Impedance, volume pedal and Pre-EQ

[William Steward]

Dumb electronics question : when I wire my Goodrich volume pedal (mod. 120) to the pre-EQ patch on my Peavey amps (Session 400LTD, 112)and then add a Goodrich Matchbox (mod. 60) into the signal chain [guitar-Matchbox-amp]....the range of the pedal is reduced to almost nothing. If the Matchbox and pedal are in the signal chain [guitar-Matchbox-Volume ped.-amp] the pedal range is normal. I guess I should find another 'tone' control to use with the pre-EQ patch....explanations and suggestions appreciated.

[Jonathan Cullifer]

If the matchbox is the first thing that the pickups see, you don't need to run the volume pedal in the pre EQ patch. The matchbox does the same thing you're trying to do by runnning the pedal through the Pre EQ patch.

[Mike Brown]

I suggest that you try connecting the Matchbox between the output of your guitar and the input of the amp instead of the PRE EQ PATCH. Actually, I would try it without the Matchbox altogether.

As I understand, the Matchbox is an impedance matcher, so to speak. If this is so, using the PRE EQ PATCH for the volume pedal should take care of the impedance mismatch anyway.

Mike Brown
Peavey USA

[William Steward]

Mike...thanks for your response but I was trying to be clear that the Mastchbox was not in the pre-EQ loop. It is between the guitar and the amp (if you re-read my post). I already realise I can't use it with the pre-EQ setup but it is handy as a tone control - any other suggestions?

[Mike Brown]

I reviewed your post and you are correct. I just read it quickly. Sorry.

[Jack Stoner]

As Jonathin points out, if you want to use the Matchbox, place it between the guitar and the volume pedal and you can then connect the volume pedal to the amp in. You are not gaining anything, other than the tone control, with it in the line when you connect the guitar directly to the amp input and use the effects loop for the volume pedal.

The whole theory behind using the volume pedal in the effects loop is that the guitar goes direct and sees a "constant impedence load". With the Matchbox, that amoung other things provides a constant impedence load to the guitar's pickup(s) and also provides a low impedence output to the volume pedal and thus overcomes a lot of the volume pedal tone (variable impedence load on a pickup) issues.

I can't 'splain why the Matchbox directly to the amp input is causing a problem, unless there is a problem with the Matchbox. If I remember correctly the Matchbox has a battery in it, how long has it been since the battery was changed?

[Michael Maese]

Since you have to move the volume pedal out of the signal chain and into the pre-eq patch to make the change you describe, you may be connecting the volume pedal backward at the pre-eq patch. Limited volume range is the symptom I notice when I connect my pedal backward (which I still do all too often).
Michael

[William Steward]

Thanks guys....I will give those suggestions a try. I think I have tried changing the battery in the Matchbox and reversing the IN/OUT of pre-EQ (does it actually matter?). Jack I think you probably are on the right track...I will have to try digesting that but maybe will get out my multi-tester and check impedance with and without the Matchbox.

[Jack Stoner]

An ohmmeter will not measure "impedence" since it's an AC measurement, not DC. The ohmmeter will only measure DC resistance. You need a specific impedence bridge (meter) to measure that.

e.g. if you measure a pickup and whatever it measures with a DC ohmmeter all it's telling you is the total DC resistance of the wire that was used to wind the pickup. You need much more equipment to measure the AC impedence.

[William Steward]

Thanks Jack - I told you it was a "dumb" electronics question. Bill Lawrence got a little exasperated trying to explain this concept to me once - I think I will find a basic electronics text and start doing some studying!