greiswig wrote:Ingenious building, Mark! Some very good ideas for easy tweaking in there. I'm hoping someone more knowledgeable than I will chime in and talk about the cathode and plate leads on V2...they're supposed to be run a certain way to interact with one another some, but I've never seen a definitive "this is how to do it" shot.
Thanks.
I don't think I've followed the dumble wire dress correctly... you should probably look at Heisthl and Funk's pictures for better examples. I've heard that Dumble ran the cathode and plate wires parallel and touching each other. I tend to follow the rule of thumb that you keep grid wires short and away from each other, plate wires can be long, and wires should cross at 90 degrees to each other.
I was about to get started on this build and while double checking the newest schematic against the posted layout I see that major changes have been made. Is there a newer layout available?
I'm cross-posting this from another thread so that people are clear on the genesis of this project/schematic...
mdroberts1243 wrote:
tsl602000 wrote:
dogears wrote:mdr,
I am confused as to why you built your BM around some unknown internet schematic. As you know, I had one here where I measured and documented. Why don't you follow that one instead of messing with possibly incorrect stuff.....
Now this is confusing me.... The posted schematic is the one posted in the Bluesmaster topic, right?
TSL,
Scott is referring to the genesis of that schematic... I cobbled it together by going through all the postings on the forum and with some additional input from forum members... I could get a good handle on the pi/pa from the postings but wasn't able to get a good handle on the plate/cathode/coupling values (or at least a definitive set of those values). There were rumoured values and etheral schematics floating around that suggested the values departed from the 'norm' for HRM... best summed up by the spreadsheet that ampdoc1 posted.
Today, I am still not aware of a fully documented BM, the only pics I've seen had blue goo.
For my build, reflected in schematic 11, I put in spring clips at critical places and then tried about seven different combinations of values... I settled on the 'sunnyland' rumoured values from the spreadsheet, making the obvious (with hindsight) corrections to the plate/cathode values which were flip-flopped on each tube.
I used the sunnyland values because they contributed to cleaner cleans (there is a much wider range of input levels accepted) and also tended to offer a wider range of compression in the potentiometer rotation before hard clipping sets in.
I would love to do a version of the schematic that has a real, definitive set of values from a real live dumble bluesmaster... send the values to me! I am a strong believer in having reference schematics (like #124) for a basis of discussion and tweeking.
galtjunk wrote:I was about to get started on this build and while double checking the newest schematic against the posted layout I see that major changes have been made. Is there a newer layout available?
Thanks
I abandoned doing a layout myself... once I had Funk's chassis and boards it was a lot easier to just start building!
Some others have talked about doing a layout, so someday we may have one.
EDIT: Found an error in the footswitch... wrong LED resistors... inserted newer footswitch with PAB Link feature.
A couple of weeks back I had a PM asking about a 'final' version of the schematic. I have tried various tweaks and voicing, departing from the original a little bit, but there are three things in particular that I think need to be changed in the schematic in general.
I solved a nasty problem with a double-stop intermodulation tone produced by a certain player with a certain guitar & pickup combination only in OD mode... This required changing the OD2 cathode bypass capacitor to 1uF from 4.7uF in the v11 schematic.
I found the middle pot swamped the rest of the tone stack when turned up very much and since players like to hover around 12 noon when setting the stack I've changed the middle potentiometer to a 15K linear pot from the original 50k... much more useable middlle pot now.
I've taken out the post OD coupling capacitor between OD2 and the HRM stack... I had it switched for testing and found it was either slightly detremental to tone or not noticeable at all, so I pulled it out of the schematic to clean things up a bit.
These three changes are in the updated schematic, v12, posted here and at the top of the thread.
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I'm in the middle of a BM build at present and can't figure out if R9 should create a break between Bass and Mid pots when in PAB. Is it correct on the schematic?
I know there are threads that deal with the BM PAB but for the life of me I cannot find 'em today.
If anyone can set me streight on this one, I'd really appreciate it.
Guitarman18 wrote:I'm in the middle of a BM build at present and can't figure out if R9 should create a break between Bass and Mid pots when in PAB. Is it correct on the schematic?
I know there are threads that deal with the BM PAB but for the life of me I cannot find 'em today.
If anyone can set me streight on this one, I'd really appreciate it.
Cheers, Paul.
In this particular topology, with the mid relay breaking the connection to ground, there is no purpose served by breaking the connection between mid and bass pots... everything is already lifted.
I can verify that the PAB relay in this circuit configuration does a really good job at creating the mid-hump transfer characteristic.
Two notable things: you may want to adjust the 'lift' to taste (72k gave me somewhere between 6-9dB boost IIRC, but others have gone much higher); the mid control can swamp the other controls and I found I had to use a smaller mid pot (15k) to get a reasonable range and a 'normal' high-noon setting.
Do you think I could use that pole of the relay to provide a status indication?
The ideal way to install a status indicator would be off the relay supply in the same way the foot switch gives status indication, keeping the spare relay pole free for breaking mid pot lugs for more boost, as in heisthl's BM schematic. See link below:
Do you think I could use that pole of the relay to provide a status indication?
The ideal way to install a status indicator would be off the relay supply in the same way the foot switch gives status indication, keeping the spare relay pole free for breaking mid pot lugs for more boost, as in heisthl's BM schematic. See link below:
Hmmm... once you've lifted the mid-pot I think what you do with the lugs is rather redundant. I like (the other) Mark's idea about a Jazz lift, but if you don't feel that is required then the relay is a convenient way to provide a front-panel indication of the PAB state.
mdroberts1243, thanks for the responses, I see your point. I'll be trying the configurations you mention and PAB resistor values to find what suits my taste.
Also many thanks for taking the time to put this thread together, it's got some really helpful info relating to my current project.
