Strange pedal interactions...

patrick398 · April 03, 2018, 12:16:47 PM

Hello all,
Bit of a strange one this and i just cant imagine what's causing it.
Some of you may remember the Bluff Chill hyper light with psuedo random lfo i posted a couple of weeks ago. It's all working fine on my pedalboard but i find that when i have my box of rock engaged before it the effect is way more pronounced which i love. It's so much more pronounced than normal that i have to wind the mix back from 10 to about 7.
I've just build a fulltone fulldrive for a friend which i also love and am planning to build myself one, but when i run this in front of the hyper light it's effect is way more subtle even with the mix on the hyper light maxed.

(just to avoid confusion, i'm talking about the effect from the hyper light, not the distortions)

So i'm just wondering why the hyper light is interacting so differently with the fulldrive and the box of rock. Is it something to do with the size of signal the hyper light is seeing from the two pedals? But i'm matching the volumes so surely size of signal is similar? Output impedance? I'm clutching at straws here...straws i have little understanding of.

Any ideas would be very welcome

Kipper4 · April 03, 2018, 12:23:03 PM

Output waveform?

patrick398 · April 03, 2018, 12:28:18 PM

Is that a request to measure them or a suggestion that it could be the cause of the difference?
With the fulldrive into the BOR and then into the hyperlight the effect is more pronounced. With the BOR into the fulldrive then into the hyper light the effect is lessened. It must be something to do with the output of the BOR then i guess.
I'd like the replace the BOR with the fulldrive at some point but the BOR sounds so much better with the hyper light i don't think i can

Shipwreck0316 · April 03, 2018, 12:35:28 PM

I'm thinking you nailed it with the output impedance difference in these pedals. ZVex designs their pedals with very high input but very low output impedance. The Fulldrive 2 builds largely off a tube screamer design and keeps the buffered ins and outs even thought it's true bypass. The Fulldrive 2 has a much higher output impedance and is likely interacting different with the subsequent pedal(s).

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Shipwreck0316 · April 03, 2018, 12:36:27 PM

IÂ'm thinking you nailed it with the output impedance difference in these pedals. ZVex designs their pedals with very high input but very low output impedance. The Fulldrive 2 builds largely off a tube screamer design and keeps the buffered ins and outs even thought itÂ's true bypass. The Fulldrive 2 has a much higher output impedance and is likely interacting different with the subsequent pedal(s).

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patrick398 · April 03, 2018, 12:42:35 PM

Yeah that's what it's starting to feel like. Just tried with my demo tape fuzz and that also has pronounced effect from the hyperlight. Anybody know what the output impedance on that is like? I know some of you clever sods can tell just by looking.
I'll see what the hyperlight sounds earlier in the chain, before the drives, if i don't like that i'll have to look into lowering the output impedance when i build another fulldrive

Kipper4 · April 03, 2018, 12:53:28 PM

The later was what I was enquiringly about.

And as all those pedals are probably designed for a high impedance in and much lower output impedance?
Does it suck tone? If so then maybe.

If not it's unlikely.
We want low output Z into higher Z input right.
10-100 range right?

patrick398 · April 03, 2018, 01:00:37 PM

No tone sucking going on that i can hear. From what i can tell, the hyper light is really preferring being in front of everything else. Sounds better especially before the tuner which is seeming to have the biggest effect on it. Maybe i'll just have to run it first in the chain

patrick398 · April 04, 2018, 07:41:17 AM

Whilst running the hyper light first in the chain sounds a lot better it does create a problem of the small amount of bleed through in bypass which is then amplified after going through overdrives. Now i don't know whether to focus on eliminating the bleed through or look into lowering the output impedance on the fulldrive so i can just before the hyper light.
There's bleed from the carrier freq and also clicking from the random LFO. Is there a quick cure for this? It's wired with grounded input but i suspect it's being picked up somewhere else

ElectricDruid · April 04, 2018, 08:26:50 AM

Sounds to me like you might need to revise the hyper light a bit so it plays nicely with other pedals more reliably. Have you got a link to the other thread? I did a search for "Hyper light" but didn't find anything except this thread.

Tom

patrick398 · April 04, 2018, 10:10:52 AM

Yeah there's definitely some strange things going on with my board, nothing catastrophic but would be nice to have consistency at least. I've got the Hyper Light after the drives now and the bleed through seems to have completely vanished, weird.
Here's the original thread: http://www.diystompboxes.com/smfforum/index.php?topic=119498.0
Thanks for the help

ElectricDruid · April 04, 2018, 03:48:10 PM

Thanks for the link, but no schematics, so we can't help you fix it. Unless I missed something somewhere?

T.

patrick398 · April 04, 2018, 10:25:49 PM

Hmm i thought there was one but must have misremembered. I'll have to see if Bluff is ok with one being posted. I'm guessing not if there isn't one up already. Watch this space

BluffChill · April 05, 2018, 03:16:01 PM

As requested, the schematic:

ElectricDruid · April 05, 2018, 03:46:28 PM

I'm not surprised it interacts in strange ways with other stuff. The input and output impedances aren't going to be well defined. The input is connected to the output, so the effective input/output impedance is going to depend on the voltage at the other. I can't quite get my head round how that will work, but if they're the same...it'll look like no current flows, so it'd be high impedance, whereas if they're very different, it would seem much lower?

DC conditions in some parts of the circuit are left rather vague. What sets the DC operating point of pin 3 of the LM567, for example? All the things connected to it are separated by capacitors, so its DC level is not determined by us (it might be determined by something on the chip, we don't know).

Ultimately, it's a glitchy interactive sort of pedal. I could suggest that you put buffers into various parts of it and tie down the DC conditions so it behaves more predictably, but I suspect that would somewhat rob it of its charm and character, so it's probably not worth it.

Sorry I can't provide more practical help.

Tom

BluffChill · April 05, 2018, 04:45:51 PM

Thanks for the feedback, ElectricDruid.

Yes it is a strange, interactive pedal - designed more by ear than any sense of engineering knowledge. A lot of the impedance problems might be down to the fact the input and output are tied. For the next version of this, I might try undoing that and buffering the circuit elsewhere to keep the wet/dry balance.

T

patrick398 · April 05, 2018, 07:19:09 PM

Thanks for the help Tom and massive thanks to Bluff for posting the schem. The circuit is certainly a charming one, it's become my favourite pedal on my board. Do we think perhaps adding the output buffer of the Box of Rock on to the fulldrive might solve my specific issue? That's just a thought, i'm sure there are numerous implications of doing this i'm not aware of...but if it offers a simple fix i'll look into bolting it on

ElectricDruid · April 06, 2018, 03:45:31 PM

If the Box of Rock works fine and has an output buffer, why not try adding that output buffer onto the front of the Hyperlight as an *input* buffer. After all, if you stuck the buffer on the full drive and then plugged the full drive into the hyper light, it'd amount to the same thing. But by putting the buffer on the hyper light, you stand a chance of getting a similar (hopefully positive!) result with other pedals which don't work well with it too.

Just a thought.

Tom

patrick398 · April 07, 2018, 05:12:18 AM

Yeah good thinking Tom, i'll give this a go today. Fulldrive is nearly finished so should have time. Seem to remember the hyper light + extras being one hell of a tight squeeze in the enclosure but i'll try and cram it in there somewhere.
So i'd want everything up to and including C3 right?

ElectricDruid · April 07, 2018, 09:45:17 AM

Quote from: patrick398 on April 07, 2018, 05:12:18 AM
Yeah good thinking Tom, i'll give this a go today. Fulldrive is nearly finished so should have time. Seem to remember the hyper light + extras being one hell of a tight squeeze in the enclosure but i'll try and cram it in there somewhere.
So i'd want everything up to and including C3 right?

There's no output buffer on that. I thought someone said it had an output buffer? If you're taking everything up to C3, you're taking the input buffer. Maybe it doesn't matter - try it. But I'm confused now; I don't know what order you want things in, or what order you can currently place the pedals that gets the best form the hyper light. Sorry, I got lost along the way.

Tom

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