Dlite clone Fizz help

[ampedup]

if i turn my first stage volume past half way it gets fizzy and thinner sounding distortion, not good. anyone see anything obvious in my picture. this is a clone of a dlite from parts i had laying around so its not excatly like a brownote. i used a can cap so the powersupply looks different. i had to change the dropping string to get voltages in range
v1 197
v2 202
v3 198
v4 282

v5,6 377

otherwise its a unmodified dlite.
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[/img][IMG:150:128]http://img340.imageshack.us/img340/3204/p1000187vp7.th.jpg[/img]

[Bob-I]

I'd bet your problem is high frequency oscillation. I see that you have not shielded the master volumes. That may solve your problem.

If you have a scope you can look for HF signals coming from the various plates in the preamp, if not, you'll just have to try to shield wires and see if that takes care of it.

[ampedup]

Thanks Bob, i was planning on sheilding the OD and Level but didn't think the master needed it, but would this cause the first stage to sound this way?

[Bob-I]

Thanks Bob, i was planning on sheilding the OD and Level but didn't think the master needed it, but would this cause the first stage to sound this way?

The master? yes. Very likely. I'm assuming a global master, so any oscillation from the master/PI would cause this sound.

[ampedup]

this image should be much better

[IMG:100:75]http://aycu40.webshots.com/image/40959/2000807615705859278_th.jpg[/img]


[IMG:100:75]http://aycu40.webshots.com/image/41359/2000884622887269566_th.jpg[/img]

[dogears]

I don't like the looks of your LFB network on V1. Try seperating the 22M resistors. They are touching....... Also, the bypass cap for the grid resistor of V1B is close the grid resistor of V1A.

Also, try ceramic instead of mica on the treble cap. Definately use shielded cable on all four connections of the OD pots.

Once again, I know I am a broken record, but the presence pot wiring is really wrong. Do not ever ground the 3rd lug of the presence pot. Cut the buss from the pot and ground just teh cap and 390 ohm tail to the buss. Pot is UNGROUNDED.

I know there may be more but try these first.....

[Bob-I]

That second image is better.

The Red yellow and green wires from the pots, try seperating them with a chopstick while the problem is happening. It may not stop it, but if it changes in any way you're in the right area. That green wire on top of the pots may be an issue too. Try moving that one also.

Again, shileding the right wires is the key to a stable oscillation free amp.

[ampedup]

you guys rock! i sheilded the OD and master volume, seperated some of the wires and resistors that were close to each other, changed the treble cap from 500 to 330p(ceramic) and rewired the presence. now i can turn up the 1st stage vol and get as much distortion as i can stand, its a different amp! presence seem more dramatic now. i have some new tung sol 6v6's to try in it and i may try some more of the mods from the dlite mod schematic, i assume the changes on that schematic after the PI are only if you have 6l6's, is that right?

thanks dumble dudes.

[Bob-I]

Awesome news. Glad we could help out.

[ampedup]

i have my presence going to the 8 ohm tap should i change to the 4 ohm?

[Structo]

I've heard you can do that to taste.

[dogears]

Yes. I would use a 4.7K feedback resistor on the 4 ohm tap as a baseline.

i have my presence going to the 8 ohm tap should i change to the 4 ohm?