Mod for Way Huge Pork Loin pedal (cuts bass)

[Steve A.]

The Way Huge Pork Loin pedal is pretty cool as it allows you to blend the signal from a clean preamp based on the Neve 1073 with the overdrive signal. However I was going to sell it because the bass was boomy using a neck humbucker.

I decided to look for a schematic instead and ran across a mod which may have already been incorporated in the newer pedals.

https://www.talkbass.com/threads/pork-loin-mod.1088576/



Note: While the author recommends replacing C34(1nF) with a 470pF cap it looks like newer pedals use a 220pF cap there.








Steve Ahola

[Steve A.]

Need to cut more bass for Clean preamp

The mod described above increases the overall presence of the pedal but there is still too much bass in the clean preamp. Looking at the Pork Loin schematic it looks like reducing the value of C37(100nF) going into U2A near the output would cut the bass. In tube amps we often look to a power of 10 when changing the value of coupling caps (like going into a BF/SF PI) so would I try replacing it with 10nF (0.01uF) for starters? I would leave the* leads long enough to piggyback a second cap to bring it up to 25nf or 50nf if necessary. FWIW C37 is VERY accessible on the pcb... I suspect that Jeorge designed it like that to make it easy for him to fine tune the pedal (especially if he were to customize it for a big name guitarist.)







Steve Ahola

P.S. The Clean half of the pedal is based on the design of the British Neve 1073 preamp. I couldn't find a very clear schematic of the 1073 but the BA-284 is supposed to be very similar.

[bob p]

I'm so out of touch that I don't even know what a Pork Loin is, much less how to tell a Way Huge one from an itty bitty little one. But electronically speaking, I guess it doesn't matter.

When I approach a problem like this one, I try to get a good handle on exactly what kind of LF rolloff is needed to get the tonal variation that I'm looking for, then I start crunching some numbers.

One way to approach the problem would be to look at the circuit, calculate the f3 point and slope for the existing filter, and then decide how far to the right you want to move the filter on the frequency response curve to get the desired effect; then calculate the values needed to give you what you want.

A less academic way of approaching the problem would be to just hook up a couple of R and C decade boxes and start tweaking until you've found a result that's empirically satisfying.

Then there's the brain dead approach of just sticking an EQ pedal in series after the Pork Loin to see what that will do for you.

[Steve A.]

I'm so out of touch that I don't even know what a Pork Loin is, much less how to tell a Way Huge one from an itty bitty little one.

Here is a Way Huge Pork Loin...

When I approach a problem like this one, I try to get a good handle on exactly what kind of LF rolloff is needed to get the tonal variation that I'm looking for, then I start crunching some numbers.

One way to approach the problem would be to look at the circuit, calculate the f3 point and slope for the existing filter, and then decide how far to the right you want to move the filter on the frequency response curve to get the desired effect; then calculate the values needed to give you what you want.

Looking at the formula for a passive, analog, first-order high-pass filter, realized by an RC circuit...

f = 1/2(pi)RC

... it looks like we would cut the value of C in half to raise the frequency by a factor of 2. So a 50nf cap should pitch the filter one octave higher, or two octaves for a 25nf cap...?



Looking at the WHPL schematic there is no way I could guess the actual value of R so I am assuming that it would stay roughly the same if C were replaced by a 50nf or 25nf cap.

Then there's the brain dead approach of just sticking an EQ pedal in series after the Pork Loin to see what that will do for you.

You know I tried that but I could not get the EQ pedal to tell me what value capacitor to use... heck, I even took it out to dinner and got it drunk!

Steve Ahola

[Dave H]

Looking at the WHPL schematic there is no way I could guess the actual value of R so I am assuming that it would stay roughly the same if C were replaced by a 50nf or 25nf cap.

The junction of R32 and R33 is a virtual earth so the value to use for R is 100k to 125k depending on the position of the Clean pot. C37 at 100n gives a -3dB point of 16Hz using 100k for R. I think you'd need to go a few octave up from 16Hz to cut the bass enough. I'd try 22n for C37 to start with (-3dB at about 75Hz).

[Steve A.]

The junction of R32 and R33 is a virtual earth so the value to use for R is 100k to 125k depending on the position of the Clean pot. C37 at 100n gives a -3dB point of 16Hz using 100k for R. I think you'd need to go a few octave up from 16Hz to cut the bass enough. I'd try 22n for C37 to start with (-3dB at about 75Hz).

I just looked at my 50v caps and the 22nF/47nf caps are multilayer ceramic. Should I get a mylar cap or would that work okay in that position?

Thanks!

Steve Ahola

EDIT: If downsizing an electrolytic cap is okay to switch to a multilayer ceramic (or mylar if space permits)? In particular I'm looking to replace a 1uF/50v e-cap with something 1/2 or 1/4 the value.

EDIT2: Moot question now... I see that I ordered an e-cap assortment awhile back and have 100nf to 4.7uf @ 50v, 10uf & 470uf @ 25v, and 22uf to 330uf @ 16v. Plus a different kit that has 50v caps @ 2.2, 4.7, 10, 47 and 470uf.

I guess I am starting to get the hang of nF numbers. Going from pf to nf to uf each time you reach 1000 it moves up to the next higher range, avoiding all those damned zeros. Still I like to use numbers like 1500f to indicate that it is a ceramic or mica cap rather than polyester or polypropylene...

Also no sense in capitalizing the "f" or even including it if it is clear that we are talking about caps.

[bob p]

I have amps that use 1 uF mylar caps for cathode bypass. There's no problem using them in larger sizes if you can find them and if you have room for the.m The problem is that they get bulky.

[Mark Hammer]

There are SOOOOO many places where bass content can be cut, it's not even funny. Any of those 1u caps in series with the clean path - C23/24/7/4 - are viable candidates.

Since changing any single cap - and this would also include C37 - only yields a 6db/oct cut/rolloff, that can often lead to a need to move the rolloff point waaaayyyyyy up (or down as the case may be) to get the needed attenuation in the zone where you want it. It can be more useful sometimes to approach the problem with the functional equivalent of a multi-pole filter, whose corner frequency is not as extreme , but whose effective slope is more abrupt.

So, for example, if I wanted to trim content at 100hz by 18db, I could use a single-pole filter (6db/oct) with a much higher corner frequency. OR I could use a 2 or even 3-pole filter (18db/oct) at a lower corner frequency that maintained essentially flat response from a lower point in the spectrum but introduced a sharp rolloff at a targeted point.

neither shallow nor abrupt rolloffs are necessarily "better". It would depend what you're aiming for. I'm just saying there are multiple points of intervention in the clean path that could achieve what you seek.

[Dave H]

I just looked at my 50v caps and the 22nF/47nf caps are multilayer ceramic. Should I get a mylar cap or would that work okay in that position?

EDIT: If downsizing an electrolytic cap is okay to switch to a multilayer ceramic (or mylar if space permits)? In particular I'm looking to replace a 1uF/50v e-cap with something 1/2 or 1/4 the value.

I prefer film caps to ceramic because of their closer tolerance and lower temperature coefficient but I'd use ceramic if that was all I had.

I think any non polarised cap is better than an electrolytic if you have the space.

[Steve A.]

There are SOOOOO many places where bass content can be cut, it's not even funny. Any of those 1u caps in series with the clean path - C23/24/7/4 - are viable candidates.

Since changing any single cap - and this would also include C37 - only yields a 6db/oct cut/rolloff, that can often lead to a need to move the rolloff point waaaayyyyyy up (or down as the case may be) to get the needed attenuation in the zone where you want it. It can be more useful sometimes to approach the problem with the functional equivalent of a multi-pole filter, whose corner frequency is not as extreme , but whose effective slope is more abrupt.

So, for example, if I wanted to trim content at 100hz by 18db, I could use a single-pole filter (6db/oct) with a much higher corner frequency. OR I could use a 2 or even 3-pole filter (18db/oct) at a lower corner frequency that maintained essentially flat response from a lower point in the spectrum but introduced a sharp rolloff at a targeted point.

I took your advice on a Way Huge Swollen Pickle Mk II pedal I just got. With the appropriate controls turned down there was still too much bass and the sound was muddy. Notes on mods for previous models suggested cutting down the value of C1 or C2 so I was going to replace the 1uf e-cap for one of the with a 0.22uf cap but decided instead to change both of them to 0.47uf which I guess would result in a -12db per octave filter pitched one octave higher. (Did I do the math?)

neither shallow nor abrupt rolloffs are necessarily "better". It would depend what you're aiming for. I'm just saying there are multiple points of intervention in the clean path that could achieve what you seek.

I like how the bass cut pot on the Timmy pedal is pre-clipping... I think it helps it get a very transparent sound at lower gain settings.

I don't know crap about ss FX pedal circuits so I rely on the people here as well as previous modders found by Google for suggestions.

I picked out C37 because it is so accessible and because it is easier to remove a mylar cap than an electrolytic can...

And because the clean signal is normally mixed to some degree with the OD signal I don't need a lot of bottom end so a -6dB filter up 2 octaves should not create any problems (there is an internal control to cut the high frequencies of the Clean signal.)

Thanks!

Steve Ahola

[Mark Hammer]

So the two-cap change worked out for you?

[Steve A.]

So the two-cap change worked out for you?

Very well! I'm writing up the mod right now as it makes the Crunch control on the Swollen Pickle more versatile. Stock it goes from Too Much Bass to Way Too Much Bass. With the mod the fully CCW position is pretty thin so I turn it up to 9:00 which is perfect for neck humbuckers, and you can still dial it up higher to get more bass than most people would ever want.

I did have a question for you: the drawing I posted of a high pass filter shows a resistor to ground after the cap. Can the resistor be located before the cap or does it have to be after the cap?

Steve Ahola

[Dave H]

the drawing I posted of a high pass filter shows a resistor to ground after the cap. Can the resistor be located before the cap or does it have to be after the cap?

The cap and resistor form a frequency dependent voltage divider with the cap as the top element of the divider. If the resistor is to ground before the cap it can't work like that.

[Steve A.]

More on the Pork Loin

I replaced C37 with a .022uf mylar cap. With the Clean signal blended with the OD signal it sounds much better, but by itself it still has too much bass. So I'm thinking of replacing it with a .01uf cap AND replacing C25 (1uf - "1J63" on rectangular box cap) on the input of the clean channel with a 220nf mylar cap. So with all of intermediate circuitry between C25 & C37 will changing both caps create a -12dB per octave cut?

BTW C25 is the only 1uf box cap that is fairly accessible, the others are in very crowded neighborhoods. C4, a 1uf e-cap is also fairly accessible so I might replace that as well with a 220nf or 470nf e-cap.

I would like to see a schematic for the Saucy Box to see how Jeorge adapted the Clean preamp for less bass...

Steve Ahola

[Steve A.]

The cap and resistor form a frequency dependent voltage divider with the cap as the top element of the divider. If the resistor is to ground before the cap it can't work like that.

Thanks!

Steve

P.S. I'm learning this ss stuff a little at a time. Like with a typical bipolar transistor the base is like the inverting input of an op-amp so you can have a negative feedback loop between the base and the collector or emitter. Cool!