The clean channels are quite good although I could use some extra bright boost on the "bright" channel. The overdrive has an American style though there is a UK/US switch on the preamp. US channel is more bassy than the UK one but both channels sound a bit muffled and lack definition, especially when the boost is off.
Therefore, I wanted to modify the overdrive to get some note definition out of it and of course, more gain! The mod comes in two parts and it's shown below.
Part1:
First, I removed R69, the input attenuating resistor and got extra sensitivity to picking. Then, I replaced R37 with a 5,7K resistor and C21 with a 47nF capacitor.
Part2:
For the second part, I replaced the R42 with a 470K resistor and R31 with a 1,5K one.
Results:
Part1 mod gives a nice treble boost on the overdrive channels and part2 gives extra gain and distortion. You can always reduce gain using the boost and gain controls as well as your guitar's volume knob.
The original Quad 100 schematic:
https://rapidshare.com/files/2168011693/quad_100dfx_kustom_guitar_amp_sm.pdf
http://elektrotanya.com/quad_100dfx_kustom_guitar_amp_sm.pdf/download.html
http://www.google.gr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CFsQFjAC&url=http%3A%2F%2Fmusic-electronics-forum.com%2Fattachments%2F16996d1327360918-quad_100dfx_kustom_guitar_amp_sm.pdf&ei=hWX3T5LrNILN8QOn7IGbBw&usg=AFQjCNE0p6znuPTalQJKMT_BRwYffgXrcw&sig2=ae7qYuMMH7JX2wR_zCJZ9Q
Part1 mod
(click to enlarge or right click to open in new tab=larger pic)
Part2 mod
Pictures:
Thanks for this. Before I open my head up, is everything surface-mounted?
ΑπάντησηΔιαγραφήNo! The only SMD components are on the digital fx separate board. Everything else is easy to modify (e.g. changing resistors/caps).
ΔιαγραφήGood luck with your project!
Thanks! I still haven't had time to perform this mod, as I'm using the head for gigging, but using an old Powerbook G4 running Pod Farm with my Toneport DI-S for amp modeling. The head just sounds bad as it is right now. I tried taking the electronics out to look at them, as a way to get me to do this mod, but I couldn't figure out how to get the head case open! I didn't have a whole lot of time to figure it out as I needed the head again for a gig, but I'll have to dig in and get it done.
ΔιαγραφήThe mod has almost the same effect as using a treble booster pedal in front of the amp. I 've tried a treble booster in front of the quad 100 in its stock form and the overdrive was very good. So, if you are not sure how to do this mod, just buy a 20$ treble booster (EH screaming bird from ebay etc) and try this solution instead.
ΔιαγραφήMany high gain amps(ss and tube) get quite "farty" and compressed on the OD channel. Therefore, I turn the channel's gain down a bit(even at 12'o clock on some amps) and use a treble boost to make up for the gain loss. The result is usually way better than the stock od channel.
Oh... I forgot to ask in the last comment... by 5,7K resistor, do you mean the comma to indicate a thousand (as in 5,700 ohms) or did you mistakenly put a comma there instead of a period (as in 5.7 ohms)? I'm a bit rusty on figuring out what I need to do figure out any sort of voltage drop or current limiting in the circuit, so I figured I'd ask you instead. Thanks!
ΔιαγραφήIt's 5700 OHMS ! (5 thousand and 7 hundred Ohms)
ΔιαγραφήI've got a Brownie Classic OD pedal that will make up most of my gain; I only need a little from the amp for that extra oomph. Playing around with the amp controls with the pedal plugged in, though, was less than satisfying. I just couldn't dial in a decent sound without it becoming muddy and compressed. Hence, the desire to do this mod :)
ΔιαγραφήThat's what I figured; you were using the standard notation, but I wanted to be absolutely sure since I've fried a few resistors in other projects due to the comma/decimal swap goof. Thanks for your comments and patience with me :)
ΔιαγραφήHi there!
ΔιαγραφήI did almost the same mods as you and I encountered a major problem: I have internal feedback looping (I believe this is how is called in English).
My mods:
R69 - 1 M (1000k)
C21 - 470 nF
R37 - 4,7 K
R31 - 1,8 K
R42 - 330K
These mods are made on a Kustom QUAD200HD which is almost the same except the output IC.
I get the feedback on the OD channel with the Gain(Balls) knob at 3 o'clock and the lead Volume knob at 9 o'clock and on the distortion channel (bigger balls) with the Gain knob at 1 o'clock and the Volume knob at 8-9 o'clock.
I love the way it sounds now with these mods but due the annoying feedback I can't crank up the volume wick is a frustrating feeling and also I'm not able to play live at these volume (too low).
Hello Andrei,
ΔιαγραφήIs there a guitar connected to the amp when the feedback kicks in? Guitar pickups tend to get microphonic when the gain and volume is high.
However, if the amp does the same thing without a guitar plugged in, it's a matter of internal oscillation and you 'll have to reduce the gain a bit by reversing a few mods.
More gain on the od channels increases noise and feedback but you could reduce that by changing a few things:
A good idea would be to replace the R31 and R37 resistors with trimmers(4.7K and 25k linear ones). With these 2 trimmers connected as variable resistors(2 out of 3 lugs used), you can control the amount of internal gain and tweak it on the fly without soldering!
To reduce feedback, you could also replace C6 and/or C34 with 470pF capacitors.
Cheers,
Thanos