Pickup simulator question

[Perrow]

In the pictures thread Barcode80 posted the below statement about his pickup simulator which he uses as a buffer between a mp3 player and the effect he's debugging:

regardless of the audio, the impedance needs to be matched to that of a pickup in order to properly evaluate a circuit build. As such a pickup sim is a good idea when using this method.

I don't buy that straight off. It's true that the first effect (turned on) in the effect chain "sees" the pickup, but any following sees the impedance of the effect before them.

I don't really know anything about this and therefore ask for a second opinion, or further explanation, so I can hopefully learn something (in a new thread to save the pictures thread from a few posts).

[CynicalMan]

I think Barcode is referring to testing and designing effects, where you would normally test them alone outside of your pedal chain.

[PRR]

> pickup simulator which he uses as a buffer between a mp3 player and the effect he's debugging:
> I don't buy that straight off. It's true that the first effect (turned on) in the effect chain "sees" the pickup, but any following....

I don't see "any following" in the quote or the bit of the massive discussion you cite.

Some inputs don't load a pickup. Will sound the same with a low-Z source such as a Walkman.

Some inputs DO load a pickup. Won't sound the same with a low-Z source such as a Walkman.

Sanity prefers un-fussy inputs. However there are pedals with good reason to load a pickup. These may not work "right" when fed from a non-pickup source.

Certainly many builders and fixers never use a pickup simulator. Most faults are gross (no sound, horrid squeal, unmusical distortion). When you fix the fault it sounds better. If it does not sound quite right on the artificial test source, you grab the Strat as a for-real test.

Barcode may be like me: I do a LOT of wringing-out with various test signals on the bench, and have resorted to phono pickup sims to verify a phono preamp's loading effects before I even hooked it up to a phono. It's one good way to work. If you are not buying it today, that's OK too.

[Barcode80]

All true. Perrow, you may have misread me. There are no other pedals involved. Let's say you are testing a pedal you just built. So let's say the chain goes:

Guitar (pickup) -> pedal -> Amp

Great. True representation of how the pedal will react when you play through it, because you are! However, let's say you don't want to hold the guitar and play, maybe you want to tweak some stuff while signal is going through. You could strum a note or chord, then tweak until it dies out, repeat, etc.

However, another alternative would be to send a pre-recorded audio signal into the pedal. And this work just fine. The problem can be that in general, an audio player/computer/cd player will not have an output impedance that matches the impedance from pickup loading. SO if you ran the audio player directly to the pedal, the pedal's color or tone could be different than if you have a guitar plugged in.

Enter the pickup simulator. It would basically load down the pedal like your guitar's pickup does, making whatever audio you are pumping through be a closer match to how the pedal will behave with the guitar plugged in. It isn't always as simple as audio in -> audio out. For example, the output impedance of the guitar is CRUCIAL to the signature sound of the fuzzface. This is why a lot of people recommend nothing before it, so that it directly sees the pickup load.

Make sense? It's not necessarily right or wrong (as my post probably implied), it's just a good way to get the pedal to behave just like a guitar is plugged in, without having to plug one in and keep strumming.

[Perrow]

And I may have been misread. I'm writing in a foreign language, it was late and I've got a cold so my thinking is kind of slow. There was no major discussion about this, I just didn't understand all that was said and thought I'd try and learn something.

So am I correct to assume that this would be most useful when testing effects with low input impedance?

If I've learned something (and that may not be the case) effects with jfet or opamp buffers have high input impedance, so how do I recognize those that don't? Everything else? Tubes?

[alparent]

OK it's time to hijack this thread!
Every body in the back.........face down!

Just kidding! 

But this is exactly what I want to build! Any schematics or layout of this pickup sim?

Enter the pickup simulator. It would basically load down the pedal like your guitar's pickup does, making whatever audio you are pumping through be a closer match to how the pedal will behave with the guitar plugged in.

[alparent]

I thinks I got it!

Is this the one people are building? Barecode80? Others?

http://www.muzique.com/lab/pickups.htm

[Barcode80]

And I may have been misread. I'm writing in a foreign language, it was late and I've got a cold so my thinking is kind of slow. There was no major discussion about this, I just didn't understand all that was said and thought I'd try and learn something.

So am I correct to assume that this would be most useful when testing effects with low input impedance?

If I've learned something (and that may not be the case) effects with jfet or opamp buffers have high input impedance, so how do I recognize those that don't? Everything else? Tubes?

No, it is actually pretty useful no matter the circuit. No matter the input impedance of the pedal, it's still going to react differently to a pickup load than it would from the output of an audio player. It's just another way to test circuits as they will actually sound once you plug a guitar in. If you do all your debugging by playing a guitar into the pedal, it's not necessary or particularly useful. But if you wan a constant audio stream into the pedal so you don't have to keep strumming, you can substitute another audio source into a pickup simulator in place of the guitar, set the player on repeat, and you have a constant source of audio while leaving both hands free.

[deadastronaut]

hmmmm...thats quite useful..

i use a pedalboard (clean).and use the record loop function...its handy...for 2 handies......

i get p****d off with the riff..after a while .but its great for trying stuff out...