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Author Topic: BM Treble Cap Value Question  (Read 4539 times)
mwdavis14
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« on: January 02, 2014, 05:13:01 PM »

I'm in the process of building an HRM Bluesmaster 50W.  My mod choices include the 3 way mid boost.  In discussions w/Nik, it came out that the cap values included w/the mod were built on the presumption that the treble cap on the board was .001 uf.  Per layout, it is actually .002 uf on the BM - the other OTS models appear to have the .001 (no, i've not checked all of them).  This seems quite a large value.  Consider that Fender uses 250pf and you'll see what I mean.  Anyway, I have seen innumerable postings complaining that the BM is "dark".  Can anyone offer insight into whether a simple change of the cap on the board to .001 would eliminate that problem?
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sduck
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« Reply #1 on: January 03, 2014, 12:20:23 AM »

1n vs. 2n is a really tiny difference as far as caps go. Considering that caps are generally 5-10% tolerance, I wouldn't worry about this small a difference.

The "dark" nature of BM amps is more due to them having a ton of low end, rather than a lack of high end. I run the bass knob down at about 2, and that seems to balance things out.
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plasticvonaband
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« Reply #2 on: January 03, 2014, 01:47:21 AM »

It can also depend on the speaker choice as well. I find the BM to be warm but really more of a full range, due to the bottoms end that it has. I run mine thru two Weber 1265 Alnico with the "pre rola" treatment, and they are well broken in by weber and myself. They are 16 ohms run in parallel, so I run at 8 ohms. This seems to bring balance to the amp. Since the speakers are a bit tight, I can run the bass a lil higher around 6 of so, and with the deep switch on, it tightens things up even more.

The slope resistor value is also lower than the rest of the OTS series, which allows for more low end, and also changes the entire curve of the eq to be more  "full range" as well, a bit more raw, but yet a bit more musical than others; there's a lot of low end and high end harmonics there just waiting to be found.

A lot of guys change out the slope resistor to a higher value to change the eq curve and basically make the amp a tad brighter. I have all the parts to make the slope resistor variable, from the stock value all the way to 120, just haven't found the time to do it.

Basically, the amp isn't really dark, it just has a ton of low end due to the slope resistor, and the way the PI is setup as well. It just takes some dialing in and speaker swapping to find what you like. The EVM 12L is a good choice, or it's eminence clones the Delta 12a and the Delta 12 pro A. Both are very close to the EV and half the price, they just need a good heavy break in. I used the 20 year old equivalent of the Delta 12a that I had in my 4x12 for a while til age and dry rot took their toll.

I hope this helps!
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Overdrive is like peanut butter. Some like it crunchy, some like it creamy.
Bluesmaster 50 2x12 combo and some guitars.
mwdavis14
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« Reply #3 on: January 04, 2014, 05:21:12 PM »

Thanks much everyone!
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gigs
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« Reply #4 on: January 07, 2014, 11:03:20 PM »

100W BM. Clean mode with a strat / tele, I run the bass down to 4. Clean mode with the Les Paul, I run the bass down to 2. Fulltone Fulldrive II (comp cut) and Fulltone OCD pedals in front of amp as well for some extra gain in clean mode on occasion.

OD I only use with the Les Paul and keep the bass at 2. Internal bass trim turned down as well. Don't forget to set these internal trims for good OD tone.

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TennAmp
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« Reply #5 on: March 06, 2014, 08:09:41 AM »

The BM has a .002 with a 390p in series.  That's effectively 326 p.  When the mid boost in engaged, it puts the 390p cap in parallel, giving an the effective value of 2390p.

Other models are similar - some just disengage the small cap completely when the MB is engaged. The Modern Eagle has a 0.001 in there with a 390 in series - that's 280p/1000p.

The OTS lunchbox is like the modern eagle - 280p normally, 1000p with MB engaged.

If you wanted a lower effective value, you could use a .001 with a 330p.  That would give you 1330p in mid-boost and 248p without the mid boost engaged.

Or use a .002 with a 330 - yields 283p/2330p.

Please check my logic and math.

The main thing to keep in mind is that the effective value with MB off is controlled by the small cap and the mid boosted value is controlled by the big cap.

I think I might just swap out the 390 on mine for a 330 and get myself closer to Fender territory.
« Last Edit: March 06, 2014, 01:37:52 PM by TennAmp » Logged
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