Another DIY tube based fuzz

SBD · 24th July 2012, 03:41 PM

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

6n2p-ev Fuzz.png

S.B.D

kevinkr · 24th July 2012, 04:12 PM

Welcome to the forum! Note that I moved this when I approved it to the appropriate forum.

djgibson51 · 26th July 2012, 07:57 PM

Cool. Did you try it with the tone stack after the distorting tubes? Too much bass going into the distorting tubes doesn't give me good results. (There is no reason not to have tone before AND after your sound generating tubes either). Keep us up to date.
Regards & welcome.
JimG

BrunoP · 29th July 2012, 08:11 PM

Too much bass = blocking distortion in my experience. It looks like you're not cutting much bottom on the front end of your design. The other thing that comes to mind is oscillation. Did you check it with similar settings, but without input signal? Just my 2 cents.

SBD · 29th July 2012, 10:42 PM

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

djgibson51 · 3rd August 2012, 07:01 AM

Your current tonestack values appear to work as a 'tilt' control - treble/bass cut/boost, but no mid scoop.
With your 500k pot, and changing R18 to 33k, C9 to 22n, C10 to 5.6n you can have an 8dB scoop at 350hz.
Hours of fun.
Cheers
JimG

SBD · 5th August 2012, 06:38 AM

Hi JimG,

You're absolutely right. I wanted to give the option of a flat response as the starting point.
Why do all tone stacks I've encountered have this high-mid to low-mid scoop?

Thanks,
S.B.D

razorrick1293 · 5th August 2012, 05:50 PM

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?

SBD · 5th August 2012, 10:21 PM

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.

TUBE FUZZ PS.png

S.B.D

razorrick1293 · 6th August 2012, 10:42 PM

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.

24th July 2012, 03:41 PM	#1
SBD diyAudio Member Join Date: Jul 2012	Another DIY tube based fuzz 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 6n2p-ev Fuzz.png S.B.D

24th July 2012, 04:12 PM	#2
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Welcome to the forum! Note that I moved this when I approved it to the appropriate forum. __________________ "Extraordinary claims require extraordinary evidence." - Carl Sagan

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Fuzz Face DIY: need more fuzz	ThomasDIY	Instruments and Amps	12	17th September 2009 03:06 AM
DIY Fuzz Factory in Arion enclosure- with a difference	lordofthethings	Instruments and Amps	0	23rd November 2008 08:21 AM
sound clips -DIY green ringer / tycobrahe octavia / axis fuzz / rangemaster and more!	hellwood	Instruments and Amps	5	8th October 2007 03:17 PM
diy disco lights? (based on diy rear projection tv idea)	dion_lilley	Parts	0	4th July 2007 01:34 PM
tube based CCS	GAK	Tubes / Valves	9	12th February 2004 04:58 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

26th July 2012, 07:57 PM	#3
djgibson51 diyAudio Member Join Date: May 2010 Location: Hawkes Bay	Cool. Did you try it with the tone stack after the distorting tubes? Too much bass going into the distorting tubes doesn't give me good results. (There is no reason not to have tone before AND after your sound generating tubes either). Keep us up to date. Regards & welcome. JimG

29th July 2012, 08:11 PM	#4
BrunoP diyAudio Member Join Date: Mar 2012	Too much bass = blocking distortion in my experience. It looks like you're not cutting much bottom on the front end of your design. The other thing that comes to mind is oscillation. Did you check it with similar settings, but without input signal? Just my 2 cents.

29th July 2012, 10:42 PM	#5
SBD diyAudio Member Join Date: Jul 2012	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

3rd August 2012, 07:01 AM	#6
djgibson51 diyAudio Member Join Date: May 2010 Location: Hawkes Bay	Your current tonestack values appear to work as a 'tilt' control - treble/bass cut/boost, but no mid scoop. With your 500k pot, and changing R18 to 33k, C9 to 22n, C10 to 5.6n you can have an 8dB scoop at 350hz. Hours of fun. Cheers JimG

5th August 2012, 06:38 AM	#7
SBD diyAudio Member Join Date: Jul 2012	Hi JimG, You're absolutely right. I wanted to give the option of a flat response as the starting point. Why do all tone stacks I've encountered have this high-mid to low-mid scoop? Thanks, S.B.D

5th August 2012, 05:50 PM	#8
razorrick1293 diyAudio Member Join Date: Nov 2010 Location: England Hertfordshire	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?

5th August 2012, 10:21 PM	#9
SBD diyAudio Member Join Date: Jul 2012	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. TUBE FUZZ PS.png S.B.D

6th August 2012, 10:42 PM	#10
razorrick1293 diyAudio Member Join Date: Nov 2010 Location: England Hertfordshire	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.