Simplistic NJFET RIAA

[42001]

Phono

What do you mean by amp? Salas designed phono?

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Yes, I am near completion now and wonder how people think it performs!

 

[alexkosha]

This is the best RIAA compare to my 2 other phonos. I have tube MM (Marantz 7C based) that I use with SUTs and BHL phono. Salas FSP is much better. Amazing sound.....


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[damuffin]

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)

It looks like R3x should fix it.

Thanks everyone for your help

 

[Salas]

You did not get your Q3x from eBay, right? Low Idss it may chance a lot in genuine K117GR too and that's fixing with revised R3x but beware of noise in case of fakes

 

[42001]

No, i got the stuff from Tea-Bag. They look genuine!

 

[AndrewT]

Sj, did you measure anything, before assembly?
Like check the resistor values, check the jFET Idss, check the capacitances?

 

[42001]

I allways do before mounting Andrew. Didnt know Q3x was that critical.

 

[AndrewT]

Vdrop = Ir * R

 

[Salas]

Didnt know Q3x was that critical.

It wasn't but it seems that the 4-5mA Idss range then common when the guide was written start to deplete and weaker ones tend to average as picks now

 

[42001]

No problem! That is what this thread is for And it works!

 

[damuffin]

I installed the 6.2k that was in the resistor kit and didn't think any thing of it at the time. By replacing it with a 10k I am now at 3.6V on TP1-Tp2.

 

[42001]

Hurray! You did it!

 

[lucylu]

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

 

[simon2a3]

Thanks Salas! Just ordered a 2 x 18V with 230V primaries R-Core.

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.

 

[Salas]

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

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

 

[42001]

R Cores

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.

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!

 

[simon2a3]

Hopefully everything will be fine for you Sjoerd and I was a one off. It's a shame as r cores aren't that easy to come by.

 

[42001]

Nothing yet

Hopefully everything will be fine for you Sjoerd and I was a one off. It's a shame as r cores aren't that easy to come by.

Hi Simon,

No response yet..... beginning to wonder now......

 

[42001]

Hmmm. website says: en cours de traitement...... So it looks like they sent it to me.

I will wait for 1 more week....

 

[simon2a3]

Hi Sjoerd, that sounds promising.

Simon.