass3x. I could buy it very cheap several years ago, but I didn't use it since today just because I miss an amplifier.
I'm looking for a common, simple, cheap SS amplifier, a neutral one, to hear really the sound of the Pass3x. BUT to be used with this preamp, the amp needs a high imput impedance, 100 Kohms I think.

Is somebody, here, can advise me a solid state amplifier to go with this tube preamp ?
Or an other option : I have always dream about a Quad 405... Is it possible to tweak this power amp, to use it with the Dyna preamp ?
Thank you for your advices ! 😱🙂
Michel
 
#3
rayma said:
The Quad has a 20k input impedance, but the PAS preamp is best suited for 100k loads.
That wouldn't be a good match, you'd have to add a buffer stage between them.
Click to expand...
Hello Rayma,
I know the Pas needs an amp with an imput impedance a lot higher than seen usually (between 20k and 50 kohms generally). But perhaps there's a model of an SS amp, common, cheap, and suited for the Pas ? Perhaps someone, here, could experiment a nice association...? 😕
 
#5
rayma said:
A ss amp with an fet input stage (esp. cascoded) can have a higher input R.
Click to expand...

Exactly! FETs, like tubes, are high impedance voltage controlled devices.

The OP can use a Quad 405, IF he builds a buffer for the PAS. Even something built around FET I/P opamps will do.
 

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#6
Eli Duttman said:
Exactly! FETs, like tubes, are high impedance voltage controlled devices.
The OP can use a Quad 405, IF he builds a buffer for the PAS.
Even something built around FET I/P opamps will do.
Click to expand...

Here's a low cost option. The board can use an FET input IC, set up for unity gain.
It's possible to mount this inside the PAS, and run the pcb off the +/-12V filament supply,
in which case nothing else is needed other than the op amp. There is ripple on the filament supply,
but the op amp circuit will reject it well enough. Dual OP Amp Board Preamp DC Amplification PCB for NE5532/OPA2134/OPA2604/AD826 | eBay
 
#7
rayma said:
Here's a low cost option. The board can use an FET input IC, set up for unity gain.
It's possible to mount this inside the PAS, and run the pcb off the +/-12V filament supply,
in which case nothing else is needed other than the op amp. There is ripple on the filament supply,
but the op amp circuit will reject it well enough. Dual OP Amp Board Preamp DC Amplification PCB for NE5532/OPA2134/OPA2604/AD826 | eBay
Click to expand...
Yes !! This looks like made for me! 😉
With one little board, and a dual OP on it, I can have, from my Pas3, an output impedance low enough to be used with a Quad 405 ? And powered by the voltage for the filament ? Cool !!!
A OPA2604 is exactly what I need, or there are best suited OP for what I want to do with ?
An thank you for all ! 🙂
 
#8
yoplaboum said:
I can have, from my Pas3, an output impedance low enough to be used with a Quad 405 ?
And powered by the voltage for the filament ? A OPA2604 is exactly what I need.
Click to expand...

Use a 100k or higher for the pcb's input resistor, and a DUAL fet input op amp
that is unity gain stable. The OPA2604 would work.

To modify the pcb: Replace R1 with a 100k. Remove R3. Replace R4 with a wire.
Then you have a unity gain buffer with Rout = 47R, that can easily drive a 20k amp.
The board has a mild low pass filter at the input. If you don't want that, remove C1.

Make sure that you wire the pcb to the filament supply in the right polarity!
The center tap of the filament supply is connected to ground, which results in
filament voltages of +12VDC and -12VDC, and makes this possible. Use a meter
to verify these voltages before you start, in case someone has altered the circuit.
 
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#9
rayma said:
Use a 100k or higher for the pcb's input resistor, and a DUAL fet input op amp
that is unity gain stable. The OPA2604 would work.

To modify the pcb: Replace R1 with a 100k. Remove R3. Replace R4 with a wire.
Then you have a unity gain buffer with Rout = 47R, that can easily drive a 20k amp.
The board has a mild low pass filter at the input. If you don't want that, remove C1.

Make sure that you wire the pcb to the filament supply in the right polarity!
The center tap of the filament supply is connected to ground, which results in
filament voltages of +12VDC and -12VDC, and makes this possible. Use a meter
to verify these voltages before you start, in case someone has altered the circuit.
Click to expand...
So... I think that now, I know all what I have to know ! Thank you VERY much for all these informations ! I will be carefull to these voltages, and now I have to find a nice Quad 405.
I will post pictures of the Pas mods when it will be done. Thanks for all ! 🙂
 
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