Would this Aron Nelson mod work on a solid state amp?

[2deaconblues]

Here's a mod from Aron Nelson's page on mods.

"Refine" your pedal and smooth the tone out

A Jake Nagy special! Put a smallish value capacitor on the output lugs of your volume pot (from signal to ground) to clear up the high end "buzz and hash" from your pedal and give it instant smoothness!

Try different values from 220pf to .0015uF or even larger values depending on the amount of high frequency content you want to remove.

Would this work on a solid state amp? I'd like to tame the early breakup on a Danelectro Nifty Fifty 15watt amp.

[5thumbs]

I believe that is commonly called a capacitor "shunt".  When I've used capacitor shunts, they act as frequency-dependent filters that will "darken" your tone to a degree, depending upon what size capacitor you select.

For example, in Dan Haught's 'Trotsky Drive" (http://www.beavisaudio.com/Projects/TrotskyDrive), he uses a SPST-switchable 0.022μF capacitor shunt as a basic tone control to give you a bright/dark sound.  I've used them for similar purposes in a couple of designs of my own.  They won't give you more headroom.  Cap shunts will give you a fixed change in the tone curve of your amp's output.

Given that, I don't think a capacitor shunt would give you any more headroom in your Danelectro amp.  I'm not familiar with the architecture of this amp, but it is likely distorting in either the preamp, power amp or speaker distortion.  All the shunt capacitor would do is make the tone darker, not reduce the gain (or increase the headroom of the amplifying op amp or transistors, with the given power supply voltage.)  I wouldn't be surprised that Danelectro designed this amp to breakup in the fashion you've described (for that vintage feel), so you might have some luck increasing the headroom if you can get a schematic for the amp.  Even so, it will take a bit more work than a shunt cap to accomplish your goal.

[2deaconblues]

Thanks for the response... and very interesting.

Unfortunately, no one seems to have a schematic of this amp. I've been asking around for three years, and others have been asking for longer. I doubt if Danelectro actually designed this characteristic. It is by no means a musical breakup. I actually don't like using that term here, because the sound is more like a cracked speaker than what you would normally term "breakup." And it's not just my amp, it's a known fault of the amp. There's very little modding of  little solid state amps, so there's not much information out there. Someone claims to have had success with putting a low pass crossover between the amp and the speaker. I tried this, and didn't see any change.

There's just something in the circuit design that doesn't work. If there was an actual schematic I'm sure someone on a board like this could figure it out, but I'm certainly not the one.

[5thumbs]

Have you opened up the amplifier box to see what the circuit looks like?  Is it all surface-mount bits or is it using discrete components (or yes on both?)  The reason I ask is because I have a couple of Kustom Tube 12 amps lurking about that sounded somewhat OK...that is, until I opened them up and swapped the sole op amp in it (a Korean RC4558P) for BB OPA2134PA op amp and saw a big difference.  It went from being muddy and somewhat splatty (with distortion) to actually being quite a pleasant-sounding little amp.

So the idea there is to see if there are op amps and/or transistors you can identify and replace with functionally-equivalent, higher-fidelity components.  If they are discrete through-hole components, you can remove the stock op amps/trannies, install sockets and then audition replacement parts until you get the increased headroom you're looking for.

[2deaconblues]

Thanks for the suggestions. I pulled the board out and discovered two op amps marked "MAL TL072CN". So I can't identify a manufacturer, but I'm certainly willing to replace them. I plan to put in sockets so I can see what differences I can come up with.

[5thumbs]

Not that I'm familiar with those exact chips, but from the markings, one could deduce they are Malaysian copies of the venerable TL072 chip.  The TL072 has a high-impedance FET input, so if you replace them with low-impedance input op amps, you'll need to see if you get a noticeable increase in volume or distortion.  If so, you'll have to audition other FET-input op amps.

I often use the TL071IP / TL072IP as my "try first" op amp in builds/mods.  Some circuits don't respond well to the FET input...and others don't clean up enough with it.  If the TL07x doesn't sound good, I'll usually try an OPA134PA / OPA2134PA next.  They have a flatter frequency response curve to them when compared to the TL07x op amps.  However, they often smooth out unwanted, splatty breakup pretty well.

I've recently heard about LM358 chips being well-behaved in often-splatty circuits like the BOSS DS-1 (along with the OPA2134PA), so you might try those as well.

Swapping the op amps will be one of the easiest mods you can make right off the bat, so it sounds like you're off to a good start.  Good luck!