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Overdrive For Non-overdriven Amps


ROBERTLATHAM1
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ok guys tell me if im right or wrong here, but i think this will work.

here are the mods(od and tone stack)

http://i49.photobucket.com/albums/f279/rob...harmonymods.jpg

here is the original amp

http://i49.photobucket.com/albums/f279/rob...am1/harmony.jpg

i would really like the real amp techs here to tell me what they think. is this a posable mod or will this never fly?

thanx

robert latham

:D

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Depends upon what you mean. If the goal is to add gain so that one can overload one or more triode stages without introducing a lot of solid state distortion, this circuit does not do that

The distortion part, in the middle of the drawing has an op amp which overloads in either of the two gain positions since it is driven by at least a few volts of signal from the first tube. (I am assuming that the plate reisistor for this tube and its connection to the B+ have been omitted by accident.) The output of this op amp is connected to the output of another op amp configured as a voltage follower with grounded input (no input signal). This should mostly short out the gain stage, reducing the output level and increasing the distortion, but I do not know exactly what the intent was. The output then is clipped by a pair of GAS diodes (although it might not reach clipping level under some conditions) and then drives a tube stage with a cathode follower, with some negative feedback around this pair of tubes. The gain control in the feedback path of the op amp is really an adjustable low pass filter. It does not affect the low frequency gain.

Additional tube gain follows this circuit.

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well i agree that it is getting more along the lines of the jcm 900 with the jfets, but this circuit is what is used in my marshall 8100 hybred for the boost channel. i do like the way it can go from clean to blues crunch and then with the click of a switch you can go from classic rock to insane distortion. the tone stack has far more control than just the bass and treble(bass being master control) cuts of the harmony. however i do like the pristeen clean and warmth of the 5881's in the harmony so when i went to ad this circuit i wanted to be able to switch between an undisturbed harmony pre-amp and the hybred pre-amp for flexability as the harmony made a very good blues tone but volume had to be around 5 and as it is rated at 30watts this is way too loud for some places that i play. hence the need for the o.d. section as run my rig in stereo.

i can also a/b switch between the two amps. this gives me the ability to get that clean jazz tube tone and still be able to come back to a big high gain sound. on the marshall i have added foot control to select between od 1 and od 2 as this was not a stock option. hence the same set up on the harmony. why settle for a vw when you can have a bugati!

:D

harmony-------\

guitar----ibenez ts 9-----alesis quadraverb+--< --- 4x12 cab with center bridge for stereo.

marshall vs100/

p.s. i thought almost all the new tube amp lines use op amps now. is this not true?

thanx

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p.s. i thought almost all the new tube amp lines use op amps now. is this not true?

A lot of tbe amps avoid putting op amps in the main signal path, but use them to drive the reverb and amplify its signal, etc. Solid state can be extremely clean and transparent, while tubes have a "sound", even when played clean. You have to work hard to get good distortion from SS, while tubes pretty much just do it themselves.

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you might as well be playing a Peavey Bandit™

lmao! i liked those little amps back in the day LOL!

well i do like tube tone, but i guess i am not what you would consider a purist. i like the tone that i am getting by using both a ss/hybred amp and a pure tube amp togather and would like to have the common features between the 2. so i guess the mod is possible, but not a recomendation for the tube purist ?

has anyone here had the chance to use a marshall vs100(8100)? if you have ? you have to admit the amp does have good tonal quality and does have more warmth than a ss amp. grant it, it is no jcm! but does have a certain degree of warmth, not found in ss amplification.

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you might as well be playing a Peavey Bandit™

lmao! i liked those little amps back in the day LOL!

well i do like tube tone, but i guess i am not what you would consider a purist. i like the tone that i am getting by using both a ss/hybred amp and a pure tube amp togather and would like to have the common features between the 2. so i guess the mod is possible, but not a recomendation for the tube purist ?

has anyone here had the chance to use a marshall vs100(8100)? if you have ? you have to admit the amp does have good tonal quality and does have more warmth than a ss amp. grant it, it is no jcm! but does have a certain degree of warmth, not found in ss amplification.

Ok... I'll bite.

All you are doing with your modification is building a fuzz stompbox into an amp. Why not just use a fuzz stompbox in front of the amp? It'll be a heck of a lot easier... especially considering the errors in your hand-drawn schematic (e.g. where is the B+ coming from for the first tube stage?)

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especially considering the errors in your hand-drawn schematic (e.g. where is the B+ coming from for the first tube stage?)

from the b+ supply. i failed to draw it in. but i am very aware of where it is fed from. as for the fuzz stomp box this is a pre amp section from a marshall vs100, which does not sound like a fuzz tone, fuzz face, ect... in fact it is very versatile amp. it can go from a clean unsaturated sound to a blues top of the wave clipped signal or switch to the od 2 channel and get the "brown sound" run a ts-9 in front and go further or switch back to the original harmony stock undisturbed pre-amp for a really close fender twin tone. as for the errors on the drawing i admit it was thrown togather, but i know clearly what should be where lol. this is my absent mind at work again!

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