loud noise problem

[mat]

I just changed the 2 wires going to OD master to shielded and tried different size presence pot. Result: loud noise
Only the OD master or clean master (when OD not engaged) brings the noise. No other pot execpt presence affects to the noise, not eaven the pre volume. When maxing the presence pot the noise goes away (in OD mode).

I swapped tubes, relays, presence pot(+cap), coax.. no cure Voltages are ok on V1+V2.

Moving the coax cables makes HUGE difference to the noise level. Also pressing the V2a cathode firmly against the chassis with chop stick lowers the noise level dramatically

Spent six hours trying to figure this out

I have no idea what might cause this. Any suggestions ?

[Funkalicousgroove]

Post pics of your build, sounds like you may have an oscillation.

[mat]

Ok, I swapped all coaxes going to the masters. Still noise but it can be taken to quite low level when rerouting the coaxes. The noise stops immediatly when touching with finger the .05 couplincap going to d-lator. It was actually the d-lator cathode wire that made the quieter when pressing it to the chassis.
Touching the pin 1 or 2 or 3 of the d-lator with voltmeter brobe makes the noise go away. No other pin does not take the noise away. No help with swapping the D-lator tube.

OD mode - clean master at zero -> no noise
OD mode - clean master more than zero -> noise!???
CLEAN mode - no noise at any settings.

Also I noticed that th middle control does nothing ? Pot ok. Connection to the .01 mid cap ok..

The layout: http://www.pichotel.com/pic/16028B31e/147347.jpg

I'll take pictures if You tell me where to shoot.

edit: I'll have to add that the amp starts to sound really good Amazing how much the few coaxes have to do with smoothing the sound Also thanks dogears for the tip: I replaced the 100k with 220k after HRM and like it a lot

Thanks,

[Funkalicousgroove]

Take a jumper wire and bypass the D-lator and see if the noise goes away, at that point at least we'll know it's something in the D-lator circuit.

[mat]

Take a jumper wire and bypass the D-lator and see if the noise goes away, at that point at least we'll know it's something in the D-lator circuit.

Ok, spooky stuff to come I followed Your suggestion and lifted the d-lator coupling cap and put a jumper wire to PI input. Works perfect. I took then the jumper wire and put it to the lifted end of the cap and other end to the turret where it was soldered. Works ok !? I then soldered the cap to turret and the noise is back Unsoldered and jumpered -> no noise Can it be the cap itself ?

[Funkalicousgroove]

Sure, try swapping the cap.

[heisthl]

reverse the polarity on the cap - even though there is no + or -, one leg is more of a shield than the other.

[Funkalicousgroove]

Just had another thought:

If it works with the cap attached to the lead while the cap is off the board, but makes noise when you attach to the eyelet, perhaps you have something making contact with the eyelet on the underside of the board?

[dogears]

Hey Mat,

How does the amp sound without the Dumbleator? Harsh issues gone??

[mat]

Hey Mat,

How does the amp sound without the Dumbleator? Harsh issues gone??

It is better with D-lator, smoother. I'm beginning to like this amp very much How does it sound to You ? http://media.putfile.com/hrm-works

The amp was on for few hours before I recorded the clip. Definitely better sound than immediatly after power up.

Sure, try swapping the cap.

Tried. No help.

reverse the polarity on the cap - even though there is no + or -, one leg is more of a shield than the other.

Tried.No help.

Just had another thought:

If it works with the cap attached to the lead while the cap is off the board, but makes noise when you attach to the eyelet, perhaps you have something making contact with the eyelet on the underside of the board?

Sorry, wasn't clear enough. I lifted the cap only on the other end (front end). Then jumpered the lifted end to the turret -> works. Soldered the end to the turret -> does not work ?!?

I rerouted the wire from the cap going to the PAB relay and the noise is at quite low level now. I start to suspect the OT secondary wires that come inside the chassis about underneath of that particular cap. I might try to route them outside of the chassis and then through chassis nearer to the output jacks..

[heisthl]

[I start to suspect the OT secondary wires that come inside the chassis about underneath of that particular cap. I might try to route them outside of the chassis and then through chassis nearer to the output jacks..

I've made this mistake before, the OT secondary wires are some of the worst when it comes to imparting noise and need to be at least an inch away from running parallel to anything in the signal path. It's tempting on a new build to mouint the OT toward the edge of the chassis where the preamp tubes are mounted, which is fine unless you bring the wires in too close to the early stages. Better to have the primary and secondary wires come in between the output tubes and circuit board ala Fender.

[mat]

[I start to suspect the OT secondary wires that come inside the chassis about underneath of that particular cap. I might try to route them outside of the chassis and then through chassis nearer to the output jacks..

I've made this mistake before, the OT secondary wires are some of the worst when it comes to imparting noise and need to be at least an inch away from running parallel to anything in the signal path. It's tempting on a new build to mouint the OT toward the edge of the chassis where the preamp tubes are mounted, which is fine unless you bring the wires in too close to the early stages. Better to have the primary and secondary wires come in between the output tubes and circuit board ala Fender.

Thanks heisthl, I'll definitely route the wires differently.

[mat]

[I start to suspect the OT secondary wires that come inside the chassis about underneath of that particular cap. I might try to route them outside of the chassis and then through chassis nearer to the output jacks..

I've made this mistake before, the OT secondary wires are some of the worst when it comes to imparting noise and need to be at least an inch away from running parallel to anything in the signal path. It's tempting on a new build to mouint the OT toward the edge of the chassis where the preamp tubes are mounted, which is fine unless you bring the wires in too close to the early stages. Better to have the primary and secondary wires come in between the output tubes and circuit board ala Fender.

Could the OT pri and sec wires come from same hole inside to the chassis ? Or should they come from separate holes ?

[heisthl]

I've done it both ways and not noticed a difference. I usually separate them because they are going different places and the 5/16 snap in hard grommets(3/8 hole size) I use seem crowded with more than 4 wires.

[Tonegeek]

Mat,
I had a similar issue with my onboard d'lator. Got hum at certain settings. I moved wires around too and it seemed like it made a difference, but not really. I ended up adding a 100k resistor ahead of the .047 coupler to the d'lator. Don't know why this works, but since the noise was the worst when my clean master was off, I was thinking that somehow the cathode follower does not like seeing ground on its input which is what happens when the clean master is all the way down. I think a 10k resistor would work just as well, long as there is some resistance there. Give it a try.