Simplistic NJFET RIAA

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#15,083
Salas said:
When you can't reach 35V+ with R3x 9.1k it means that Q3x is from a low IDSS range and you should compensate with higher value R3x than what is now installed. That resistor with VR2x (in series) convert the current provided by Q3x to voltage. Q4x and D1x contribute 0.6V+1.8V and the rest comes from the resistances. So either add 2.7k in series with 9.1k R3x or install 12K in its place. That should do it. Because it looks like you got about 3mA @ 10V IDSS Q3xs that do about 2.5mA current under 0.6V they work in the circuit. On the other hand its good because low IDSS ones have lower Vgs (off) and work better under low VDS voltage (Q4x's Vbe that is)
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It looks like R3x should fix it.

Thanks everyone for your help
 
#15,093
I have had this working for a few days its a good one allright, but the left channel is weaker than right not a huge amount I can also hear very slight crackle when I put my ear to speaker
Has anyone any idea where I should start to look cheers
 

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#15,094
SjoerdSmits said:
Thanks Salas! Just ordered a 2 x 18V with 230V primaries R-Core.
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I hope you have better luck than me Sjoerd - have you received it yet? I ordered 3 r cores from Selectronic a couple of months ago and all went well right up until I paid and then nothing. No transformers, no communications - they wouldn't even acknowledge me. I had to raise a claim through PayPal (they didn't respond to PayPal either) and only repaid once I'd raised the claim to a dispute, and only when PayPal put pressure on them.

I still don't really understand what this was about - they seem a reputable company and were very helpful initially.
 
#15,095
lucylu said:
I have had this working for a few days its a good one allright, but the left channel is weaker than right not a huge amount I can also hear very slight crackle when I put my ear to speaker
Has anyone any idea where I should start to look cheers
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Make sure that the undersides of the PCBs are fully clean from flux residue. Flux can make a high impedance JFET gate unstable. If that one check proves unrelated check the voltages from drain pin to ground across all JFETs in case one has significantly different voltage than its sibling in the good channel so it draws different current and replace it. If nothing like that happens, try with another C3 in the left channel first just to make sure its not about a dud NOS USSR sample. Also the metal capacitors bodies should not be in contact to alternative size capacitor pads located underneath them
 
#15,096
R Cores

simon2a3 said:
I hope you have better luck than me Sjoerd - have you received it yet? I ordered 3 r cores from Selectronic a couple of months ago and all went well right up until I paid and then nothing. No transformers, no communications - they wouldn't even acknowledge me. I had to raise a claim through PayPal (they didn't respond to PayPal either) and only repaid once I'd raised the claim to a dispute, and only when PayPal put pressure on them.

I still don't really understand what this was about - they seem a reputable company and were very helpful initially.
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Hi Simon,

That's a bommer! I have not received anything yet. I'send them an email and see what happens...... Thanks for the warning!
 
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