BM_Build in a Funk_Chassis

heisthl · Post by **heisthl** » Tue Oct 02, 2007 12:30 am

Just finished this one, haven't heard it yet. It got the BM stack,PI and PAB. If there's sufficient interest I'll post the schematic.

heisthl · Post by **heisthl** » Tue Oct 02, 2007 12:31 am

More Pics

jelle · Post by **jelle** » Tue Oct 02, 2007 12:55 am

Please post the schem...

TIA!

Jelle

mat · Post by **mat** » Tue Oct 02, 2007 4:20 am

Wow

Gorgeous !

Is there an half power switch in the back ? Does it have two masters ? Yes it would be cool to see the schem

heisthl · Post by **heisthl** » Tue Oct 02, 2007 5:33 am

For those of you that "paint by numbers" there is an error in the photos - the bias caps are backwards (aaaaargh!!!!) luckily I caught this before I powered it on. With no tweaking at all this thing sounds amazing - good enough to post the schematic as built. It has a much fuller clean tone (read hotter) and the OD is very respectable (maybe a touch bright, but not annoyingly so) until you hit the boost and then its incredible, in a very non-HRM kind of way. Set the entance to about 50% and the timmers to 40%T, 55%M and 65%B.

mdroberts1243 · Post by **mdroberts1243** » Tue Oct 02, 2007 11:28 am

heisthl wrote:For those of you that "paint by numbers" there is an error in the photos - the bias caps are backwards (aaaaargh!!!!) luckily I caught this before I powered it on. With no tweaking at all this thing sounds amazing - good enough to post the schematic as built. It has a much fuller clean tone (read hotter) and the OD is very respectable (maybe a touch bright, but not annoyingly so) until you hit the boost and then its incredible, in a very non-HRM kind of way. Set the entance to about 50% and the timmers to 40%T, 55%M and 65%B.

Heisthl,
Did you try the 0.01 coupler into the HRM yet?
Any comments on the difference with/without?
Thanks,

mdroberts1243 · Post by **mdroberts1243** » Tue Oct 02, 2007 11:40 am

In the schematic you show the NFB resistor coming off of the 4 ohm tap... I understood that this should change to 8 ohm when you go for 100k???

Your Bias supply is different than others I've seen... was more range required? Or is the transformer tap a different voltage?

Thanks,

dogears · Post by **dogears** » Tue Oct 02, 2007 3:21 pm

NFB is off of 4 ohm tap in the BM. Using the 8 ohm tap can tame a 50 watt BM build... This is a 100 watter.

mdroberts1243 wrote:In the schematic you show the NFB resistor coming off of the 4 ohm tap... I understood that this should change to 8 ohm when you go for 100k???

Your Bias supply is different than others I've seen... was more range required? Or is the transformer tap a different voltage?

Thanks,

heisthl · Post by **heisthl** » Tue Oct 02, 2007 3:23 pm

mdroberts1243 wrote: Heisthl,
Did you try the 0.01 coupler into the HRM yet?
Any comments on the difference with/without?
Thanks,

I didn't try a cap there, as I said the HRM is maybe as touch bright and this would only emphasize that.

mdroberts1243 wrote: In the schematic you show the NFB resistor coming off of the 4 ohm tap... I understood that this should change to 8 ohm when you go for 100k???

Your Bias supply is different than others I've seen... was more range required? Or is the transformer tap a different voltage?

I wanted the extra gain so I used the 4 ohm tap for presence (many Marshalls do this). The bias is HAD's more modern design - 47uf as a first filter and another 47uf on the trim output. He used 3k9 feed with 24k trimmer tail, I used 3k3/27k.

dogears · Post by **dogears** » Tue Oct 02, 2007 3:23 pm

You used the 47pf on the low gain network. I don't think it is there in the BM.... Try removing.

heisthl wrote:For those of you that "paint by numbers" there is an error in the photos - the bias caps are backwards (aaaaargh!!!!) luckily I caught this before I powered it on. With no tweaking at all this thing sounds amazing - good enough to post the schematic as built. It has a much fuller clean tone (read hotter) and the OD is very respectable (maybe a touch bright, but not annoyingly so) until you hit the boost and then its incredible, in a very non-HRM kind of way. Set the entance to about 50% and the timmers to 40%T, 55%M and 65%B.

JimiB · Post by **JimiB** » Tue Oct 02, 2007 4:17 pm

very nice!

mlp-mx6 · Post by **mlp-mx6** » Tue Oct 02, 2007 5:13 pm

mdroberts1243 wrote:Did you try the 0.01 coupler into the HRM yet?
Any comments on the difference with/without?
Thanks,

I tried that in one of my builds. Hated it. IMMEDIATELY went back to no cap feeding the HRM stack. It made it thin, shrill, and harsh. Like a bad distortion pedal.

mat · Post by **mat** » Tue Oct 02, 2007 5:33 pm

15 differencies + wiring differencies on the preamp section only comparing to my HRM BM build

Heisthl, how much is Your B+1 ?

heisthl · Post by **heisthl** » Tue Oct 02, 2007 5:42 pm

mat wrote:15 differencies + wiring differencies on the preamp section only comparing to my HRM BM build

Heisthl, how much is Your B+1 ?

441

mat · Post by **mat** » Tue Oct 02, 2007 5:47 pm

heisthl wrote:
mat wrote:15 differencies + wiring differencies on the preamp section only comparing to my HRM BM build

Heisthl, how much is Your B+1 ?
441

I have 485 on my build. I might try another PT for the fun. I noticed on Your schem that You have 177 on the V1a plate. Is it something to shoot for on this kind of schem ?

The Amp Garage

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