An Idea for a Universal Input Buffer/Booster (onboard)

[JTEX]

Input buffers, flat boosters, EQ'd boosters - they can all be built around the same basic template consisting of a noninverting op amp and a few passives around it.

I did just that, using a DIP switch for set-and-forget settings and an ON-ON-ON toggle to go between 3 main operating modes: treble boost, unity gain buffer, and bass or flat boost. With the op amp specified, the whole circuit has the same self noise as a single 4k resistor (plus whatever gain you dial in) and draws just 0.3mA (lasts >1000 hours on a 9V battery). For best results install onboard, get rid of the original 250k or 500k volume pot (you can keep the original tone pot, before the buffer), and use a 10k volume pot after the buffer instead. 25k will do if you can't find a 10k in guitar size, but 10k or even lower is preferable for lowest noise and output Z.

Equally suitable for guitar and bass.

 

[lrgaraujo]

Nice work! Thanks for sharing it!
Impedance is one of the many concepts in this hobby that give me a bit of a headache, and I was confused to see a 145k input impedance option. Isn't that a little lower than we'd expect on a buffer?

 

[JTEX]

Pretty low, yes, but it's just one of many options going all the way up to 10 megs.

 

[Passinwind]

Nice work! Thanks for sharing it!
Impedance is one of the many concepts in this hobby that give me a bit of a headache, and I was confused to see a 145k input impedance option. Isn't that a little lower than we'd expect on a buffer?

The just depends. If you do the math on the loading given by a 250k volume pot, 250k tone control plus associated cap, and typical 300k-1Meg amp input, all more or less in parallel, not necessarily.

 

[JTEX]

I have one guitar where I replaced the usual tone cap by a tone... resistor. Variable load for the pickup. Works great!

 

[giovanni]

Is D1 for voltage protection? I thought that job would be better suited for a series diode?

 

[JTEX]

I don't want the permanent voltage drop from a series diode where its protection is only needed for brief, accidental reversal events. This is especially true for onboard installations. Any reverse voltage would be very brief, while you fumble with the battery clip, so a paralel diode is suitable. It can handle 1A permanently and probably 10 or 20A briefly - which neither a 9V battery, nor a pedal PSU can deliver. I protect my circuit, while you're supposed to protect your PSU against shorts.

 

[giovanni]

I’m definitely intrigued by this buffer…

 

[JTEX]

I'm totally making a product out of it. I put it here so you don't have to bother tracing it Favorite feature: it does not pop while switching the toggle around. Not even a little.

 

[szukalski]

I love the ghetto mods in SMD. Respect.

 

[JTEX]

I love the ghetto mods in SMD. Respect.

Yeah, the proto is built on the wrong board

 

[Passinwind]

Yeah, the proto is built on the wrong board

Sounds all too familiar. Nice timing though, as I'm currently gearing up to do a new buffer for the acoustic guitar I just bought. It has one of those janky plastic boxes on the upper bout, and JST connectors for all the wiring, so a pretty easy retrofit from the looks of it.

 

[Robert]

I put it here so you don't have to bother tracing it

Wait..... what?

Couldn't you have posted this about AN HOUR AGO!?

 

[Cybercow]

Pretty cool. Thanks for sharing.

One point I'd like to bring up about DPDT (On-On-On) toggles, that used to confuse me, and I'm sure will be a "gotcha" for those unaware that there are two (2) types of DPDT (On-On-On) toggles - "Type 1" & "Type 2". The internal lug joins are different (opposite) from one another in the middle position. Taiway DPDT (On-On-On) toggles (LoveMySwitches) are always "Type 1", whereas the DPDT (On-On-On) toggles from Tayda all seem to be "Type 2".

 

[JTEX]

Wait..... what?

Couldn't you have posted this about AN HOUR AGO!?

Legend has it that you can trace a circuit before there's even a PCB for it

 

[JTEX]

One point I'd like to bring up about DPDT (On-On-On) toggles, that used to confuse me, and I'm sure will be a "gotcha" for those unaware that there are two (2) types of DPDT (On-On-On) toggles - "Type 1" & "Type 2". The internal lug joins are different (opposite) from one another in the midle

Indeed, thanks for pointing that out. One has to be careful with On-On-On's. This is why I specified the part# I used, with some clippings from its datasheet.

Edit: I just checked four first-tier switch manufacturers (C&K, NKK, E-Switch and Multicomp) and their On-On-On's are all like this in the middle position. This is the same as the Tayda On-On-On, which is allegedly made by the same factory that makes E-Switch:

 

[jwin615]

Type 2 definitely seems to be the most common. It looks as if LMS specify all there III switches as type 2.

 

[JTEX]

I'm curious who even came up with this whole Type 1 vs Type 2 designation. Is it actually defined somewhere, or some dude just randomly called one of them #1 and the other #2 and everyone went with it? I can't seem to find anything called "type 1 or 2" reference in any actual datasheet, and those are the actual official documentation for the parts.

 

[Cybercow]

I'm curious who even came up with this whole Type 1 vs Type 2 designation. Is it actually defined somewhere, or some dude just randomly called one of them #1 and the other #2 and everyone went with it? I can't seem to find anything called "type 1 or 2" reference in any actual datasheet, and those are the actual official documentation for the parts.

So far, the only Google hits on "Type 1 and Type 2 toggle switches" are those references here in the PedalPCB forum by Caldo71, BuddyTheReow, Fojo and FeralFeline that I can find.

 

[Robert]

Dailywell (who is a switch manufacturer) refers to them as Type 1 / Type 2.
https://www.dailywell.com.tw/en/faq/Dailywell-FAQ-09.html (Check out those 4PDT ON/ON/ON's!)

This image has been around since before the dawn of PedalPCB:

I've mentioned this elsewhere, but the reason I use type 2 is because when a supplier carries them they generally specify that they are "Type 2".
Rarely a supplier offers Type 2 and doesn't indicate which type they actually are.

Similarly, it seems when a supplier just calls them "ON/ON/ON" with no indication of the type, they turn out to be Type 1.

Adding to the confusion, Tayda calls theirs Type 2 but they are actually Type 1.

When in doubt go with Taiway, I've yet to see a Taiway that is Type 1.

I generally order either Taiway, or these from StompBoxParts:

DPDT Toggle Switch ON/ON/ON - Solder Lug

Top Quality Parts for Guitar Effects Pedals and DIY Music Devices. Knobs, Pots, Switches, Kits, LEDs, Enclosures, Jacks, Wire, Resistors, Capacitors, Semiconductors

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