GGG Brassmaster: Does anyone know the correct resistor values?

[fogwolf]

If someone could summarize in 1 message what those all those exact changes/fixes are and how to build this project correctly with the existing PCB image, what to change in the parts layout/wiring exactly and any parts that need to be changed (or if there's an updated BOM and layout file to follow to apply to the old image) that would be greatly appreciated. Sorry, I'm just lost in both a few people trying to work it out and others wanting to add mods and adapt other circuits into it and I would simply like to be build a working clone as was originally intended.

Thanks!

[Plinky]

If someone could summarize in 1 message what those all those exact changes/fixes are and how to build this project correctly with the existing PCB image, what to change in the parts layout/wiring exactly and any parts that need to be changed (or if there's an updated BOM and layout file to follow to apply to the old image) that would be greatly appreciated. Sorry, I'm just lost in both a few people trying to work it out and others wanting to add mods and adapt other circuits into it and I would simply like to be build a working clone as was originally intended.

Thanks!

RG's update to the BM is at the top of the GEOFex site. The .pdf file lists the fixes for the old pcb layout that's sold by GGG.

[fogwolf]

Great - thanks!!

If someone could summarize in 1 message what those all those exact changes/fixes are and how to build this project correctly with the existing PCB image, what to change in the parts layout/wiring exactly and any parts that need to be changed (or if there's an updated BOM and layout file to follow to apply to the old image) that would be greatly appreciated. Sorry, I'm just lost in both a few people trying to work it out and others wanting to add mods and adapt other circuits into it and I would simply like to be build a working clone as was originally intended.

Thanks!

RG's update to the BM is at the top of the GEOFex site. The .pdf file lists the fixes for the old pcb layout that's sold by GGG.

[airplanehuh]

Not to keep beating a dead horse here...but...

I got my brassmaster working great. I love this pedal for bass. I need to add a sensitivity knob to the outside of the box as well as a switch to change the input impedance for use with different guitars and basses. This brings me to my question: Would changing the input impedance help me regain the lost high frequencies through the dry channel specifically? I haven't noticed a lowpass filter in the circuit to mess with. What component would be best to try different values with in order to bring back the highs? Even for bass I find the high roll off to be a bit too drastic compared to the sound when bypassed. If the highs were brought back in would that reduce the lows?

[DavidRavenMoon]

Not to keep beating a dead horse here...but...

I got my brassmaster working great. I love this pedal for bass. I need to add a sensitivity knob to the outside of the box as well as a switch to change the input impedance for use with different guitars and basses. This brings me to my question: Would changing the input impedance help me regain the lost high frequencies through the dry channel specifically? I haven't noticed a lowpass filter in the circuit to mess with. What component would be best to try different values with in order to bring back the highs? Even for bass I find the high roll off to be a bit too drastic compared to the sound when bypassed. If the highs were brought back in would that reduce the lows?

The Sensitivity knob is supposed to be on the outside.  It's key to getting many cool tones!

Yes, increasing the input impedance would help.  Or run your bass into something that will buffer it first.  My bass is active so it doesn't cause that dulling effect.

However, I used to love putting an EH Mole bass booster before the Brassmaster.  So I'd have a thick slab-O-bass from the clean channel with the bright fuzz on top of it.

[airplanehuh]

Yes I agree, I've been running a DOD Meatbox into the BB-1 and that makes for one really thick bass sound. I just sort of want a switch that will add more clarity for use with guitar too.
Would raising both C1 and R1 increase the impedance or just R1.

...I totally forget everything that I learned about impedance in college. I'll have to look up impedance info on the web.

[Meanderthal]

 Oh yeah, the mole(hog's foot) sounds great in front of this thing... I stuffed my brassmaster in a big enclosure with one, and a flipster also... it's screwed down on my pedalboard in pre-fixed filter version... one of these days I oughtta mod it to get it workin right, but even 'wrong' it's got a permanent place on my pedalboard... thanks for figuring this out guys!

[DavidRavenMoon]

Yes I agree, I've been running a DOD Meatbox into the BB-1 and that makes for one really thick bass sound. I just sort of want a switch that will add more clarity for use with guitar too.
Would raising both C1 and R1 increase the impedance or just R1.

...I totally forget everything that I learned about impedance in college. I'll have to look up impedance info on the web.

Go back a page in this thread and read what Gus wrote:

R.G I was drawing up an 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.

At the very least you can tack on a JFET buffer stage before the main circuit.  There are plenty of those circuits around.

[Plinky]

Finally got around to debugging my BM clone - had R13 & R14 crossed. It now has more of a level boost like DRM mentioned when the BM is set for a clean tone.

Now to tweaking.

The friend I'm building this for made one observation and I'm thinking this would work, but I thought I'd run it by the experts.

I'm at work so I don't have the pedal with me, so bear with me. I can't remember which pot controls the amount of fuzz in the circuit (brass volume?). The adjustment is very touchy, so it's easy to add too much fuzz. All the pots are 10k linear. Would changing this pot to log taper (or other taper) make it so the change from no fuzz to all fuzz is a bit more gradual instead of almost immediate? He likes the tones out of it, but it's hard to dial in a subtle amount of fuzz.

[DavidRavenMoon]

but it's hard to dial in a subtle amount of fuzz.

Check your wiring, it shouldn't be that touchy.  I dial in the clean bass tone, and then turn up some fuzz.  You can get a small amount of fuzz with no trouble.

[Plinky]

but it's hard to dial in a subtle amount of fuzz.

Check your wiring, it shouldn't be that touchy.  I dial in the clean bass tone, and then turn up some fuzz.  You can get a small amount of fuzz with no trouble.

I'm still quite foreign to using this pedal (not a bass player). What are your settings for clean tone, just to make sure we're on the same level?

[DavidRavenMoon]

but it's hard to dial in a subtle amount of fuzz.

Check your wiring, it shouldn't be that touchy.  I dial in the clean bass tone, and then turn up some fuzz.  You can get a small amount of fuzz with no trouble.

I'm still quite foreign to using this pedal (not a bass player). What are your settings for clean tone, just to make sure we're on the same level?

If you turn the "brass" (fuzz) down, and turn the bass up, that's more-or-less the clean signal. I'm getting a little fuzz bleeding into my straight signal, but that's probably something to do with the layout of the wires.  But the clean signal is not totally pristine on a passive bass due to the imput impedance not being high enough.

So start with the straight signal, and then mix some fuzz into it.  Also the sensitivity control is important for different effects.  Turned up it's a lot of fuzz, and turned almost all the way down gives you more of a grunty tuba fuzz with less sustain.

The Brass and Harmonic switches change the tone of the fuzz, from fuller to thin, and with more of an upper octave tone.

[Plinky]

That's about how I had it set, and I'm not having any problems dialing the brass in. I'm thinking it's being nitpicky more than anything. I just don't know a lot about these pedals, so it's hard to explain to someone who says they know what it should sound like. It switches quiet, the clean setting sounds very close to bypass IMO, and every control makes a smooth transition back and forth (at least that's what I hear).

If he doesn't like it, I'll keep it for myself. I've spent enough time with this for parts money, and I haven't even started on the enclosure. 

[Rob Strand]

I had to look at this stuff for a recent post.   I've got these notes which tried to summarize the final results.

This one took ages to resolve partly because the original circuit has some dodgy things which throws everyone off the trail.   Luckily gtrgeek1 had a real unit to help decipher the final circuit.
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Thread Summary

Maestro BB-1 Bass Brass Master

Pot tapers (linear) missing on all but the original schematic.
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Thread started 2007, revived 2008, resolved 2009

gtrgeek1, RG, George Giblet, DavidRavenMoon

https://www.diystompboxes.com/smfforum/index.php?topic=56690.0
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Thread   Re: GGG Brassmaster: Does anyone know the correct resistor values?
DavidRavenMoon:   29  December 29, 2008

The guy that did the layout said he took the "incorrect" schematic and redrew it into Circuitmaker and was able to verify that the schematic is in fact correct, and matches the real pcb. He also said the Q1 supply is not marked, but it should be fed from the 8 volt supply.
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Thread:   Re: GGG Brassmaster: Does anyone know the correct resistor values?
page 5
gtrgeek1:      03 Jan 2009

Hey Guys,

I finally got the original Brassmaster on my bench and have the following info for your reference:

Transistors
The transistor designations follow the original factory schematic.
Q1,2,3,4,6,7 are 2N3392 factory marked 83930. All have an orange dot on the top, possibly matched or selected.
Q5 is 2N5308 factory marked 135 43C. Pinout matches 2N3392 not schematic pinout.

Maestro Bass Brassmaster Voltage Chart 01/03/09  (03 Jan 2009)
V1 = 9.3V
V2 + 8.0V
                 E         C         B
Q1         193 mv 2.107V 0.793V
Q2          63.9mv 4.68V 0.656V
Q3           4.04V 5.16V 4.68V
Q4 H1     1.319V 9.34V 1.918V
Q4 H2     3.195V 9.34V 3.796V
Q5 H1B1 28.2mv 7.58V .907V
Q5 H1B2   61mv 5.88V .980V
Q5 H2B1   6.5mv 8.7V .816V
Q5 H2B2 40.8mv 6.92V .937V
Q6          267mv 2.986V .870V
Q7          2.391V 8.04V 2.987V

H1 = SW2 closed / 82K connected
H2 = SW2 open
B1 = 47K resistors selected in filter
B2 = 6.8K resistors selected in filter

Diodes
All Diodes 1N457A

Transformer (measured in circuit)
Primary = 680 ohm CT
Secondary 572 ohm
500 mv 1K sinewave into secondary, measured 500 mv on primary
The transformer on this particular unit is much smaller than others I have seen. Mounting tabs did not line up with pads in pcb and were folded flat.

Resistors
All 1/2 watt carbon comp
All pots 10k CTS with 1971 date code

Capacitors
.01, .005 (x2), .05 in filter are ceramic disc
.05 on base of Q3 is ceramic disc
Electrolytic as marked on schematic
All others mylar 100V

PCB
C.M.I. 980 018260

Since the owner paid a boatload for this thing, I am a little hesitant to unsolder anything for a more accurate measurement, but I did compare all voltages to a clone built on RGs layout and all voltages match.

Since I will have to return this treasure soon, please let me know if there is any other info needed.

Regards,
gtrgeek1
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Thread:   Re: GGG Brassmaster: Does anyone know the correct resistor values?
page 5
George Giblet:   03 Jan 2009

What is interesting is:
- the circuit was correct all this time (except for the minor 8V/9V thing) ***
- the suggested transformer MOUSER 42TM018 should be spot on
- Everyone should have *already* been building bm's cones (apart from those who had the wrong pinout).
  Nothing has changed other than the knowledge in our heads.
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Thread:   Re: GGG Brassmaster: Does anyone know the correct resistor values?
page 6
George Giblet:   04 Jan 2009

Regarding the bias shifting - that is strange.  I can only guess it's an oversite, or something disregarded.

Regarding the generally "poor" biasing - who knows, oversite vs. deliberate sound shaping?

BTW:  Using gtrgeek1's voltages I've estimated the hfe of the non-darlingtons (2N3392) to be about 130.
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*** "The minor 8V/9V thing" is that Q1 should get power from the +8V rail.
It is unclear or unspecified on the original schematic.

[Rob Strand]

Schematics Summary

Maestro BB-1 Bass Brass Master
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Schematics

Maestro_BB-1_Bass_Brass_Master.pdf / maestro_bb-1_001.gif
   Original
   Identifying feature: parts table in top left
   Shows pot tapers as Linear
   R & C have no designators
   Bugs:
   - Q1 connection to +V unmarked.  It should go to +8V.

Maestro_BB-1_Bass_Brass_Master.jpg
   Some changes but they are wrong
   Identifying feature: parts table replaced with notes, mentions filter redrawn for clarity.
   Changes:
   Filter redrawn
   R & C designators added.
   Bugs: 
   - filter is drawn incorrectly (missing connection to C12)
   - filter switching incorrect, uses SPDT switch paralleling resistors
   - Pot tapers missing

ggg_brassm_sc.pdf
   Close to original, but modernized slightly
   Identifying Feature:  (17 Nov 2009 JD Sleep)
   Changes from original:
   - 1M5 on input added
   - 1M5 on output added
   - Reverse polarity diode added
   - 2N3391 transistors
   - The true-bypass wiring is different to the original
   - LED added
   Bugs:
   - post taper missing should be linear
   - shows 2N3391 transistors, should be 2N3392 as per original schematic
    (The 2N3391s have higher gain.  George Giblet said gtrgeek1's measurements
     match hFE = 130, which is more like the 2N3392.)
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The ever-hanging issues which were resolved:
(rg) The voicing is a band-pass filter.
(gtrgeek1 measurements) The bias does change when the switches are in different positions.
The original schematic was correct (except for Q1 connection to +8V)
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Parts
- Transformer 1:1 with centre tap,
  DC Resistance primary 680 ohm + ct,
  DC Resistance secondary 572 ohm
  42TM018 very close match (10k:10k)
- Q gains  (2N3392, hFE approx 130)
- original diodes were 1N457A despite schematics showing 1N4148/1N914
- pots should be linear taper
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