The Amp Garage Forum Index The Amp Garage
A tube amp builder's community
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

A good master volume circuit

 
Post new topic   Reply to topic    The Amp Garage Forum Index -> Technical Discussion
View previous topic :: View next topic  
Author Message
dehughes



Joined: 23 Mar 2006
Posts: 1110
Location: Portland, OR

PostPosted: Tue Apr 11, 2006 11:59 pm    Post subject: A good master volume circuit Reply with quote

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
Back to top
View user's profile Send private message Send e-mail
Funkalicousgroove



Joined: 25 Jul 2005
Posts: 2230
Location: Denver, CO

PostPosted: Wed Apr 12, 2006 3:31 pm    Post subject: Reply with quote

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???

_________________
....But it was tuned when I bought it!
www.bludotone.com
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
Back to top
View user's profile Send private message Send e-mail Visit poster's website
dehughes



Joined: 23 Mar 2006
Posts: 1110
Location: Portland, OR

PostPosted: Wed Apr 12, 2006 3:58 pm    Post subject: Reply with quote

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!


david
Back to top
View user's profile Send private message Send e-mail
Funkalicousgroove



Joined: 25 Jul 2005
Posts: 2230
Location: Denver, CO

PostPosted: Wed Apr 12, 2006 4:33 pm    Post subject: Reply with quote

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.
_________________
....But it was tuned when I bought it!
www.bludotone.com
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
Back to top
View user's profile Send private message Send e-mail Visit poster's website
dehughes



Joined: 23 Mar 2006
Posts: 1110
Location: Portland, OR

PostPosted: Wed Apr 12, 2006 4:41 pm    Post subject: Reply with quote

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!


david
Back to top
View user's profile Send private message Send e-mail
Funkalicousgroove



Joined: 25 Jul 2005
Posts: 2230
Location: Denver, CO

PostPosted: Wed Apr 12, 2006 5:03 pm    Post subject: Reply with quote

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.
_________________
....But it was tuned when I bought it!
www.bludotone.com
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
Back to top
View user's profile Send private message Send e-mail Visit poster's website
dehughes



Joined: 23 Mar 2006
Posts: 1110
Location: Portland, OR

PostPosted: Wed Apr 12, 2006 6:32 pm    Post subject: Reply with quote

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!


david
Back to top
View user's profile Send private message Send e-mail
SECONDandBOWERY



Joined: 23 Mar 2006
Posts: 9

PostPosted: Thu Apr 13, 2006 5:45 pm    Post subject: Reply with quote

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
Back to top
View user's profile Send private message Visit poster's website AIM Address
dehughes



Joined: 23 Mar 2006
Posts: 1110
Location: Portland, OR

PostPosted: Thu Apr 13, 2006 11:04 pm    Post subject: Reply with quote

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... Smile


david
Back to top
View user's profile Send private message Send e-mail
SECONDandBOWERY



Joined: 23 Mar 2006
Posts: 9

PostPosted: Fri Apr 14, 2006 1:44 pm    Post subject: Reply with quote

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.

See - there are two sets of lugs and only one shaft.

Did that make sence or did I just confuse you further?
Back to top
View user's profile Send private message Visit poster's website AIM Address
Funkalicousgroove



Joined: 25 Jul 2005
Posts: 2230
Location: Denver, CO

PostPosted: Fri Apr 14, 2006 2:17 pm    Post subject: Reply with quote

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.
_________________
....But it was tuned when I bought it!
www.bludotone.com
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
Back to top
View user's profile Send private message Send e-mail Visit poster's website
SECONDandBOWERY



Joined: 23 Mar 2006
Posts: 9

PostPosted: Fri Apr 14, 2006 2:31 pm    Post subject: Reply with quote

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

Rock'n'Roll,
--Andy
Back to top
View user's profile Send private message Visit poster's website AIM Address
dehughes



Joined: 23 Mar 2006
Posts: 1110
Location: Portland, OR

PostPosted: Sat Apr 15, 2006 12:23 am    Post subject: Reply with quote

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


david
Back to top
View user's profile Send private message Send e-mail
Display posts from previous:   
Post new topic   Reply to topic    The Amp Garage Forum Index -> Technical Discussion All times are GMT
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum


Powered by phpBB © 2001, 2005 phpBB Group