Fender M-80 is one of the best solid state guitar amps from the eighties, simple design, loud and clean channel really bring out that old fender chime. The overdrive stock channel though is really bright and almost unusable, really difficult to find a sweet spot.

After fully analysis on the simulator and a lot of experiment on the amp itself we have made the following mods in order to upgrade and improve the amp. The upgrade can be done in 4 different levels with the most important the first one – the overdrive channel.

1)Overdrive channel – tonal response, we have made a total tweak on the tonal response, especially on the tone filter capacitors  at the presence and the contour controls, while we wanted to keep the character of the diode clipping stage.

C4–>0,033 —>0,047 Wima MKS2 to allow more medium lows
R15,R17–>3.3K–>4.7K less gain more bottom end

C10—>560pF–330pF less Hi End Contour high pass filter cap

C13–>0,0033uf—>0,022uF Presence Lowering low pass filtering frequency to more usable range,
C14–>0,0015uf—>0,01uF Presence Lowering high pass filtering frequency to more usable range

2)Both channels upgrade all signal capacitors with Wima MKS2 (1-4.7uf) and Nichicon Muse NP (22uf)

C3,C30—>22uf Nichicon Muse ES BP
C9–>0.047—>1uF Wima MKS2
C19–>2.2uF Wima MKS2
C20–>22uF Nichicon Muse ES BP
C28–>0.033—>1uF Wima MKS2
C35–>2.2uf—>3.3uF Wima MKS2

3) Improve and  increasing  filtering capacitance and replace power filter resistors with Metal oxide  lower tolerance.

C48,49–>4700uf 50V—>5600uf 50v
added parallel 100uf 50v panasonic FM
C50, 51–>47uf 25V—>220uf 25v Panasonic FM
added parallel 220nf film capacitors
Filter Power Resistors
R94,95–>330Ω 5watt 10%–>330Ω 5watt 1% MOX

4)Power Amp Upgrade power resistors with higher accuracy and better characteristics

R84,85,86,87–>0.47Ω 5Watt 10%—>0.47Ω 5Watt 1% MOX
R88–>0.22Ω 10Watt 10%—>0.22Ω 10Watt 5% MOX

C40, 41–>22uF 50V Elna or nichicon KZ
C42, 44–>100uF 16V Nichicon Muse ES BP
C38, 39–>47uF 50V Elna or nichicon KZ

Negative feedback & poles
C36,38–>2.2uF Wima MKS2
C37–>4.7uF Wima MKS2

Check out the most of the mods on the following picture: