A good master volume circuit

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dehughes
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A good master volume circuit

Post by dehughes » Tue Apr 11, 2006 11:59 pm

Okay, a great one. That's what I want. Pre PI, post PI, etc etc etc... I've been looking around at schematics of amps that I know have good master volumes, but I figure it would be good to ask all you guys what you've found to work well.

Thanks in advance,


david

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Funkalicousgroove
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Post by Funkalicousgroove » Wed Apr 12, 2006 3:31 pm

Depends on what you want the amp to do!! to make a twin distort at club volume I like a post PI master, if I want more clarity and just lower volume I like a 1M wired as a voltage divider just before the PI.

What kind of amp is it for and what do you want it to do???
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dehughes
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Post by dehughes » Wed Apr 12, 2006 3:58 pm

Funkalicousgroove wrote:Depends on what you want the amp to do!! to make a twin distort at club volume I like a post PI master, if I want more clarity and just lower volume I like a 1M wired as a voltage divider just before the PI.

What kind of amp is it for and what do you want it to do???
Thanks man! I'm building an AC30ish clone with two channels, one EF86 and one 12AX7. Think something along the lines of a DC30 Matchless, but not quite... Anyway, I just want something that is transparent and lets me get the amp distorting a bit earlier on. I'm not looking for bedroom volumes, necessarily, but just something that will be relatively natural and transparent and let me get the amp to give up the goods a bit sooner. I'd gladly sacrifice "bedroom gain" for overal clarity and vibe, if that makes sense....

Many thanks!


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Post by Funkalicousgroove » Wed Apr 12, 2006 4:33 pm

For that particular amp I'd reccommend a restive attenuator between the output and the speaker Like a Dr. Z Airbrake. The PPI will cost you that top end clarity, and that amp won't have enough gain to really make a pre PI master worth it, it won't overdrive. I have a Rocket Myself that I've experimented with a bit and it's sounded best cranked through an attenuator, or by itself wide open. It didn't like the PPI MV at all, it made LOTS of distortion but it no longer had that "Cranked" AC30 sound and feel. JMHO.
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dehughes
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Post by dehughes » Wed Apr 12, 2006 4:41 pm

Funkalicousgroove wrote:For that particular amp I'd reccommend a restive attenuator between the output and the speaker Like a Dr. Z Airbrake. The PPI will cost you that top end clarity, and that amp won't have enough gain to really make a pre PI master worth it, it won't overdrive. I have a Rocket Myself that I've experimented with a bit and it's sounded best cranked through an attenuator, or by itself wide open. It didn't like the PPI MV at all, it made LOTS of distortion but it no longer had that "Cranked" AC30 sound and feel. JMHO.
Very cool. Much appreciated!

So (for clarity's sake...) I assume that PPI is "post phase inverter", and you're contrasting this with a "pre PI" when you're saying that the post phase inverter will loose top end clarity, and the pre PI master is not worthwhile due to the lack of front end gain, correct? This would imply that a pre phase inverter master will provide more overall clarity than a post PI?

Thanks!


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Post by Funkalicousgroove » Wed Apr 12, 2006 5:03 pm

Yes, a pre-PI master has better clarity than a Post-PI master, but the post PI master allows you to overdrive the PI to get more gain. with a Post-PI you'll never be able to get that "Cranked" sound.
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dehughes
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Post by dehughes » Wed Apr 12, 2006 6:32 pm

Funkalicousgroove wrote:Yes, a pre-PI master has better clarity than a Post-PI master, but the post PI master allows you to overdrive the PI to get more gain. with a Post-PI you'll never be able to get that "Cranked" sound.
Excellent. Thank you!


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SECONDandBOWERY
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Post by SECONDandBOWERY » Thu Apr 13, 2006 5:45 pm

Why not wire a pre-PI voltage divider and a post-PI crossline with a dual ganged pot so you get the best of both circuits?

Has anyone tried this?

Rock'n'Roll,
--Andy

dehughes
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Post by dehughes » Thu Apr 13, 2006 11:04 pm

SECONDandBOWERY wrote:Why not wire a pre-PI voltage divider and a post-PI crossline with a dual ganged pot so you get the best of both circuits?

Has anyone tried this?

Rock'n'Roll,
--Andy
You'll have to explain that a bit for this newbie here... :)


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Post by SECONDandBOWERY » Fri Apr 14, 2006 1:44 pm

David: Ok, I'll explain this as best I can. The Pre-PI Voltage Divider master volume is just a pot wired with one lug grounded, one lug feeding into the PI, and one lug being fed from the preamp. The more you turn the pot, the more of the signal is sent to ground instead of the PI, so there is less signal to amplify. This is probably the most common kind of MV. If a stock Marshall or Fender has a MV, it will most likely be the pre-PI voltage divider (there's one or two Marshall amps that used a differend kind but they're not very popular). The Post-PI Crossline Master Volume is used alot by Matchless. It involves hooking up a pot with one lug wired to each coupling cap coming off of the PI. When you turn the pot, the two signals begin to overlap. Since they are out of phase, some of the signals will cancel each other out. The more you turn the pot, the more signals are cancelled, and thusly, the lower the volume.

Now, since a 1M pot works good in both applications, if you wired them up with a dual-ganged 1M pot, which is essentially two 1M pots in one casing, both controlled by the same shaft.
[img:128:91]http://www.tubeampparts.com/Merchant2/g ... l-gang.jpg[/img]
See - there are two sets of lugs and only one shaft.

Did that make sence or did I just confuse you further?

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Post by Funkalicousgroove » Fri Apr 14, 2006 2:17 pm

I think that kind of defeats the purpose doesn't it? I mean the Idea (or so I thought) was to be able to get a good cranked sound at reasonable volumes, but the pre-PI MV wouldn't allow enough signal through to drive the PI into distortion.
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Post by SECONDandBOWERY » Fri Apr 14, 2006 2:31 pm

Funkalicousgroove: I guess you're right. Maybe I should think before I type from now on...

Rock'n'Roll,
--Andy

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Post by dehughes » Sat Apr 15, 2006 12:23 am

Thanks guys. That makes a lot of sense, and helped me in my overall understanding of your "typical" preamp circuit. Super cool.


david

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