BM Build Pictures

[ayan]

Still working on getting the hang of this circuit...

Gil

[mat]

Very Impressive !

Lots of stuff on a neat order

Congrats !!

[odourboy]

Niec clean work - looks fantastic!

When you're finished taming this beast, I hope you'll post the vitals (tweaks, trimmer settings, voltages....).

Cheers!

[ayan]

Niec clean work - looks fantastic!

When you're finished taming this beast, I hope you'll post the vitals (tweaks, trimmer settings, voltages....).

Cheers!

I can measure voltages and post them later, sure. However, this uses a TF135 PT, so it has ~440 VDC on the power tube plates, etc. -- so I don't expect any surprises in the voltage department.

The only things that are different than in the schematic/other builds I've seen are:

1. PAB implemented via 82K tail resistor on the middle pot. The effect is not really subtle, but it is mellow.

2. Other half of PAB relay used to switch the .005uF jazz cap between: (a) Inout of middle control, so at 50K to ground -- rather than at ground -- in "normal jazz mode", and that adds a bit of sparkle; (b) I lift it off with the PAB, which makes the "jazz PAB mode" same a "rock PAB" and thefore much livelier. This is similar, I believe, to what we see in 234 and the LC amp.

3. I use a .001uF (orange disc on the HRM board, mounted on eyelets) bypassing OD2 Rp to tame the top end "hardness" a bit. Makes the usable treble control range on the HRM wider.

4. I use a 50K RA presence pot, which has a faster of taper than a 25KL. My presence control begins working at 10 o'clock.

5. OD Trimmer is set at 40K to ground. I originally had a 250KL drive control, with which I needed to keep the trimmer very low to avoid harsheness. I changed that to a 250KA pot, and now I can set the trimmer higher since that "threshold" of gain is much less sensitive on the front panel control.

6. Still playing with the HRM settings. I have the bass "turned on" (i.e, anything past 100K or so, after that it seems to sound basically the same); middle 2/3 of the way up; treble 1/3 of the way up. These settings seem to make the amp smoother than with everything halfway up.

Overall, to me the amp is good at either low gain (vintage Clapton gain levels) or high gain (rock, metal and beyond). Medium gain territory is better covered by the non-HRM with 220K/150K plate loads, IMHO.

I will post stats later.

Gil

[kleinm]

Excellent build! I always enjoy seeing the insides of amps like this. Thanks for posting your tweaks, too.

[odourboy]

Fascinating! I'm a novice at the d-clone stuff and to see what sorts of tweaks you experienced folk are doing to achieve your goals and why is really cool!

Thanks, Brian

[BobW]

Excellent workmanship Gil! I really like the chassis and board work. Is that one of Funk's chassis?

[stelligan]

Thanks for posting this. Of special interest to me is the detail you have shared regarding the wiring of your PAB. This is an area I am still tinkering with to get it to be more usable for me in my HRM. I find I almost never use it on the clean tone and always on the OD tone with a midboost as well. Does your method yield not a more subdued volume jump than standard on the clean side, but a less harsh tonality? Is that "not subtle but mellow"? Fabulous looking build by the way.

thanks,
Dave

[ayan]

Thanks for posting this. Of special interest to me is the detail you have shared regarding the wiring of your PAB. This is an area I am still tinkering with to get it to be more usable for me in my HRM. I find I almost never use it on the clean tone and always on the OD tone with a midboost as well. Does your method yield not a more subdued volume jump than standard on the clean side, but a less harsh tonality? Is that "not subtle but mellow"? Fabulous looking build by the way.

thanks,
Dave

Dave, I have to qualify a few things: is your amp a Blues Master HRM? If not, i.e. if you have a Skyliner EQ, then my boost approach will not work in your amp.

Provided yours is a BM, by "standard" do you mean the boost where the ground of the middle control is lifted? If so, my PAB is a much smaller effect than that. There is of course a jump in volume when you're playing clean (the jump depends in part on where your middle control setting is) and a jump in amount of gain when there is overdrive present (whether you are one the clean channel, but with some gain going on, or on the overdrive channel).

What I didn't like about the "mega boost" was that it was "too much." Thus, to avoind having the amp sound harsh in PAB mode, I would have to set the gain much lower, which rendered the overdrive channel too clean. Limiting the boost with my 82K resistor (many people indicated they use a 470K resistor, which I found to be waaaaay to much for me), you can set the amp for your desired overdrive level and the PAB will not make all hell break loose.

I still have to post the voltages -- I have been forgetting to do that -- but I will do so tomorrow, afterw I get a chance to measure them.

Cheers,

Gil

[Fischerman]

3. I use a .001uF (orange disc on the HRM board, mounted on eyelets) bypassing OD2 Rp to tame the top end "hardness" a bit. Makes the usable treble control range on the HRM wider.

Gil,
In another recent thread you mentioned a treble bleed off of the 'top' lug of the Lead Master. Is the Rp bypass cap mentioned here used instead of that...for a similar effect? Is it an 'either/or but not both' thing?

Purty build!

EDIT: I'm glad you mentioned the bass ON/OFF thing. A 1M-L seems extremely hard to dial in there...it seems a 500K-A would be better.

[mdroberts1243]

[quote="ayan
What I didn't like about the "mega boost" was that it was "too much." Thus, to avoind having the amp sound harsh in PAB mode, I would have to set the gain much lower, which rendered the overdrive channel too clean. Limiting the boost with my 82K resistor (many people indicated they use a 470K resistor, which I found to be waaaaay to much for me), you can set the amp for your desired overdrive level and the PAB will not make all hell break loose.
Gil[/quote]

Hi Gil,
In my amp I found "mega boost" and the 470k to be too much as well... I went for a +6dB boost and settled on a 72k ohm resistor... the 82k gave me 8.4dB, BTW.

[mlp-mx6]

Mark,

Is your schem updated with that change?

[mdroberts1243]

Mark,

Is your schem updated with that change?

Not yet... I'm just bringing the amp up now and annotating the changes... I'll post the updated schematic in a couple of days.

[ayan]

3. I use a .001uF (orange disc on the HRM board, mounted on eyelets) bypassing OD2 Rp to tame the top end "hardness" a bit. Makes the usable treble control range on the HRM wider.

Gil,
In another recent thread you mentioned a treble bleed off of the 'top' lug of the Lead Master. Is the Rp bypass cap mentioned here used instead of that...for a similar effect? Is it an 'either/or but not both' thing?

Purty build!

EDIT: I'm glad you mentioned the bass ON/OFF thing. A 1M-L seems extremely hard to dial in there...it seems a 500K-A would be better.

Well, the treble bleed is something I use in my non-HRM amps and it hangs to ground AFTER the 150K output resistor. So it is placed after the .005uF coupling cap and after the 150K resistor, where it joins the "lead master" volume control.

In the HRM amp, the .001uF resistor connects the output end of the plate load resitor to ground. So this occurs earlier in the circuit than in my non-HRM amps. You can definitely do a treble bleed after the 100K output resistor which comes after the HRM tone controls. However, at that point of the circuit the same cap will kill a lot more highs, so you probably would have to use something on the orderof maybe 220pF to get a similar effect.

Gil

[ayan]

Hi Gil,
In my amp I found "mega boost" and the 470k to be too much as well... I went for a +6dB boost and settled on a 72k ohm resistor... the 82k gave me 8.4dB, BTW.

Very cool, it validates my ears. Thanks Mark.

Gil