building a "Buffer Sampler"

[mg.audio]

I am planning a stompbox project for the single purpose of experimenting with buffers in guitar rigs. It's essentially going to be a box with six or so different buffers in it, which will be selected by a rotary switch. I'll have two BJT buffers, two FET buffers, and two op-amp buffers, maybe a couple more for good measure...

I am concerned about avoiding interference between the buffers: I want to avoid altering the tone of a buffer by having a bunch of other buffers on the same power rail. Do you think I would need to isolate each circuit with a bunch of buffered power supplies or voltage regulators? Or, would I be fine with feeding all of them from a standard 9V supply with a 100uF filter capacitor?

[thermionix]

My non-professional half-informed opinion is that there's no need to isolate.  There aren't LFOs or clocks or anything that would put noise on the power line.

[teemuk]

If you're overly concerned, you can decouple power supply of each buffer with a plain RC filter.

[EBK]

Hmm...  So, you are going to build a box with a rotary switch where the output will sound the same regardless of switch position? 

[bool]

... or go full monty if you're so concerned with the ultimate authenticity of your test: use a seperate battery for each buffer circuit.

[Groovenut]

Hmm...  So, you are going to build a box with a rotary switch where the output will sound the same regardless of switch position?

Hey I built one of those once as a psycho-acoustic experiment. input jack>5 pos rotary (all inputs pins connected to the output pin)>output jack.

It worked beautifully 

Next time I'll connect the input jack straight to the output jack and use the 5 pos rotary for different LED colors. Should get about the same results, but I bet there will be more variation in listener response based on the LED color 

[bool]

I'm not sure about the merit of a-b-c-d-e ... type switching for comparing different cckts.

If you're going for a "king of the hill" elimination / incremental improvement type of comparison, a simple A-B switching will work best and be simplest. (previous best, vs. current DUT).

Also, as teemuk said, you can pre-filter the PSU for each circuit.

But, if you want a real-world test - if you plan to use batteries - that's what you need to test with. Some circuits sound and "feel" different with a battery vs. a PSU.

[TejfolvonDanone]

Hmm...  So, you are going to build a box with a rotary switch where the output will sound the same regardless of switch position?

You don't have to be rude about something you know nothing about.
There are quite a lot of things where buffers can be different like input impedance output impedance filtering gain distortion. OP haven't listed anything regarding actual parameters of the buffers.

@mg.audio: If you switch the input and output of the buffers you shouldn't run into any problem. All the buffers should have a stable current draw when no input is present which won't interfere with the other buffers. If you run on batteries having 4 unused buffers just drains the battery faster.

[ElectricDruid]

You don't have to be rude about something you know nothing about.

He wasn't being *rude* really. It was just a little gentle mickey-taking.

There are quite a lot of things where buffers can be different like input impedance output impedance filtering gain distortion. OP haven't listed anything regarding actual parameters of the buffers.

But that's kind-of the point, isn't it? If the buffers are any good, the input impedance should be so high you don't notice, the output impedance should be so low you don't notice, the filtering should allow all audio to pass unaffected, and the distortion figure should be so low it's basically not there. That only leaves the gain, and a buffer with gain is actually a booster!

In practice, there will be measurable performance differences between the types mentioned, but whether that reaches the threshold of audibility is an interesting question. It's very decent of mg to have decided to study this important and under-researched area of modern science on our behalf!

Tom

[GibsonGM]

Sarcasm has always been ok here.  I doubt if Eric meant anything more than a small joke by the comment.   

It is a good thought exercise, MG., altho yes, the properties of buffers are so very very similar you may not hear a thing different between them.   I used to build things just to prove to myself that "yes, that is what they said it would be", too.   Maybe that's all you want to do, which is perfectly fine.   

It's nice that you wished to look out for a new member, TejfolvonDanone!

[EBK]

No rudeness intended (other than a playful jab).  If you read the stuff I post, you can hopefully see that I am a huge fan of any experimental pursuit, even if there are issues of practicality or apparent utility.  I've even accidentally strained the patience of a few people who had taken my questions too seriously while I was on a purely academic detour.
I think my comment was mostly intended to be a light-hearted invitation to Matt to explain the ways that his project was not as I described (since I wasn't telling him anything he didn't already know), if that makes any sense.  I apologize for the wording of my comment if it was received as ridicule rather than curiosity. 

[karbomusic]

Just a sanity check they every guitarist doesn't want 100% purely unaffected signal from a pristine buffer - sometimes they don't even know this and mistake the purity of the buffer as a problem with the buffer. What this means is the test idea should be fine so long as it isn't necessarily predicated on exact always = best choice.

[mg.audio]

Looks like I should just try the most simple solution first, especially since I'm only dealing with buffers, as thermionix said. That makes sense to me. One power rail with the typical filter cap.

First, yeah this is a totally experimental thing that I thought of doing when having some friendly banter with a co-worker at the guitar shop some time ago, about tube screamers and true bypass vs. buffered pedals. Recently, a friend asked me to build a buffer for his rig, and since there are a handful of different options, I figure this is a good time to do this. So, it's half serious experimentation and half joke pedal. I'm definitely not intending to use this as a component in my (or anyone else's) rig. The idea is to get all my guit-fiddling friends to try it and see if they can pick out the effects a buffer has on their rig, and to see the subtle differences in performance, if any, between the different types of circuits. This is ideal for those who have nothing but true-bypass stuff (or maybe just one buffered pedal) on their pedalboard.

There's also a little more to this project than I've led on so far. I'm going a bit further than just in/out jacks and a bypass switch, it's going to be sort of a guitar rig laboratory with buffers: In/Out jacks, a master bypass switch, a buffer bypass switch (which then leads to the rotary switch), FX loop jacks (for a pedalboard), and a pre/post switch to set the buffer pre or post FX. Guitar will go straight into the box with a 10 to 20 foot cable, and a short cable from the box to the amp. Connect the pedalboard with a very short cable from send to the board, and a longer cable from the board to the return jack.

Now we can switch between the following setups without un-plugging any cables:
1. Guitar straight to amp
2. Guitar to pedalboard (no buffer) to amp
3. Guitar to buffers to pedals to amp
4. Guitar to pedals to buffers to amp
(not to mention the switching between different buffers)

My friends and I are going to have a little "tone party" (yes I can hear your eyes rolling) and try not to get too stoned or drunk while we take notes and try to figure out this whole god damn buffer thing. I'll also make a single buffer and compare it to this project to see if there is anything noticeable happening with this power supply issue. I'm guessing there won't be anything noticeable.

[blackieNYC]

Ah, well that sounds fun.  At first, you see a guy who is new to the forum saying he's going to build 6 buffers, you have to wonder if a fuzz should be on that list after building the 3rd of 4th buffer
You should have one of the "buffers" just as a straight wire but label it "Ge Super Buffer".

[dschwartz]

Or use a non inverting opamp stage with 2dB boost..
I'll bet it would be praised as the best one with no loss at all.. name it the "secret mojo buffer"

[ElectricDruid]

You should have one of the "buffers" just as a straight wire but label it "Ge Super Buffer".

Yes, this. Definitely this.

Or use a non inverting opamp stage with 2dB boost..
I'll bet it would be praised as the best one with no loss at all.. name it the "secret mojo buffer"

Yes, this too!

Get some placebos in the box and see how many people can actually tell that the Super Ge Buffer does nothing, or that the op-amp makes everything...well, it sort of "comes forward", like it has more "presence". It's the buffer that seems to make your signal like *more* of your signal etcetc.

Have some fun with it.

[EBK]

I'm afraid to have fun in this thread now, but I'll risk it.
The best fake mojo buffer is probably a compressor tuned just barely on the imperceptible side of "is it on?"

[bool]

Or use a non inverting opamp stage with 2dB boost..
I'll bet it would be praised as the best one with no loss at all.. name it the "secret mojo buffer"

Interesting. That's very close to what I used in my live basses (slightly below 3dB gain with precisely tweaked corner frequencies). These basses were actually used on a couple of albums I did in 90's; some producers actually favored these over some expensive axes I had then (passive MEC PJs + a 10-euro DIY buffer).

[duck_arse]

You should have one of the "buffers" just as a straight wire but label it "Ge Super Buffer".

for mojo placebo, have two straight wire switch positions, cover one panel marking with tape and say that position "is not working right".

[EBK]

Here's a 10-placebo-buffer sequencer.  You just need to run your signal wires close to and parallel to the timer output to pick up some switching noise.