V90 Ch1 Tweed mode hiss

[philosopher]

So, tbh I initally didn't found the Tweed mode to be any interesting, so it was left alone.

Thought yday to give it another try, only to find out there's a serious constant hiss coming out the speakers, when engaged.

Switched to clean, hiss gone. Switched to tweed, hiss is back.
Took the cable out, gone. Put back, hiss again.

Increase volume/gain/treble, all result to louder hiss.
FX on/off/bypass makes no diff.

Sounds a lot like pink noise, not like tube noise.
In any case, I swapped all tubes one by one.
Unless two of them failed at the same time, tubes is not the problem.

Afaik all other channels/modes are unaffected, only ch1 Tweed mode has the issue.

Could be a resistor somewhere along the tube gain path?

Any similar experience?

 

[rarebitusa]

So, tbh I initally didn't found the Tweed mode to be any interesting, so it was left alone.

Thought yday to give it another try, only to find out there's a serious constant hiss coming out the speakers, when engaged.

Switched to clean, hiss gone. Switched to tweed, hiss is back.
Took the cable out, gone. Put back, hiss again.

Increase volume/gain/treble, all result to louder hiss.
FX on/off/bypass makes no diff.

Sounds a lot like pink noise, not like tube noise.
In any case, I swapped all tubes one by one.
Unless two of them failed at the same time, tubes is not the problem.

Afaik all other channels/modes are unaffected, only ch1 Tweed mode has the issue.

Could be a resistor somewhere along the tube gain path?

Any similar experience?

FWIW... from what I can tell briefly looking at the schems is M3, mode 3 relay for "Tweed mode" brings in C7 and R216. The tube voltages don't change for Tweed mode so there's probably not much else going on with it circuit wise. It may be one of the component areas to look at. In my V:90 Tweed is significantly louder then FAT or Clean and there is more hiss in comparison.

 

[spawnofthesith2]

I have some noise on tweed mode too

 

[philosopher]

Thanks both. However, in my case, I wouldn't call it "more" or "some" noise.
It's a big difference, especially compared to Clean/Fat mode of the same channel.

I'll need to check it somehow

 

[DECEMBER]

I've had two Mark V 90W heads. The first one was returned because of severe noise that wasn't remedied by new tubes. Low-frequency hum in the reverb and a high-pitched squealing in the clean channel that was much worse on Tweed.
The one I have now (since April) also has a slight high-pitched squeal in the clean channel that is worse on Tweed. Tweed is the noisiest voicing in the amp. I don't know why it is, and different/new tubes don't help.

 

[Eevil]

I've had two Mark V 90W heads. The first one was returned because of severe noise that wasn't remedied by new tubes. Low-frequency hum in the reverb and a high-pitched squealing in the clean channel that was much worse on Tweed.
The one I have now (since April) also has a slight high-pitched squeal in the clean channel that is worse on Tweed. Tweed is the noisiest voicing in the amp. I don't know why it is, and different/new tubes don't help.

To me it feels like the clean channel is the least filtered channel on the amp and tweed the highest gain mode of that channel -> small turd early in the chain will be amplified and is more audible compared to other channels.

That’s just a gut feeling and my guts have not served always in a most reliable way

 

[mace]

Is the GAIN set high, like 2 oclock or above? Tweed will be noticeably noisier than FAT at higher gain settings.

 

[DECEMBER]

Is the GAIN set high, like 2 oclock or above? Tweed will be noticeably noisier than FAT at higher gain settings.

My Tweed has a high-pitched whine no matter where the gain is set.

 

[bandit2013]

The tweed mode shorts out a series resistor (100k, R216) and disconnects a pull-down resistor (475k, R110) with Relay RYM3A before it funnels into V1B, this raises the signal level considerably so there will be more noise floor on that mode. With clean and fat, the 745k pull-down resistor helps in signal reduction and the grid stopper R216 keeps the noise floor at a much lower level. That may be an inherited characteristic of the tweed mode. You could try a Mesa SPAX7 in V1 as it does have a slight less gain and less noise. If tweed was a must use mode, a noise gate may be needed like the Fortin ZuuL. I am not fond of noise gates, but I have one for a different amp that is nothing but noise floor.

 

[DECEMBER]

The tweed mode shorts out a series resistor (100k, R216) and disconnects a pull-down resistor (475k, R110) with Relay RYM3A before it funnels into V1B, this raises the signal level considerably so there will be more noise floor on that mode. With clean and fat, the 745k pull-down resistor helps in signal reduction and the grid stopper R216 keeps the noise floor at a much lower level. That may be an inherited characteristic of the tweed mode. You could try a Mesa SPAX7 in V1 as it does have a slight less gain and less noise. If tweed was a must use mode, a noise gate may be needed like the Fortin ZuuL. I am not fond of noise gates, but I have one for a different amp that is nothing but noise floor.

There's so much noise in my apartment, I need 3 gates in the chain.
I've had SPAX7, RCA 12AX7, EHX 12AX7, Mullard CV4004, Tube Store 7025 in V1 (and every position) and they make no difference in noise. They definitely change gain character and levels, especially if I work in the JAN Phillips 5751 or 12AT7.

 

[philosopher]

OK so I see tweed mode noise is common ground. The circuit design seems to encourage more noise on that mode.
I'm sure cables, pedals, shared outlets add even more noise. I'll try to isolate and see if this is the case and file the case as 'by design'