Which circuits need buffers?

[Flynn]

I am building a multi-effects unit that has several distortion & fuzz units, high-pass filters, FX sends for blending in external effects, and a small mixer.

Everything is patchable using short cables (except for perhaps any long cables to and from any external FX that may be plugged in to the internal FX Send or one of the internal effects).

Questions being:

1)  Should i buffer the input on all of these things?
2)  Should I buffer the outputs of anything?  (The FX Send maybe?)

Since it will integrate with other effects units on perhaps long cords I am just trying to do the basics needed to have everything be happy together.

[Flynn]

I like what ScreaminFX does on their fuzz boxes which is an on/off switch for the input buffer.  Very cool option; big difference in sound.

[blackieNYC]

Agreed. Don't buffer the inputs of "fuzzes", that is, specifically fuzz-face style designs. Or anything that simply sounds better with no buffer before it. Try a buffer like a Boss pedal, off, in front of it.  Does it sound worse, different, better, or the same?
I will say that fuzz-face designs are "generally considered" better without an input buffer, and if you happen to like a buffer in front of one, make it switchable. Eventually you may find that due to your ever-increasing familiarity with fuzzes(as you build more and more) you may appreciate the fuzz without the buffer better, and come to share the opinion of the majority. Make sense?

I think very few designs around here require an added output buffer.  Usually if you see an output stage that doesn't appear to be "part of a distortion or eq circuit or contribute to an effect circuit" it will be a gain make-up stage, a booster but not a buffer. You want a low enough output impedance to get a full frequency range to the next pedal of course. Or amp. And then input impedance of the next input comes into play.  Could do a listening test with a long cable I suppose. 

[Flynn]

Thanks much for the info, blackieNYC.

I am thinking maybe I should simply build a few dedicated buffer modules into this whole unit (with patchable ins and outs) and use them as-needed instead of hard-wiring them into everything.

Still curious if the FX sends should have the buffer built in.  Could be on a switch, i reckon.

[Flynn]

by the way, I saw you built the Escobedo PWM.  the first multi-effects unit i built has that in it and i love it...   i also put in his TMK distortion, the VCF, the clean boost, the ring-mod, and my favorite (which i mod'd a great deal): the bronx cheer.

[iainpunk]

Id always buffer the fx send and return. You could maybe put a switchable 10k on the output of the send for pedals that need a high impedance signal.
Id also put a volume control before the fx send buffer, so that the pedals in the loop can get a smaller signal, which makes some pedals sound better. If you do that, id put a boost in the fx return buffer (1 to 10 times maybe) to recover any volume losses from the loop.

The buffer units dedicated in stead of them being hard wired is a good idea for most things, but the fx loop is another story in my opinion.

Cheers, Iain

[Flynn]

Hi Iain,

Thanks a lot for that info - I figured that FX send would need the extra help I just didn't know what exactly.

You cleared it up, cheers!

[stonerbox]

I've been planing to do the same thing but in the meantime I'll subscribe to this thread. Looking forward to see what you come up with Flynn! I got the recommendation to control several circuits volumes, tones and distortion levels using only a few potentiometers that influences LDRs. What are your plans on that front? Maybe you're into doing individual pots for each effect?

[Flynn]

Hiya Stonerbox,

Thanks a lot! 

Your idea sounds really cool; i'd be glad to hear about what effects' pots would be 'ganged' with the LDRs.  Very cool idea.

This thing i'm working on is an early 60's dual-mono tube turntable in a suitcase.  The turntable was burned up and so i removed it and am putting a number of effects and the mixer in its place.  I also did a lot of mods to the tube amps so they are geared for guitar and also a bunch of options, like you can switch the negative feedback in and out, remove the tone stack, boost it, remove the cathode bypass cap, switch in a 500pf on the volume control, etc.  Individually on either amp channel. 

I like putting ins/outs on everything so it's as flexible as possible; and dedicated pots too!

I also just simulated a 3-band Bandpass filter (sort of like the front end of the Quadrafuzz) so i can split a guitar signal into 3 different bands (each with their own output) and effect them all individually before mixing them back together.

[stonerbox]

Hiya Stonerbox,

Thanks a lot! 

Your idea sounds really cool; i'd be glad to hear about what effects' pots would be 'ganged' with the LDRs.  Very cool idea.

This thing i'm working on is an early 60's dual-mono tube turntable in a suitcase.  The turntable was burned up and so i removed it and am putting a number of effects and the mixer in its place.  I also did a lot of mods to the tube amps so they are geared for guitar and also a bunch of options, like you can switch the negative feedback in and out, remove the tone stack, boost it, remove the cathode bypass cap, switch in a 500pf on the volume control, etc.  Individually on either amp channel. 

I like putting ins/outs on everything so it's as flexible as possible; and dedicated pots too!

I also just simulated a 3-band Bandpass filter (sort of like the front end of the Quadrafuzz) so i can split a guitar signal into 3 different bands (each with their own output) and effect them all individually before mixing them back together.

Now that sounds like something I would love. Very great man, best of luck and be sure to post the results if you feel like it. The LDR thing was not my idea, anotherjim and ElectricDruid suggested it in this thread.

http://www.diystompboxes.com/smfforum/index.php?topic=116502.msg1079097#msg1079097

[R.G.]

(1) Figure out the input impedance of your effects circuits. Some have low input impedances, and will load a guitar. Some naturally have high input impedances and would not need additional buffering.
(2) Decide which effects will ever be driven directly by a guitar. Effects never driven by a guitar directly probably don't need buffers.
(3) Exceptions are the Fuzz Face and its many clones and derivatives, where the input loading is part of the intended sound. There are always exceptions.

[Flynn]

@ stonerbox:  yeah i'll do a post with pix and vid when it gets closer to demo time!  thanks for sending that link.  that concept opens up some cool possibilities.

@ R.G.:  i'd like to be able to run guitar direct into any of them.  i reckon the dedicated optional buffer stages are the best route to take (aside from the FX send and the mixer).  i appreciate you taking the time to help; i'm a big fan of yours and GeoFex.com!

[PRR]

> an early 60's dual-mono tube turntable in a suitcase

That immediately reminds me of some shocks I have got. 1940-1970, tube amps were often "transformerless" and Hot Chassis. They could give a strong shock. In a plastic-box radio, or a phono where the pickup wires were hard to reach, this could be entirely safe. Hot-chassis guitar amps (you must be able to touch circuit common on your guitar plug) sold one-jump-ahead of increasing UL limits on leakage current, dubious circuit tricks, until transistors ate the tubes' lunch.

If you have addressed this, I'm happy.

[Flynn]

hey PRR!

It's not an auto-former, it does have an iso transformer and i've already put a grounded cable on there.  that was the first thing i did!