Master/Volume pots on a Fender Blues Deluxe

[ksor]

I have always had this problem with my guitar amp - it is way too loud when using it in my living room !

I can't adjust the MASTER and the VOLUMEN down LOW enough for using it in my living room - on stage it's just cracked up and working fine.

There are lots of videos/links out there showing the problem and different fixes BUT ...

nearly ALL of them mentiones that the amp has LINEAR potmeters and a switch to LOGARITMIC potmeters should cure the problem - maybe that's correct BUT...

Today I was confirmed from a Fender repair store that the Blues Deluxe allready IS fitted with LOG potmeters !

Now I'm confused - OK, as some mentiones too - some amps was fitted with LIN pots as a failure and MAYBE mine is from a production run in the late 1990's where this COULD be the case.

I looked at the pots in my amp and they have this stamped on them:

MASTER      : 10A1M9422            (in the schematic it's R21)
VOLUMEN  : 15A250K9448      (in the schematic it's R7)

The last 4 digits is production year/week, I think.

The 1M and 250K is the ohm value, I think.

Then MAYBE the 10A and 15A could tell IF it a LIN or LOG-type - but they can't be the same type LIN or LOG, and I have the problem on both of them.

It's a little hard to take the pots out to do some measuring on them.

Anyone here knowing the meaning of the 10A and 15A ?

Maybe know a fix for that problem with the Fender Blues Deluxe amp ?

 

[CJ]

do not know what the 10 and 15 mean.

those numbers would seem to indicate audio parts,

those amps are hard to work on when it comes to changing pots, requires circuit board removal,  :'(

there might be some less invasive surgery possible,

these might include:

1)changing the preamp tube to a lush sounding 12AY7, the best sounding first tube IMHO,

6072 mil version is sweet but $$$,
JJ now has a 12AY7 and we are anxious to try that out,

2) change the phase inverter to 12AT7, not a huge gain reduction but when combined with option 1) it might help


3)  solder a resistor across the pot, maybe a 1 meg across the 1 meg pot etc,

4) see if there is a resistor underneath the master volume pot, if so,  jumper it

5) use 12AY7 tubes for every preamp tube,

6) replace pots - even if they are log taper, they might come on too soon, to check, put ohm meter from center lug to ground and write down ohms at 1-2-3-4-5-6-7-8-9-10

if position 5 is too high, you might be better off with a different brand pot,

you can use different pots by using wires from pot to pc board,

if all of the above do not work, then you can re-engineer the circuit by installing or tweaking existing voltage dividers, using smaller value caps, reducing screen voltage by adding resistance, installing cathode resistors, connecting an 8 ohm speaker to 4 ohms,

could not find thread where we fixed this problem, thought we posted on this, will search again,

 

[ksor]

Thx to CJ for this massive answer !

If I change the tubes I think I'll reduce the gain when I'm on stage too - right ? - so that's not an option, I think. Too I'm afraid it maybe change the "sound" of the amp - maybe I'll miss a little of that warm overdrive,

I already have the PCB out so I'll go and see about the resistor in 4) and try out the LESS invasive change - just jumper the 4) resistor OR 3) put in a resistor - I think you mean a resistor from ground to the slider (center lug) on the pot - right ?

Oh, a setting on 5 will blow your head off right away !

The ohm measuring in 6) requires I have the pot off of the PCB - right ?

 

[abbey road d enfer]

do not know what the 10 and 15 mean.

I would think 10A and 15A indicate the taper, A being generic Log and the number defining the taper at mid-rotation.

 

[abbey road d enfer]

I have always had this problem with my guitar amp - it is way too loud when using it in my living room !

I can't adjust the MASTER and the VOLUMEN down LOW enough for using it in my living room - on stage it's just cracked up and working fine.

That is quite surprizing. I must admit the pots in this amp do not have the smoothest taper, but maybe you're expecting too much...
The main question is "what is low enough"?
Does it get better using Input 2 instead of input 1? (Input 2 has 6dB less gain the Input 1)
Then can't you turn down the volume on the guitar? I know it changes the tone, but anyway you can't expect decent sound from a cranked down amp...

Anyone here knowing the meaning of the 10A and 15A ?

10%Log and 15%Log tapers.

Maybe know a fix for that problem with the Fender Blues Deluxe amp ? 

You may want to try inserting an attenuator between the Preamp out and Amp in jacks. Easiest would be a volume pedal, but you can wire a potentiometer between two male 1/4".

 

[ksor]

>> abbey road d enfer

In general I think it would be better if the pot had larger movement at LOW volumen - within 1 or 2 degrees around 2 on the scale it goes from not audiable to way, WAY TOO LOUD ... and it's not just dirt in the pot !

The problem goes for BOTH MASTER knob and VOLUMEN knob =same pattern - so I think the pots are of the same type (LIN/LOG) so the 10A/15A has nothing to do with the "taper" ... is that the right trm ?

 

[PRR]

> attenuator between the Preamp out and Amp in jacks

+1

This amp has _3_ stages before the power section. Various attenuations hung off it, but that's still a LOT of gain. The amp is scaled to play LOUD.

Plug out the Pre Out jack, tip to top of 10K Audio pot, wiper to plug in Pow Amp In jack, both grounds to pot bottom. As this is a fairly low impedance loop, you may not need a metal box (and it is safe to touch) if wires are short. Trim-down to taste. When you get a gig, turn full up or just yank the pad out of the jacks.

Mark the plugs Pre and Pow so you get them in again right.

 

[CJ]

ok we found the repair log for this problem, what we did was install a 250K audio in place of the 1 Meg

we could still reach 95 percent power but have more resolution at lower volumes,

 

[abbey road d enfer]

ok we found the repair log for this problem, what we did was install a 250K audio in place of the 1 Meg

we could still reach 95 percent power but have more resolution at lower volumes,

I don't think teh actual value has much to do with this issue, except that 250k loads the preamp atad more than 1 Meg, which results in slightly reduced overall gain. I really think the actual taper is the most important factor. The problem with the original pots is they have an elevated taper. A more appropriate taper would be 10% Log, but manufacturers use elevated tapers because the amp seems to be louder; "I just turn it up to 3 and it peels the wallpaper".

 

[CJ]

yes, a little more loading plus we used an old school 250K that had a smoother taper, those Fender pots do come on quicker than a audio taper  Alpha or CTS,

 

[ksor]

OK, it seems a little more complicated than the impression you get by links/YouTube videos so I think I'll take the LEAST invasive solution - the pot in the effectloop !

No capacitor needed ?

Thx for your time and proposals !

 

[ksor]

YES - just what I needed !

I only had a 20K LOG potmeter - placed in the effect loop it solved my problem - now I have a nice wider range for adjustning at LOW volumen.

Again - thx to all for your time and proposals ! ;-))