Hi folks I need help and I may not find it here but I figure a tube forum would be the most likely place too find some tube educated people so here we go.....
I'm a guitarist looking to improve the tone of my amp, Its a mesa boogie DC-10. Has 4 russian 12ax7-A's, reverb driver is a 12ax7-lps, the phase inverter is a 12at7, and four harmonix 6L6's. In many ways I love the amp but for one problem. The lead channel has an incredible amount of distortion however it is a very undefined buzzy/ grainy type sound. I've looked into it quite a bit but it seems like the best bet I've come acrossed so far is to put a Low Pass filter some where in the preamp signal. I'm tryin to keep the high gain character but tighten/ focus the sound so its not so grainy in character. The lead channel has four stages of gain. I have the chassis out of the cabinet right now and have been mapping out the tone stack for the lead channel, however after playing with the treble, mid and bass capacitor values in a computer program it seems like this will not solve my problem. I have a fair amount of knowledge as far as circuitry goes and can find my way around but I'm not a wizz(I've re-wired an old stromberg intergrated tube p.a. into a guitar amp), Any suggestions would be really great. Again so far all I've found is to run a low pass filter from the end of the preamp chain to ground....but dont know what value to start with or which socket to run it off of ( the phase inverter or the last tube in the lead circuitry.
Your 2 cents would be much appreciated
Thanks,
Jake
I'm a guitarist looking to improve the tone of my amp, Its a mesa boogie DC-10. Has 4 russian 12ax7-A's, reverb driver is a 12ax7-lps, the phase inverter is a 12at7, and four harmonix 6L6's. In many ways I love the amp but for one problem. The lead channel has an incredible amount of distortion however it is a very undefined buzzy/ grainy type sound. I've looked into it quite a bit but it seems like the best bet I've come acrossed so far is to put a Low Pass filter some where in the preamp signal. I'm tryin to keep the high gain character but tighten/ focus the sound so its not so grainy in character. The lead channel has four stages of gain. I have the chassis out of the cabinet right now and have been mapping out the tone stack for the lead channel, however after playing with the treble, mid and bass capacitor values in a computer program it seems like this will not solve my problem. I have a fair amount of knowledge as far as circuitry goes and can find my way around but I'm not a wizz(I've re-wired an old stromberg intergrated tube p.a. into a guitar amp), Any suggestions would be really great. Again so far all I've found is to run a low pass filter from the end of the preamp chain to ground....but dont know what value to start with or which socket to run it off of ( the phase inverter or the last tube in the lead circuitry.
Your 2 cents would be much appreciated
Thanks,
Jake
Jake,
Have you considered upgrading the coupling caps. in the amp?
I'm not a guitar amp guy, but Steve Oda IS. Surf over to Audio Asylum (www.audioasylum.com). Steve hangs around the Tube Forum.
Have you considered upgrading the coupling caps. in the amp?
I'm not a guitar amp guy, but Steve Oda IS. Surf over to Audio Asylum (www.audioasylum.com). Steve hangs around the Tube Forum.
Hi sourgrout,
Try different tubes in the lead channel position. Are you sure that there should be a 12AX7 type driving the reverb? Normally I see a 12AT7 there. The 12AX7LPS is more of a first stage tube anyhow.
I wouldn't worry about the coupling caps unless they are defective. This is more of a "home amp" thing. You might look at the plate load resistor in the lead stage too. It sounds like the stage is distorting too early.
-Chris
Try different tubes in the lead channel position. Are you sure that there should be a 12AX7 type driving the reverb? Normally I see a 12AT7 there. The 12AX7LPS is more of a first stage tube anyhow.
I wouldn't worry about the coupling caps unless they are defective. This is more of a "home amp" thing. You might look at the plate load resistor in the lead stage too. It sounds like the stage is distorting too early.
-Chris
Yeah I've already tried a gang of different tubes in all positions, I think theres too much signal being feed into one of the gain stages of the lead channels signal path, it has four stages of gain so a little too much would obviously make a huge difference (if early on).... I can have it modified by a company called voodoo amps, I talked to them about it but they want to charge me 495 bucks to do it, thats insane!!! But atleast I know it can be done just wish I knew what they were doing to fix it.
$495 sounds like a substantial rebuild. Would the amp even sound the same I wonder. Either that or they figure they are the only competent techs in the world. This is obviously not the case.
What did you think of the 12AX7LPS in the first stage? Quieter hum wise?
Get the schematic and start looking. Also talk to a customer that has had their amp modified by voodoo amps.
-Chris
What did you think of the 12AX7LPS in the first stage? Quieter hum wise?
Get the schematic and start looking. Also talk to a customer that has had their amp modified by voodoo amps.
-Chris
You will find on amps like this that "four gain stages" does not tell the story. There are four stages, but one does not just flow right into the next. They use multiple stages for tone shaping rather than just cranking the most gain out of one or two stages. If you find a resistor in series with the output cap from one stage going into the grid of the next, that resistor forms a voltage divider with the grid resistor of the following stage to knock the level down before entering the stage.
If it is too fizzy for you , look for such things as small caps across the gain controls - they bypass the highs around the controls. A resistor in series in the signal path with a cap in parallel with the resistor is the same thing. The cap passes the highs around the resistor. In these cases, removing or reducing the value of the cap will knock off some of the high end fizzy.
Cathode bypass caps make a difference too. If you find a stage with a small bypass like .69uf, try kicking it up to 10uf or something to add some bottom.
Lower gain tubes will in fact help. 5751 is a nice alternative to the 12AX7, but is less of a gain drop than the 12AT7 represents. Or even play with the ECC832/12DW7/7247.
The tone stack really isn't the place to get rid of fizzy.
If it is too fizzy for you , look for such things as small caps across the gain controls - they bypass the highs around the controls. A resistor in series in the signal path with a cap in parallel with the resistor is the same thing. The cap passes the highs around the resistor. In these cases, removing or reducing the value of the cap will knock off some of the high end fizzy.
Cathode bypass caps make a difference too. If you find a stage with a small bypass like .69uf, try kicking it up to 10uf or something to add some bottom.
Lower gain tubes will in fact help. 5751 is a nice alternative to the 12AX7, but is less of a gain drop than the 12AT7 represents. Or even play with the ECC832/12DW7/7247.
The tone stack really isn't the place to get rid of fizzy.
Enzo:
"If it is too fizzy for you , look for such things as small caps across the gain controls - they bypass the highs around the controls. A resistor in series in the signal path with a cap in parallel with the resistor is the same thing. The cap passes the highs around the resistor. In these cases, removing or reducing the value of the cap will knock off some of the high end fizzy.
Cathode bypass caps make a difference too. If you find a stage with a small bypass like .69uf, try kicking it up to 10uf or something to add some bottom."
thank you!!!
As well as everyone else. Its not that I want less gain as much as a reduction in the grainy texture. when playing single note stuff like blues solos etc its ok but when I play chords its mushy and you cant really hear any definition between the notes that make the chord.
Again thanks
"If it is too fizzy for you , look for such things as small caps across the gain controls - they bypass the highs around the controls. A resistor in series in the signal path with a cap in parallel with the resistor is the same thing. The cap passes the highs around the resistor. In these cases, removing or reducing the value of the cap will knock off some of the high end fizzy.
Cathode bypass caps make a difference too. If you find a stage with a small bypass like .69uf, try kicking it up to 10uf or something to add some bottom."
thank you!!!
As well as everyone else. Its not that I want less gain as much as a reduction in the grainy texture. when playing single note stuff like blues solos etc its ok but when I play chords its mushy and you cant really hear any definition between the notes that make the chord.
Again thanks
Jake,
I don't have a DC-10 schematic.
Does the DC-10 use 220k plate resistors in the preamp gain stages? If so, try 100k. You may find that with less gain you can remove some of the caps that are placed across the plate resistors and get back some of the guitar's actual tone. Good luck, Mesas can be tough amps to work on because they seem to be on the verge of instability and some of them are very cramped inside.
Regards,
Mike
I don't have a DC-10 schematic.
Does the DC-10 use 220k plate resistors in the preamp gain stages? If so, try 100k. You may find that with less gain you can remove some of the caps that are placed across the plate resistors and get back some of the guitar's actual tone. Good luck, Mesas can be tough amps to work on because they seem to be on the verge of instability and some of them are very cramped inside.
Regards,
Mike
I fixed it
Ok guys I did what enzo said to do, there was a .047 cap that bypass's a resistor in the signal path and sends some of the signal straight to the fourth "lead stage" which bypass's the gain pot. I simply disconnected one side of the cap and what a difference!!. Still has plenty of gain but its way more useable and the fizzy overtone is not as prominant as it was before. The amp sounds tighter and warmer than before, which is way more pleasant to the ears.
Thank you very much for the input, saved me from having to pay some outfit 500 bucks...
Now I'm thinking of building a simple EL34 AB1 guitar amp with tube rectification. Any good schematics available? Who makes nice transformers for something like this, and where can I find good parts, orange drop caps, good ceramic sockets etc.? Looking for a simple design no frills just good tone (thats what its all about right?)
Thanks
Jake
Ok guys I did what enzo said to do, there was a .047 cap that bypass's a resistor in the signal path and sends some of the signal straight to the fourth "lead stage" which bypass's the gain pot. I simply disconnected one side of the cap and what a difference!!. Still has plenty of gain but its way more useable and the fizzy overtone is not as prominant as it was before. The amp sounds tighter and warmer than before, which is way more pleasant to the ears.
Thank you very much for the input, saved me from having to pay some outfit 500 bucks...
Now I'm thinking of building a simple EL34 AB1 guitar amp with tube rectification. Any good schematics available? Who makes nice transformers for something like this, and where can I find good parts, orange drop caps, good ceramic sockets etc.? Looking for a simple design no frills just good tone (thats what its all about right?)
Thanks
Jake
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