Greater than Unity Gain Buffer?

[Barracuda]

I've been working on a fuzz design but it compresses this signal quite a bit, its also followed by a twin t and then a buffer. When the twin t is fully notched its probably at unity gain with my clean, but I want to increase the gain a little, and still keep the buffered sound because it makes a big difference. Is there a technique to do this? I have tried using simple boosters but they don't have the same sound as the buffer and ruin the tone of the fuzz a fair amount. The main purpose of the buffer was to have a volume pot buffered so there was no tone sucky business going on, but it also gave the twin-t clarity.

[DavidRavenMoon]

Just increase the gain on the buffer. Is it an op amp? Add some resistance to the feedback loop.

Also, fuzzes always compress the signal. That happens when they clip it.


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[Eddododo]

What are you using for the buffer? Transistor or Op amp

[Barracuda]

Hey I'm using a BJT transistor, but I could also use a FET. I'm building this on small stripboard so I'm quite limited for space and I see an op amp as a last resort I suppose. And yes, I know fuzzes compress, but I've used certain techniques that have compressed it quite a lot more for a specific sound, and then combined with a bridged T gives quite low output. Sounds good though! just need to figure out how to add more gain without compromising the sound, preferably with the same buffer transistor.

[karbomusic]

Very loosely speaking, all a buffer is, is a preamp minus gain. So, shop around for BJT circuits that amplify and you may be able to figure out how to add some gain to what you have. Do you have a schematic of your current buffer? In simplest terms it may be a simple as making the emitter resistor smaller than the collector resistor but my BJT kung fu is surely weak.

[Barracuda]

All I'm using is the Boss/Ibanez input/output buffer, but I'm not entirely sure what values to change for more ouput

[Plexi]

If I'm not wrong: R3?

[antonis]

For BJT satisfactory buffer, bootstrapping is the only way.. 

Make R3=1k, place a 10μF cap in series with a 4k7 resistor from Emitter to Base, lift lower leg of R2 and place it to junction between 10μF Cap & 4κ7 resistor - so bias current should go from +4.5V through R2+4k7 to Base and 10μF negative plate to Emitter..
(although, bias with a voltage divider of 2 x 10k resistors from +9V should be advisable..)

Below is a scheme of bootstrapped amplifier but it can be easily modified for an Emitter follower by omitting R_C and moving OUT to Emitter..

[Digital Larry]

Just remember that an emitter follower has "low" output impedance (depends on transistor current gain and base circuit impedance as I recall), while the common emitter amplifier shown just above has output impedance = Rc.

[duck_arse]

All I'm using is the Boss/Ibanez input/output buffer, but I'm not entirely sure what values to change for more ouput

the emitter follower circuit shown is a follower, it doesn't have gain. you get varying degrees of less signal out than you put in.

[amz-fx]

This should sound very much like the buffer you are using but has a gain just under 2x.



Best regards, Jack

[Barracuda]

Hey guys thanks for the helpful replies! What interested me the most was the bootstrapping technique, I'm going to do a bit of research and breadboard this up in a little while. Thanks for the help Jack also, you're website was a great help to me a while back. While I am considering the op amp way, I'm going to do what I can to avoid it, just to save money and fit it on a size of stripboard I have a lot of!

[amz-fx]

Thank you for your kind comments!

Best regards, Jack

[Barracuda]

I have settled with a similar setup to what I had which adds a bit of gain (maybe not enough) but its enough for now. I found that most methods will distort the signal further which kinda messed with the tone too much so I ended up with a BJT -

10k -Emitter (VCC)
1m  -Base    (VCC)
1k   - Collector (Ground)

It had a similar tone to the buffer, but with more gain, is there a way I can measure/calculate the output impedance to compare?
I have a feeling its around 10k like the resistor on the emitter.

Thanks for the help!

[Digital Larry]

You can calculate the impedance by measuring the voltage drop into a load compared to when there is no load. 

Here's a way to do it with an adjustable load.  There'a also a way to do it with an arbitrary resistive load, but I forget the math off the top of my head.

http://www.learnabout-electronics.org/ac_theory/impedance73.php

[Eddododo]

I've used and loved this setup.. unsure if it takes too much room but this general topology is one of my favorites

[PRR]

> I forget the math off the top of my head.

Resistor divider. If it drops 10%, then obviously the load is 9 times the source to get the 9/10 output.

[antonis]

I ended up with a BJT -

10k -Emitter (VCC)
1m  -Base    (VCC)
1k   - Collector (Ground)

Did you use a P-N-P BJT or is just a typo..??

Anyway, as said above, output impedance of a N-P-N BJT amplifier is the parallel combination of its Collector (Emitter for P-N-P) resistor and impedance of whatever it drives..

That equivalent resistance should also be taken in mind for actual gain calculation..
(i.e. a CE amplifier with Collector & Emitter respective resistors of 10k & 1k driving a load of 10k has a gain of 5 - and not 10..)