Author Topic: Buffer question  (Read 284 times)

Timko

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Buffer question
« on: March 11, 2019, 03:59:45 PM »
In a soon to be published build report, I built a pedal with an internal switch for a buffer.  It's a pedal that goes early in my chain, and I don't use a Boss tuner, so I've always counted on the first pedal to buffer my board.  I built the simple buffer that Joe Gore's Tonefiend guide shows:

http://www.tonefiend.com//wp-content/uploads/DIY%20Club%20Project%203%20v02.pdf
(the circuit schematic is on page 19)

When I breadboarded the circuit, I used some 2n5457s I have left over.  However, not having many of them, I tried the veroboard version with a few different transistors:  A J113 and a PF5102.  After some searching I found some people recommend them as decent replaces in buffers (in particular this article http://stompville.co.uk/?p=763).  However, when I had the buffer engaged and turned my tuner pedal on in front of it, I got an awful hum.  After spending a lot of time ensure I didn't wire or solder something incorrectly, I removed the transistor from the vero and put in a socket.  The PF5102 had the same result, but the 2n5457 had none of the nasty hum.  So while I'm glad that I discovered the issue, I do have some questions.

1. There are slight differences in the specs between the PF5102 and the 2n5457.  Which one of those particular specs should I be looking at in terms of buffers?
2. Now that the 2n5457 is out of print (and getting a little too pricey), how are people building FET buffers now?  Is there part of the schematic I should look at altering?

somnif

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Re: Buffer question
« Reply #1 on: March 11, 2019, 04:06:21 PM »
On one small part of your question,  th 2n5457 is still readily available as an smd part, mmbf5457. You can get small adapter boards to use them in thru-hole applications.

Timko

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Re: Buffer question
« Reply #2 on: March 11, 2019, 09:59:51 PM »
I knew I could use some SMD parts, but I was hoping to try thru hole.  This whole exercise made me realize I don't understand the properties of transistors and their various applications as well as I thought, so I figured it's a good time to learn.

Timko

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Re: Buffer question
« Reply #3 on: March 14, 2019, 07:59:35 AM »
An update after a lot more research:

I had wired a buffer to replace the bypass wire of my 3pdt switch.  The buffer itself was on a dpdt switch so I could either turn it on or turn it to true bypass.  I noticed a lot of popping when I had it engaged, and noticed a gum/fuzzy sound when I had another pedal in front of it (like a tuner) engaged.  After a lot of research, I found that Aion Electronics new Klon Klone has the same buffer/true bypass switch found on the KTR.  That switch appears to be a 3pdt instead of a dpdt. 

So while I could have something more complicated in the circuit, there's a good chance I'm just going to switch to buffered bypass and be done with it (especially since my tuner is true bypass).  The circuit I'm using is Jon Patton's Fallstaff circuit, and it begins with a buffer.  And after looking at the AMZ tube screamer buffer mod, I am going to try that.  So back to the drawing board.

But hey, the enclosures (which are etched and painted) look GREAT.