Not really. This circuit is basically a tweaked MXR Dynacomp into a Electra style distortion with variable diode clippers. The Expand control sets the compression just as the Sensitivity control in the MXR Dynacomp. The Drive control blend in hard diode clippers at the end of the circuit.
By the way, would you have, by any chance, any plan to release layouts for the other Multivox JAM pedals as well (I'm thinking about the phaser, the filter, the octaver, etc)?
Yes, i plan to try to do layouts for these as well since I have the schematics. Not sure when since they are way more complicated circuits than they ones I alrady uploaded. Especially the phaser....
Thank you. I like their chunky design, and i'm curious to try it... but there is no hurry at all : i still haven't built the Jen phaser you posted several weeks ago!
Funnily enough, I just found this (in case you didn't know it already) : all the schematics are present: https://music-electronics-forum.com/forum/schematic-requests/34201-multivox-big-jam-guitar-pedal-schematics
I was going to build this one and sat down to compare the layout to schematic and wanted to double check some things:
On Q2, Schematic shows the 56n going from Q2 emitter to base of Q6 - the layout has it coming from the collector. Can someone double check me and make sure I'm not missing something fundamental. Looks like the fix may be rearranging a bit to get the 56n to the emitter, or flipping the transistor and running the 10k's to their correct collect and emitter connections?
Got it working, couple of other little changes: The 100k to ground off the offset pot (G2 to L2) should be 1Meg. The 100k to ground off pin 3 of the 3080 (Q7 toV7) should be 1Meg.
I reduced the resistor off the emitter of Q6 to 390 ohms. It was barely over unity with the 1k.
For Q3/Q4 I used 2N2222's with an HFE of around 150. I usually try and match the gains on those as close as possible. I originally had 2N5088's (HFE about 340) in, but when I put the lower HFE transistors in, I got a lot more volume.
Last thing - the level pot need to have lug 1 connected to ground.
It's a really cool pedal, I happened to have a few 3080's around and I love the big jam stuff. It should be relatively easy to do a LM13700 layout for people that don't have 3080's.
I dig the chunky design of Multivox JAM pedals, thank you!
ReplyDeleteOn this pedal, is the "EXPAND" feature actually a dynamic expander, or more a FUZZ (like some early fuzz pedal like the SuperFuzz)?
ReplyDeleteNot really. This circuit is basically a tweaked MXR Dynacomp into a Electra style distortion with variable diode clippers. The Expand control sets the compression just as the Sensitivity control in the MXR Dynacomp. The Drive control blend in hard diode clippers at the end of the circuit.
DeleteOh, interesting!
DeleteThank you for the insight.
By the way, would you have, by any chance, any plan to release layouts for the other Multivox JAM pedals as well (I'm thinking about the phaser, the filter, the octaver, etc)?
ReplyDeleteYes, i plan to try to do layouts for these as well since I have the schematics. Not sure when since they are way more complicated circuits than they ones I alrady uploaded. Especially the phaser....
DeleteThank you. I like their chunky design, and i'm curious to try it... but there is no hurry at all : i still haven't built the Jen phaser you posted several weeks ago!
DeleteFunnily enough, I just found this (in case you didn't know it already) : all the schematics are present:
ReplyDeletehttps://music-electronics-forum.com/forum/schematic-requests/34201-multivox-big-jam-guitar-pedal-schematics
I was going to build this one and sat down to compare the layout to schematic and wanted to double check some things:
ReplyDeleteOn Q2, Schematic shows the 56n going from Q2 emitter to base of Q6 - the layout has it coming from the collector. Can someone double check me and make sure I'm not missing something fundamental.
Looks like the fix may be rearranging a bit to get the 56n to the emitter, or flipping the transistor and running the 10k's to their correct collect and emitter connections?
I didn't catch anything else.
I got 27 cuts on the layout too.
Thanks for noticing!
DeleteFixed.
Got it working, couple of other little changes:
DeleteThe 100k to ground off the offset pot (G2 to L2) should be 1Meg.
The 100k to ground off pin 3 of the 3080 (Q7 toV7) should be 1Meg.
I reduced the resistor off the emitter of Q6 to 390 ohms. It was barely over unity with the 1k.
For Q3/Q4 I used 2N2222's with an HFE of around 150. I usually try and match the gains on those as close as possible. I originally had 2N5088's (HFE about 340) in, but when I put the lower HFE transistors in, I got a lot more volume.
Last thing - the level pot need to have lug 1 connected to ground.
It's a really cool pedal, I happened to have a few 3080's around and I love the big jam stuff. It should be relatively easy to do a LM13700 layout for people that don't have 3080's.
Great job!
DeleteThe layout is updated and tagged with some of your suggested mods.