Too much treble and bass

[dude]

I've been trying to get the treble down, I use 1 or 2 other wise too bright ,past 5 ice picking.

Bass is too heavy, I use 1 on bass, need to change the range, on ten it distorts.

Here is the simple tone circuit. It's the deluxe reverb

al

[AZJimC]

Try a bigger mid resistor. I have 10K/20K switchable on a Similar treb/bass tone stack. Also gives a bit less tone stack loss.

[tubenit]

I don't know if you're actually referring to a AB763 Deluxe Reverb or just that tone stack?  IF it's a DR, then here are some ideas for you:

- Lower cathode caps in the preamp from 22uf to 5uf or 2.2uf    This will lower some bass and increase some smoothness in the overdrive

- Use a lower value coupling cap after the LTPI  .1 to .047          This will lower some bass and boominess

- Use a Dumblish style tone stack to increase mids and have less ice-picky treble

IF I were going to build a Deluxe Reverb type amp, this is how I would attempt it.

With respect, Tubenit

[jjasilli]

I don't know if you're actually referring to a AB763 Deluxe Reverb or just that tone stack?  IF it's a DR, then here are some ideas for you:
- Lower cathode caps in the preamp from 22uf to 5uf or 2.2uf    This will lower some bass and increase some smoothness in the overdrive
- Use a lower value coupling cap after the LTPI  .1 to .047          This will lower some bass and boominess
- Use a Dumblish style tone stack to increase mids and have less ice-picky treble
IF I were going to build a Deluxe Reverb type amp, this is how I would attempt it.
With respect, Tubenit

+1.  The Fender tonestack is known to work well, without the issues described in the first post.  This tends to indicate the the issues arise in place(s) other than the tonestack.  Hence, you should post the entire schematic of your amp.

[sluckey]

And don't forget speakers. Your speaker choice will have a huge effect on the tone of your amp.

[dude]

The mid resistor is 15K, the pic I posted was just a copy of the tone stack I have, it's one of the simplest amp circuits I ever worked on a BF 1967 Vibro Champ.

It all started when I decided to fix the Tremolo, found a tread here that says it's best to just replace the small e caps in the trem circuit and check resistors for drifting and leaking caps. I did all this, found a lot of drifted resistors and ones that crumbled in my hands this untouched V Champ is 46 years old, hardly anything was done except a power resister replaced. The tremolo worked, so I decided to check everything, replacing two thirds of the components.

The amp played Ok but the bass pot had a small range on the bass and the treble worked fairly good, a little bright but I could turn it down to 4 or 5 and it was fine.  The amp is what it is, I had a few vintage paper OT's from an old stereo, I had put one in a Tweed Princeton copy and the amp sounded killer with an 8 and 4 ohms load, so I decided to put the other one in the Vibro Champ, while I was at it, I replaced the the filter can cap with three inside the chassis caps to be sure everything was redone. No hum but I did ground the preamp filter on ground side of the 220K from pin 5 of the 6V6...? Maybe go father down the rial and find a ground...?   

With the new OT the champ came to life and sounds wonderful but I had to keep the treble on 1, and the bass on 1, turning the treble up to 4 and ice-picking started, turning the bass up pass 1 caused floppy bass and then bad distortion.

Everything is stock values except the OT and the changes I made below. I did use a 33uf for the first filer cap rather than a 20uf.

Here's the schematic, so simple. I don't feel I need to start changing cathode caps on the first stage and getting into it not being a Vibro Champ anymore. Since the amp plays great but with both treble and Bass on 1, I was thinking the three caps in the tone stack could be changed, maybe to match the OT I put in....?

I changed the 250pp, to 200, and the two caps to .07uf from .1 (had that strange value laying around) and the .047 to .022uf. The amp then was just the" opposite of what I wanted", more ice-picking and floppy bass.... I'm getting confused here did I go the wrong way....?

I used windows picture to post pic.

[dude]

Here's some pic's, I really need some help. I feel it's a simple change I'm missing.

I didn't drill any holes in the chassis for the standoffs, used the PT bolts and the old cap can left in, used one of the tabs to hold the other standoff. Ran preamp filter ground to the first gain stage off the 1K5 and 25uf/25 at the inputs.

Thanks for any help
al

[sluckey]

Reverse the red and blue wires on the OT. Does that help? Or make it worse?

[dude]

Reverse the red and blue wires on the OT. Does that help? Or make it worse?

Almost blew my ears out, that's not it.

Could it be the potentiometers, I doubt it as they worked ok before except the bass hardly ever had any effect on tone. Raising that 250pp cap on the treble would only increase the ice-picking right?

I used a Mallory .1 cap on the tone stack, only .1's I had.  I used an orange drop on the .047, maybe use another brand?

What about the .02 feeding the grid of the 6V6, maybe try a .047?

Could it be the power tube, I'm using a 7402 old tube...? Guess I could try another. I'm using several different speakers too, not that.

I really appreciate your help, you have taught me so much, this has me baffled.

al

[dude]

OK, I'm getting somewhere.

Put the .1 coupling tone cap back, left the other off the bass pot to .022 instead of .047.

And change the 6V6 to a new JJ, big difference, the treble pot works great now. Seems that old 7402 had it's days although it tested good...?

Only problem now is the bass, much better range but still too bassy. when I hit notes on low e string up the neck, it flops out wit ha dull sound. So, now the only problem is the bass, the new 6V6 cure the treble issue made the bass pot better but still that dead bass on the low e up the neck..?

al

[sluckey]

Time to follow tubenit's advise. Change the cathode caps on the first AND second triodes to 2.2µF.

[dude]

Time to follow tubenit's advise. Change the cathode caps on the first AND second triodes to 2.2µF.

Yeah, I'll change that cathode cap to 2.2uf or the like, I have a few 5ufs anything higher doesn't tight'n the bass and even maybe a .068 like a Marshall.

Also, my guitars, strats, seem to do this on some of my other amps. I'm thinking the 150K resistor and smoothing cap I have on the volume pot of my strat to keep the highs when I turn it down, might have something to do with this floppy bass up the neck. But who plays bass E notes on the 15th fret

Thanks, I'm happy and I'm sure that cathode change on the first gain stage will do the trick.

Thanks all for your help.
al

[terminalgs]

If I read it right, all this frequency change came when you swapped in an old HIFI OT?  Without knowing the details of that OT, you don't really know what frequencies it responds,, especially its bass floor. 

[dude]

If I read it right, all this frequency change came when you swapped in an old HIFI OT?  Without knowing the details of that OT, you don't really know what frequencies it responds,, especially its bass floor.

The lower cathode cap on the first stage help a lot with the bass control, used 4.7uf.

I have two of these old stereo receiver OTs, came out of an old tube stereo running two ?????, each tube had it's own single ended OT. I did check the specs with a small PT 12.6vac  6.3-0-6.3 acv. 7.3v was going in the primary and one the secondary was  .20v (not sure if I should have checked both sec together or added .20 twice to get .40 ?) so the turns ratio was about 36:1 Sq that gives 1296 x 4 ohms = 5184 or about 5K at 4 ohms (good for 6L6's) 1296 x 8 ohms = 10368 or about 10K4 (if I did the math right) a little high for 6V6's but with 6V6's both 4 and 8 ohms seems to be the same loudness, the 8 ohm is a tad bit louder.

I don't know much about frequency range, but the other OT when in my friends Tweed Princeton copy and sounds killer @ 8 ohms, no bass E string problem on the low E down the neck.

I think the sound I'm hearing is the Champ's Tremolo bleeding a little and I can only hear it on low frequencies, like the E string up the neck...? The Champ has no on or off for the trem, you just turn the knobs down. I don' t have an RCA  connected foot switch, perhaps if I did, that would turn the Vibro off...?

Does this make any sense?

al

[terminalgs]

Since you replaced the filter caps, make sure all your cap connections are good,  both to ground and to their B+ nodes. It a preamp filter is virtual "missing" because of a weak solder or poor ground, you can get phase cancellation across the stages ( Who knows, perhaps leaving you with lots of high end). 


If you replaced plate resistors, make sure you got the correct values in there (i.e. you didn't install a 10K instead of a 100K...)..

[sluckey]

I don' t have an RCA  connected foot switch, perhaps if I did, that would turn the Vibro off...?

Yes, it would turn it off. You can also turn it off just by shorting out the RCA jack. Or just pull the tube. Then you'll know if it's a factor.

[jjasilli]

If I read it right, all this frequency change came when you swapped in an old HIFI OT?  Without knowing the details of that OT, you don't really know what frequencies it responds,, especially its bass floor.

+1. 


Your amp has substantially different components than the stock schematic you posted.  Terminalgs thought is worth pursuing.  Guitar amp OT's typically have limited frequency range.  Hi-fi OT's may pass far more bass & treble which could cause, or contribute to, your issue. Is your amp SE?  Is the OT designed for SE or PP?


E.g., the value of the bypass cap on the Power Tube may may produce too much bass through a hi-fi OT

[jojokeo]

ahh, the days of playing with a champ/vibrochamp circuit... sometimes where "the addiction" all begins  watch out dude have you had your immunization vaccine? 

[dude]

If I read it right, all this frequency change came when you swapped in an old HIFI OT?  Without knowing the details of that OT, you don't really know what frequencies it responds,, especially its bass floor.

+1. 


Your amp has substantially different components than the stock schematic you posted.  Terminalgs thought is worth pursuing.  Guitar amp OT's typically have limited frequency range.  Hi-fi OT's may pass far more bass & treble which could cause, or contribute to, your issue. Is your amp SE?  Is the OT designed for SE or PP?


E.g., the value of the bypass cap on the Power Tube may may produce too much bass through a hi-fi OT

The Vibro Champ is very close to all stock values, only changes are the first stage cathode is lowered to 4.7 from original 25uf. And in the tone stack - 210pp from 250pp stock - .047stock  to .022 That's it, except the OT which  is "singled ended" as I stated above. With these values the amp is much better except the bass control, works OK and treble fine but still a little too much bass when amp volume is up to just pass breaking up around 6 or 7....?

al

[dude]

I don' t have an RCA  connected foot switch, perhaps if I did, that would turn the Vibro off...?

Yes, it would turn it off. You can also turn it off just by shorting out the RCA jack. Or just pull the tube. Then you'll know if it's a factor.

Your right, I shorted the the vibro jack and no vibro, it's off.  Notes on low E up the neck are basically gone but still the bass is a little too strong. I put a 4.7uf 1st stage cathode, helped a lot. The only other e caps are a 10uf @25, keep it stock, it's on valve 1b around the feedback loop, should I lower that to 2.2uf or the like? See schematic above.

And last is the e cap for the vibrato @ 25uf, left it alone.

Just want to cut a little more bass. On the first stage that I changed  to a 4.7uf , I could go to 1uf or .68uf those are the lowers  small e caps i have in my drawer. Maybe try the .68 like Marshall usually has? 

thanks, al

[Willabe]

I'd try the 1uF.


          Brad   

[sluckey]

The only other e caps are a 10uf @25, keep it stock, it's on valve 1b around the feedback loop, should I lower that to 2.2uf or the like?

Change the cathode caps on the first AND second triodes to 2.2µF.

And put that cheap original OT back in. And play it thru a cheap 8" speaker.

[dude]

I hear ya.

The speaker that came with the champ was not original, it was an "8 ohm" not 4 ohm.  And not a Fender but some Radio Shack 8" ceramic that weighted 2 lbs if that (probably 5 watts). I put the original 15W Alnico 4 ohm, Weber SigA-S  speaker in, only difference from original is one rib in the middle of the cone for a hair later break-up.

I'll change the 2nd half of the 12AX7 to 2.2uf but that original OT was 5 watts, broke-up at 3 or 4 pass that - crunch... like a metal head to me at 9 or 10. I might even put a switch on the negative feedback to turn it off, if I can find a hole without drilling or just hang it.... haven't done anything I can't reverse.

Thanks, maybe that second cathode gain stage cap will do the trick. Don't get me wrong the amp sounds pretty dam good, I'm just getting carried away, like we all do at times seeking perfection "that probably isn't even there...."  .

al

[Willabe]

but that original OT was 5 watts, broke-up at 3 or 4 pass that - crunch... like a metal head to me at 9 or 10. 

But with what speaker? The Radio Shack 8" ceramic?

Did you try the Fender OT with the Weber 8"?


                Brad   

[dude]

but that original OT was 5 watts, broke-up at 3 or 4 pass that - crunch... like a metal head to me at 9 or 10. 

But with what speaker? The Radio Shack 8" ceramic?

Did you try the Fender OT with the Weber 8"?


                Brad   

No, but I probably should now (didn't have it then). The reason I wanted to try the old vintage stereo OT was I had two, put one in a friends Tweed Princeton copy and it sounded so good, way better than then the kit's 5 watt one.

I will try the Champ original OT in time but with your advice and Sluckey's the last change was it, the 1uf first stage cathode, 2nd stage 4.7uf sounds like classic rock tone. Turning the guitar volume down a hair, cleans things up and the treble and bass change the tone with slight changes. I love the amp, I think it's perfect for recording.

Thanks again for all the advice, I guess I can be a little anal at times searching for that special tone, I'm just a tone freak, I feel I play so much better with great tone.

al