Easy Guitar Pedal to Rackmount Question

Quick and easy, I want to adapt a couple of guitar pedals to rackmount units at line level, just want to double check my idea before I start.

I'm going to follow NYDave's reamp (10k:150) in and then a simple 150:10k transformer with a resistor before it at the output of the effect?

My question is gain wise will I be messing things up at all? I want to come back at line level, not mic level if possible.

Thanks guys.

That would work for the input, but not for the output. The output impedance of a pedal is generally between 1 and 10kOhms; it wouldn't drive properly the xfmr. You NEED active buffering of the output.

FWIW:

http://www.geofex.com/circuits/Adjusticator.gif

The average guitar signal is in the range of 50mv to 100mv rms with peaks on the pick attack of 1vrms or more.

How well it works will depend a lot on your guitar pedals as the design varies greatly on their input and output stages.

A 10k:10k will work on the input, but you may have to use a pad if you drive it with a line level signal.

The output is where it gets sticky. If you have a Boss, Ibanez or similar design pedals that have a buffered output, you could probably get away with a 10k:10k on the output. Some guitar pedals have a very high output impedance and/or a large value pot hanging on the output... such as a Fuzzface that uses a 500k volume pot on the output.  You can always use a buffer pedal last in line to give a consistent output impedance and drive.

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

http://www.muzique.com/lab/patent1.htm

regards, Jack

AMZ-FX said:

The average guitar signal is in the range of 50mv to 100mv rms with peaks on the pick attack of 1vrms or more.
http://www.muzique.com/lab/pick.htm

Click to expand...

Nice article.

About levels, I recall we had a discussion about this on this forum a while ago and at least for bass I'd say the peak levels can be noticably higher. I recall drinking a few mugs of coffee, then picking & oscilloscope-looking & got more in the 4 .. 10 Vpp range IIRC (passive bass, heavy pick, healthy player, strong coffee, sunny day).

Partly FWIW, since as was in that discussion back then also mentioned (PRR?), slightly distorting the highest peaks can pass unnoticed.

But while at it, I'd say take somewhat higher peak-levels into account, at least when you forsee bass-use.

Regards,

  Peter 

whilst not particularly helpful with your design concept, ( which does have a few problems ). Broadcast Pro Audio makes a unit specifically to meet this situation. The Missing Link MkII does all the impedance and level translations for guitar to +4 balanced and back again, or from +4 bal to guitar level and back. See here : http://broadcastproaudio.com/new.htm

Thanks for all the help and articles guys. I'm thinking it'll be easiest to maybe just do the DI output and then run it into a mic pre for the make up gain.

Night of the living threeeaaad!
I'm considering rack mounted delay pedals (DMM, Echo blue,...) for my studio as well. So the idea is basically to have some sort of reamp box on the front and a di at the end, right? So why not just putting a 600:10K transformer for the input and a 10K:600 for the output (that's what a passive di is, right?)
And what if a pedal has a really high impedance, like 100K? Would a di work as well?

Here you are messing with levels even more, you have a line level input, after a 600:10k you have 4 times that level, when you want ~1/10th of that level for a guitar input, same at the output, you have 10k:600, so you have 1/4th of that level when you want 10 times. Also, as discussed here 600Ω won't be driven from a guitar pedal output. At the input you could use a 10k:600 transformer and maybe a pad or 10k:10k and a pad, at the output you need an DI to get to line level directly, usually passive DI will use something like 10k:600 and then go to a mic input. You could use a FET DI and couple of BJT to archive your low impedance line level output, or go, as said here with a mic pre using the onboard DI. To stay cheap I would go with an opamp balanced input with an attenuator going to the pedal and then FET buffer going to a BJT opamp to drive the output. Maybe with a NE5532 and a TL071 you can do all that. You could go for more expensive opamps but I don't see the point in doing that for a guitar pedal, they are not that low noise or anything, NE5532 is probably overkill for this app, but I think cheap enough and good for simple line driver, do it impedance balanced output to get good CMRR at your receiver.

JS

Another thread hijack!

I've been looking into this as well, and would like opinions on: increasing the power supply, e.g. from 9vdc to +/-15vdc, buffering the output, and changing any other gain component(s) to make the effect a line level effect? The Craig Anderton compressor has one resistor change for guitar level to line level. 

This maybe much too complicated on anything other than maybe an opamp based circtuit (Also assuming a schematic is available.) I am mostly looking at this from a prefab pcb/kit standpoint, where you can start from scratch substituting components/cutting traces/etc isn't as much of a hassle.

(I may have another post on this here, I posted on this on another forum, so forgive me if I'm duplicating a query.)

I just picked up a Radial EXTC for doing this. I had used a reamp and a bo hanson DI, but wanted something in the rack.
The blend function is really nice to have.
I haven't tried enough different things to know how the input will work yet (10k input impedance).

Blue Jinn said:

Another thread hijack!

I've been looking into this as well, and would like opinions on: increasing the power supply, e.g. from 9vdc to +/-15vdc, buffering the output, and changing any other gain component(s) to make the effect a line level effect? The Craig Anderton compressor has one resistor change for guitar level to line level. 

This maybe much too complicated on anything other than maybe an opamp based circtuit (Also assuming a schematic is available.) I am mostly looking at this from a prefab pcb/kit standpoint, where you can start from scratch substituting components/cutting traces/etc isn't as much of a hassle.

(I may have another post on this here, I posted on this on another forum, so forgive me if I'm duplicating a query.)

Click to expand...

I don't know your actual pedals, but you probably need to scale some resistors working as current sources and other components, it can be done but with some care on the design, also make sure that the used opamp is ok to deal with ±15V but that shouldn't be a problem in most cases.

JS

joaquins said:

Blue Jinn said:

Another thread hijack!

I've been looking into this as well, and would like opinions on: increasing the power supply, e.g. from 9vdc to +/-15vdc, buffering the output, and changing any other gain component(s) to make the effect a line level effect? The Craig Anderton compressor has one resistor change for guitar level to line level. 

This maybe much too complicated on anything other than maybe an opamp based circtuit (Also assuming a schematic is available.) I am mostly looking at this from a prefab pcb/kit standpoint, where you can start from scratch substituting components/cutting traces/etc isn't as much of a hassle.

(I may have another post on this here, I posted on this on another forum, so forgive me if I'm duplicating a query.)

Click to expand...

I don't know your actual pedals, but you probably need to scale some resistors working as current sources and other components, it can be done but with some care on the design, also make sure that the used opamp is ok to deal with ±15V but that shouldn't be a problem in most cases.

JS

Click to expand...

Thanks. I was looking at a few  (opamp) compressor boards at tonepad as a possibility.