Channel bleeding into other channel - Dual lite Plus

[Wonder2121]

- Thousand blessing on all your houses for 2024 - 

http://sluckeyamps.com/dual_lite/dual_lite.pdf

Build Slucks Dual lite plus with added MV over Xmas, great amp, very happy, only issue...
When either one of the two channels is activated via the DPDT switch, Alls good until volumes increased on the grounded channel (rushing water hiss sound) bleeds through into active channel..


Changed switch (wired correct)
Changed grounding - PI node has own ground point with MV/OT/output jack grounded here
Changed - Each node now has own B+ voltage from Cap-Can (screen side)

First thought was coming through filter caps, now thinking bleeding through PI..Is this just a case of living with the fact or can something be done..

Pete¬

 

[d95err]

I would make the channel switch mute at the volume pot wiper for each channel, and wire the input to both channels permanently. That should take out any channel bleed.

It would also mute any noise coming from the unused channel preamp gain stage as well.

[sluckey]

When either one of the two channels is activated via the DPDT switch, Alls good until volumes increased on the grounded channel (rushing water hiss sound) bleeds through into active channel..

My amp doesn't do that. Did you build exactly according to my schematic? Any mods? Show us some gut shot pics of your amp.

[Wonder2121]

I need schematic software to upoload mods..
Tried ExpressSCH, not enough guitar amplifier symbols, must be easier software....DIYLayouts what I use...
I dares upoload gut shots, it's mess at min, doubt anybody would make head nor tail of whats going on, all the pots are outside chassis with leads fired over, my grounds are alligater cliped here and there (even when soldered into place problem persists)...Some resistors temped in, hanging in air....

If I upload pic, all I'll recieve is remarks on how dangerous, soldering techniques, all that...
Amp was built beautifully and works great, just the channel bleed situations made me delve into making mods, hence why its a mess right now!...

Ef86 & 12ax7 nodes have own B+ with 16uf filters, 12ax7 parallel triodes with split cathodes one side has 2.7k/1uf bypass cap other has 690ohm unbypassed...I tried adding bypass cap to this side, didn't stop signal bleed...Type2 MV grounded at PI, tried different grounding points...
Added PI ground point between input and PT ground thinking signal was coming through there, no avail..
Added mixing resistors, helped somewhat....I removed tone pot for now...I'm using 32/32 can cap, most of my B+ lnes are coming from screen side so not sure if signals entering from here...I'm sure it's through the PI...But surley the signal should be grounded from the switch....Replaced switch with another dpdt 6 prong on-on wired like schem with the cross grounding..
But yeah 2 days chassing this down....Learnt a few things along the way so all good!! I always say if you don't have problems your not pushing yourself hard enough...
 

[sluckey]

I suspect your building techniques may be a factor. Several of these amps have been built using my layout. You're the first to mention channel bleed.

[Wonder2121]

Guys do you think cause is me splitting the cathodes on the 12ax7 channel?

Its parrallel tiodes - I have V1a bypassed and V1b unbypassed...Maybe the signal is swinging back into phase before hitting the PI thus not cancelling out...

[HotBluePlates]

... When either one of the two channels is activated via the DPDT switch ... volumes increased on the grounded channel (rushing water hiss sound) bleeds through into active channel...

My amp doesn't do that. Did you build exactly according to my schematic? ...

"Bleed" probably isn't the right phrase.  When he turns up the volume on the unused channel, hiss is increased.

I agree with d95err below, in that the issue seems to be that both channels are "active" in that they have their tube, Tone & Volume controls always connected to the phase inverter.  So turning up the unused channel results in more noise, if the parts used in either channel tend to exhibit noise.

Could be your amp has quieter resistors.  A fix for Wonder2121's situation might be to have the switch occur at the wipers of each Volume control (with the ability to ground the Volume-side of the coupling caps going in to the phase inverter).  A less-fun option might be relays to switch both the grid-inputs and the Volume-outputs of the channels to ensure zero extra noise.