Journey of my Bassman Micro build

sds1

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Ah cool. I've never heard of those but sounds and looks interesting.

I got this cheapo from HF, works fine for a occasional-use hand tool, same as @2L man I sometimes use it to press in rivnuts for chassis mounting to cabinet.
 

King Fan

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Riv-nuts, AKA rivet nuts, are pretty cool. I like the Harbor Freight price, but if you're just doing a few on occasional projects, it's possible to DIY without the tool. This video has the basics...



though I made a longer/handier 'tool' than his out of aluminum bar stock...

IMG_1348.jpg
 

joulupukki

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Thanks guys. Those look like they’d work great and would keep the top side nice and tidy. Just a matter of checking the positioning for the least noise and then I’ll drill away. :)
 

joulupukki

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Alright, all the values are now written in on the resistors and caps. I think this is ready to go. I should be able to check out how the plates turned out later today and maybe even get some of those holes drilled.

Asset 5@3x-80.jpg
 

King Fan

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Nice. If your build is even half as tidy as your diagram, it's gonna rock.

Here's the most trivial suggestion you’ll receive this whole build — heck, this whole year. :) You don’t need to elongate or loop the green household safety wire when you use an IEC inlet, since pulling out last if the amp drops off the stage at Woodstock isn’t a thing.
 

joulupukki

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Nice. If your build is even half as tidy as your diagram, it's gonna rock.
Thanks, I sure hope so! It’s definitely been fun planning it. I better learn how to play better now so I can do a decent demo of it. :)

Here's the most trivial suggestion you’ll receive this whole build — heck, this whole year. :) You don’t need to elongate or loop the green household safety wire when you use an IEC inlet, since pulling out last if the amp drops off the stage at Woodstock isn’t a thing.
Hehe. Ok. I didn’t know what that was for really. I guess that makes sense if it’s not IEC … it won’t pull out. I mean if the cord gets yanked on it’ll pop out of the IEC socket.
 

joulupukki

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Excellent catch @Lowerleftcoast ! Thank you. I just updated the presence and NFB wiring in that related area too. At build time I'll see if the cap & resistor have long enough trails to reach the circuit board in a PTP fashion to the ground buss. The other option would be to tie them right in with the tone stack switch's ground but I'm guessing that location is gonna get cramped.
Asset 6@3x-80.jpg
 

joulupukki

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Have a read through the Valve Wizard grounding article. It may change your mind as to how you use your ground bus.
I've read some of that article and refreshed just now. It's probably beyond me to understand exactly what I'd do to veer away from Rob's design too much. I'd likely make whatever I did worse ... in fact, I may have already done so, it sounds? :)
 

joulupukki

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Don't try this at home kids!

Ok, so I just hooked up the power transformer and placed it on the spot I have planned and then hooked up the output transformer to various outputs I was thinking of using. In these pictures it's hooked up to the 4 ohm white and violet wires. Then, I've got it attached to an instrument cable that then goes into a small amp with the volume cranked. There is definitely big hum where I had planned to put the OT. If I move it as far away as possible from the PT the hum is nearly gone. However, the leads from the OT aren't long enough to then reach where they need to go. Am I doing this wrong?

Here's a video of what I'm seeing:


IMG_0751.jpeg

IMG_0753.jpeg
 

King Fan

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Somebody who knows upright PTs is gonna have to comment. Do I recall reading it can be better to point the bell housings crosswise / away from the OT -- on average? I could be wrong; 50:50 chance....
 

joulupukki

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Somebody who knows upright PTs is gonna have to comment. Do I recall reading it can be better to point the bell housings crosswise / away from the OT -- on average? I could be wrong; 50:50 chance....
Well, tried that without much improvement. When I connect to the wires that I'll be using for 8 ohm, man it's noisy. There are a lot of pictures of Bassman Micro amps on Rob's website and they've got the transformer rotated 90°, but that makes everything even worse. Maybe my expectations are just too high for these transformers?

 

joulupukki

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Have you tried it on the z axis? It may need to mount on angle iron.
@Lowerleftcoast that’s a really great idea. After playing around with it, I discovered that if I tilt the OT just slightly the hum goes almost entirely away even though it’s really close to the PT and choke. Here’s a vid I took to show that. I wouldn’t have discovered it without your suggestion to try Z axis…

 

andrewRneumann

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@Lowerleftcoast that’s a really great idea. After playing around with it, I discovered that if I tilt the OT just slightly the hum goes almost entirely away even though it’s really close to the PT and choke. Here’s a vid I took to show that. I wouldn’t have discovered it without your suggestion to try Z axis…


I know it’s cool to have it hooked up to an amp, but headphones are more representative of what you will actually hear. The hum from magnetic coupling is not amplified like what you’ve got there.
 

joulupukki

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If it’s the quietest position with an amp, wouldn’t it be the quietest position with headphones as well?
 

andrewRneumann

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If it’s the quietest position with an amp, wouldn’t it be the quietest position with headphones as well?

Maybe, I am just trying to make life easy on you. If you are considering angle brackets or shims or whatever, it might not be necessary if the hum is so small that it can’t be heard. Ask @Tom Kamphuys he has first hand experience. :):)
 

2L man

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I've read some of that article and refreshed just now. It's probably beyond me to understand exactly what I'd do to veer away from Rob's design too much. I'd likely make whatever I did worse ... in fact, I may have already done so, it sounds? :)
So far you have done great "publishing looking work" here which future builders might follow and I hope you could make them good all the way because it is very easy! Just extend the Common "ground bus" full board length and detach the power tube cathode resistor/capacitor from the chassis. So simple change make all the operative current return straightest path to power supply!

If you use layout you have post the pre amp current return thru the chassis and current "leak" to chassis at amp input which is worst possible place because symmetrical instrument cable is connected there and amplifier will amplify all of the signal there is in cable hot. Instrument cable is long so some noise will transfer to hot pair. There is a concept "signal/noise ratio" if you want to recearch it more...

The use of Chassis as a part of operative circuits, which use Mains for power, has been forbidden in commercial manufacturing at least 50 years. I had thought this is in all advanced industrial countries? If its not forbidden in USA perhaps it is because your Mains voltage is half what the Mains is here in Europe?
 
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