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PostPosted: Wed Jul 18, 2012 9:41 am 
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Road King
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chipaudette wrote:
Hey Boogiebabies,

Good to see you around!

I think that the OP has a III+. Isn't that 1000pF cap the heart of the III+ mod? If MikeB doesn't do that, what does he do?

Chip


On the ++'s I have seen they have the 20pf and two 3.3M resistors in paralell for the circuit to the lead input and output, a 1000pf cap across the second lead stage plate resistor and the .02 cap that feeds the 680K resistor to the lead input (.02 not on schematic, but it's in the middle of the board) is removed and wired directly to the 680K lead input.


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PostPosted: Wed Jul 18, 2012 2:50 pm 
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Mark II
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BB I'm assuming you're referring to C30? If so then no. I split the difference and went with a 500pf. For whatever reason, and this may be a misconception, I find the 1000pf cap adds compression to the lead gain. I do use a TS-9 to add sustain to the lead channel. The gain on the TS is set to minimum with the volume set at 1:30. For a while I had no cap in C30. I preferred the "open" sound that it produced but it also introduced a lot of unwanted sizzle.

Chip I did take your advice on the tone stack settings and this did help a bunch. Not sure if I took a mental leave of absence or not in forgetting how much influence the tone stack has on these amps. :oops:

Thanks again guys for all the advice!

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PostPosted: Wed Jul 18, 2012 4:02 pm 
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You went 500pf, huh? Very interesting.

Again, I don't have a Mark III, but on my IIC->IIC+, I modded the amp to made this cap switchable so that I could try different values. Prior to my mod, I actually felt that my IIC+ was a little too smooth. I wanted more sizzle.

So, I opened her up, lifted up one leg of the cap, stuck in a little wiring, and a on-off-on switch in place of the Slave knob. With this switch, I can use the original 1000pF that MikeB put in, or I can switch to a 500 pF (or is it 1000 || 500 = 333pF, I can't remember), or I can switch to no cap at all (which is the stock Mark III, I think). Unless I'm specifically going for Metallica AJFA, the "no cap" setting is too buzzy for my tastes. The 1000pF setting is good, but a little too smooth/muffled some times. Most of the time (low gain, mid gain, or non-Metallica high gain), I find myself on the 500 pF (or 333pF) setting.

Of course, I believe that the Mark III is generally considered to be much brighter / buzzy than the IIC+...even beyond just the effect of this cap. So, with its inherently brighter sound, maybe I would have prefered the 1000pF in the Mark III. But, maybe not. I'm thinking that your 500 pF is probably a good call. It certainly gets you far away (in a good way?) from the stock configuration that has no cap at all.

Chip


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PostPosted: Thu Jul 19, 2012 3:33 pm 
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Road King
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You have to admit there are a ton of ceramic disc caps in the "famous" Boogie lead channel.
This no doubt has some effect, but it also has a ton to do with how the gain is structured.

My memory of an actual MK III is fuzzy. Maybe we should compare it to a IIC+. It seems on the III schematic that it should be less bright than a IIC+, but no MK III I have come across is as smooth in the overdrive. If you/anyone has a pic I am curious if there is a 180pf off the grid of V3A to the cathode or ground.


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PostPosted: Sat Jul 21, 2012 7:38 pm 
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Mark II
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I'll try to get into my amp and take a pic tomorrow. I have to admit, ever since I got my III+ there has been this little voice in the back of my mind saying "you really should just get a IIC+ and stop messing around". :idea:

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Mk III+ DRG
Fuchs TDS100
BFDR Clone (heavily modded)
Custom built guitars w/humbuckers
PRS HB II
79 Les Paul Standard
Marshall 4x12 (loaded with 2 EV's and 2 ToneTubby's in X pattern)
and more pedals than one man should own.


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PostPosted: Sat Jul 21, 2012 10:27 pm 
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That "little voice" is the Devil. Ask me how I know. :wink:

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PostPosted: Mon Sep 24, 2012 10:36 am 
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Bottle Rocket
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Boogiebabies wrote:
If you/anyone has a pic I am curious if there is a 180pf off the grid of V3A to the cathode or ground.


I'm now converting Mark III (SRX S/N 17052) to IIC+ :-) and it has 120pF off the grid to ground.

But each of the PI plate resistors is also bypassed by 120pF caps.

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PostPosted: Sat Oct 06, 2012 8:52 am 
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Mark III

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12ay7


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PostPosted: Mon Mar 06, 2017 4:17 pm 
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Bottle Rocket

Joined: Sun Feb 26, 2017 11:27 am
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Direwolf wrote:
Hey guys. I've got a question here about a Mk III Blue Stripe that has been modded to a III+. I'm not a metal player so I've been wondering what mods I can do to reduce the amount of gain in my lead channel. I know there's the obvious "turn the gain knob down" answer but I find the tone diminishes when I do this. I've tried a lower gain tube in V3 but it really starts taking away from the bottom end and overall tone response. I know the blue stripe is said to have the most gain but buying a new amp just isn't an option at this point. So my question is this. What can I do to the circuit in the lead channel to reduce the amount of drive? I really love this amp and the tone it produces. I just want less gain. Any thoughts and ideas are greatly appreciated!



Hi, I put a 1000k in C30 and another 1000K above C30. Can't remember location...it came off a pin in V3 to ground on circuit board. It took away all buzz and fizz. It allowed me to jack up the Lead Drive to silky smooth but biting tones. Love my Blue Strip now.

Cheers, Paul


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