Is hiss normal for a Dumble build in OD mode?

[titser_marco]

Hi! I just did a D-style build and when I dime all controls (including the OD Trim) I get loads of hiss. Is this normal?

[norburybrook]

In my limited experience yes I have built two.

Gain is gain, and when you pile it on in an analogue valve circuit you're bound to get some noise.



Obviously there will be different levels of 'noise' depending on your choice of components etc. Metal film resistors are supposed to be quieter than Carbon for example.


Marcus

[titser_marco]

In my limited experience yes I have built two.

Gain is gain, and when you pile it on in an analogue valve circuit you're bound to get some noise.



Obviously there will be different levels of 'noise' depending on your choice of components etc. Metal film resistors are supposed to be quieter than Carbon for example.


Marcus

Got it! I was just checking for any issues with the amp dimed as I had some parasitic oscillation at some point before moving wires around and changing V1, so I never really got to check its ratio against an actual guitar signal. Thanks!

[Structo]

Yes, you can get that air/ hiss sound on any tube amp.

What wattage is your amp?

If 100w, then you probably would never crank everything up when playing.

Many amps will squeal if you turn everything up, but that's not real world.

If you suspect a parasitic oscillation, double check lead dress and component placement.
The Dumble layouts represent how the amp should look inside.
Pay attention to the ground points as well.

If you have access to a scope, you should be able to find where the oscillation is taking place.

[titser_marco]

Yes, you can get that air/ hiss sound on any tube amp.

What wattage is your amp?

If 100w, then you probably would never crank everything up when playing.

Many amps will squeal if you turn everything up, but that's not real world.

100w indeed. Plus I haven't really tested it yet in a gigging scenario - i.e. me facing away from the speaker - so I am suspecting that it's the close distance between myself and the amp that may also be doing this. Additionally, I also need to mention that it's more pronounced with P90s. But then P90s are notorious for being noisy when paired with ANY AMP.

If you suspect a parasitic oscillation, double check lead dress and component placement.

The Dumble layouts represent how the amp should look inside.
Pay attention to the ground points as well.

If you have access to a scope, you should be able to find where the oscillation is taking place.

I have been doing that indeed and just now I twisted the plate and cathode wires for the preamp tubes together and have gained a significant decrease in noise. I have yet to sort out the lead dress as far as which wires could be cable tied together for minimal issues as well as neater wiring.

Any tips? I use shielded on all signal wires except tone controls; should I use shielded wire here too?

[/quote]

[Structo]

Using too much coax in the amp can stifle the tone, especially the top end.
If you refer to pictures and layouts you will see where it should be.
On the input and on the OD output.

Your best guide for lead dress is to view other peoples amps that are nicely done.

Also the ODS layout is key for ground locations and wiring.

I don't recall, did you build a Dumbleator yet?
That also helps smooth the tone.



This photo is courtesy of UltraHookedOnPhonix.

[titser_marco]

No, I didn't build the Dumbulator and I don't think will just yet. I think looking at others' builds is surely helpful, but I'm in a sort of quandary since my build is more like a salvage build. Its a chassis I got from this fake Fender that used terminal strips in its original config. I guess what would be helpful for me is knowing which wires shouldn't be near which ones.

So far the only thing that seems to work is turning the presence knob down to tame the harshness. With that however comes a compromise of course.

I'm curious though: has anyone here or anyone you know tried cranking their ODS style amps? How was it?

I've also read somewhere on TAG about Gil'd experiments using larger value pots for the OD and OD Level controls. I think I will try that this weekend.

[Structo]

I have 250K pots on the OD, seems to thicken the tone a bit.

[ayan]

I have 250K pots on the OD, seems to thicken the tone a bit.

I'll piggyback a question for you here. I think the choice of 100K linear pots for the OD has two drawbacks: (1) if you set the overdrive level low enough, the clean have the same volume (or less) as the overdrive and I like my overdrive to be quite a bit louder than my clean; (2) the overdrive tone can have too much high end depending on a number of things. However, one thing the 100K linear pots do is make it pretty easy to set the overdrive channel because by the time you point them halfway up, the changes in either direction are pretty subtle.

I have not tried the 250K pots, at least not in years, but I have always wondered if audio taper pots (and I mean the Alpha variety, 15% taper) wouldn't feel too slow, and if 250K linear pots wouldn't be too fast. So, Structo, my question is: what type of pots did you use and can you comment of their "feel" VS 100KL pots?

Thanks,

Gil

[Duble]

I have yet to sort out the lead dress as far as which wires could be cable tied together for minimal issues as well as neater wiring.
Any tips? I use shielded on all signal wires except tone controls; should I use shielded wire here too?

I tend to keep with the idea, B+ and Signal should not be zip tied together and my amps are pin drop quiet. The Master vol doesnt need coax cable in most cases. Coax only used for the higher gain parts of an amp & the grids on gain stages. But thats the normal dumble afair.

My built in Dumbleator is grounded at its tube location including the filter cap. I put the components on the board, and run wires to the socket like the other gain stages. Running the plates and cathode wires in parallel like other stages helps with noise too.

[Structo]

I believe I have a PEC 250KA on the OD Volume and a Alpha 250KA on the Drive.

These are my regular knob settings.
Volume___1:00
Treble____2:00
Middle____12:00
Bass_____10:00
Drive_____1:00 - 2:00
OD Vol____1:00
Master____1:00
Presence___1:00

Then I adjust the overall volume with the Dumbleator Output control.
I think I have the OD trimmer around 28K with relay on.
Any of this would probably change depending if I was gigging or at home.

[ayan]

Thanks.

G.

I believe I have a PEC 250KA on the OD Volume and a Alpha 250KA on the Drive.

These are my regular knob settings.
Volume___1:00
Treble____2:00
Middle____12:00
Bass_____10:00
Drive_____1:00 - 2:00
OD Vol____1:00
Master____1:00
Presence___1:00

Then I adjust the overall volume with the Dumbleator Output control.
I think I have the OD trimmer around 28K with relay on.
Any of this would probably change depending if I was gigging or at home.

[Charlie Wilson]

I suppose a 2-35 250kA pot might be a good choice. Tom, I am curious, do you still have snubbers on V2?
CW

[Structo]

Yes I have snubbers.

I believe I have 220pf caps on V2.