SHO original input capacitor

[eddyc666]

Hello people,

I have a quick question which i can not find the answer too online. The zvex super hard on, the input capacitor wich value is it in the original unit? all the schematics show a 0,1uF, but i have read about clones having more bass then the original and zvex posting a schematic in the past with a 10nF cap on the input...and what about the supa dupa? really hope somebody who has seen the original guts can help me out..thanks

[Elijah-Baley]

I'm going to build a SHO, but I still miss some parts. I can find different schematic, old version and new version... but I even find some schematic with 100nF input cap, some with 150nF.
I don't know how is the original SHO schematic, I have just what I found in the web.

Emulating the schematic it seems have a very large band, with very low frequency slightly boosted, really slighlty. Using a 150nF instead a 100nF input cap you can get further boost in the very low frequencies, with a less drastic cut of the low end. I imagine that 220nF could work fine with a bass guitar.
A 10nF cap definitely cut these lower frequencies, and maybe to save the low end that a guitar can need.

In these last time I built pedals I'm considering the chance to not follow necessarily the original schematic, but I decide to make some mods to make the pedal sounds better to my ears, and cahnge the input cap, or the output cap is the easier way to increase or decrease the low end.
Indeed, before decide what cap I'll use in my SHO I soldered two socket pin to decide what cap solder on it.
Make some tests, and let us to know your results!

[Rob Strand]

really hope somebody who has seen the original guts can help me out..thanks

You could try searching for some pics.  A 10n would be smaller than  a 100n.

The problem with the SHO is there's more pics of clones than real units, so you have to be *really* careful about what you are looking at.  The clones will most certainly have the 100n.

[duck_arse]

is this the SHO with a pair of 10M bias resistors? what's the cutoff frequency of a 100nF cap and 5M input Z?

and, eddyc666, welcome to the forum.

[Elijah-Baley]

I found this: http://ilovefuzz.com/viewtopic.php?f=151&t=4677
You can see an image of an orginal PCB of the... Super Duper, which is a dual SHO, where the second add a master volume. (A sort of half Box Of Rock? )
The two little caps are, indeed, little. So it could be 10nF.
We can see it better here: http://revolutiondeux.blogspot.com/2012/01/zvex-super-duper.html and precisely an user has pointed that the cap should be 10nF. But this doesn't mean that the original SHO has a 10nF. At least until nobody can confirm this.

The schematic we have of the Box of Rock show a 100nF as input cap in the first stage, and a 100nF in boost stage. Maybe it's just the Box of Rock that has the 100nF and the misunderstanding was born from here. If the SHO really has a 10nF.

Anyway, you can find here some pics of the Box of Rock: https://www.thegearpage.net/board/index.php?threads/the-pedal-guts-pics-thread.481823/page-4, the caps we can see are really small, I can't say if there's any 100nF.

And here other pics of the Box of Rock, maybe another version: https://toy-love.hatenablog.com/entry/20061121/1164047828. Again, I have no idea if there's some 100nF (and at least one should be there in the tone section. About this there are some discussion about it, because some clones sounded too much harsh. A 10nF cap in the tone section caused this, and I guess, a 100nF was the real value).

Duck_arse, I tried to emulate the frecquencies of the SHO schematic using the 100nF input cap. The band is really large, I guess.
The boost is pretty flat, under the 30Hz there's a even a tiny boost, and under 6Hz, finally, start a cutoff. This is what I got.

[eddyc666]

Thank you..been lurking for a couple years and most of the time i can find everything here that i need,  great forum!

And thanks Elijah, very helpful!

I  already looked at pictures from original SHO's, Everytime i can't really see what capacitor it is..i have one picture where i believe to see 104 on the cap so that would be a 100nF. I can recognize the originals quit easy by the terrible way zvex wire's the jack's😝.. i wanted to make a unit for a friend that sounds exactly like the original. But I think i will just make one with a toggle switch on the input cap so he can switch between 10nF 100nF and 220nF, i think that would be much cooler 😎 .. but first back to my breadboard ..thanks guys 👍

[Fenton Bresler]

I can't really see it making any audible difference. The cutoff frequency is far far below 20Hz in either case. I might even venture to say that you could go lower than 10nF before losing any appreciable bass. I suspect a switch with 10nF, 100nF and 220nF will not be of great use.

[eddyc666]

I read on a german site somebody advising putting a 1-10nf on the input and said it made it sound more like a treble booster.. anyway i will breadboard it this week and i will see if the switch is worth it, and what values sound the best..

[Fenton Bresler]

I read on a german site somebody advising putting a 1-10nf on the input and said it made it sound more like a treble booster.. anyway i will breadboard it this week and i will see if the switch is worth it, and what values sound the best..

I've tried running a few simulations, it looks like this could indeed be the case. The cutoff frequency seems to go up as you turn up the gain.

[Elijah-Baley]

I can't really see it making any audible difference. The cutoff frequency is far far below 20Hz in either case. I might even venture to say that you could go lower than 10nF before losing any appreciable bass. I suspect a switch with 10nF, 100nF and 220nF will not be of great use.

I experimented something like this on another Zvex pedal, casually. The Wooly Mammoth.
The input cap is a 220nF, and the pedal has a lot of low end, I thought to use a three way switch to get 220nF, 100nF and 22nF values. But I can't hear much difference between 220nF and 100nF with the guitar. A two way switch with 220nF and 22nF should be fine.

[anotherjim]

Maybe a 10nF was not only fitted in the coupling cap position but also from input to ground for a "more bass" response. Not really more bass, actually a little less treble but sounding warmer/deeper. This to save owners of bright guitars from having to back the tone control off a little to cure harshness.

As said, the coupling cap could also be 10nF and still pass plenty bass.

[amz-fx]

There is a schematic of the SHO on the official ZV site under the Inventobox page. Just click on the Module Overview pdf and it shows the C1 input cap as 10n.

https://www.zvex.com/guitar-pedals/inventobox

Best regards, Jack

[eddyc666]

Wow thank you so much! I heard it should be on the zvex site but couldn't find it.. seems like the schematic's online are a little bit off, also for the fuzz factory

[PRR]

> There is a schematic of the SHO on the official ZV site under the Inventobox page. Just click on the Module Overview pdf and it shows the C1 input cap as 10n.  https://www.zvex.com/guitar-pedals/inventobox

Marked 0.01u which is 10n.



This feeds two 10Meg resistors and a >1,000Meg Gate. Using the values proposed here:
0.1u = 0.33Hz for -3dB
150n = 0.22Hz
220n = 0.15Hz
10n = 3.3Hz
1n = 33Hz

Bass guitar runs to 42hz or a bit lower. For "True" response we would aim for -3dB at 21Hz, although no speaker you own has dB accuracy below 50Hz.

On paper even 1.6nFd is *ample* for bass, even detuned bass. I can't see how larger can be audibly different.

In practice stray capacitances can be some fraction of 1.6nFd (100pFd of stray would cause a small broadband loss). And since all these few-nFd caps are the same price and size, 10nFd seems like a perfectly happy practical value.

For bass-shave, on paper you could try like 220pFd. In practice that may allow more buzz pickup than we'd like. It would be smarter to find a bass-shave in a later stage (perhaps C2).

[Rob Strand]

I can't see how larger can be audibly different.

Yeah.  I can't imagine the zener doing much but I'm open to someone measuring the frequency response to prove it.

[amz-fx]

This feeds two 10Meg resistors and a >1,000Meg Gate. Using the values proposed here:
0.1u = 0.33Hz for -3dB
150n = 0.22Hz
220n = 0.15Hz
10n = 3.3Hz
1n = 33Hz

High pass corner freq will vary because R1 is in a negative feedback loop from the drain to gate and its effective resistance varies with the amount of gain, so the input impedance goes down with increasing gain. Even so, 10n is adequate for complete low end response with a guitar or bass up to 10x gain (+20db).

Best regards, Jack

[Fenton Bresler]

High pass corner freq will vary because R1 is in a negative feedback loop from the drain to gate and its effective resistance varies with the amount of gain, so the input impedance goes down with increasing gain. Even so, 10n is adequate for complete low end response with a guitar or bass up to 10x gain (+20db).

Best regards, Jack

Brilliant, I was about to ask about this. In my tests, I was experiencing an increased bass roll off when turning up the gain, and I assumed that the input impedance was indeed dropping but I couldn't explain the mechanism in which this was happening. Thanks a lot!

[Rob Strand]

R1 is in a negative feedback loop from the drain to gate and its effective resistance varies with the amount of gain

Good catch.

[PRR]

> High pass corner freq will vary because R1 is in a negative feedback loop

You are right, I was blind.

And it is probably a good feature. More gain, you want less bass coming in to mudd-up the sound.

And that is a musical judgement, so experimentation becomes the best path.

It is hard to see how that gain-stage can be gain over 50(?), so 80nFd would be "full bass/mud" and likely values could be 80nFd to 8nFd. The stock 10nFd/0.01uFd seems a likely happy-value for a hypothetical "average" musician.