Description of the Series 7 from the source:
Designed to mimic the unique overdriven tones of the rare Vox 4&7 series amplifiers in a small and easy to use stompbox. An unknown amp to most, the 4&7 series amps were most famously used by the Beatles during the Revolver era and Jimmy Page on numerous tracks from the second Zep album. Think Paperback Writer style of tones and, yes, Whole Lotta Love.
The 7 Series Overdrive captures the aggressive qualities of the solid state preamp found in the 4&7 series amps by using a pseudo hybrid setup consisting of a specifically selected silicon transistor for the first stage which adds a distinct bite and growl. That pushes an FET stage into clipping adding some warmth, sustain and amp like dynamics to the tone and feel. The end result is a highly effective emulation of the amp and a unique sonic blend that could be characterized as a "fuzzy overdrive."
As it's been pointed out there are some pictures with the 2.2uF coming off the emitter to ground as 4.7uF. I've seen pictures with 2.2uF as well, so I'm under the assumption that there's multiple versions as the pedal has changed names over the years. I changed the value of the cap so now there's 2 different layouts. With the 4.7uF cap the pedal should fatten up more compared to the 2.2uF.
Nice addition! Lumpy's makes great pedals.
ReplyDeleteQ1 is BC108B
You can replace the 6K8 resistor by a trimmer for biasing Q2.
Voltages:
Q1
1 4.58vdc
2 .79
3 .2
Q2 JFET
1 4.84
2 .61
3
Ok call this verified! You must have been reading my mind Zach as i've been searching for a layout/scheme for this all week. Was working great then I saw zosotone's post and decided to check voltages which were spot on apart from the drain for the JFET (was initially measuring ~3.80v). Tweaked it with a trimmer to get 4.80v and it sounds great, really tight but hairy overdrive. Wouldn't say it sounds vastly superior to the voltage with stock 6.8k drain resistor but it's nice to have (i'm assuming) Lumpy's original voltages. Noisy as hell at the moment but should be fine when boxed. Thank you Zach and zosotone.
Deleteits works very well !! Used also BC108B hfe 280. Thanks
ReplyDeleteThanks Zach! I tried tracing this one from pictures earlier this year. I don't know how I missed that schematic @ the usual place...
ReplyDeleteThis one has 6 cuts, right?
ReplyDeleteyea. i forgot the one under the 22nF cap. my bad
Delete+Zach, Just a quick word of THANKS for this site and all that contribute. I will only build a handfull of the pedals here, but I am amazed at the work and effort that goes into all the layouts here. Thanks for doing this!
DeleteCheers man. Enjoy the builds.
DeleteWell I built this, managed to get the 2N5457 biased to 4.8V with a 6K2 resistor and it doesn't sound very good at all! It doesn't distort and just sounds clean and very bassy. I checked my BC108 and it's a BC108C - will that be the difference?
ReplyDeleteTypically BC108C, and any BC series transistor with a C suffix, is a high gain version. The letters denote gain ranges when sorting, A being lower, B middle, C high, while thrills with no suffix are inspected. I suspect, based on the one that verified the layout that you want a lower gain silicon transistor. Also, see if your voltages match what's been posted, and check for any errors.
DeleteCheck the Collector voltage of the BJT too. You want it at about 4.5V as well. Also, try other Jfets - even though yours biased right, it could be a dud 2N5457.
DeleteI am in the process of breadboarding this before I decide to build it and would like a schematic. Anyone know where I can find one? Also, the 2 BC108s I have measure 691 and 782 hfe. Based on Zach's post above, a lower gain silicon transistor would work better. Any suggestions on other NPN silicon trannies?
ReplyDeleteSchematic is in the usual place (FreeStompBoxes). Other NPN's: 2N2222, BC109B, 2N3984.
DeleteI had to socket the 6.8k resistor spot and use a 12k to get Q2 to bias to ~4.5 on my build but it sounds great now. Thanks for the layout and build advice everyone!
ReplyDeleteGot it working on my breadboard. I measured 5.7V on Q2 with the 6.8k resistor. Tried a 8.6k (5.0V) and a 10k (4.2V). I am reading 3.9V on the collector of Q1 with no change when I swapped out the 6.8k with the 8.6k and 10k. I have several other NPN transistors with lower hfe that I am going to experiment with. I also have a couple germanium NPN (2N388) with lower hfe's (65 to 195 hfe)that I am going to try also. Anyone tried a germanium transistor in this pedal?
ReplyDeleteBuilt this and there is a curious issue. I got between nothing and very poor fuzz when I used the 6.8k resistor - tried a few different BC108s, and realised they were too high gain. So,
ReplyDeleteI replaced the 6.8k with a 10k trimmer and biased the Q2 drain to 4.8V and it sounds great!! well the fuzz sounds great but over the top there is a loud ticking - is this because its not boxed? I cut one leg off the trimmer to make it fit the two holes of the resistor - has this caused a grounding issue perhaps?
Thanks
Hmm, about the trimmer, not really. The ticking (which I also believe is a grounding issue) must lie somewhere else, unless you missed some cut or there's a solder bridge somewhere nearby the trimmer.
DeleteBuilt it. Paired with my p90 lespaul this thing just barks! (instant vintage tone).
ReplyDelete6k2 resistor for the fet drain and a 410hfe ME 4003 for the silicon transistor. Lower gain transistors gaves above 5.30v collector readings; now is spot on the original.
This comment has been removed by the author.
ReplyDeleteMember Music6000 posted something interesting to try at the forum:
ReplyDelete"I have studied half a dozen different vero's of the original online & he definitely uses a 4U7 Electro from 2N5457 Source to Ground instead of 2u2. It also appears that he might use an 4u7 Electro instead of 2u2 from BC108B Emitter to Ground.
I made both these changes & it just sounds wayyy better.
2N5457 bias to 4.84v
BC108B bias to 4.54v
My 2 Cents!
Cheers music6000"
I noticed that even with the gain at the lowest setting it still had quite a bit gain. Would it be possible to lower the gain?
ReplyDeleteMaybe lowering the 10k resistor to ground after gain 1...?
Probably by switching back to 2.2uf capacitors ;)
DeleteHey, thanks.
DeleteI noticed this stock as well.
I´ve made the changes today; Just put a 4.7uf in there, (FET I think), and now it has more body without losing its middy character.
Didn´t try plaing with the 10k resistor. Will do it tomorrow.
Would love to build one of these. How does it sound with humbuckers vs. single coils?
ReplyDeletehttp://topguitarpedals.com
There was a 4 knob version, with a pre gain control (pre gain maxed is the stock 3 knob sound), giving lower gain sounds. Would like to have a schematic for that version.
ReplyDeleteI have the regular 3 knob version, and it sounds better (to me) without a buffered pedal in front. Not so harsh, and a bit fatter.
Just finished the board and hooked everything up and am not getting any sound. I will recheck for solder bridges etc. Have a question on "Filter 1 to Input". Do I run another wire between the board input (or center terminal of the 3PDT switch) and Filter1? This is a little confusing since the input is already connected to the 3PDT switch.
ReplyDeleteYou could run 2 wires from the switch, or connect filter 1 to the same board input hole connection.
ReplyDeleteThanks Gilberto. Ran two wires from the switch and re-soldered the socket for the transistor and it is working now. Getting 4.5V on Q2 using a BC183 with 290hfe. Will try out various NPN transistors to see which one sounds the best. Can't get any sound out of a 2N388 Germanium with 195hfe. Will have to recheck the pinout.
DeleteI have revisited this one because I really wanted it to work! Now I have a 2N5457 biased at around 4.7VDC and a BC-something-or-other with an hfe of 295 with 4.5VDC on the collector. It took a 27K resistor on the drain of the Jfet to get it to bias.
ReplyDeleteIt sounds great. I left the 470pF cap out altogether because people were saying it was extremely bright and my pedal sounds like I imagined it should. If I turn gain past halfway I get some squeally oscillation but that's ok because I never need that much dirt. With P90s it sounds pretty darn good from gain on zero to 1/4. The Filter knob works well.
Thanks for all the info guys!
I ended up using a BC183 with 280hfe and the pedal sounds fantastic. I have been using this as my main overdrive/fuzz on my pedal board and I can get a mild crunch/overdrive all the way up to a decent fuzz tone sound. If anyone is going to use the BC183, be aware that the pinout is different than the BC108 as shown on the layout.
ReplyDeleteJust finished and I get no output at all...
ReplyDeleteI'm a noob so I ask: must the potentiometers be connected to ground? This is the only issue I can guess: double checked all components, tracks, connections. It only give a buzz sound.
Thanks!
My guess is rather this one: you MUST use a multimeter to check the voltages on the transistors - the most crucial here is the JFET "D" voltage that should be around (but not necessarily) 4.5V - you adjust these voltages by changing the resistors going to the transistors (or using trimpots) - in this case, for the BJT (first transistor) the resistor to be changed is the 22K one. For the JFET you want to change the 6.8K resistor (try this one first). Good luck!
DeleteGreat-sounding effect once you get it dialed in. It's definitely important to bias Q1 and Q2 to about half whatever your supply voltage is. I ended up using a 27K resistor on the collector of Q1 to bias a little below half. Voltages that are much greater than half start yielding too clean of tones.
ReplyDeleteI ran a mix of a 4.7uf cap on the emitter of Q1 and a 2.2uf on the Source of Q2. I also bumped up the 10k resistor to ground off Gain lug 1 to 22k, again for more grit (the original pedal value I believe is only 1K...way too clean for most of the gain pot rotation).
Hey all, just wrangled with this one boxing it up. Getting lots of RF radio fun when it's active, of course played with grounding issues. Putting a 100pf from q1 base to ground helped clear it up nicely. Happy building :D
ReplyDeleteGetting ready to make a couple more of these and want to use a 10k trimmer in place of the 6.8k resistor. A previous post mentioned cutting off one of the legs of the trimmer but caused a hum/ground issue. What is the best way to install the trimmer? Do I use just 2 of the legs? Which one would I cut off?
ReplyDeleteDoes any one have any info, schematics, layouts for the latest 5 knob version?
ReplyDeleteFor the price he is asking for these I would rather just buy it, than go through the work to build this, but it's not available on his site now and he is completely non-responsive to my email enquiries.
Just built this using all 4.7uf electros, had to use a 33k resistor to bias the JFET to around 4.5V, the pedal is very high gain with the distortion knob causing oscillations past halfway, despite this it is really easy to dial in a good tone. The filter knob seems quite subtle although that might be my general setup rather than the pedal itself. Really captures that Revolver sound and can see it staying as a mainstay on my board. Thanks for all your help guys.
ReplyDelete