A somewhat different way to bias a FF like circuit

[Gus]

A little different FF like circuit.  Discuss

[mac]

Interesting. I'll try it.
Those 5089 have a lot of gain, what about an emiter resitor at Q1 to tame voltage gain?

BTW, this is my way to bias a Silicon FF,



R7 adds base current, or "leakage", sending C1 closer to B1, 0.4v to 0.6v like in a germ circuit.
At the same time I can use the standard resistors at Q2 C.

mac

[Gus]

Interesting biasing Mac. I am surprised you did not make the 2.2meg resistor two resistors something like a 1meg and 1.2meg and use a cap at the middle to filter supply noise

The circuit I posted is another way to bias and control gain around Q1.  I have seen a commercial FF like circuit with a 2K gain control in the mid 90's

I was bored with seeing circuits with a trim at the collector of Q2.   I think that is not the correct way to bias a FF.

FWIW there are schematics of mine on the web with a 100 ohm for the added emitter resistor and a 10 K collector resistor for Q1.
This was up before Jack posted his circuit.

[Davelectro]

this is my way to bias a Silicon FF,

I have used that biasing method in a couple of 2n2369A-based FFs. Works like a charm.

[Gus]

This was up at effectroincs before DIYStompboxes


I build it a little different now I change two resistor values and the low pass cap value.
Note the input cap is 10uf one can change that to taste
Note the lowpass at the output. IIRC this was up before the axis face

[Bill Mountain]

What is the extra 1M doing?

[Gus]

The 1meg helps set the bias

The 100k and 10uf with the 1meg set the closed loop gain around Q1 along with what is before Q1s base(Q2E to Q1B feedback bias and closed loop gain)

This is another example of somewhat disconnecting The AC gain from the DC bias/feedback

[jrod]

Hey gus, if R5 at 1M does not result in approx. 4.5V at Q2C, do you adjust R5 until you get the right voltage? Or, is this for biasing just Q1?

[mac]

I was bored with seeing circuits with a trim at the collector of Q2.   I think that is not the correct way to bias a FF.

I agree. By changing the 8k2 you get a different freq distribution at the end.
I prefer pre than post biasing (IMHO),
This is another reasing why I use a big resistor at Q1 from Vcc to base, because the input impedance is low.

In silicon FF, increasing the emiter resistor helps to get closer to 8k2 at the collector. Biasing from there was a cool idea too.

FWIW there are schematics of mine on the web with a 100 ohm for the added emitter resistor and a 10 K collector resistor for Q1.
This was up before Jack posted his circuit.

I had that schematic on my mind when I asked you about the emiter resistor
It's been on my HD for a long, long time.

Interesting biasing Mac. I am surprised you did not make the 2.2meg resistor two resistors something like a 1meg and 1.2meg and use a cap at the middle to filter supply noise

mac

[Gus]

Mac

I think I will build a circuit like you posted using 2n2222s(because I have them)
Funny that the new builders have not seemed to pick up on your adjustment

Gus

[Gus]

Another sim in a thread
I was hoping for more posts from others in the thread
This one is the EH muff fuzz biasing
http://www.diystompboxes.com/smfforum/index.php?topic=104715.20

[Gus]

EH muff fuzz to ff like circuit
2.7K is now a 1K gain and 5K external bias with a gain limiting 100 ohm added
Q2 collector resistor is now a 1.8K and 8.2K (10K) with a lowpass filter added .01uf cap
Closed loop gain around Q1 is somewhat limited by R6 the 1k omit or adjust value to your liking
NOTE Q2 collector voltages with a 2N2222 and a 2N5089 lower to higher hfe very little change
Note R4 and what the Q2 2.7K emitter total  and the added R4 100k do
Compare this to a muff fuzz schematic you can find on the web


NEXT step could be remove R6 and add a resistor and cap in series both in parallel with the 100k feedback to reduce the closed loop gain around Q1 try a 100K and 1uf to start

[mac]

I'd use a 2.5K-B pot as fuzz pot to have more control over gain, and a 1K trimmer to make the tuning. At 200 ohm Q2C should be 4.5v.

mac

[Gus]

Mac
Good points about the gain and bias with different value controls
that would be a nice way to build it for the 4.5VDC at the collector
This is another nice variation on the circuit

I did not post why I like 1K and 5K (I have a bag of 5K controls) a 1K for the gain and a 2.5K bias for the 5k would work
I sometimes mark the external 5K bias gated close to 0 ohms to compressed greater than 1.5K ohms
This gives a gated to compressed range

[Gus]

2N2222 and 2N3055 look interesting


I am going to build this last sim with a Q2 emitter leg bias control, lowpass output filter across the 1.2K and a TO220 2N3055 or TIP29.

[Gus]

Build this cool one knob fuzz who needs Ge

Built the circuit in the post before this post with the following changes
input cap .1uf
output cap .1uf
100k volume at the output
C1 .01uf bigger will tighten up the lows works as a kind of EQ more gain below the C1, R7 RC less gain at higher frequencies (about 50K feedback) DC bias separate from part of the AC feedback because of C1
added a 47uf across R3, 2.7k
Q1 mot/onsemi 2N2222, Q2 TI TIP29
Used EH muff fuzz biasing (used R4)

Set it up as a one knob fuzz
My thinking was to use a 100K collector resistor at Q1 to limit the current drive to Q2
Made Q2 a med power device large die being run at low collector current (more miller etc) did not need to add any roll off cap across R6, you can if you want

Sounds really good and cleans up with guitar volume

Sim was on, battery measured 9.6VDC put that in the sim and the voltages matched what I measured in circuit.  The sim screenshot above was done with 9VDC

Who is going to try this?  I am working on a box to install this build. I like it.  I might add a 10k potentiometer in series with a 47uf across R3 as a gain control or I might leave it as a 1 knob fuzz

if you want a more heavy sound increase the input and/or output cap values