New circuit: the QUITAPENAS Jfet amp emulation

[wui223]

I built this circuit on a perfboad but encounter some problems.

First, i measure the voltage of the Q3 and found out the reading keep on dopping. But fow the other 2 FETs, this do not happen.
My question is: Could this be due to faulty FET or the trimmer connected with it ?

If the FET is faulty, could i replace it with 2N5458 or anyone has any suggestion?

If the trimmer is faulty, a replacement of 50K trimmer would make any difference?

The trimmer is setting the bias voltage of the FET, but where the 9V supply goes? Is the trimmer set the amount of current delivered to the FET as well?

Thanks.

[Xavier]

For some reason I can't edit my first post. I've made a correction in the layout so here it goes



Hey Wui, doble check your connections, as for the transistor, you can also try a J201 although it as more gain. The 9v supply is the upper rail and basically it provides current for the FETs.

[wui223]

Basically i follow the original schematic except i omit the diodes in front of the third FET. Xavier, you replace the diodes with 47k resistor, could you tell me the reason?

[wui223]

Just put the 47k resistor in-front of Q3. The voltage dropping problem is solved. But the gain is somehow not to my expectation,the overdrive is abit 'tame'. I guess putting the diodes instead of the 47k would enhance the gain. Might try it out later. Thanks for the schematic and helps, Xavier.

[Xavier]

Just put the 47k resistor in-front of Q3. The voltage dropping problem is solved. But the gain is somehow not to my expectation,the overdrive is abit 'tame'. I guess putting the diodes instead of the 47k would enhance the gain. Might try it out later. Thanks for the schematic and helps, Xavier.

Thanks Wui. What do you mean by "tame". This circuit should not be a high gainer, specially with 2N5457's. If you want more gain, try switching to J201's.

You can also add 2 (1+1) back to back diodes instead of the 2+2.

Please let me know how it turns !!

[wui223]

I replace the 47k with 2+2 back-to-back silicon diodes, the result is satisfying. I like it. But sooner or later i have to replace the pots coz they are not in good conditions and i omit the Volume pot coz run out of 1M pot even 500k pot is out of hand.

The overdrive sound is good for playing blues (just my own opinion), and i run a DS1 in front of it to play solo.