Perreaux SM-2 need help with output transistors

[couguarek]

Hi,

I want to rebuild my Perreaux SM-2 preamplifier. As far as I know small transistors are MPSA92/42 and outputs are VNO116N2, VPO116N2 (aren't available).

Could you please tell me if it's possible to swap output devices with e.g IRF610/9610 or smth similar?

Thanks!

 

[abraxalito]

I'd be inclined to substitute 2SK213, 2SJ76 for those output FETs. Available on Taobao and Aliexpress.

I doubt that vertical FETs (like the IRF610 you've suggested) will have sufficient bias stability, laterals are self-stabilizing.

 

[couguarek]

I'm afraid that I will buy chinese fakes :/ Is there are any other options ?

 

[abraxalito]

Is there any evidence of fakery going on with obsolete lateral MOSFETs?

 

[couguarek]

I didn't saw, but who knows...
As I can see there are not too many lateral mosfets for this purpose

 

[abraxalito]

If you really can't bring yourself to try ordering the LATFETs then you could substitute some bipolar transistors : KSA1381 and KSC3503 will most likely work but the biassing may well need tweaking.

 

[couguarek]

OK, I will try 2SK213/2SJ76. I don't wanna change tone of this preamp using bipolars

Thank you for advice.

I have one more question about gain in this preamplifier. It sounds so good, but when I slightly turn the volume up, I have about 1-2V on output. As you can see in pdf below, this pre have 27V max output voltage :O. Can I change R122 or R139 for reduce gain ?

http://www.perreaux.com/files/dmfile/029-SM2.pdf

 

[abraxalito]

I suspect, from looking at the biassing string (3 diodes and 1 zener) that it originally had normal (vertical) FETs in circuit rather than laterals. Laterals would need at most 2 diodes for bias so you'll probably want to short one diode and the 4.7V zener.

Reducing the gain would be a bit tricky. I'd use a step-down transformer on the output myself to get lower gain.

 

[couguarek]

OK, so maybe I will try to use IRF's before and measure BIAS fluctuation.

 

[aparatusonitus]

OK, so maybe I will try to use IRF's before and measure BIAS fluctuation.

I would not do that ... at least not without vgs multiplier without one amplifier will go into thermal runaway... pufff.

What I would do is get 10 pieces of ZVN3310A and 20 pieces of ZVP3310A, and tried to find the best couples among the N-channel and P-channel M-fet. These M-fets are of the same type as those you want to replace, but you'll need to set up a heat sink on them that will connect them to thermally and dissipate excessive heat (without a heatsink they can dissipate approx. 220mW max.), it will not be too difficult because they have the front and back flat. Buy this from ebay seller from Israel, they are genuine (I have)

 

[Zen Mod]

Hi,

I want to rebuild my Perreaux SM-2 preamplifier........

I tend to agree with aparatusonitus, regarding output mosfets

besides that - care to clarify what's "rebuild" - working on old one (in that case - why replacing these ?) or making new, improved one ?

 

[couguarek]

Thanks ZM

I have broken one and wanna repair it.

OK, so I will order ZVN & ZVP and we will see.

 

[Zen Mod]

also , you can try with 2SK213/2SJ76 , bias them little more (say 15mA and up , taking care of PSU capabilities ) and see (hear) do you like them more

 

[couguarek]

One more question.
Don't touch bias circuit or mod it like the abraxalito said ?

 

[Zen Mod]

don't touch , for start

string of diodes ZD1-D5-D6-D7 is there just to limit maximum voltage across RV10

it would need to be altered (increased voltage) for vertical type of mosfets , they usually needing 3-4V at gates for biasing (so twice that across RV10)

 

[bigspeaker]

wanting a copy of the Perreaux 2 circuit

Hi,

I want to rebuild my Perreaux SM-2 preamplifier. As far as I know small transistors are MPSA92/42 and outputs are VNO116N2, VPO116N2 (aren't available).

Could you please tell me if it's possible to swap output devices with e.g IRF610/9610 or smth similar?

Thanks!

hi how are you guys i am repairing a perreaux SM- 2 preamp with a mute relay problem i was wondering would you mind suppling me a coppy of the circuit thanks Ian eletrontube42@gmail.com

 

[margannai]

Hello, with which mosfet can I replace the complementary VNO of my burnt SM3? Thank you