Fender M80 Overdrive Channel

[JSpina911]

Has anyone done any tweaking to the overdrive channel of this amp to make it usable?

I want less shrill highend,more lows,and less gain....All the gain currently comes in very quickly on the control..

The tone on this channel is just thin and harsh...

Would someone look at the M80 schematic(I have it) and let me know where I can change some cap/resistor values to make this channel usable...

The clean side of this amp is very nice!

Thx

[olddawg]

Might just want to consider a pedal or 2. (Eq and a dirt box?) And .. Then tweek the dirt box. Much easier than messing with the amp if it works well and has a good clean sound.

[JSpina911]

Might just want to consider a pedal or 2. (Eq and a dirt box?) And .. Then tweek the dirt box. Much easier than messing with the amp if it works well and has a good clean sound.

Totally agree and I do have plenty of pedals.I do see myself only using the clean channel.

I enjoy tweaking stuff so it was at least worth asking.

Maybe someone else has done some mods and will chime in?

[JSpina911]

Now if we were talking tube amps...Bias,tone caps,tone stacks,coupling caps,MV mods,Phase inverter mods,gain stages,etc...I can talk the talk..SS stuff I'm still trying to get a better handle on...

I Love working on the earlier Fender,Marshall,Traynor,Vox,some earlier Peavey stuff..Just easier to get a handle on stuff,especially the h/w and ptp amps!

[J M Fahey]

If you find it shrill, tone controls as shown already provide ways to tame that.
Set contour to 0 and also presence to 0 .
As of gain, that´s what the gain control is frr.
If uncomfortable to use , you can pad dirt channel by 20dB which is a lot, by tack soldering a 47k resistor across R18 .
That said, the best sound improver is plugging it into a real cabinet, with a 4x12" best and closed back 2 x 12" quite acceptable.

[loudthud]

I don't have one of these amps so these are just guesses.

Gain problem: Change R15 and R17 to 10K.

Shrill overdrive: Reduce C4 to 0.01uF or 0.005uF. Reduce C10 to 330pF or 270pF. Change one of the LEDs LD1 or LD2 to a different color.

[JSpina911]

If you find it shrill, tone controls as shown already provide ways to tame that.
Set contour to 0 and also presence to 0 .
As of gain, that´s what the gain control is frr.
If uncomfortable to use , you can pad dirt channel by 20dB which is a lot, by tack soldering a 47k resistor across R18 .
That said, the best sound improver is plugging it into a real cabinet, with a 4x12" best and closed back 2 x 12" quite acceptable.

Thx JM...An EQ in the efx loop is also something I've done in the past....

[JSpina911]

I don't have one of these amps so these are just guesses.

Gain problem: Change R15 and R17 to 10K.

Shrill overdrive: Reduce C4 to 0.01uF or 0.005uF. Reduce C10 to 330pF or 270pF. Change one of the LEDs LD1 or LD2 to a different color.

Cool....Thx for this..No harm in trying!

[JSpina911]

If you find it shrill, tone controls as shown already provide ways to tame that.
Set contour to 0 and also presence to 0 .
As of gain, that´s what the gain control is frr.
If uncomfortable to use , you can pad dirt channel by 20dB which is a lot, by tack soldering a 47k resistor across R18 .
That said, the best sound improver is plugging it into a real cabinet, with a 4x12" best and closed back 2 x 12" quite acceptable.

The problem with the overdrive side of this amp though is having to set presence and contour at 0...Even the gain can't be set over like one or it gets very crappy,buzzy,and harsh...Hence the desire to at least correct some of that.I'd probably never use this channel,but it would be nice if it would be better.

[JSpina911]

I don't have one of these amps so these are just guesses.

Gain problem: Change R15 and R17 to 10K.

Shrill overdrive: Reduce C4 to 0.01uF or 0.005uF. Reduce C10 to 330pF or 270pF. Change one of the LEDs LD1 or LD2 to a different color.

Ok so I understand that changing the one Led gives us asymetrical clipping, the resistors drop the gain, and dropping the 560pf cap will remove highend.What happens when we drop C4 and I would think we'd increase that cap? Would you just explain what C4 will change? Thx again.

[JSpina911]

I don't have one of these amps so these are just guesses.

Gain problem: Change R15 and R17 to 10K.

Shrill overdrive: Reduce C4 to 0.01uF or 0.005uF. Reduce C10 to 330pF or 270pF. Change one of the LEDs LD1 or LD2 to a different color.

You were really on target....I did exactly as you posted except I made C4 .047. At C10 I went with a 330 pf mica cap.I have the small stock red LED in one spot and a clear larger 5mm yellow LED in the other slot.

This channel is warmer,not as obnoxious sounding,and the gain is more controllable...This channel has alot of mids compared to the more scooped mids of the clean channel..

Thx so much.This really did make a difference.The channel is usable now!

[loudthud]

Fender called these amps part of HM series. So the overall EQ is for some target Heavy Metal tone. Problem is the tone might not work well with your guitar and speakers. The symmetrical clipping is part of the raspy HM tone, it doesn't sound so good with moderate overdrive.

The parts around C4 form (what looks to me like) a mid scoop network. There is a path for the lows and a path for the highs. The lows go through R12 and R13, C5 and C6 roll off the highs for that path. C4 is the path for the highs. Reducing C4 just reduces the highs and also affects the mids. Increasing C4 probably increases the mids. The same kind of thing happens with C10.

The parts in these networks interact quite a bit. So if you have the energy to keep pulling the PCB and changing parts until the amp is dialed in the way you like it, go for it. If it were me, I'd pull all the parts in those networks and install wires (or maybe tiny eyelets) so I could "Sky Wire" things without having to pull the PCB for every little change. One wire for input, one for output and one for ground. Then after finding what works the way I like it, pull the PCB and install the parts. Less wear and tear on the PCB.

[JSpina911]

Fender called these amps part of HM series. So the overall EQ is for some target Heavy Metal tone. Problem is the tone might not work well with your guitar and speakers. The symmetrical clipping is part of the raspy HM tone, it doesn't sound so good with moderate overdrive.

The parts around C4 form (what looks to me like) a mid scoop network. There is a path for the lows and a path for the highs. The lows go through R12 and R13, C5 and C6 roll off the highs for that path. C4 is the path for the highs. Reducing C4 just reduces the highs and also affects the mids. Increasing C4 probably increases the mids. The same kind of thing happens with C10.

The parts in these networks interact quite a bit. So if you have the energy to keep pulling the PCB and changing parts until the amp is dialed in the way you like it, go for it. If it were me, I'd pull all the parts in those networks and install wires (or maybe tiny eyelets) so I could "Sky Wire" things without having to pull the PCB for every little change. One wire for input, one for output and one for ground. Then after finding what works the way I like it, pull the PCB and install the parts. Less wear and tear on the PCB.

Hi LT...I used some chip holder pieces and soldered them into the board so I wouldn't have to keep taking the board in and out etc.for the substitution of components.

I can leave the board all bolted down and not have to mess with it..I'm careful to not stay on components too long so as not to lose the connections under the board.

Your ideas got me almost perfect to where I wanted the channel to be...I have a .047 at C4 actually and I guess I Like it..

The channel is still pretty bright and I may try lowering C7 from 470 pf to say 250 pf across that gain pot..

Seems that the presence pot either doesn't work or it's just very subtle?

Other than that,this channel is "alot" better and it's actually an overdrive now in a sought of Tube Screamer kinda way which I Like.Your idea got me so close to perfect and I thank you for that!

[loudthud]

The Presence pot frequency may be set too high where it only affects the raspy part of the distortion or the highs that were removed by the C10 change. Try increasing (edit) C13 and C14. Each time you double the capacitance, the frequency comes down one octave. The Presence pot can only boost the high frequencies by 6dB. You can get a little more "boost" by increasing R26, (maybe 100K) but what you are really doing is reducing the lows. Just turn up the Overdrive Volume to compensate.

Edited to correct Cap numbers.

[JSpina911]

The Presence pot frequency may be set too high where it only affects the raspy part of the distortion or the highs that were removed by the C10 change. Try increasing C14 and C15. Each time you double the capacitance, the frequency comes down one octave. The Presence pot can only boost the high frequencies by 6dB. You can get a little more "boost" by increasing R26, (maybe 100K) but what you are really doing is reducing the lows. Just turn up the Overdrive Volume to compensate.

Did you mean increase C13 and C14? I don't see C15 anywhere? The channel is still pretty bright and what are your thoughts on lowering C7 to say 250 pf? Otherwise the channel is pretty much where I want it

I still like keeping the gain down and cranking the volume up on this channel.

I sure appreciate your help!