GGG Brassmaster: Does anyone know the correct resistor values?

[gigimarga]

Just finished a Brassmaster clone using R.G. Keen's layout (i waked up at 6AM on 01.01.09...i am a little crazy).

After looking carefully at the schematic and at the layout i saw that on the layout Q6 (my 2N5308 has the pinout as here: http://files.muziq.be/schematics/maestro_bb-1_001.gif) is reversed, even the pins are written well.

I wired the "Sensitivity" trimpot as an external pot and the "Bass/Brass volumes" using a dual 10K liniar pot, as a blend pot.

I used the suggestions made by gtrgeek above about the resitors of the filter: 47k replaced with 56k, 3.3k with 3.9 k and 22k with 24k.

And...wooow...it sounds very well, both switches makes strong differences in the sound!

The only (possible) problem is that it sounds a gated with the Sensivity pot at maximum, but i will measure the voltages later to see if some of the transistors are misbiased...but after I re-listened to the clips of charlie (http://www.moosapotamus.net/THINGS/brassmaster.htm) i my clone sounds the same as his clone (my gated sound is the same as the sound of BB1guitWet.mp3).

Thx a lot all!

[DavidRavenMoon]

has someone got a mouser number for the little xfmr??

42TM018-RC
XFMR 10KCT-10KCT

[gigimarga]

My voltages, using a 9.30V battery and both switches on (R.G. Keen's layout):

Q1: E=0.81          C=2.22          B=0.21
Q2: E=0.87          C=2.67          B=0.25
Q3: E=2.68          C=8.45          B=2.08
Q4: E=0.64          C=4.60          B=0.04
Q5: E=4.60          C=5.32          B=4.00
Q6: E=0.01          C=7.78          B=0.95
Q7: E=1.92          C=9.30          B=1.31

What do you think, are OK?
To me, Q6 seems very strange, but i rechecked it and the same result...

Thx a lot all!

[DavidRavenMoon]

To me, Q6 seems very strange, but i rechecked it and the same result...

From reading the various Brassmaster threads on various forums, it's looking like Q6 is probably the culprit.

[R.G.]

To me, Q6 seems very strange, but i rechecked it and the same result...

From reading the various Brassmaster threads on various forums, it's looking like Q6 is probably the culprit.

It does look funny. I wonder if the pinout issue is all there is.

Of course, I still don't like the bias funnies.

[PerroGrande]

Q6's voltages look squiffy.  It is possible that somehow the emitter is getting grounded?

I think you may also have E & B reversed when reporting the other voltages.  They look "reasonable" -- just reversed.

[DavidRavenMoon]

Q6's voltages look squiffy.  It is possible that somehow the emitter is getting grounded?

I think you may also have E & B reversed when reporting the other voltages.  They look "reasonable" -- just reversed.

In the schematic the emitter of Q6 is grounded though a 1K resistor, and the output is coming from the collector.  I'm not all that good with transistor circuits, but that looks kind of screwy without it having another transistor following it.

[R.G.]

From simulation I get, by comparison, in parentheses:

Q1: E=0.81   (0.862)      C=2.22   (2.25)         B=0.21 (0.227) ( I believe you have base and emitter mixed up. What you're calling E is actually B and vice versa)
Q2: E=0.87   (0.945)      C=2.67    (2.73)        B=0.25  (0.307)
Q3: E=2.68   (2.73)        C=8.45    (9.3)         B=2.08  (2.1)
Q4: E=0.64   (0.684)       C=4.60  (4.38)         B=0.04  (0.061)
Q5: E=4.60    (4.38)       C=5.32   (5.61)         B=4.00  (3.71)
Q6: E=0.01    (0.04)       C=7.78   (7.24 or 8.       B=0.95  (1.05) (Q6 is a darlington here)
Q7: E=1.92    (2.06)       C=9.30   (9.3)           B=1.31 (1.41)

When I make Q6 be a 2N5088, not a darlington, I get collector voltages of 5.05 and 6.24V depending on the setting of the Brass hi/lo switch.

Q6 almost seems to need the base-current bleed through the Twin T resistors to bias better. Very strange. Very inconsistent.

[PerroGrande]

Oh yeah -- Q6 is a Darlington -- my bad.

I can see, however, why the resistor network might get into the biasing equation. There is a DC path to ground via the selected resistors in the twin-T portion -- via the 150K resistor and the Brass volume control (10K).  Every other path is AC coupled.  At least when looking at this schematic: http://files.muziq.be/schematics/maestro_bb-1_001.gif

When I first looked at the circuit, I (incorrectly) thought that the bias problem might be related to the Hfe of the transistor.  A quick run of the snippet through my sim cured me of that myth.  However, my voltages were nowhere near what RG encountered...  That is, until I added the twin-T network's path to ground, and now my values are very close.

[R.G.]

I started replacing transistors with opamps.

I *think* I can get away with two dual opamps, and one transistor for the signal path. For the switching, I think it makes sense to replace that 3PDT switch with a CD4053 and the hi/lo switch with a P-FET to get the switching on the board and minimize the wiring.

By the way, the input impedance of this thing sucks treble, bad. The input impedance is about 17K. That may be a "feature". Anyway, it's easy to make it that bad if needed. 

[moosapotamus]

By the way, the input impedance of this thing sucks treble, bad.

Well, it is a "BASS" Brassmaster!

~ Charlie

[George Giblet]

The biasing improves if Q6 (RG layout) is a non-Darlington.

What is right is unknown until gtrgeek1 posts his voltages.

[chicago_mike]

Can we combine this thread and the one over at the other place?

[gigimarga]

Thx a lot all!!!

R.G. you're wonderful!
I will try to replace Q6 with another 2N3392 and to see what's happening...i hope that the mistery will be solved soon

[DavidRavenMoon]

I just noticed something with mine.  I decided to look up the pin layout on my particular 2N5308, since there had been some talk about it not matching the diagram on the original schematic.  I hadn't thought to check it when populating the board, and just followed the layout for orientation.

So I looked up this particular Fairchild 2N5308 using the data sheet link at Mouser... and guess what?  It's the opposite of the way it's marked on the layout, with the base going to R19. I can't be the only person this happened to, since I just assumed the orientation of the case matched the layout.  I should have double checked it first.   

If I get a chance tomorrow I'll replace it with a new 2N5308 installed in the right direction and report back!

[gigimarga]

...
So I looked up this particular Fairchild 2N5308 using the data sheet link at Mouser... and guess what?  It's the opposite of the way it's marked on the layout, with the base going to R19. I can't be the only person this happened to, since I just assumed the orientation of the case matched the layout.  I should have double checked it first.   

That's what i did...my 2N5308 must to be reversed according to the layout...but no good news...look a couple of posts above

[gigimarga]

I replaced 2N5308 with a 2N3392, but no major changes...it sounds less gated, but still too gated for my taste

Anyway, it's obvliously that when Hi/Lo it's on the volume increases a lot...and the action of the Brass 1/Brass 2 switch i think it's still too subtle (but i have no ideea about how the original sounded).

[R.G.]

I posted a re-engineered version of the circuit at GEO - The Bass Ackwards.

Simulation says it runs, but simulators sometimes lie. I think it's a fruitful place to dig. In this version, the transformer/diode ring seems to give a fairly smooth doubling. We'll see.

I replaced the 3PDT with a 4053, used an LM386 for a bias generator, did a few other cleanup things. As soon as I can locate the breadboard, I'll hack one together.

[DavidRavenMoon]

I replaced 2N5308 with a 2N3392, but no major changes...it sounds less gated, but still too gated for my taste

Anyway, it's obvliously that when Hi/Lo it's on the volume increases a lot...and the action of the Brass 1/Brass 2 switch i think it's still too subtle (but i have no ideea about how the original sounded).

The original has that gated tone also.  In this version the louder setting on the harmonic switch is kind of like the original, but too thick, and the other setting is too thin...  But you were supposed to mix some fuzz in with the dry signal, and the fuzz was bright and had that upper octave thing going on.  It was never very useable with just the straight fuzz signal with no bass, unlike something like a Big Muff Pi.

The Brass switch was a higher or lower version of the fuzz.  The Harmonic switch did something with the octave tone from what I remember.  They were subtle changes, and some of the settings were very thin and fizzy.  I remember I had

A good example of a vintage Brassmaster is the section in Close to the Edge about 6:01 right after one of the choruses.  That's a typical Brassmaster setting... a thin envelopy type of thing. Close to the Edge (excerpt)

And from his solo album Fish out of Water, Hold Out Your Hand (excerpt) and Silently Falling (excerpt).  A reminder on why Squire is so great.   

So that's the sound there.  It's a quirky little device, and certainly wasn't for everyone back then, or today even.  Also I don't there were any effects for bass players, so who ever thought of the thing was being pretty radical at the time.  That's pretty much what mine sounded like.  The clone is close, except for the filter section. 

Here's a funny story... when I heard about the Brassmaster I went looking to buy one.  So I went to the 48th Street music store district in NYC, and to the famous Manny's Music.  I talked to a salesman telling him what I was looking for. He was an older gent who was probably into jazz.  He said to me "you don't want that thing!  It sounds like thunder and lightning!"  I said "yes!  That's exactly what I want... thunder and lighting!"  He refused to sell me one or even let me try it out!  So I left Manny's and crossed to street.. maby to Rudy's or Gracin and Towne or something, and bought it untried!

[Gus]

Bass Ackwards thoughts

What kind of noise is at the output of the 386 used for bias?  I did not see a RC filter.

Maybe make the 820K at the filter section a fixed min value and and pot to have fun with the gain.