Clon JC2

[alpefe]

hello again I put another preamp that is pretty good, the price is something more than the C-3850, but it is still cheap, has good measures something offset 40mv, but once it is with signal there is no noise and much more open sound than the C-3850, I like it more I have tried with several OPA and there is little difference, so I put screenshots, greetings.

Muse 03 Yellow Op07 Pink 300khz

NE5534 vs OP07 300khz

NE5534 vs Muse 03 300khz

as you can see at 100khz there is almost no difference.

be careful with the first one, the one with the potentiometer has a lot of distortion, I'm going to give it to a friend.

 

[Kleinhorn]

I have the same green preamp board bought at Aliexpress. Have you 2 transformers in use ? I tried with only one transformer and get some hum.
The other black board i own too. Its not only the pot, the components or the design give some white noise to the output.. Not much, but i can hear it with putting my ear near too my AMT. Another yellow board, JC2 Clone sounds good. It has a blue Alps pot on board.
See post 126 https://www.diyaudio.com/community/threads/clon-c-3850.416050/page-7

Greets
Peter

 

[alpefe]

I have changed the 100r input resistor for a 470r and the noise has disappeared, putting 2 transformers does not solve anything.

 

[Kleinhorn]

Okay...thank you very much...👍

 

[alpefe]

Do you have the ground connections on both sides of the board? If you still have noise, you can connect a 2uf MKP capacitor to
the output ground.

 

[Kleinhorn]

Hi,
thank you for that advice. I have to wait for the delivery of the transformators, staying at german customs.

Greets
Peter

 

[alpefe]

sorry I was wrong on the JC2 clone (bad) averages, they are not that bad, but worse than the other one or the C-3850.

 

[alpefe]

the last measures that I have put is of the second JC2, the one that brings potentiometer as the yellow one, only changes the color.

 

[alpefe]

if you compare the measurements of the two types you will see that they are different.

this is the one without potentiometer, it is better than the other one and has OPA TL07.

this potentiometer.

this potentiometer.

without potentiometer.

 

[ilorev]

Second best version

 

[ilorev]

Error in the power diode bridge incorrect diodes for the positive

 

[Kleinhorn]

Hi,
that is another pcb from an other company. At a first look, all seems similar, but you are right, the diodes seem to be not correct.
I will make a measurement on my board to check it out.

Greets
Peter

 

[Kleinhorn]

I have made a measurement to control the rail voltage...everything seems to be fine with the diodes...two cathodes connected together, two anodes connected.
With my 15-0-15 Volt transformer i get +19,2 Volts and -19,4 Volts.

Peter

 

[ilorev]

It seemed at first glance .But it is correct

 

[ilorev]

PCB made in a hurry and not checked yet. It is useful to check for any errors. I don't have time at the moment. I intend to try this pre. Thanks