Fender Blues Deluxe Volume Cont Linearity

[cablercdd1]

Does anyone know what would be needed to change the volume and master controls on the Blues Deluxe so that the amp volume can be adjusted across the entire 1 to 10 range of the control and not just 1 to 3. It's very hard to get the amp volume where it's needed with so little control. Did they use linear taper on these pots?
Thanks,
Paul

[MWJB]

The problem is partly because of the gain from the plate fed tone stack, plus the way the volume control is wired. They tend to ramp up real quick.

Fender use Audio pots on these amps & the volume control is 250K rather than the usual 1M.

Assuming that you are happy with the tone, you just want more sweep on the knob, I would try a combination of:

1) increasing the value of R6 by tacking a 220K to 330K resistor in series, this will calm down the pot slightly, may reduce fidelity a little, so I wouldn't go mad here, 470K at the absolute max.

2) Next, set the volume to just about the highest setting that you will ever use (not easy to do this at home, without the background of bass & drums), measure the ohms value between input & wiper (middle tab) of R7/volume pot & record (the connection of the other end of the pot to the wiper will show a short). Now set the pot to where you want your new "max" volume to be...I wouldn't go as far as to have this at 10-12, I'd aim for 2/3 rotation to give you some leeway. Now measure the pot again.

What you need to do is to tack a resistor accross the 2 working tabs of the pot to make the value at your new "max" point match that of the old max volume. E.g if your original max volume was 40K (I am making this figure up for purposes of illustration, be sure to use measured values), then the value you measured at 2/3 rotation was 120K, you need to tack in a resistor that brings 120K down to 40K, so that you now read 40K at 2/3 rotation.

...if 120K*68K = 8160 ...68K being the estimated size of the new resistor.

8160/(120K+68K) = 43.4K

So in this example a 56K to 68K resistor would do the job.

The math is simply working out parallel values, if you don't get it, just post the values you actually measure.

If this doesn't do the whole trick - A lot of guys also find these amps have little headroom & not a great clean tone, often subbing V3 for a 12AT7 and/or V1 for a 5751 helps headroom & gets an "airier" more traditional Fendery tone. Be aware that changing these tubes will also affect the "Drive" tone if you use this feature.

[CharlieP]

The volume pot is audio and the master is probably linear like the HRDx. On my HRD I ordered another 250k Fender audio pot and replaced the linear. Antique Electronic Supply has them.
I have a 12au7 in V1 and a 12at7 in V3.

[ziggy007]

x2 for charlieP. I changed the master & volume pots to Audio pots in my HRDx (note the correct size pot base as its tricky to get onto the cct board) but a huge difference and well worth it. Definitely play round with the tube types as well.
Gavin

[CharlieP]

Originally Posted by ziggy007

x2 for charlieP. I changed the master & volume pots to Audio pots in my HRDx (note the correct size pot base as its tricky to get onto the cct board) but a huge difference and well worth it. Definitely play round with the tube types as well.
Gavin

Why would you change the volume pot? It was already an audio pot and not a linear. The master was a linear tho and that is why I only changed that pot. I also did the brite mod, adding a couple of caps to the volume and drive pots. Then I changed a few small caps and a slope resistor and clipped out the resistor under the reverb. R103. Sounds great now. I used the Fender 250k audio pot because it was just a clean replacement and same style as I took out, bracket and all. I didn't want to go to a 500k or 1M pot because of the extra work needed to fit it in.

[ziggy007]

hey CharlieP, My bad. It was only the master ( i'll blame the time of the morning)
Yeah I have also done the bright mod and a whole heap of others . It sounds pretty good now. (still no BF thou) Haven t done the R103 reverb cut one. might try that when next in there.
cheers
Gavin

[CharlieP]

Originally Posted by ziggy007

hey CharlieP, My bad. It was only the master ( i'll blame the time of the morning)
Yeah I have also done the bright mod and a whole heap of others . It sounds pretty good now. (still no BF thou) Haven t done the R103 reverb cut one. might try that when next in there.
cheers
Gavin

It is the easiest mod to do and makes considerable difference in the reverb. I like the reverb now and before it was crap. All you have to do is pull the back panel, locate it under the reverb pot and clip it out. Nothing else to do. If you don't want to clip it out yet just clip one end. Try the reverb and if it doesn't suit you then solder the end back together. I don't think you will be hooking it back up tho.