You should never do that. If we cannot trust you that the schematic you post is actually what you built, all bets are off. It's often these 'that doesn't matter' things that are the culprit.
Ok.. Sorry Jan.
I´m kind of new here.
I wanted to make it cleaner for the JFET part
It does seem kind of unlikely that FET would oscillate like that, its transconductance isn't all that high and that much C should take out its steam. I assumed you probed around while it was making ugly waveforms, to see whether the pulses show up on the power supplies? (And are you by any chance using low-dropuout voltage regulators?).
Also look for places that cause output changes when you probe them.
Also look for places that cause output changes when you probe them.
I just came here to give some update and bwalso digged it.
Problem solved guys!
Wel... it wasn´t the fet...
And by simplifing the schem as I did you could never find out the problem.
Just after the fixed equalizer I have an output for the spring reverb circuit. As the reverb tank wasnt attached, for some reason this circuit was oscilating in a high frequency. I would never guess that was coming from there... So I keept the hipotesis of the fet...
Well, thanks a lot everybody!
I´ll still stick with your tips.
Later on I´ll post the full schematic.
BTW, the amp is sounding amazing now, mainlly the clean channel.
I´ve tried with both a EL84 push pull pair and a class D power amp, both sounded really good (In fact, I´m almost liking the class D more than the tube)
Soon I will start woking on a version with a drive channel only with cascading fets for overdrive
Told you a week ago.
What is the saying - when the mind is ready, a teacher will appear....
Well done.
Jan
Very cool, glad you are happy with it! BTW you are thinking of cascading fets for drive, I would suggest simply substitute 2 fet stages where the diodes stage is. Your drive pot would need increase to maybe 100K, or 500 K, and you have a buffer op amp after that for drive. U2b would have no problem pushing fets to saturation, cutoff or wherever you set them. I have to resist the habit of biasing fets the ''right way'' as for audio, for guitar I find that biasing them ''badly'' usually sounds better! ;-)
That is what bugs me about ROG putting them at 1/2Vdd all the time.
That is what bugs me about ROG putting them at 1/2Vdd all the time.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.