Have I mismatched impedance somewhere?

Steve Lipsey · From: Portland, Oregon, USA

I'm getting a little hair on the clean tone that might be impedance...
I'm going from Rains SD-10 with Wallace Trutone to a pedalboard with Plutoneium Chi Wah Wah buffered Wah pedal, TU-2 tuner, Keeley 4-knob compressor, and Crowther Hotcake OD/distortion, then into a Hilton volume pedal and a Matchless HC-30 amp.....

The Keeley is a 4-knob with an input level control that I backed off, which helped a lot, but it occurred to me that it might not be just a level problem, it might be impedance also...

Any thoughts?

David Nugent · From: Gum Spring, Va.

My guess would be the TU2 tuner, try removing it from the signal chain and see if that helps.

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

Plug straight into the amp and see if it's the amp. An HC-30 isn't exactly a 'clean-machine', and hotly-wound (by 6-string standards) PSG pickups can sometimes overdrive the input section of amps that aren't designed for high input levels (or guitar-oriented pedals that are in front of them).

Then add one effect at a time and see if you can isolate the source. You have a lot of stuff in the signal path, and overloading any of them at the input could cause this. I assume you have the Hotcake off?

I'm not exactly sure what you mean by 'impedance mismatch'. If you're talking about the instrument-level voltage signals into your amp, relative impedance levels between devices affect the voltage transfer. The voltage transfer ratio from the source (first device) to the load (second device) is Z_l/(Z_s + Z_l), where Z_l is the load's input impedance and Z_s is the source's output impedance.

Problems arise when the load impedance is not much greater than the source impedance - significant voltage gets dropped over the source impedance instead of where you want it, over the load impedance. Since these impedances are typically complex and frequency dependent, low load/source impedance ratio (IMO, anything less than at least 100-1000) may also affect your sound by emphasizing some frequencies over others. But poor voltage-transfer should not, by itself, produce harmonic distortion if these devices are reasonably designed at all.

There could be some other issue causing distortion at any point in the signal chain - again, I'd suspect some device is getting pushed too hard. I think the best way to diagnose this is to examine the effect of each device in the signal chain, one by one, in sequence.

Steve Lipsey · From: Portland, Oregon, USA

Thanks, Dave....

One more question...would these devices affect the signal either due to level or impedance when they are off? The Wah is buffered, but I don't know if the designs of pedals would simply pass through a signal that was stronger than they expected to see....

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

Anything is possible. I believe the Hilton volume pedal has the capability of greater than unity gain but has a level pot so you can pull that back. The others may also - the Hotcake obviously does, so do most compressors.

I don't know if these pedals have true bypass or not. Some players like it, some don't like to lose the buffering when they bypass. The effect of source impedance can only reduce the level, never increase it.

The large number of factors is why I suggest you start from scratch, and then carefully put each pedal in line and work with it before moving on. Pedal order can also make a big difference.

For example, I don't use a compressor for PSG, but for guitar, I almost always put that first, unless I want a volume pedal in front of it. I use a passive volume pedal for PSG - I like a little treble rolloff as I pull it back. But if I was using a Hilton, I'd put it first in the signal chain. It's designed for pedal steel, thus has the necessary headroom to cleanly handle hot PSG pickups (not necessarily true of all guitar-oriented pedals), and this approach gets your buffering done right at the beginning of the signal chain. From the Hilton, you should be able to pad the signal down to whatever levels your other pedals want.

{OD/Distortion then wah} vs. {wah then OD/Distortion} is a personal choice. All of these choices - levels, device-ordering, bypass vs. non-bypass - can affect the sound greatly. Even with just a few simple pedals, variations can make a big difference.

Steve Lipsey · From: Portland, Oregon, USA

thanks again...will try the pedals one at a time to see what gives...

I put the volume pedal last so it doesn't affect the sound from the other pedals - e.g., the Hotcake would be clean at low volume if the volume pedal cut down the input to it...

...and the wah is first only because I want it next to the volume pedal and didn't want to run cables back and forth (trying to keep electrical and mechanical pedal order the same)

...the Keeley is the only one with an input level control, maybe that should be first, electrically....I leave it on but at minimum sustain, just to give a little fullness to the PSG, seems to make the notes a little "rounder"...probably wouldn't want/need that with a humbucker..

Mike Wheeler · From: Delaware, Ohio, USA

Checking each pedal separately is good advice, but I suspect that with your volume pedal last you are hitting the pedals with the full output of your pickup. Most steelers have the vol. pedal first. Then the subsequent pedals rarely see the full pickup signal.

Keep us posted on your investigation.
_________________
Best regards,
Mike

Steve Lipsey · From: Portland, Oregon, USA

I did some experimenting, and I think that the grit I'm hearing is just the normal Matchless chime....it sounds kind of brittle by itself, but is wonderful in a full band....tried it all with a regular guitar, through the effects and straight in, and heard pretty much the same thing, varied the input with the Keeley input pot and level control and it didn't change much....totally clean at low volume, and a bit gritty up high...

I'll experiment some more (getting a Sarno Black Box shortly), but I think it is actually all just what you get for a Matchless 30 watt tube amp...in the full band, it sounds so wonderful that I guess I don't care what is really going on...

Steve Lipsey · From: Portland, Oregon, USA

Actually, finally got my bigger amp home for a bit, and yeah, a 30-watt amp has much less grit than a 15-watt amp. Matchless amps are very conservatively rated, 30 matchless watts is easily double that compared to other amps, esp. solid state, even 15 is way loud enough for a gig but I guess headroom was the issue, not power. After all, it is a tube amp, and isn't clean all the way up..

So it really was just the amp beginning to break up...which on a Matchless often can sound a tad brittle by itself, but is truly wonderful in the full band situation....somehow the brittleness goes away in the mix and the sustain remains...so I'll still use them both for gigs, but I'll choose based on knowing how they will sound, now....

Dave Grafe · From: Hudson River Valley NY

15 watts of saturated distortion is always going to sound vastly "louder" than 50 watts of clean power.

Steve Lipsey · From: Portland, Oregon, USA

Not what I'm saying, Dave....although I'm pretty sure you know more about all of this than I do, given what you do.

I'm just saying that 30 watts of Matchless tube power sounds as loud as a typical 50 watt tube amp, for some reason the (pretty much) Class A design seems to just be louder per watt...not just my opinion...and I do play the 15 watt Matchless in a full band, with the gain turned way down low (i.e., as clean as it gets), and it easily keeps up...

That obviously won't be as completely "clean" as a solid-state amp, but in my experience, tube amps, when run "clean", still sound as loud as a much higher wattage solid-state amp. Maybe they aren't completely clean at that level....but that sound is why some of us prefer them to more sterile solid-state amps.

Not trying to restart that age old solid-state vs. tube thing here, just saying this is how I personally feel, and have, ever since I bought my first 1967 Blackface Twin Reverb.....which I did in 1967....

I'd actually be curious to hear what you have to say about all this....my experience, although lengthy, is certainly not a deep as what you have, and my steel experience is very limited as yet....and every time I drag 85 lbs of amp out to a gig, I wonder why I just can't deal with solid-state (although the Sarno Black Box that is on its way to me might change that?)

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