What's This Cap For?

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FourT6and2
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What's This Cap For?

Post by FourT6and2 »

This schematic shows the Phase Inverter (V3) and power section of a single-channel, high-gain, Marshall-ish amp. One thing I'm wondering about is C40. What is going on there? I haven't seen a cap used in this position before.

Schematic: http://img06.deviantart.net/d3db/i/2017 ... rwsd.jpg?1
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xtian
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Re: What's This Cap For?

Post by xtian »

That cap will shunt some high frequencies to ground. Look up "Vox Cut control"
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Cameron
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Re: What's This Cap For?

Post by Cameron »

It's a cap I added to see if someone would copy everything.....it does cut some high end....but it's so small ...maybe makes the tone a tiny bit warmer.......but mainly just to F with people.....I started doing this mod in 1995.....after some other modders started to copy it ...I stopped doing this version of it...... I still do this power amp tho......the voicing control ...or thump switch on this schematic ..... for the resonance is a little trick I came up with ...it's also something I have been doing since the mid 90s and its very cool in keeping that Marshall mid thing wile adding the boost in the low end.....
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martin manning
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Re: What's This Cap For?

Post by martin manning »

Even if you can't hear it it will help suppress ultrasonic oscillations. Kind of redundant here as there is already 50pF across the PI anodes.
FourT6and2
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Re: What's This Cap For?

Post by FourT6and2 »

martin manning wrote: Tue Jun 06, 2017 9:04 pm Even if you can't hear it it will help suppress ultrasonic oscillations. Kind of redundant here as there is already 50pF across the PI anodes.
Yeah, I figured it was to fix some parasitic oscillation. Maybe red-plating power tubes. Not necessarily inherent to any "design" in the sound of the amp, but to maybe make sure the particular amp was running smoothly.
FourT6and2
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Re: What's This Cap For?

Post by FourT6and2 »

Cameron wrote: Tue Jun 06, 2017 8:20 pm It's a cap I added to see if someone would copy everything.....it does cut some high end....but it's so small ...maybe makes the tone a tiny bit warmer.......but mainly just to F with people.....I started doing this mod in 1995.....after some other modders started to copy it ...I stopped doing this version of it...... I still do this power amp tho......the voicing control ...or thump switch on this schematic ..... for the resonance is a little trick I came up with ...it's also something I have been doing since the mid 90s and its very cool in keeping that Marshall mid thing wile adding the boost in the low end.....
Not sure I understand. Won't a 22pF cap + 100K resistor form a low-pass that cuts something like 72KHz and up? I thought humans can't hear past 20KHz...
Cameron
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Re: What's This Cap For?

Post by Cameron »

FourT6and2 wrote: Wed Jun 07, 2017 2:03 am
Cameron wrote: Tue Jun 06, 2017 8:20 pm It's a cap I added to see if someone would copy everything.....it does cut some high end....but it's so small ...maybe makes the tone a tiny bit warmer.......but mainly just to F with people.....I started doing this mod in 1995.....after some other modders started to copy it ...I stopped doing this version of it...... I still do this power amp tho......the voicing control ...or thump switch on this schematic ..... for the resonance is a little trick I came up with ...it's also something I have been doing since the mid 90s and its very cool in keeping that Marshall mid thing wile adding the boost in the low end.....
Not sure I understand. Won't a 22pF cap + 100K resistor form a low-pass that cuts something like 72KHz and up? I thought humans can't hear past 20KHz...
Yes you can hear it a bit ....but ..if you take it out ...it won't make much of a difference....you could also just use 100pf instead of 47pf in the PI ..again it's just something I put in to see if people would copy everything........that was really more why it's there ....and people did leave it in when they copied it.
Cameron
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Re: What's This Cap For?

Post by Cameron »

FourT6and2 wrote: Wed Jun 07, 2017 1:58 am
martin manning wrote: Tue Jun 06, 2017 9:04 pm Even if you can't hear it it will help suppress ultrasonic oscillations. Kind of redundant here as there is already 50pF across the PI anodes.
Yeah, I figured it was to fix some parasitic oscillation. Maybe red-plating power tubes. Not necessarily inherent to any "design" in the sound of the amp, but to maybe make sure the particular amp was running smoothly.
It's not there for any fix. I wouldn't over think it......
FourT6and2
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Re: What's This Cap For?

Post by FourT6and2 »

Cameron wrote: Wed Jun 07, 2017 4:58 am
FourT6and2 wrote: Wed Jun 07, 2017 2:03 am
Cameron wrote: Tue Jun 06, 2017 8:20 pm It's a cap I added to see if someone would copy everything.....it does cut some high end....but it's so small ...maybe makes the tone a tiny bit warmer.......but mainly just to F with people.....I started doing this mod in 1995.....after some other modders started to copy it ...I stopped doing this version of it...... I still do this power amp tho......the voicing control ...or thump switch on this schematic ..... for the resonance is a little trick I came up with ...it's also something I have been doing since the mid 90s and its very cool in keeping that Marshall mid thing wile adding the boost in the low end.....
Not sure I understand. Won't a 22pF cap + 100K resistor form a low-pass that cuts something like 72KHz and up? I thought humans can't hear past 20KHz...
Yes you can hear it a bit ....but ..if you take it out ...it won't make much of a difference....you could also just use 100pf instead of 47pf in the PI ..again it's just something I put in to see if people would copy everything........that was really more why it's there ....and people did leave it in when they copied it.
Interesting, thanks. I'm not copying this amp or anything. I just thought it was weird to see that cap there in the schematic. Seems like it actually IS weird, because you say it was a 'trick' of sorts lol...
Cameron
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Re: What's This Cap For?

Post by Cameron »

FourT6and2 wrote: Wed Jun 07, 2017 11:30 am
Cameron wrote: Wed Jun 07, 2017 4:58 am
FourT6and2 wrote: Wed Jun 07, 2017 2:03 am

Not sure I understand. Won't a 22pF cap + 100K resistor form a low-pass that cuts something like 72KHz and up? I thought humans can't hear past 20KHz...
Yes you can hear it a bit ....but ..if you take it out ...it won't make much of a difference....you could also just use 100pf instead of 47pf in the PI ..again it's just something I put in to see if people would copy everything........that was really more why it's there ....and people did leave it in when they copied it.
Interesting, thanks. I'm not copying this amp or anything. I just thought it was weird to see that cap there in the schematic. Seems like it actually IS weird, because you say it was a 'trick' of sorts lol...
I don't mind if you do use any of my circuits ......have fun building something cool!! It's the amp guys that sell amps that are copies of my stuff .....and give no credit to where they got the circuit from and act like it's there's.... and they put in the time it took to fine tune it .....when all they did .....was copy the amp or just used a wrong schematic from the internet......but....I don't have any problem with someone who wants to make one for himself or are just learning about this stuff ....if you have any questions about any of my amps or circuits ....please ask....
FourT6and2
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Re: What's This Cap For?

Post by FourT6and2 »

Cameron wrote: Wed Jun 07, 2017 8:28 pm
FourT6and2 wrote: Wed Jun 07, 2017 11:30 am
Cameron wrote: Wed Jun 07, 2017 4:58 am
Yes you can hear it a bit ....but ..if you take it out ...it won't make much of a difference....you could also just use 100pf instead of 47pf in the PI ..again it's just something I put in to see if people would copy everything........that was really more why it's there ....and people did leave it in when they copied it.
Interesting, thanks. I'm not copying this amp or anything. I just thought it was weird to see that cap there in the schematic. Seems like it actually IS weird, because you say it was a 'trick' of sorts lol...
I don't mind if you do use any of my circuits ......have fun building something cool!! It's the amp guys that sell amps that are copies of my stuff .....and give no credit to where they got the circuit from and act like it's there's.... and they put in the time it took to fine tune it .....when all they did .....was copy the amp or just used a wrong schematic from the internet......but....I don't have any problem with someone who wants to make one for himself or are just learning about this stuff ....if you have any questions about any of my amps or circuits ....please ask....
Will do, thanks. I'm currently in the research phase of a build. Gonna be a Cali-type circuit. Just trying to figure out how to voice it to my specific preferences. It'll involve a lot of swapping of this and that to see how it sounds I guess. But I'm trying to do as much reading as I can on what components do what and how various combinations and value changes affect the sound. I mean... I can look at RC Time Constants and graphs and do the math all day, but that doesn't really tell me much in terms of the sound coming out of the speaker. But I have a good starting point.

I play modern prog rock and metal. So I'm not after the VH sound at all. I like a really angry, pissed off high-gain sound. Tight low-end. Smooth highs. Pronounced, snarly/growly mid range. Definitely NOT after the brown sound...
Cameron
Posts: 244
Joined: Sat Aug 05, 2006 4:38 am

Re: What's This Cap For?

Post by Cameron »

FourT6and2 wrote: Wed Jun 07, 2017 10:43 pm
Cameron wrote: Wed Jun 07, 2017 8:28 pm
FourT6and2 wrote: Wed Jun 07, 2017 11:30 am

Interesting, thanks. I'm not copying this amp or anything. I just thought it was weird to see that cap there in the schematic. Seems like it actually IS weird, because you say it was a 'trick' of sorts lol...
I don't mind if you do use any of my circuits ......have fun building something cool!! It's the amp guys that sell amps that are copies of my stuff .....and give no credit to where they got the circuit from and act like it's there's.... and they put in the time it took to fine tune it .....when all they did .....was copy the amp or just used a wrong schematic from the internet......but....I don't have any problem with someone who wants to make one for himself or are just learning about this stuff ....if you have any questions about any of my amps or circuits ....please ask....
Will do, thanks. I'm currently in the research phase of a build. Gonna be a Cali-type circuit. Just trying to figure out how to voice it to my specific preferences. It'll involve a lot of swapping of this and that to see how it sounds I guess. But I'm trying to do as much reading as I can on what components do what and how various combinations and value changes affect the sound. I mean... I can look at RC Time Constants and graphs and do the math all day, but that doesn't really tell me much in terms of the sound coming out of the speaker. But I have a good starting point.

I play modern prog rock and metal. So I'm not after the VH sound at all. I like a really angry, pissed off high-gain sound. Tight low-end. Smooth highs. Pronounced, snarly/growly mid range. Definitely NOT after the brown sound...
Since you have a good idea of where you want to start.....I would just build it ...and then tune it to where you want it to be ....then you can hear how the difference in parts will actually effect the end result.....and also the feel of the amp. Doing all the math and all that really won't give you useful end results....at least for me ....haha....for me it's always been better to just make it and then grab the guitar and play and swap parts and see where I can go with it....plus you can really hear what each part does and how it effects the overall tone and feel in real time.....which isn't always the same end result for every amp.....

The circuit wasn't made to get the brown sound ...it's way more gain in some ways then Eddie used. Eddie's tone was mostly a stock amp and the way he set it up .....using Marshall's and other amps to be power amps to the loaded down and variac'ed main Marshall.
FourT6and2
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Re: What's This Cap For?

Post by FourT6and2 »

Cameron wrote: Tue Jun 13, 2017 11:58 pm
FourT6and2 wrote: Wed Jun 07, 2017 10:43 pm
Cameron wrote: Wed Jun 07, 2017 8:28 pm

I don't mind if you do use any of my circuits ......have fun building something cool!! It's the amp guys that sell amps that are copies of my stuff .....and give no credit to where they got the circuit from and act like it's there's.... and they put in the time it took to fine tune it .....when all they did .....was copy the amp or just used a wrong schematic from the internet......but....I don't have any problem with someone who wants to make one for himself or are just learning about this stuff ....if you have any questions about any of my amps or circuits ....please ask....
Will do, thanks. I'm currently in the research phase of a build. Gonna be a Cali-type circuit. Just trying to figure out how to voice it to my specific preferences. It'll involve a lot of swapping of this and that to see how it sounds I guess. But I'm trying to do as much reading as I can on what components do what and how various combinations and value changes affect the sound. I mean... I can look at RC Time Constants and graphs and do the math all day, but that doesn't really tell me much in terms of the sound coming out of the speaker. But I have a good starting point.

I play modern prog rock and metal. So I'm not after the VH sound at all. I like a really angry, pissed off high-gain sound. Tight low-end. Smooth highs. Pronounced, snarly/growly mid range. Definitely NOT after the brown sound...
Since you have a good idea of where you want to start.....I would just build it ...and then tune it to where you want it to be ....then you can hear how the difference in parts will actually effect the end result.....and also the feel of the amp. Doing all the math and all that really won't give you useful end results....at least for me ....haha....for me it's always been better to just make it and then grab the guitar and play and swap parts and see where I can go with it....plus you can really hear what each part does and how it effects the overall tone and feel in real time.....which isn't always the same end result for every amp.....

The circuit wasn't made to get the brown sound ...it's way more gain in some ways then Eddie used. Eddie's tone was mostly a stock amp and the way he set it up .....using Marshall's and other amps to be power amps to the loaded down and variac'ed main Marshall.
Yup, I guess I'm gonna have to tinker a bunch. Will probably invest in some decade boxes so I can swap values of various components back and forth quickly. One thing I'm sort of stuck with is the iron. I went with Marstran 1202-55 power transformer (350-0-350v) and an O'Netics "Retro M" output tranny (3.4K) just to see what it's all about. Haven't decided on a choke yet. But probably a 5H of some sort.
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