freestompboxes.org

Also I am trying to draw a schematic of this circuit, the resistor that is hidden is a 4k7, the biggest electrolytic capacitor is 100uf. But the greatest difficulty will be knowing the value of ceramic capacitors.

The beginning of it is basically a rangemaster treble booster with npn.

The English Channel by RunOffGroove has 5 J201 JFETS (??)

http://www.runoffgroove.com/englishchannel.html

Fuzzy GERM clipping + JFET OverDrive (??)

interesting combination....

Black Sabbtah rules

Some capacitor values and some doubts

I made a board clone derived from the shots and found the schematic by tracing.
I added two guessed values in the schematic.
Four capacitor values unreadable.
Here the SprintLayout-file packed in an Zip-file.

The germanium transistor is CV7351 not CV7371. I've traced it from that same photos a couple of years ago, but i think i got to know somehow the values of those capacitors. IF, i can find the schematic that i traced back then i will post it.

The JFET section looks similar to the AMZ Booster 2.

rs wrote:The germanium transistor is CV7351 not CV7371. I've traced it from that same photos a couple of years ago, but i think i got to know somehow the values of those capacitors. IF, i can find the schematic that i traced back then i will post it.

Sorry, my fault it is a typo.

Great work Manfred!
rs, it would be great if you could find your old trace for those last few missing caps. If not, then perhaps similar pedals could offer some clues.

Catalinbread Sabbra Cadabra
viewtopic.php?f=7&t=25043&start=20#p249151

Laney Super Group Emulator
http://effectslayouts.blogspot.nl/2015/ ... lator.html

There are likely to be more, the Paranoid and Sabbath from MASF may very well hold some answers as well. Just as the Musician Sound Design Paranoid.

Hi Cub

rs, it would be great if you could find your old trace for those last few missing caps. If not, then perhaps similar pedals could offer some clues.

You have misunderstood me, I have no old trace, I found the schematic by tracing the board layout.
I will find more guessed values by calculation and circuit simulation.

I cannot build the real circuit for trial and error, because I absent for the next view weeks.

Manfred wrote:I have no old trace,

I know, that was for our forum brother rs.
Enjoy your holiday!

I redrew the schematic and filled in further guessed capacitor values,
which are marked by red borders.
I rearranged the tone control parts, so the structur of it becomes better recognizable.
It is a simplified Marshall tone stack, the bass pot is omitted the mid pot is shorted out.

Please notice that the electrolytic cap on CV7351's emitter is 47uf as per standard Rangemaster value, not 100uf.
Hope to give a look at the rest of the schematic as soon as I can.

Also, the resistor in parallel appears to be a 3K9 (also standard Rangemaster) in one of the photos (the one posted by beedotman » 04 Mar 2013, 17:07). Matter of biasing, I guess. In the same picture, the resistor on the CV7351's collector is 10K instead of the 22K seen in the other and more recent examples.

More than everything else, can't we find some other pictures? Or - best of all - can't anyone read directly from his pedal the ceramic caps' exact values?
Of course I trust the guessing made by Manfred, but I'm also curious - i.e. the bigger ceramic on the extreme right of the board could be also a bigger value, too...

I would check the Laney amplifier Iommi played through for those values. looks like he's going for a rangemaster into Laney topology on this one as stated in the title of the above video.

I built this pedal, using the vero layout at tagboardeffects; I replaced the 100uF on the Rangemaster's emitter by a 47uF (as pointed out by Blues1911), and the tone pot by a linear 100k (as is clearly seen in the original pics). I also added a switch to bypass the Rangemaster, so I can hear only the 'amp'.
It doesn't sound bad at all, BUT there's quite a lot of top end. I would imagine this has something to do with some of the circled caps in Manfred's (very nice) schematic. For example the 470p 'bright cap' across the gain pot, and the 2n2 parallelling the 100K.

OK, some more about these two caps I mentioned:
- found the Laney schematic (http://drtube.com/schematics/laney/Supe ... preamp.pdf) and it shows NO bright cap on the gain, and a 270p + 470k where we have 2n2 + 100k.
- someone on a Vintage Amps forum mentioned that his Laney LA100BL has a 100p bright cap
- the very similar Catalinbread Sabbra Cadabra has a 47p on the gain, and no cap across its 470k.

So... yes, I could experiment a bit, but I don't have the original to compare. In other words: would still be great if someone can figure out those original values!

So this is a frontend based on a rangemaster followed by a modified BSIAB.

Laney LA100 Supergroup was essentially a slighty modified Marshall Super Bass.

As Manfred told before, the Treble control of the pedal works around a simplified Marshall (Super Bass) tone stack - in that sense, according to Laney LA100 schematic, the tone stack capacitor value could be 270pf instead of 220pf.

Also, I found a bit difficult to understand the reason of the 2n2 value for the ceramic capacitor in parallel with the 100K: I'm not sure about it, but if it's a bypass capacitor just like the one found on Marshall amps Bright Channel's 470K mixer resistor, maybe a 500pf or 560pf would be more appropriate.

Same for the "bright cap" on the Gain control: on Marshall JTM45 and JTM 45/100 was 100pf, so maybe 470pf is way too high... I'd try with a 100pf.

Actually I have no idea about the unknow capacitor right after the output of the first (Rangemaster) stage to ground.

Please notice that I'm just guessing, haven't done any frequency calculation or whatever, so please take all these observations as food for thought.

Blues1911 wrote:Also, I found a bit difficult to understand the reason of the 2n2 value for the ceramic capacitor in parallel with the 100K: I'm not sure about it, but if it's a bypass capacitor just like the one found on Marshall amps Bright Channel's 470K mixer resistor, maybe a 500pf or 560pf would be more appropriate.

I believe the classic Marshall sound is a 470pf on the 470k. Actually it makes a lot of sense that Manfred chose the 2n2 here, because I think we want to keep R x C the same? We're using a 100k here, and 470k x 470pf ≈≈ 100k x 2200pf . However, since the Supergroup schematic I linked to in my previous post shows a 270pf there, a 1n2 might be an even better choice for the pedal (because 270pf x 4,7 = 1269pf) .

Hi tassosmavr,

The PCB-Layout in PDF format as desired.