I need to build a stand-alone discreet buffer (cannot use IC opamp).
This is supposed to be the buffer circutry used in Tube Screamers.

http://beavisaudio.com/techpages/buffers/Buffer_TSTransistor.gif

Will this circuit work as a stand-alone buffer? (I am using the 2N3904 transistor, if that matters)

Quote from: SamJenkinsRides on August 29, 2024, 01:38:18 AMI need to build a stand-alone discreet buffer (cannot use IC opamp).
This is supposed to be the buffer circutry used in Tube Screamers.

http://beavisaudio.com/techpages/buffers/Buffer_TSTransistor.gif

Will this circuit work as a stand-alone buffer? (I am using the 2N3904 transistor, if that matters)

It will work but as a stand alone buffer you can toughen it up a bit and also add some anti-pop resistors and anti-oscillation resistors.

The thing is what input impedance do you want to target?
To get 1M input you need to be more selective of the transistor.
2N3904 isn't the best choice for a buffer.




You might want to look-up the Cornish buffer.

I'd proceed to Rob's suggestion with bias resistor bootstrapped, like configuration (B) below..



Of course, with R2, C2, R4 & R5 (in Rob's scheme) added..

P.S.
In case of no high gain BJT availiable, go to (C)..

edit: Welcome, of course...

Let's see what should be the behavior of your choice as a stand-alone buffer..

I have built this circuit twice and keep getting a very loud buzzing (loud enough to drown out any guitar signal, if in fact any guitar signal is actually getting through) when 9v is applied.
I've checked each transistor after I pulled them back out of the circuit and they test operational (used new ones each build, regardless). Tested continuity and voltage, and all seems to be what it should be, where it should be (down to the 9v and 4.5v points in the circuit. I have no idea what milivolt values I should be getting anywhere).

I am just starting out on my journey as an electronics technician, and have an extremely basic understanding of how these things work. I am able (have been a mechanic and an electrician), but ignorant.

I don't actually know what I specifically need from this buffer. All I know is one of the pedals on my board behaves radically if there is not a discrete buffer placed after it, I don't have room to shove another pedal in there to take advantage of its buffer, and I'm not paying over $100 for a buffer that I can build myself, and I want to use the opportunity to learn more about the circutry within the things that I enjoy.

Quote from: SamJenkinsRides on August 29, 2024, 03:43:04 PMwhen 9v is applied

Applied from what? This circuit has zero ripple rejection, if you're not using a regulated power supply (or a battery) you're definitely going to hear it.
It might also just be EMI. Can we see a picture of the build?

Try to place a 47 to 100 μF cap on R1/R2 junction..

Quote from: antonis on August 29, 2024, 04:26:41 PMTry to place a 47 to 100 μF cap on R1/R2 junction..

Sorry, the guy who created that schematic labeled two different resistors as R2. Do you mean place the cap between the two 100k resistors, or between the pair of 100k resistors and the 510k?
The omittance of this capacitor is what's causing the extremely loud buzzing?

If the build is out in the open under a fluorescent lamp, it will BUZZ.

If a ground path is omitted, it will buzz (in most rooms).

Many audio inputs buzz if left open, less if shunted with a guitar.

Transistors do not buzz!! They don't know the pitch. (If it was a 78.91Hz buzz you would notice the musical mismatch; so you have 50/60Hz "wall power" buzz.) They sure can amplify buzz from the air, or add side-paths for buzz to come in on.

If you have "an extremely basic understanding", then it is time to show what you are doing and hope for gentle lessons and corrections. When I was young, I could wire a lamp or toy-train but not an audio cable; its an additional knowledge-base, signal grounding and shielding.

Quote from: SamJenkinsRides on August 29, 2024, 05:05:08 PMSorry, the guy who created that schematic labeled two different resistors as R2. Do you mean place the cap between the two 100k resistors, or between the pair of 100k resistors and the 510k?
The omittance of this capacitor is what's causing the extremely loud buzzing?

Referring to the toughened version:

C4, the cap across, can help with reduce buzz  (value 10uF to 100UF)
C5, the cap across R8, can help reduce buzz (value 10uF to 47uF)
R5 the resistor in series with the output prevents the buffer oscillating when connected to a cable.

Bad construction and layout or lack of shielding are other things which cause buzz.
Using a plastic enclosure instead of a metal enclosure will promote buzz.

Does the buzz go away when the guitar's volume knobs are set to 0?

Quote from: SamJenkinsRides on August 29, 2024, 05:05:08 PMSorry, the guy who created that schematic labeled two different resistors as R2. Do you mean place the cap between the two 100k resistors, or between the pair of 100k resistors and the 510k?

It should make no difference 'cause both R2s and R1 are connected on the same point..
(the other leg of the cap to GND, of course..)

See Rob's C5 in respective schematic..
(in which schematic, a low value resistor in series with +9V and C4 positive leg should also help..)

Quote from: SamJenkinsRides on August 29, 2024, 03:43:04 PMI have no idea what milivolt values I should be getting anywhere

For +9V supply, you should get 4.36V on 100k/100k junction (maybe a bit lower due to your meter loading), 2.92V on Q1 Base and 2.31V on Q1 Emitter..

Of course, decimal numbers precision is strongly dependent both on items tolerance and BJT's current gain..

Quote from: PRR on August 29, 2024, 05:27:54 PMIf the build is out in the open under a fluorescent lamp, it will BUZZ.

If a ground path is omitted, it will buzz (in most rooms).

Many audio inputs buzz if left open, less if shunted with a guitar.

Transistors do not buzz!! They don't know the pitch. (If it was a 78.91Hz buzz you would notice the musical mismatch; so you have 50/60Hz "wall power" buzz.) They sure can amplify buzz from the air, or add side-paths for buzz to come in on.

If you have "an extremely basic understanding", then it is time to show what you are doing and hope for gentle lessons and corrections. When I was young, I could wire a lamp or toy-train but not an audio cable; its an additional knowledge-base, signal grounding and shielding.

I had an insufficient ground connection. Thank you for your help.

Thanks everybody.
With your help, I have found the source of the buzzing, but new issues have arisen concerning multiple buffers and their relationships to other pedals.
I am going to start a new thread entitled "bufferz 'a poppin'" if any of you would like to take a crack at figuring out an issue that an actual electronics engineer couldn't figure out.