The Much Anticipated (?) Bluesmaster Build Thread

[Raoul Duke]

Understood, thanks Martin. That’s what I was thinking - but wanted to be certain just in case.

[Raoul Duke]

Today’s trivial question:

Been meaning to ask about the shielded cable from the input jack to V1. In this amp, I see that HAD grounded it at the terminal strip. Is there any technical reason he chose that location vs. the lugs up by the jack? Does it make any difference - ground is ground, right (except of course the way he divides the nodes’ grounds)?

Given his ability to design and incorporate second and third order effects into advantages rather than liabilities always has me wondering about these small details…

Thanks!

[martin manning]

I can think of reasons you might want to do it either way, but maybe it really doesn't matter. In my ODS all of the coax shields are grounded at the front of the chassis.

[Raoul Duke]

Ok, good - thanks Martin! The front is my preference also - mainly because I didn’t grind the finish off under the terminal strip at V1, and the terminal strip screw eyes just don’t look as beefy as a real grounding lug (I used mini strips because I already had them). I have plenty of room by the jacks, so easy enough.

Just did the polarity bench test on the OT. Feeding the 9vac through the 4 ohm tap and measuring at the 16 ohm tap to each plate lead (after grounding the primary CT and secondary common) I got 149vac on the blue and 192vac on the brown, so brown goes to V5.
I did have to drill new holes for the OT. It’s a little more shallow front to back than a Bassman OT and neither sets of holes put it in a good spot, so all 4 had to be drilled. Luckily, Taylor’s chassis has countersunk holes for the board standoffs underneath the OT. The little details like this are very much appreciated and show some great forethought in the design.

Also, checking out the PT - this one has the orange shield wire coming out with the rest. I’ve seen old Fenders grounding that with the secondary CT; is that acceptable for this or should it go somewhere else?

Got the foot switch all finished up and tested with 102. Works as it should. I still chuckle at how painful it was understanding it the first time. I still feel the need to apologize for that, lol. On this one, I somehow managed to drill the left LED hole 1/16” higher than the right. Funny thing is I drilled it last Friday, so I guess it’s “Friday foot switch” for sure.

Moving’ right along…

[Raoul Duke]

Also looking ahead to the relay wiring; just wanted to ask a couple of clarification-type questions regarding the “OD Relay Separate Masters HRM, Bluesmaster” board plans, especially since the connections are a little different than the layout:

Cl = “clean” i.e. Cl Vol Wiper is the volume pot next to the jacks center/wiper lug? (NC1 connection)
OD entrance = the 470k resistor with the 470pf cap piggy-backed? (Com2 connection)
Cl 2C Cap = .02uf cap above the 120k plate load going to V1? (NO2 connection)

NC1 and NO1 should be co-ax?

Thank you!

[martin manning]

Yes, Cl = Clean, but the Clean Volume and OD Volume are the level controls at the outputs of the Clean and OD sections, respectively. On the layout, the clean volume is called the Master. I suppose that's because it is in the same location on the panel as the Master in the Master/Ratio system.

OD Entrance is the 470k//470p, Cl 2 C Cap is the 0.02 coming from the plate of the second stage of V1.

Refer to this MDRoberts schematic for wiring that is consistent with the connections as labeled in the eyelet boards pdf: https://ampgarage.com/forum/viewtopic.p ... 94#p223194

As for which runs are coax, refer to the layout, and look at the pot terminals.

[Raoul Duke]

Thanks Martin!
I don’t think I would have made the correlation regarding the section outputs without some help.

I’m able to keep the layout, board plans, and schematic in perspective most of the time; but I do get turned around here and there. My ability to translate the schematic doesn’t seem to be consistent from day to day; but I continue to use it and make “discoveries” every day. I’m slowly getting accustomed to reading them and understanding the terminology. Still frustrated by the relay com connections lately. I wasn’t planning to link PAB and OD - maybe I’m tripping on that modification?

Question about the layout: are the ceramic caps shown all missing a zero, and are the square caps micas? Example: is the mid switch cap a 39pf 1kv cap or the 390pf shown in the schematic? I ask because the OD entrance shows 47pf over the 470k resistor (on both the layout and schematic if I’m reading correctly), but you referred to it as 470p above - which is what caught my eye.


Hopefully my question makes sense?

Thanks again

[martin manning]

As I've said before, it's best to refer to both a schematic and a layout when building. Unfortunately there isn't a schematic that exactly matches the layout, which makes it tough on the new players. Unless you are live on stage and need to switch into OD + PAB quickly, you might as well keep them separate.

I wrote 470p above without checking since that's what you wrote in the post above ;^) It's clearly marked 47p in the layout.
The mid switch cap is marked 391, which is read as 39 x 10^1 = 390, in pF.

Also, checking out the PT - this one has the orange shield wire coming out with the rest. I’ve seen old Fenders grounding that with the secondary CT; is that acceptable for this or should it go somewhere else?

Yes ground that at the reservoir filter/CT ground.

[Raoul Duke]

Thanks Martin,
This build is proving a little more challenging than I expected just because of the different references, but I’ll get it.
Apologies for creating my own miscommunication with the 47pf - definitely my goof up, lol.

I read the mid cap as a 39pf 1kv and the V1b cap as a 50pf 1kv. Guess I better fix those. Everything else clearly shows “pf”, so I think I got those right. Looks like the 501k in the layout is a 390pf in the schematic? Why the relatively small difference I wonder?

[Raoul Duke]

Got up this morning feeling like I wanted to do something with this build that I actually understand, so I spent the morning making the cabinet. A little detail that I started putting in my cabs about a year ago are 4” long 1/4x1/4” “sliders” for the chassis. This way I can slide the chassis in to where I can start the screws without juggling. Works great if I do say so…

IMG_0370.jpeg

As I was finish sanding, the brown truck pulled up with a Mouser box for me; so yadda yadda - got the trimmer on the relay board. Clipped it up to check the sweep after getting it in and everything works as it should. I had single turn 500k hanging around and tried it a couple of days ago. Worked great too, but realized I couldn’t adjust it once installed due to positioning and side adjustment.

Overall, fairly productive day.

[GAStan]

You mean like this?

Yes I agree, it absolutely works great!

20240502_082909.jpg

[Raoul Duke]

Ha! Great minds Glenn!

Seemed like a simple solution. Makes life easier.

[Raoul Duke]

Ok, got some time today to hopefully wrap up the relay wiring. Based on my previous questions about the OD relay and Martin’s super helpful explanation along with looking at the schematic and layout - I think the relay wiring is as follows:

COM1 - Loop send tip & return switch (orange and blue on the layout)
COM2 - OD entrance 47/470 (green on the layout)
NC1 - OD vol wiper (actually at NC1 on the layout) co-ax
NC2 - ground (actually at NO2 on the layout)
NO1 - Cl vol (Master vol on layout) wiper (red on the layout)
NO2 - Cl vol (Master vol on layout) CW to NO2 to V1b C-cap (NC2 on the layout - orange) - first part of run from MV/CW co-ax?

Am I reading this right?

Thanks !

[martin manning]

Am I reading this right?

Yes, I think so. Compare the eyelet boards .pdf. Basically, wrt the layout, the NO and NC's are swapped for "OD on" when the relay is energized.

[Raoul Duke]

Ahhhh… ok; now it makes sense, thanks Martin.

I’ve compared the schematic, layout, and board plans exhaustively - even drawing out the three and comparing. I was wondering if the difference had to do with the relay power. It seemed like the only answer - but again my lack of knowledge prevented me from being more confident in that conclusion.

I think I learn (literally) a hundred new things every time I build one of these.