Drastic Volume Change on Jazz/Rock Switch - Dumble ODS #102 Clone

[frusciante89]

Hi all,
Just wrapped up a Dumble ODS #102 build and something's off with the Jazz/Rock switch. I've built a few of these over the years, but I'm getting a major volume difference when toggling the switch - way more than I remember from previous builds.
It should just be switching the 0.005uf in the bass circuit, but this feels more like a gain stage dropout or something. The tonal shift is there, but the volume change is throwing me off.
Anyone else experienced this? I don't recall it being this pronounced before.
Cheers

[martin manning]

Check your connections carefully. Jazz mode does three things:
Disconnects bass pot input and wiper from bottom of treble
Connects 100k from bass pot wiper to treble pot wiper
Connects 10n from bottom of treble to ground

[frusciante89]

Thanks Martin! I’ve checked the connections more than 10 times, but will do it again with a fresh set of eyes tomorrow. Also all grounds are in place, at this point I wonder whether the switch itself has failed after multiple soldering/desoldering to its tabs.
So you confirm the change would only be tonal, not volume increase?
Thanks

[martin manning]

There is a volume reduction in jazz that varies with frequency, 4-8 dB, more in the scooped low-mid. That might be what you are hearing.

[Colossal]

Check your connections carefully. Jazz mode does three things:

Connects 10n from bottom of treble to ground

Martin, is it 10n to ground? I thought Jazz was 5n? Deep has 1M//10n.

[martin manning]

Correct, 5n.

[frusciante89]

Hello guys,
thanks first of all for the replies. I did some more investigation today. Upon triple checking the wiring and not finding anything, I've redone the soldering of the rock/jazz switch. Also took out the switch and replaced it. I think the problem is still there, the volume change is quite noticeable and in the lowest volume setting it sounds thin and quite weak bodied. I'm attaching a video for reference. Also, attaching some pics of the area (the deep switch still misses a jumper, forget about that).
What do you suggest? I tracked all voltages down but I might have to do it again... running out of stamina in hunting down this problem

Thanks for the help






copy viewer link after upload

[martin manning]

I think it's acting as it should. Bode plot below shows R vs. J with TMB all at noon.

[frusciante89]

Are there some voltages I can measure affected by the rock/jazz mode? As I’m not sure I’ll be able to get a Bode plot out of this

[martin manning]

This is all AC behavior. Notice the drop at the mid scoop, 200-300 Hz, is around 16 dB... about as much as the FET boost gain.

[martin manning]

PS I suppose you could feed a signal in, measure AC voltage at the input and output of the tone stack and calculate the delta in dB. A digital oscilloscope would speed that process up.

[La Truite]

My #102 clone has a massive drop in volume from Rock to Jazz too

[frusciante89]

Thanks guys. I finally had some time to take voltage readings yesterday night. Here they are (also attaching the schematic with my notes):

B+ (STANDBY) = 492
With amp on:

B+1 = 463
B+2 = 459
B+3 = 440
B+4 = 334
B+3 = 326

Tubes:
V1-1 = 207
V1-3 = 1.69
V1-6 = 203
V1-8 = 1.8V

V2-1 = 211
V2-3 = 1.74
V2-6 = 206
V2-8 = 1.86V

PI node: 432
after 110k = 294
afetr 120k = 292
bias = -46V (30/32mA measured at the 1Ohm resistors)

6L6 plates = 460

LM7812 reg = 11.72
OD trim = set to 25k, measured with amp on to GND.
The FET section hasn't been set yet.
(I’m using a Fluke 289)

What do you think? anything that looks suspicious?

[ElectronAvalanche]

Hi there,

With the Jazz setting you need (!) to turn up the mids and bass to get back the volume/level. That is simply how this works. I think all is fine with your rock/jazz wiring.

Best, Electron

[frusciante89]

Thanks Electron.
Am I correct to assume the voltages look in line with a 102? Anything that stands out?