GGG Brassmaster: Does anyone know the correct resistor values?

[DavidRavenMoon]

Here's what the real thing sounds like at various positions:

http://www.malekkoheavyindustry.com/index.php?page=b-assmaster

Personally I wouldn't mind having the filter work even if it's not "authentic." 

It's funny you mentioned doing it with op amps, I was thinking the same thing today.

So do you have any idea how to make this version work?   

[malekko]

I told RG a couple of months ago I'd give him the proper schematic...

[DavidRavenMoon]

I told RG a couple of months ago I'd give him the proper schematic...

That's very generous.  I've been eyeballing your version for a while now... it's very cool.

[fogwolf]

I told RG a couple of months ago I'd give him the proper schematic...

This would be fantastic. I've been wanting to build this but shying away from it because of the reported issues. RG?

[R.G.]

I do remember something about that. A quick search of my mail logs didn't turn up the email though.

I don't remember how that ended up. Malekko, was that a simple donation?

[malekko]

It was a phone conversation, you are supposed to swing by Malekko (in Round Rock) so we can do some 1spot testing with our E600

feel free to call me again 431 5428
Josh

I do remember something about that. A quick search of my mail logs didn't turn up the email though.

I don't remember how that ended up. Malekko, was that a simple donation?

[R.G.]

Ahah! That's it. I put that into the mental "pending" bin while I waited on the 1Spots.

They're here now. What are you doing next week?

[malekko]

Ahah! That's it. I put that into the mental "pending" bin while I waited on the 1Spots.

They're here now. What are you doing next week?

hanging out with you!

[chicago_mike]

I have a picture of the component side, but I really need a picture of the trace side. DOes anybody have that???

[Celadine]

That wack tone section seems like more trouble than its worth.  IMO most of the sound must come from the way the transformer is used - the signal is crudely amplitude modulated by a half-wave rectified version of itself.

[George Giblet]

As RG hinted at, one problem is people think the twin-T circuit should be a notch but it doesn't have to be.  The twin-T can be used as a band-pass also.  Given the circuit was called a *brass*master you would think that the aim of the filter would be to emulate a brass instrument.  Brass instruments tend to be more band-pass in nature so I suspect the filter should act as a band-pass.  Some time back the Brassmaster came up and the conclusion was it was bandpass.

This original circuit shows a working connection along these lines:

http://files.muziq.be/schematics/maestro_bb-1_001.gif

The "original" circuit extracts shown earlier are actually modified drawings.

As far as the sound goes for the maestro_bb-1_001.gif I'm not so sure people will like it as it's a very exaggerated response.  The savior, and perhaps the key, can blend.

So are the part values correct? (perhaps so see second post)

[George Giblet]

> but I really need a picture of the trace side. DOes anybody have that???

I've got a picture of the top side only and I can make out 2x47k, 1x6.8k, 0.05uF caps, 3-way switch, transistor near 1k + 1.5Meg + 47? resistors.   With a stretch it looks like 3x 0.05uF caps and a larger one which could be 0.01uF.  So many values seem to agree with the original schematic.

[analogguru]

I think one definite problem is the connection of the 82k going to SW-2:
If switched on, together with the brass volume control it will shift the bias of Q4.
Therefore the 82k should be connected in any case before the 0.1µ capacitor directly at the transformer.

Maybe this could solve some problems ?  

For the rest, here are the results of the austrian simulation jury (using 2x 2N5088 as models):
Low-Filter plot
High-Filter plot

merry christmas,
analogguru

[George Giblet]

> Therefore the 82k should be connected in any case before the 0.1µ capacitor directly at the transformer.

It's very likely.

The issue came up in this earlier thread (this thread has the clear pcb pic)

http://www.diystompboxes.com/smfforum/index.php?topic=57420.msg446262#msg446262

[R.G.]

I think one definite problem is the connection of the 82k going to SW-2:
If switched on, together with the brass volume control it will shift the bias of Q4.
Therefore the 82k should be connected in any case before the 0.1µ capacitor directly at the transformer.

Maybe this could solve some problems ?

Probably. See the earlier thread referred to and also reply #15, this thread.

There are other issues lurking in there as well, but the shift in bias issue is known.

Merry Christmas!

[George Giblet]

I suppose one thing to question is whether the diodes are actually connected to the transformer that way.

The traditional diode ring multiplier has the diodes connected in a ring with two centre-tap transformers.  There are two input terminals and one output terminal.

The traditional frequency doubler has a single winding transformer on the input side, the diodes connected as a bridge rectifier, and a single-ended transformer on the output side.  (There's also a traditional doubler which uses two diodes, like the tychobrae.)

The bm connection doesn't match either, and is assymetrical.  That doesn't mean it is wrong, or that it can't work - it's just something to check.   BTW, the phase-splitter on the bm doesn't have a centre-tap output to emulate the input side transformer of the ring multiplier.

[George Giblet]

The bm doubler seems to work ok, it provides clipping which shouldn't be an issue,

http://www.geocities.com/george_giblet/effects/bm_doubler.png

[analogguru]

If you imagine the center tap of the transformer connected to ground, "rectifiying" for both half-waves will occur, resulting in frequency doubling.

analogguru

[mancunian]

Delemna time.
I got all the bits & pieces,PCB together in preparation to do this over holiday period.
Should I wait for the updated correct schematic, or plough ahead with the build & mod in any changes at a later date?

Would appreciate any advice.

From what I gather the Brassblaster in its original guise with all its foibles is still a pretty decent (albeit limited) bass fuzz(?)

Merry Christmas to all & all the best for 2009 to everyone

Nick
http://www.myspace.com/nickdawsonbass

[DavidRavenMoon]

I think one definite problem is the connection of the 82k going to SW-2: If switched on, together with the brass volume control it will shift the bias of Q4.
Therefore the 82k should be connected in any case before the 0.1µ capacitor directly at the transformer.

I rewired mine to have the 82K on the transformer side of the cap.  It made an improvement to the tone of that Harmonic switch setting, but still doesn't fix the Brass 1 & 2 settings.