fldrvr wrote:Hey Tabbycat! Any luck? Thanks!
tabbycat wrote:...didn't really work until out i linked the wiper of the level pot to ground. don't think this was in the schematic. but it seemed to make the magic happen so i'm not going to question it. will try putting that level 2 to ground it on the vero instead of offboard, but seeing as it works like this may as well go with it. it's hardly a heartbreaking addition. I typed in
brownwhopping wrote:How can I learn by reading threads an making circuits, when some day I can see a lawsuit or somebody beat me in the face for that?
Nocentelli wrote:tabbycat wrote:...didn't really work until out i linked the wiper of the level pot to ground. don't think this was in the schematic. but it seemed to make the magic happen so i'm not going to question it. will try putting that level 2 to ground it on the vero instead of offboard, but seeing as it works like this may as well go with it. it's hardly a heartbreaking addition. I typed in
The induction schematic has lug1 grounded, lug2 from the output cap, and lug 3 to output. This is how many DBA and some catalinbread volume pots are wired, and it works ok. I swapped lug 2 and 3 for a standard volume pot. The vero doesn't match either of these arrangements, even allowing for the pot working backwards.
tabbycat wrote:oh well, my rep is dirt until i get this reposted.
deltafred wrote:tabbycat wrote:oh well, my rep is dirt until i get this reposted.
Far from it, as we used to say where I worked "if you never make mistakes it's because you never do anything" (and there were plenty who never made mistakes!)
brownwhopping wrote:How can I learn by reading threads an making circuits, when some day I can see a lawsuit or somebody beat me in the face for that?
brownwhopping wrote:How can I learn by reading threads an making circuits, when some day I can see a lawsuit or somebody beat me in the face for that?
Nocentelli wrote:Looking again, i think if you just swap volume 1 and 2 wire connections and ground strip C it's pretty much the graphic fuzz.
deltafred wrote:Just looked at the schematic. The voltage divider for the half supply voltage bias is all wrong.
It doesn't want a cap across the upper resistor. This makes an AC potential divider* instead of a low pass filter.
deltafred wrote:The value of the cap needs to be higher, and/or the resistor values need to be higher as the cut off frequency is 160Hz, way too high to filter out mains hum fundamental. I would go for 100k resistors and 1uF electrolytic which would bring the cut off freq down to 1.6Hz (only because I have about 4000 100k resistors and a huge bag of 1uF caps).
Goodrat wrote:Hey guys, I worked at ESR as one of the two technicians there in the customer service repair. It was back in 1978 and my first electronics job. Sometimes we would just play guitar all day.
What I remember about the Graphic Fuzz box is they oscillated like crazy. The other Tech, Tony, made some improvements.
As far as the schematic, I remember there were two 10K resistors as a divider with the center going to ground to make the +/- supply and whatever caps on that.
The IC was a 741.
A lot of amp designs were ripped of from Peavey and they got in trouble eventually for that..
deltafred wrote:*If it is run on a power supply and there is any hum on the 9v it will be halved by the potential divider of the 2 x 100nF caps (and 2 x 10k resistors) and fed into the opamp. Removing the top cap creates a low pass filter with the 10k and the lower 100nF with a cutoff frequency of 160Hz,
deltafred wrote:Just looked at the schematic. The voltage divider for the half supply voltage bias is all wrong.
It doesn't want a cap across the upper resistor. This makes an AC potential divider* instead of a low pass filter.
tabbycat wrote:i think induction took his lead from this drawing at d*a*m http://www.stompboxes.co.uk/forum/downl ... hp?id=1835
found here http://www.stompboxes.co.uk/forum/viewt ... 6&start=40
induction wrote:deltafred wrote:Just looked at the schematic. The voltage divider for the half supply voltage bias is all wrong.
It doesn't want a cap across the upper resistor. This makes an AC potential divider* instead of a low pass filter.
That depends what you mean by "all wrong". I didn't redesign the sonic characteristics of the circuit, I just converted it to standard negative ground so it could be daisy-chained. People like the original design, so I left it alone as much as possible, "all wrong" or not. The caps and resistors in the bias network are true to the original, based on the schematic I was working from.
induction wrote:Sorry, I guess my post came out snarkier than I intended it.
greenskull wrote:Thanks for revisiting this circuit! I had a go at it on the breadboard some years back, but for some reason I didn't commit to a build. I think I'll give it another shot and try some of those tricks.
I wish I knew what John over at Basic Audio added to his version of this pedal...... it sounds extra nasty!
Return to Vintage Stompbox Corner ( ... - 1975)
Users browsing this forum: No registered users and 1 guest