Hi,
First post in this forum so hello to you all.
A couple of month ago I decided to build and experiment with a tube based fuzz .
I read numerous articles on tube theory and looked at hundreds of schematics.
Yesterday I finished building my first working prototype.
Goals:
-High plate voltage. Not like the starved plate designs I found around the net.
-Use the low price soviet 6n2p-ev
-Add a single POT tone stack - the muff design was chosen
The design uses two 6n2p-ev dual triodes. A cathode follower as an input two gain stages and another CF at the output.
I do have a problem with the tone stack that will need to be fixed...when I shift the pot towards the bass, the signal gets really weird. Maybe I am loading the input stage CF ???
I attached my design schematics and a link to a short clip I took showing the output of the fuzz with a 1kHz 100mVp-p input.
Your wise comments are appreciated!
DIY tube based fuzz - YouTube
S.B.D
First post in this forum so hello to you all.
A couple of month ago I decided to build and experiment with a tube based fuzz .
I read numerous articles on tube theory and looked at hundreds of schematics.
Yesterday I finished building my first working prototype.
Goals:
-High plate voltage. Not like the starved plate designs I found around the net.
-Use the low price soviet 6n2p-ev
-Add a single POT tone stack - the muff design was chosen
The design uses two 6n2p-ev dual triodes. A cathode follower as an input two gain stages and another CF at the output.
I do have a problem with the tone stack that will need to be fixed...when I shift the pot towards the bass, the signal gets really weird. Maybe I am loading the input stage CF ???
I attached my design schematics and a link to a short clip I took showing the output of the fuzz with a 1kHz 100mVp-p input.
Your wise comments are appreciated!
DIY tube based fuzz - YouTube
S.B.D
Hi,
Thanks for the help and comments. This is what I came up with today.
With the input floating I see 50Hz oscillation and the tone stack interacts with these oscillation - chopping and messing with it to form a weird signal that measures around 1.5khz on the scope. I earthed the secondary side of the transformer (negative rail), this helped a bit... now the tone stack does not seem to destroy the signal coming out of the function generator, but still I see the 50Hz oscillations when the input floats. When the function generator is connected with the output disabled I don't see the 50Hz noise.
What is the most likely source of the 50Hz? The heater supply rail or B+ voltage rail? I have only a single 1000uF cap after the diode bridge on the 6.3V heater transformer output (I have seen designs with 6000uF on the heater supply).
Also, did I make a mistake by connecting the heater negative supply and the B+ negative rail together?
Tomorrow I will change the tone stack 100k pot to a 500k pot. According to the LTspice simulation, it is loading the higher frequencies and does not get them to clip over 6-7khz. I verified this with the function generator and scope (nice to see that the spice model is very close to reality). This makes the sound very bright and clear,but I do want a more versatile pedal.
Thanks,
S.B.D
Thanks for the help and comments. This is what I came up with today.
With the input floating I see 50Hz oscillation and the tone stack interacts with these oscillation - chopping and messing with it to form a weird signal that measures around 1.5khz on the scope. I earthed the secondary side of the transformer (negative rail), this helped a bit... now the tone stack does not seem to destroy the signal coming out of the function generator, but still I see the 50Hz oscillations when the input floats. When the function generator is connected with the output disabled I don't see the 50Hz noise.
What is the most likely source of the 50Hz? The heater supply rail or B+ voltage rail? I have only a single 1000uF cap after the diode bridge on the 6.3V heater transformer output (I have seen designs with 6000uF on the heater supply).
Also, did I make a mistake by connecting the heater negative supply and the B+ negative rail together?
Tomorrow I will change the tone stack 100k pot to a 500k pot. According to the LTspice simulation, it is loading the higher frequencies and does not get them to clip over 6-7khz. I verified this with the function generator and scope (nice to see that the spice model is very close to reality). This makes the sound very bright and clear,but I do want a more versatile pedal.
Thanks,
S.B.D
Leaving the input floating usually picks up a lot of noise and hum, if you use a switched jack, the input can be grounded when nothing is plugged in. I dont think the cathode follower is necessary on the input, it may be better to make a normal gain stage with a fair bass cut/treble boost, but you might have to increase the impedance of the tone stack (base values around 220k maybe?)
Do you have a diagram of the power supply?
Do you have a diagram of the power supply?
Hi Razorrick1293,
I still could'nt find the time to play with the tone stack (missing some resistor and cap values...). I want to test a 500k pot and tune the circuit accordingly.
Regarding the input CF, I did think of converting this to a gain stage as you suggest, it will be nice to have the option to clip stronger if desired - maybe reach transistor sound ...
.
My problem with this is that the effect output will be out of phase with 3 inverting gain stages - and I want to keep the CF output. I never design an audio circuit that the output is not in phase with the input.
I attached a schematic of the power supply I use in this circuit.
S.B.D
I still could'nt find the time to play with the tone stack (missing some resistor and cap values...). I want to test a 500k pot and tune the circuit accordingly.
Regarding the input CF, I did think of converting this to a gain stage as you suggest, it will be nice to have the option to clip stronger if desired - maybe reach transistor sound ...
.My problem with this is that the effect output will be out of phase with 3 inverting gain stages - and I want to keep the CF output. I never design an audio circuit that the output is not in phase with the input.
I attached a schematic of the power supply I use in this circuit.
S.B.D
It may be overkill, but what about an interstage transformer/output transformer to correct the phase after?
As for hum, I did have a problem with a DC heater supply, the hum did seem to get into the signal path, but adding a 12v zener 10 ohm resistor and 4700uF capacitor helped (12v supply, though a 6v zener, 5 ohm resistor should still be fine). Only problem is that resistor had to have a fairly high power rating, maybe 5 watts. other source of hum could be a ground loop, I usually connect HT ground and heater ground at chasis ground with no problems.
As for hum, I did have a problem with a DC heater supply, the hum did seem to get into the signal path, but adding a 12v zener 10 ohm resistor and 4700uF capacitor helped (12v supply, though a 6v zener, 5 ohm resistor should still be fine). Only problem is that resistor had to have a fairly high power rating, maybe 5 watts. other source of hum could be a ground loop, I usually connect HT ground and heater ground at chasis ground with no problems.
I don't see any smoothing in your heater supply. You appear to have a very large reservoir cap but no subsequent smoothing filter. As it stands I reckon you will get a sawtooth waveform (4 volts peak to peak riding on the DC component) which will be noisier than 6.3 volts AC. Hope I'm wrong.
Cheers
JimG
Cheers
JimG
Last edited:
Yes, the circuit was built and tested. Fuzz effect was very "round", even at full throttle.
For some reason my friend who is a heavy metal player really liked the sound, I thought it needed at least one more gain stage to give the required headroom I like in an effect.
I changed the last stage from a follower to CC for the extra gain I thought needed. It did help, but for some reason I think I would have liked a bit more.
I did have some hum noise, but did not get into trying to insulate the problem.
I will post a picture of the built circuit later on today.
For some reason my friend who is a heavy metal player really liked the sound, I thought it needed at least one more gain stage to give the required headroom I like in an effect.
I changed the last stage from a follower to CC for the extra gain I thought needed. It did help, but for some reason I think I would have liked a bit more.
I did have some hum noise, but did not get into trying to insulate the problem.
I will post a picture of the built circuit later on today.
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