Maestro - Brass Master : the corrections  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...

Re: Maestro Brass Master request

Postby chicago_mike » 01 Jan 2009, 22:08

I have time this weekend to breadboard and build this according to all the new info we have.

All my findings Ill post, unless we by then have this figured out. :)

3 pages for a bass fuzz, this place is too cool. 8)
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Re: Maestro Brass Master request

Postby malekko » 01 Jan 2009, 22:17

unbeliever wrote:
malekko wrote:(cause it's not)


I guess someone needs to purchase and reverse one of your pedals, if you can't / won't be more useful than that.


I've already offered the corrections to RG, i think we are getting together sometime soon. It's really not that difficult to figure out...and honestly it's been over 2 years sinve i've looked at the schematic so i dont remember off the top of my head but if you guys havent already figured it out by then RG should have a correct schematic soon
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Re: Maestro Brass Master request

Postby chicago_mike » 01 Jan 2009, 23:06

To me it seems already kinda figured out.

Im interested in possible mods.

One thing, My tech boss, thinks I could get away with a 10k / 2k transformer, or even a 10k / 5k...with some work. Wich of course I will try. :)
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Re: Maestro Brass Master request

Postby DavidRavenMoon » 01 Jan 2009, 23:26

chicago_mike wrote:3 pages for a bass fuzz, this place is too cool. 8)


This place IS VERY cool. I found this place looking for info on this pedal. Glad I found it too... so many clever people and good info!

And it's not just any bass fuzz. :wink: This is the mother of all bass fuzzes.

malekko, we are all just impatient ... :D I've only been looking for this fix for a couple of weeks, but apparently a lot of people have been trying a lot of mods for a while.

I think the error is going to involve Q6. It doesn't look right to me. Why is the output coming from the collector and not the emitter? I'm no expert on transistor circuit design, so maybe that point is eluding me. But everyone seems to be focusing on Q6 lately.

Now that I'm done cramming for the last minute subbing gig I had for New Year's Eve, I can sit and tinker with the circuit. The more details that come out on this subject, the more confusing it gets! That probably means it's a very small error.
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Re: Maestro Brass Master request

Postby rcubed » 02 Jan 2009, 19:44

chicago_mike wrote:To me it seems already kinda figured out.

Im interested in possible mods.

One thing, My tech boss, thinks I could get away with a 10k / 2k transformer, or even a 10k / 5k...with some work. Wich of course I will try. :)


I did a couple of mods. I added the suggested input and output pull down 1M resistors. This virtually eliminates the sound of the switch coming through the signal when the switch is toggled. I also increased the values of the input and output caps (C1 and C7) and the caps going into the sensitivity and bass volume controls (C2 and C8). Retains the lowend of my 5-string bass very well.
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Re: Maestro Brass Master request

Postby gtrgeek1 » 03 Jan 2009, 21:16

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
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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Re: Maestro Brass Master request

Postby DavidRavenMoon » 03 Jan 2009, 23:29

OK, I got it working!

gtrgeek1 is correct... there seems to be nothing wrong with the original schematic (except for Q1's supply voltage being 8V and not 9V), and RG's PCB is correct.

So here's what I did... first there was the issue where on RG's layout sheet R22 and R27 are swapped. So I removed them and put them in the correct locations. That did little to help the Brass switch, but I at least heard something when I switched it. I had tried moving where R29 connected to C13, but I switched that back to the original location.

I decided to check Q6, since that was responsible for amplifying the output of the filter and sending it back to the circuit. I looked up the pin out for the Fairchild 2N5308.. voilà! I had it in backwards. It did match the layout as far as where the flat side was, but it had the emitter and collector swapped!

So I carefully unsoldered it and flipped it around.

Here's the results. First you hear the two settings of the Brass switch, then I flip the Harmonic switch, and then switch the Brass switch again. You go from very full to very thin, just like the real thing. The very thin setting is what Squire used a lot, as in the example I play from Close to the Edge, which has the dry signal mixed back in.

Brassmaster Fixed

I don't have a real one in front of me to compare, but going from memory, this is pretty much nails the tones I remember using.

Yay! :D
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Re: Maestro Brass Master request

Postby gtrgeek1 » 03 Jan 2009, 23:48

Hey David - I have the original on my bench. Just let me know if you want to come by to do an A/B.
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Re: Maestro Brass Master request

Postby DavidRavenMoon » 04 Jan 2009, 00:06

gtrgeek1 wrote:Hey David - I have the original on my bench. Just let me know if you want to come by to do an A/B.


How long will you have it? We must do that.

Maybe tomorrow?
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Re: Maestro Brass Master request

Postby chicago_mike » 04 Jan 2009, 00:29

Is it important for the 3392's to be matched or could I buy bulk from mouser and be cool?
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Re: Maestro Brass Master request

Postby DavidRavenMoon » 04 Jan 2009, 00:34

chicago_mike wrote:Is it important for the 3392's to be matched or could I buy bulk from mouser and be cool?


I just bought them from Mouser.
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Re: Maestro Brass Master request

Postby chicago_mike » 04 Jan 2009, 00:53

Cool. Should have this ready to go after my mcmeat and polyphase.

hey, got an idea...mix a jetphase with a brassmaster. 8)
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Re: Maestro Brass Master request

Postby R.G. » 04 Jan 2009, 05:24

chicago_mike wrote:Is it important for the 3392's to be matched or could I buy bulk from mouser and be cool?

There's no matching to be done. They're all doing different jobs, so matching is superfluous.

I'm still kinda miffed that I just believed the pinout for the darlington that Maestro put on the schematic. Boy, talk about a silly beginner mistake to make. I know better than that and still didn't go look it up. That appears to be problem with any of these ever built.

The wringing-out exercise has resulted in simulating the entire mess, reworking and updating the original layout, and the (re)design of the function into an opamps-version that should be less temperamental and will have far fewer wires hanging off the board - I cold-switched the twin t filter.

More writing to do, but I'll put the whole mess on GEOFEX when I get it documented. David and Gtrgeek were absolutely instrumental in getting this done; I've never seen a Brassmaster in real life, so getting real, on-the-spot data helped filter out some of the hash.

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Re: Maestro Brass Master request

Postby rcubed » 04 Jan 2009, 07:22

DavidRavenMoon wrote:OK, I got it working!

gtrgeek1 is correct... there seems to be nothing wrong with the original schematic (except for Q1's supply voltage being 8V and not 9V), and RG's PCB is correct.

So here's what I did... first there was the issue where on RG's layout sheet R22 and R27 are swapped. So I removed them and put them in the correct locations. That did little to help the Brass switch, but I at least heard something when I switched it. I had tried moving where R29 connected to C13, but I switched that back to the original location.

I decided to check Q6, since that was responsible for amplifying the output of the filter and sending it back to the circuit. I looked up the pin out for the Fairchild 2N5308.. voilà! I had it in backwards. It did match the layout as far as where the flat side was, but it had the emitter and collector swapped!

So I carefully unsoldered it and flipped it around.

Here's the results. First you hear the two settings of the Brass switch, then I flip the Harmonic switch, and then switch the Brass switch again. You go from very full to very thin, just like the real thing. The very thin setting is what Squire used a lot, as in the example I play from Close to the Edge, which has the dry signal mixed back in.

Brassmaster Fixed

I don't have a real one in front of me to compare, but going from memory, this is pretty much nails the tones I remember using.

Yay! :D


Awesome. So by R.G., you mean R.G. Keen's layout dubbed the Brass Blaster, the PCB that General Guitar Gadgets sells? 'cause that is the one I have but have not soldered up yet. Are you using this layout: http://www.generalguitargadgets.com/dia ... master.pdf ? If it's just Q6, then maybe R22 and R27 are correct?
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Re: Maestro Brass Master request

Postby DavidRavenMoon » 04 Jan 2009, 07:34

rcubed wrote:Awesome. So by R.G., you mean R.G. Keen's layout dubbed the Brass Blaster, the PCB that General Guitar Gadgets sells? 'cause that is the one I have but have not soldered up yet. Are you using this layout: http://www.generalguitargadgets.com/dia ... master.pdf ? If it's just Q6, then maybe R22 and R27 are correct?


Yes, I bough the board from GGG. I'm using that layout in the link (geo_brassmaster.pdf). Install R27 where it's marked R22 (between R28 & C9) and install R22 between R26 & R18 where it's marked R27. If you look at the schematic you will see they are switched in the layout. The schematic is correct. I followed the traces on the board to verify this.

Check the 2N5308 you are using. The Fairchild part I used had to be installed with the flat side facing the left, which is the opposite of the layout. You want the emitter to be the top pin, and the collector to be the bottom. I neglected to check this before I installed it, and didn't think about it after. :oops:
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Re: Maestro Brass Master request

Postby rcubed » 04 Jan 2009, 07:49

DavidRavenMoon wrote:
rcubed wrote:Awesome. So by R.G., you mean R.G. Keen's layout dubbed the Brass Blaster, the PCB that General Guitar Gadgets sells? 'cause that is the one I have but have not soldered up yet. Are you using this layout: http://www.generalguitargadgets.com/dia ... master.pdf ? If it's just Q6, then maybe R22 and R27 are correct?


Yes, I bough the board from GGG. I'm using that layout in the link (geo_brassmaster.pdf). Install R27 where it's marked R22 (between R28 & C9) and install R22 between R26 & R18 where it's marked R27. If you look at the schematic you will see they are switched in the layout. The schematic is correct. I followed the traces on the board to verify this.

Check the 2N5308 you are using. The Fairchild part I used had to be installed with the flat side facing the left, which is the opposite of the layout. You want the emitter to be the top pin, and the collector to be the bottom. I neglected to check this before I installed it, and didn't think about it after. :oops:


I just changed around Q6 and there it is. Everything works. I feel about calling the schematic wrong in terms of the diagramming of the circuit. Turns out the only wrong is the pinout of the 2N5308 on there with respect to the Fairchild parts we are using. Glad to finally get this all figured out. Thanks for all the help.
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Re: Maestro Brass Master request

Postby unbeliever » 05 Jan 2009, 12:59

Great work. :applause:
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Re: Maestro Brass Master request

Postby rbstep » 05 Jan 2009, 18:49

Thanks to all. Expended a lot of energy on this circuit also.
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Re: Maestro Brass Master request

Postby RnFR » 05 Jan 2009, 20:30

great job guys!
maybe i'll finally try and tackle this beast again.

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Re: Maestro Brass Master request

Postby DavidRavenMoon » 05 Jan 2009, 21:03

Yes, do it! I'm having a lot of fun playing it now. I found my old tones again, and some new ones. :)
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