GGG Brassmaster: Does anyone know the correct resistor values?

[R.G.]

The input impedance isn't improved all that much. I found experimentally about 17kohm input in the stock circuit. It's up some, as the voltage-feedback nature of the first transistor circuit lowers input impedance with increasing voltage gain.

The input impedance is the lower 150K|| upper 150K divided by the voltage gain || base impedance of Hfe*390 (ignoring Shockley resistance). At frequency, the Ccb gets into it too. The voltage gain is lower than expected because of the 10K sensitivity pot loading and any loading from the second stage depending on the pot position.

I would either drop in an opamp, which is simple; or use a JFET in front of the first transistor in a similar circuit but using the JFET's high impedance as the buffer. But there are a million or more different ways to do this.

[Gus]

R.G I was drawing up a input with 8.2K collector R and a 2.2K emitter maybe run it at about 1/2 ma Ic set the base at about 1.7VDC gain <x8.  Maybe a voltage divider input 100K and 470K (429k from math) common resistors.  The 2.2K emitter R kind of big for the 10k bass volume pot but it might be OK.  Input R hfe x 2.2K || 100K || 470K maybe a MPSA18

1/ 2pi * 17 x10^3 *.1 x10 ^-6  = stock HP input  Might even want to move the input filter turnover frequency depending on the bass used

Like you posted many different ways to change things.

[lowstar]

I'm not sure a blend control would work well either, since some of the fuzz settings are much quieter than others.

i have mine wired with a dual linear 10K as blend, and the output of the circuit is followed by a 100K vol pot. works the same, u just have to choose different blend settings according to switch settings, then adjust vol to taste.

btw, thanks everybody who contributed to the final solving of the puzzle. i flipped the darlington yesterday, and now all the switch settings produce pronounced results. 2 settings were useable before (the very meaty and the very thin setting), but now there´s two more !
for the swapping of the resistors, i have to thank myself as well, as i posted that info more than one year ago, but nobody seemed to care really (or understand what i mean - except meanderthal). but, who cares, now everything is good.  

cheers,
lowstar

[DavidRavenMoon]

I'm not sure a blend control would work well either, since some of the fuzz settings are much quieter than others.

i have mine wired with a dual linear 10K as blend, and the output of the circuit is followed by a 100K vol pot. works the same, u just have to choose different blend settings according to switch settings, then adjust vol to taste.

With a master volume I could see it working.  The thing can get loud, so that was my one concern.  I like blend controls in my basses, so maybe I'll try that at some point. 

btw, thanks everybody who contributed to the final solving of the puzzle. i flipped the darlington yesterday, and now all the switch settings produce pronounced results. 2 settings were useable before (the very meaty and the very thin setting), but now there´s two more !
for the swapping of the resistors, i have to thank myself as well, as i posted that info more than one year ago, but nobody seemed to care really (or understand what i mean - except meanderthal). but, who cares, now everything is good.  

Well someone posted about the resistors... I hadn't even noticed that until I read it here, or somewhere.  Maybe it was you?

I was determined to get this thing working!  I spend an afternoon putting it together, so the switch dysfunction didn't sit well with me.   

Thanks for the info R.G.  Maybe I'll stick a jfet in the front.  I have a bunch of those laying around.

[lowstar]

I like blend controls in my basses

same here, i only have one bass that is vol/vol, and i really cannot get into liking that config. it´s faster to just turn the blend knob if you want to change sounds mid-song, as opposed to having to tweak two knobs.
other people swear by the vol/vol, though.
tastes are different, sad the old woman and ate the moco.

cheers,
lowstar

[Gus]

built a circuit fragment as a test.  I did not have a 470K and a mpsa18 so I used a 47K and 10K and a lower hfe 2n3904
Bias
47K, +9 to base of a 2n3904
10K Base to ground

8.2K +9 to collector of 2n3904
2.2K emitter to ground

9VDC power 5.53VDC at the collector, .931VDC at the emitter

Gain about 8.2/2.2
Adjust the input cap to the base and take the outputs from the emitter and collector.  Use a 470K and 100K bias string with a high hfe transistor like a mpsa18

[Plinky]

So is the new pcb layout waiting to be verified, or is everyone just updating with the old layout? I'd like to make another attempt at this pedal, but if there will be a new layout with pulldown resistors and such, I'll gladly wait. I had the last one running, but after all the swapping of parts and the like, the traces are starting to come up. 

[R.G.]

The new layout's posted at GEO. David and gtrgeek were going to check it for my normal forehead slapping errors and give a yea or nay.

David - you want a JFET buffer in front on the new PCB?

[DavidRavenMoon]

So is the new pcb layout waiting to be verified, or is everyone just updating with the old layout? I'd like to make another attempt at this pedal, but if there will be a new layout with pulldown resistors and such, I'll gladly wait. I had the last one running, but after all the swapping of parts and the like, the traces are starting to come up. 

I just swapped R22 with R27 and turned Q6 180° around.  It works just dandy.  To me it sounds just like the real thing, just with better parts.

But I'm going to make another one with the new layout (and goodies), which brings me to...

The new layout's posted at GEO. David and gtrgeek were going to check it for my normal forehead slapping errors and give a yea or nay.

David - you want a JFET buffer in front on the new PCB?

I will be digging into it more closely this week.  I haven't talked to gtrgeek yet to see what he's up to.

Yeah, a jfet buffer would be great.  I'm using mine with an active bass, but if I bypass the preamp or use another bass you can tell the difference.

Being that I haven't used one of these in about 20+ years, I can see room for improvement in the clean channels tone. At the time, that's what it sounded like, and it was just a quirky pedal.

I think a buffer would be a good place to start.  If I were to design an ultimate version I'd also include tone controls for each channel and maybe even a second output jack that would split the fuzz and dry channels when used.  But that's probably overkill.  Tone controls would be cool though.  Certain sounds are better with the highs removed from the bass channel, and sometimes the fuzz could use to have the top end tamed a bit.

BTW, just for fun, here's what it sounds like with guitar:

Guitar 1; various settings.

Guitar 2; sensitivity almost all the way off, and  volume on guitar half way off.

Lots of sick and twisted fun!

[Plinky]

I just swapped R22 with R27 and turned Q6 180° around.  It works just dandy.  To me it sounds just like the real thing, just with better parts.

So did I, and it does sound like the original per some friends of mine that have owned/played one, but I'm not getting any difference in the switching. A little is noticed on the SPST switch, but nothing on the 3PDT switch. I noticed the wiring to the switches is a bit different on the new layout. Will this make a difference? Sorry for sounding like a noob but I honestly never heard about this pedal until a friend asked me if I could make one for him. Little did I know of the pit I was about to fall into. 

[SonicVI]

Someday I'm going to try to use this triple pot to make a brassmaster with a continuously variable filter to replace the two position switch. It's a triple 25K. I just have to replace two of the wafers with 50K's.

[DavidRavenMoon]

I just swapped R22 with R27 and turned Q6 180° around.  It works just dandy.  To me it sounds just like the real thing, just with better parts.

So did I, and it does sound like the original per some friends of mine that have owned/played one, but I'm not getting any difference in the switching. A little is noticed on the SPST switch, but nothing on the 3PDT switch. I noticed the wiring to the switches is a bit different on the new layout. Will this make a difference? Sorry for sounding like a noob but I honestly never heard about this pedal until a friend asked me if I could make one for him. Little did I know of the pit I was about to fall into. 

Check Q6.  That was the problem with the switching. If you follow the layout Q6 will be in backwards and wont work correctly. Double check which pins are which on your particular transistor. Mine was a fairchild and needed to be flipped around. Don't fry it when you make the change either. If in doubt put a new one in. It should sound like this on the four switch settings:

Brassmaster Fixed

R.G.'s new layout is switching between two resistors instead of switching in a parallel resistor.  But I doubt it makes a huge difference. But that's the way the original is.  My clips are using the original GGG PCB.

[Plinky]

Check Q6.  That was the problem with the switching. If you follow the layout Q6 will be in backwards and wont work correctly. Double check which pins are which on your particular transistor. Mine was a fairchild and needed to be flipped around. Don't fry it when you make the change either. If in doubt put a new one in. It should sound like this on the four switch settings:

I have. I flipped it around and it made no difference. I get a very subtle difference with the harmonic switch, but nothing compared to your sound clip. I'll compare some voltages when I get a chance. I'll try to get this one working before I etch a new pcb.

[Plinky]

Well, some of my voltages are considerably off from what gtrgeek posted (sounds ok, just not switching), so I'm gonna etch a new pcb and start all over. To me this board has been abused too much to try and debug. Hopefully I can get this done this weekend.

[Gus]

http://www.aronnelson.com/gallery/main.php/v/gus/bminput.GIF.html

Two fragments for a BJT input.  Not built yet.  I would look for about 1 VDC at the emitter.  The value shown are a starting point.

Gain from the collector should be about X3.7 and inverted and from the emitter just under 1 noninverted

First input resistance hfe X 2.2K || 100K || 470K.  Second is a bootstrapped input

I would use high hfe like a MPSA18.

[Plinky]

Well, I finally finished my new pcb for this and this one works, including the switches (sounds just like DRM's soundlclip). I don't own a bass amp, but I can still get some interesting tones on my crummy Peavey bass through a SS guitar amp.

One question though - was it normal on the original BMs for the bass volume to be low? I'd like to blend in a bit of the fuzz tone with the bass tone, but the clean bass signal is a bit low when compared to the bypassed bass signal.

[DavidRavenMoon]

One question though - was it normal on the original BMs for the bass volume to be low? I'd like to blend in a bit of the fuzz tone with the bass tone, but the clean bass signal is a bit low when compared to the bypassed bass signal.

No, it's not normal.  I get a bit of a boost on mine with the clean level all the way up. 

[Plinky]

One question though - was it normal on the original BMs for the bass volume to be low? I'd like to blend in a bit of the fuzz tone with the bass tone, but the clean bass signal is a bit low when compared to the bypassed bass signal.

No, it's not normal.  I get a bit of a boost on mine with the clean level all the way up. 

Okay. Back to tweaking. 

[fogwolf]

So has the PCB image and BOM/layout been corrected at Geofex? Sorry, there's just been so much back and forth and posts about tweaking what's there what's not there I'm not totally clear. I'm looking for is an easy "just go get the updated PCB image here and follow the new wiring diagram here" 

[Plinky]

So has the PCB image and BOM/layout been corrected at Geofex? Sorry, there's just been so much back and forth and posts about tweaking what's there what's not there I'm not totally clear. I'm looking for is an easy "just go get the updated PCB image here and follow the new wiring diagram here" 

Yeah. I wish I would have waited, but I didn't know what I was getting into.  I haven't seen any updates to RG's site regarding the new BM layout. I went and redid the old one with the new info and other than a little clean up on my part it works great.