Fender Blues Deluxe - Slope Resistor

[Janglin_Jack]

I am having some trouble with my Fender Blues Deluxe. The bass is really heavy. I don't want to change the PCB Bass pot, (pain in the butt). In messing with the Duncan Tone Stack calculator, I thinkI can get what I need if I change the slope resistor from 100K to 200K. What might that affect in the rest of the amp. Does that increase/decrease the insertion loss? Is there a range of acceptable slope resistor values?

Mike

[stef]

sell it asap...these amps are too fragile to mod....pro junior is the only new fender amp that sounds good

[toner]

I didn't look at a schematic for that amp but, in general, the slope R affects mids much more than bass. Switching from 100k to 200k will probably scoop a lot of mids and gain, while only affecting the bass a little bit. If you're really set on modding it, I'd suggest finding a few coupling caps or cathode bypass caps to lower to reduce bass.

[Janglin_Jack]

I didn't look at a schematic for that amp but, in general, the slope R affects mids much more than bass. Switching from 100k to 200k will probably scoop a lot of mids and gain, while only affecting the bass a little bit. If you're really set on modding it, I'd suggest finding a few coupling caps or cathode bypass caps to lower to reduce bass.

The bass pot is 1M vs 250K, so that was my primary location to change, but even with the bass pot at zero, it has a very strong bass response. I'll check the schematic to see what coupling caps and/or cathode bypass caps might be creating excessive bass.

Thanks,
Mike

[Janglin_Jack]

what would be a better fix for the bass issue, lowerin V1a Cathode cap from 22uf to something like 1.8uf or 4uf, etc. or chaning the coupling cap at C2 from .01uf to .0022uf? I think I put in a .047uf bass cap in the tone stack, but it might have been .1uf. Since the bass control is at zero, and still too much bass, I am guessing modifying the tone stack is not going to do anything. Still searching...hints?

Mike

[toner]

I looked briefly at the schem but I've never played one of these amps so these are just general ideas. If it has too much bass with the bass pot on 0, changing the pot won't help.

I think changing C1 to around 2.2uF would help more than changing C2, but that should help too.

other options:
- change bass cap (C6) from .1uF to .022uF (if you didn't change already)
- lower or remove V2a cathode bypass (C8)
- change output couplers (C25 and C26) from .1uF to .022uF

You could also look at adding mids/treble, like raise the treble cap (C5) to 330pF, etc.

[Janglin_Jack]

I looked briefly at the schem but I've never played one of these amps so these are just general ideas. If it has too much bass with the bass pot on 0, changing the pot won't help.

I think changing C1 to around 2.2uF would help more than changing C2, but that should help too.

other options:
- change bass cap (C6) from .1uF to .022uF (if you didn't change already)
- lower or remove V2a cathode bypass (C8)
- change output couplers (C25 and C26) from .1uF to .022uF

You could also look at adding mids/treble, like raise the treble cap (C5) to 330pF, etc.

I started with C1 Cathode Bypass cap for V1a. I didn't have a 2.2uf cap, so I used a 1.5uf, which I believe will create a -3db rolloff with the 1.5K cathode resistor at approx 700hz. Since it is 1am and my kids are sleeping, I could only test at low volume, I think this may be the only change needed. Will try tomorrow at gig volume to determine the outcome.

FYI - previously I did the gain mod on the Duncan Amp forum which ties in the unused half of V2. I did some other mods to the reverb, (I forgot the source of the info, but it warms it up) and changed the input jacks to Switchcraft vs the PCB mounted ones. Put in a V30 and I think the amp is almost there.

Mike

[Janglin_Jack]

Still a little bassy on the open E. I think I will look at the PI going from .1 to maybe .047, (not sure if I should go to .022 or not) as it seems close.

Mike

[Janglin_Jack]

Well, after further thought, I decided to the the PI alone and changed the cathode bypass cap at V2a C8 down from 22uf to 10uf. That should give me an extra -3db rolloff at 100hz and below. I think that is from the open A string and lower. Same problem as last night, too late to crank it up. But I hope I have it now.

Mike

[SteadyEddie]

I'm not familiar with the Blues Deluxe but a big thing with Fenders is that they are bassy. I've got a Super Reverb and I have to turn that bass pot down to 3 or so when I'm really turning that amp up. I tried reducing the bass in other parts of the circuit and nothing sounds as good. I've tried reducing the cathode bypass cap and PI caps and it sounds better just to turn the bass pot down. Don't be afraid to crank it down. When you're playing with a band, it won't sound thin, believe me.
Other things that help are good quality signal caps, especially in the tone stack. I find CDE DME 1KV caps have a very tight response in the bass and sound good in the tone stack and as PI caps.

[Janglin_Jack]

I'm not familiar with the Blues Deluxe but a big thing with Fenders is that they are bassy. I've got a Super Reverb and I have to turn that bass pot down to 3 or so when I'm really turning that amp up. I tried reducing the bass in other parts of the circuit and nothing sounds as good. I've tried reducing the cathode bypass cap and PI caps and it sounds better just to turn the bass pot down. Don't be afraid to crank it down. When you're playing with a band, it won't sound thin, believe me.
Other things that help are good quality signal caps, especially in the tone stack. I find CDE DME 1KV caps have a very tight response in the bass and sound good in the tone stack and as PI caps.

Yes, the big issue is the bass is way too strong with the bass pot at Zero. No where left to go, but find the excessive bass elsewhere in the circuit. I have previously changed the tone stack caps to orange drops and a silver mica treble cap. I just tried it out with the two cathode bypass caps altered and I think I have it pretty close. Bass is still all the way down, but I can turn it up a bit and it is still sounding good. Would like to reduce the bass just a hair more, so I was getting the amount of bass I have now at zero, when the pot is up around 3-4.

I've owned lots of Fenders and this circuit is just has excessive bass, (at least with my Les Paul). I have owned several Bandmasters, Bassmans, Pro Reverb, Super Reverbs, Champ 12 over the years. My latest was a Super Reverb that I built housed in a Deluxe Reverb cabinet/chassis with 2x10".

The one I have finally settled on is my '61/62 Blonde Bassman 6G6-A.

Will give this config with the two cathode bypass caps a go with the band and see where I am at then.

Thanks!!
Mike

[Froumy]

For me, Kill unwanted bass early, add later...

I'm not sure your 22uF to 10uF will be audible. I'd remove the bypass altogether, and start with if a .68uF or so, if necessary. Toner has some good things to try, too.

If you look at a modern amp, say the tiny terror, you'll find all the saturation resides in the highs. Same path Marshall went down, long ago. Sounds like you've got the math, but remember those stages are stepped to the next stage, and things will be compounded. You can pull some "cleaner" bass back later, which may be the balance you're looking for-not certain. I'm guessing your love for the blonde amps is going to have you searching for the right balance for a while. Right on!

For me, I'd drop the bottom early, force some mids(taste/Strat player), and make sure some clean Fender bottom presented itself at the end....

[Janglin_Jack]

For me, Kill unwanted bass early, add later...

I'm not sure your 22uF to 10uF will be audible. I'd remove the bypass altogether, and start with if a .68uF or so, if necessary. Toner has some good things to try, too.

If you look at a modern amp, say the tiny terror, you'll find all the saturation resides in the highs. Same path Marshall went down, long ago. Sounds like you've got the math, but remember those stages are stepped to the next stage, and things will be compounded. You can pull some "cleaner" bass back later, which may be the balance you're looking for-not certain. I'm guessing your love for the blonde amps is going to have you searching for the right balance for a while. Right on!

For me, I'd drop the bottom early, force some mids(taste/Strat player), and make sure some clean Fender bottom presented itself at the end....

I hear your message about killing the bass early. My trouble is looking at a tone stack calculator or knowing what frequencies are being affected by the changes I am making, with the reality of what the tone will be like. Hearing it vs on paper. I want to keep a classic Fender tone, and fear using too small a cathode bypass cap pulling out "too much" bass and affecting the mids, etc. I don't have a .01uf cap, but my thought right now is to change the coupling cap at C9 off the plate of V2a from .022uf (bass rolloff at 72hz) to .01uf (bass rolloff at 225hz??). That might be just the right amount.

I've built and modded Fender circuits and Mesa Boogie circuits, but I have a better idea of what the changes will do in a Marshall circuit. My initial thought was to go for the PI from .1uf to .047. I did that on a tube rectified JMP50 build to cover some middle ground of .1uf of a JTM45 and .022 of a Superlead. I liked that in a Marshall, but not sure what the affect will be in a Fender.

What do you think of the change at C9, coupling cap? I am thinking that might do it. Although, I still need to see what I have with the band, first.

Mike

[Froumy]

All a matter of taste, and what your end goal is. I've seen amps that have stages rolling off 1700 Hz and below, and still sound decent(which shocked me).

If I'm looking for high gain, with a strat, .02/.01 gives a nice fat rhythm sound, but the lead sound gets a little ratty, and looses the mid focus I enjoy-especially on the first stage. Great for half distortion and clean,though.

I might try lowering C1 furthur, or going to a .002 for C2 first. Especially if the bass is really killing you. That might not exactly address your, keeping it Fender goal, though.

My Twin sounds OK on it own, but when I run it with a Marshall, I start noticing a very annoying bottom. Sounds like it lifts it leg, and literally takes a giant loud crap all over certain bottom notes. Maybe you're noticing the same thing?

That C8 is bypassing the entire frequency, too. I'd find a way to clip things in and out, so you don't ruin the circuit board. Sounds like you're hoping to gradually kill the turd notes, instead of wiping them clean, right off the bat. Guessing you're going to need to try a bunch of combos to not destroy the Fender vibe you're looking for.

[Janglin_Jack]

Tonight at practice the amp sounded great! still has nice big bottom end but not over done as before. I think the two cathode bypass cap changes worked perfectly!

Mike