Dropping gain w/o affecting tone

[iknowjohnny]

I have come to a point with my amp that has a high gain pre where i am getting tone thats just orgasmic. But i would prefer less gain. Unfortunatly the things i can do to drop the gain like no bypass caps or lowering the values on the voltage dividers are killing the tone a bit. So i'm asking, what other maybe less common ways do you know of to drop gain in a high gain pre? i do realize tone will change with lower gain, but there are i'm sure ways that will affect it less. I just wish the gain pot would drop more gain than it does thru it's travel.

[billyz]

Try a lower value plate load resistor or a split load switch ala Komet style. Do you really mean less Volume? try UR12's VVR circuit, better than a master Volume. Or use a Airbrake or Hotplate.

[iknowjohnny]

No, i mean gain or distortion. And i don't want to touch the plates and cathodes because thats how i got this tone thats making me salivate to begin with. bypass caps too are part of it.

[Jana]

Gain and distortion are two different things.

Increased gain *usually* yields an increase in distortion if the following stages are driven into a clipping or non-linear region.

I suspect, without seeing the schematic, that you have a lot of gain in the first stages and the latter stages are pushed hard into clipping. Then, when you turn the "gain" knob down in an attempt to clean it up some really all you are doing is sending a little less signal down the line but it is still plenty to push the stages into clipping. As a result, you really aren't seeing much of a reduction in the distortion. The character of the distortion might change some, but that is all.

[iknowjohnny]

actually i DO see a lot of reduction. But see, this is a VERY high gain pre to begin with. It's got more gain than any marshall easily. So while there is a good amount of reduction in the amount of distortion, theres so much to begin with it has to be turned way down to get anywhere near clean. All i want to do is lessen the distortion so it cleans up more. But so far everything i have tried changes the tone too much along with the reduction in distortion. I have tried bypassing one stage but then it's no longer a hi gain pre. I want the pre to be high gain, just not quite this much. sounds amazing tho. the harmonic complexity is off the hook.

[Jana]

put 12AU7 tubes in it.

[iknowjohnny]

I tried a AT7 and it helps a bit. A U7 however i think would be way too low, but i do have one and i'll try it. I try em in V2 so as not to disturb V1 where the bonerific tone is happening.

[iknowjohnny]

Ok, i'm going to try going back to the voltage dividers and see what i can do. there are several ways i could change them....lower the ground reference R, raise the series R, do both. but any suggestions would be welcome as to which to do and what values to try to decrease gain w/o changing the tone much. I will also look for a different tube for V2, but i need to know what values to use for the cathode and plate, as i'm always hearing that they should be changed when going from a AX& to a lower gain tube. Not sure which to use, but i know a AU7 will be too much reduction and i tried a AT7 which was too little. maybe a Y. In any case i'll see what i can find and maybe someone can tell me how to bias it compared to the AX7 in there now. but first i want to try the voltage dividers, so any suggestion will be appriciated. Heres the pre schematic....PA is 50 watt EL34.....

[img:600:643]http://i24.photobucket.com/albums/c39/dazco/pre.jpg[/img]

[jjman]

Place a resistor in between the 0.68u cathode-cap on V1B and it's ground connection. This will reduce the gain-increase that this bypass cap provides.

I don't know what values to try. Perhaps around 1k.

[iknowjohnny]

I've tried that but it seems to need that cap fully or the lows get muddy.

[Alexo]

How's about... replacing your volume pot with a dual 1M pot, wire it up, leaving your current gain control as-is, but using the second set of lugs on the pot to replace the 1M resistor in front of the cathode follower? That way, you're reducing the signal level at 2 places instead of just one. I've never tried that, but it is a "less common" way to control gain (although not that uncommon, I think the Orange Tiny Terror does something like that).

[iknowjohnny]

Sorry....thats a mistake in the schematic. that 1 meg isn't there. I think i had one there at one time to replicate the 1 meg pot (turned full up) that once was there as second gain control, but I realized theres no longer a reason for it to be there. At the time i was redoing the whole front end and that was one of those "doh!" moments.

[Jana]

If it was me, I would drop those plate resistors back to 100k, up the cathode resistor on the second stage, and try to get back to a 2204 gain structure.

But, I know you're set on the values you have and don't want to change those. So, on your 220k plates, do a divider on them and tap where you take the coupling cap off of it. Instead of a 220k, maybe a 68k from B+, and then a 150k in series to your plate. the coupling cap connects to the junction of the 68k and 150k. You still have the 220k load on the plate but you are only feeding 1/3 the signal off to the cap.

[iknowjohnny]

Sounds interesting. I may try that, thanks.

[iknowjohnny]

Hmmm....you sure this should work? i tried using what i had....180k and 33k in series. 33k from the plate, other end tied to the coupling cap and from there a 180k to the B+. Did that on the first 2 stages and theres hardly any reduction. i would have thought that would be huge.