Blues Deville reissue tone control acts like bass control in reverse

[Mars Amp Repair]

Hello folks, been very busy with biz & neglectful of forum. I'll have to change that.

Anyway, I have a reissue Blues Deville that the treble control acts more like a bass control in reverse. IOW, turn it up & the bass is cut (hi's pretty much stay the same). Turn it down & you get more bass. The bass control & mid don't seem to have as much affect on the sound as they should, but act fundamentally normal.

There are no bad components in the circuit as well there are no incorrect value controls or components. There are no bad traces or grounds missing. The tone stack is a pretty basic Fender stack as shown on schemo.

Does anyone have personal experience with this model and remember how the treble control behaves normally?

I have noticed that if I unload the stack by removing the connection to the drive control, or setting amp to 'no drive' and lifting R16 12K resistor, the treble control then operates normally (see attchd schemo).

The drive pot and R-16 are the correct values as well. Fiddling with the values doesn't seem to be of any benefit either.

I'm of a mind that this amp is operating as it was designed. Any ideas?

I notice that in the HR Deville/Deluxe, they separated the drive control from the stack by one 12AX7 stage. Perhaps this is partially the reason. Thanx, glen

[doctor]

Hello folks, been very busy with biz & neglectful of forum. I'll have to change that.

Anyway, I have a reissue Blues Deville that the treble control acts more like a bass control in reverse. IOW, turn it up & the bass is cut (hi's pretty much stay the same). Turn it down & you get more bass. The bass control & mid don't seem to have as much affect on the sound as they should, but act fundamentally normal.

There are no bad components in the circuit as well there are no incorrect value controls or components. There are no bad traces or grounds missing. The tone stack is a pretty basic Fender stack as shown on schemo.

Does anyone have personal experience with this model and remember how the treble control behaves normally?

I have noticed that if I unload the stack by removing the connection to the drive control, or setting amp to 'no drive' and lifting R16 12K resistor, the treble control then operates normally (see attchd schemo).

The drive pot and R-16 are the correct values as well. Fiddling with the values doesn't seem to be of any benefit either.

I'm of a mind that this amp is operating as it was designed. Any ideas?

I notice that in the HR Deville/Deluxe, they separated the drive control from the stack by one 12AX7 stage. Perhaps this is partially the reason. Thanx, glen

Try to replace C46 (22uF / 500V).

[Albert Kreuzer]

I just put it into Duncan's tonestack calculator with a 45k load (R15+R16, R17 shorted), and what you describe seems to be normal. Compared to a 1M load it shows -10dB attenuation and a somewhat big-muff-like behaviour.

[John G]

Hi,
Don't know if it will make a difference here but you have posted the old schemo, the reissue is different on some places.
I think the schemo is on the Fender downloads site.
John
PS my experience has been when the trb control cap is of a small value then the range does go from dark to very toppy brite.........Think AC30 as an extrem example

[J M Fahey]

What you see/hear is normal *in this case*.
The tone stack is classic Fender ... but those usually are loaded by a 1M pot and little else.
This one is *heavily* (and this is an understatement) loaded, which chokes it to death.
What were they thinking?
Your ears, and Albert K's simulation match perfectly.
Do not forget that to worsen things, it's driven by a generator with about 50K internal impedance.
Oh well, they are Fender, they have so much good Karma accumulated from Leo's era that they can do almost *anything* with impunity.

[John G]

Hi,
Blues deville/deluxes reissue schemo
John

[Mars Amp Repair]

thanx all,
I can see where the HR models have the tonestack directly feed the next stage with nearly no load. this one as mentioned has the drive control as well as the 12K resistor for non-drive scenario to set the gain of this stage. I guess the loading changes the entire action of the stack. Don't know why Fender did this, but glad to know it's apparently normal...thanx, glen

[unparalleled]

Hi did you ever resolve the treble problem?
I have one of these on my bench and it sounds like crap.
It looks like the Drive Pot and R16 (12K) are loading the tone stack and the grid of
V2 A to ground.
The Hot Rod Deville has a 250PF Cap blocking the DC from the drive circuit.

[Mars Amp Repair]

Hi did you ever resolve the treble problem?
I have one of these on my bench and it sounds like crap.
It looks like the Drive Pot and R16 (12K) are loading the tone stack and the grid of
V2 A to ground.
The Hot Rod Deville has a 250PF Cap blocking the DC from the drive circuit.

Hello Unparalleled,
Well that was a long time ago, however I checked & have no notes in my Symptom-Remedy log to indicate that I ever resolved or modded the stack to get a more favorable result. Be certain to post if you find a solution, however I have to think if it were a huge issue with end users, there would be more entries of solutions here in this forum.
Glen

[Chuck H]

The solution is pretty simple. Just increase the loaded values while keeping the voltage division. Not wanting to calculate for all the variables in the stack itself I used a CAD program and came up with:

Change R8 to 220k

Change R102 to 28k

Change R7 to 500k (drive pot)

This will likely change the taper feel of the drive pot but so what.