New Amp Build
Moderators: pompeiisneaks, Colossal
Re: New Amp Build
Looks great! Is it a hot rodded Marshall topology? How does it sound?
Re: New Amp Build
Okay, the details. Like I said, it is just a few tweaks but some that I think are very important.
The power supply:
375v B+ -- this is important. The later 50w Marshalls raised the voltage up to 460 or so and this really affects the sound.
20K resistor between the screen supply and the PI node (this is often a 10K in the later amps). Neither of these are really tweaks but more of a return to what the early models had.
The power amp:
100K bias feed resistors.
100p across the plates of the PI.
change the 470R and 10K in the PI to 820R and 15K, respectively.
old style presence, which is a 5KL and a .1uf cap with the 5K of the pot as the connection for the 15K/.1uf to ground (there is no 4K7 resistor).
47K NFB going to the 16 ohm tap.
The Pre amp:
Standard 2204 with the following changes,
There is no "LO" input.
100p from plate to cathode on the first gain stage (the one with the 2K7/.68uf).
1M resistor from the wiper to ground on the 1M gain pot. This helps to tame the muddies that a 2204 gets when the gain is turned way up. It doesn't affect the overall available gain. The .001uf brite cap on the pot is there, it is important.
The section after the second gain stage but before the gain stage that drives the cathode follower:
remove the 500p treble peaking cap.
add a 27K grid stopper to the grid of the gain stage that drives the cathode follower. (I had a 27K and not a 33K--there wasn't any rocket science going on here for that value, LOL).
So, this section is just remove the treble peaking cap and add the grid stopper.
The mode switch:
It just switches in a 100K resistor in parallel with the 470K voltage divider resistor going to ground in the aforementioned section. With the switch on, it is about 68K to ground instead of 470K. It cuts the signal down to about unity gain for that second gain stage. It isn't perfect plexi but it is really close.
Naturally, I am biased because I built the amp and I am awesome and my poop doesn't stink, but, I do think this is a really sweet sounding amp. It's a keeper for sure.
There are also other factors such as component selection, wiring, etc. One thing I would mention is that I used PEC pots and I do think they are worth the money. I used mustard caps too--do they add to the tone? In my mind they do. I had them so I used them. The RN65's add to the tone too because they are rounded on the ends like the mustard caps--that helps for that full, round bodied tone.
I would also add that the 100p caps I mentioned are not to tame errant oscillations or to "fix" anything, but are chosen for tone shaping.
That's about it.
The power supply:
375v B+ -- this is important. The later 50w Marshalls raised the voltage up to 460 or so and this really affects the sound.
20K resistor between the screen supply and the PI node (this is often a 10K in the later amps). Neither of these are really tweaks but more of a return to what the early models had.
The power amp:
100K bias feed resistors.
100p across the plates of the PI.
change the 470R and 10K in the PI to 820R and 15K, respectively.
old style presence, which is a 5KL and a .1uf cap with the 5K of the pot as the connection for the 15K/.1uf to ground (there is no 4K7 resistor).
47K NFB going to the 16 ohm tap.
The Pre amp:
Standard 2204 with the following changes,
There is no "LO" input.
100p from plate to cathode on the first gain stage (the one with the 2K7/.68uf).
1M resistor from the wiper to ground on the 1M gain pot. This helps to tame the muddies that a 2204 gets when the gain is turned way up. It doesn't affect the overall available gain. The .001uf brite cap on the pot is there, it is important.
The section after the second gain stage but before the gain stage that drives the cathode follower:
remove the 500p treble peaking cap.
add a 27K grid stopper to the grid of the gain stage that drives the cathode follower. (I had a 27K and not a 33K--there wasn't any rocket science going on here for that value, LOL).
So, this section is just remove the treble peaking cap and add the grid stopper.
The mode switch:
It just switches in a 100K resistor in parallel with the 470K voltage divider resistor going to ground in the aforementioned section. With the switch on, it is about 68K to ground instead of 470K. It cuts the signal down to about unity gain for that second gain stage. It isn't perfect plexi but it is really close.
Naturally, I am biased because I built the amp and I am awesome and my poop doesn't stink, but, I do think this is a really sweet sounding amp. It's a keeper for sure.
There are also other factors such as component selection, wiring, etc. One thing I would mention is that I used PEC pots and I do think they are worth the money. I used mustard caps too--do they add to the tone? In my mind they do. I had them so I used them. The RN65's add to the tone too because they are rounded on the ends like the mustard caps--that helps for that full, round bodied tone.
I would also add that the 100p caps I mentioned are not to tame errant oscillations or to "fix" anything, but are chosen for tone shaping.
That's about it.
Last edited by Jana on Thu May 17, 2012 11:46 pm, edited 1 time in total.
Re: New Amp Build
Colossal,
No, this isn't my hot rod Marshall--this is very close to a stock amp. I think this amp is really sweet. But, like I said, I am a bit biased. It would be cool if some other member could play it and give an unbiased review--Mark? are you there? We don't live that far apart--I can drive them over one afternoon.
No, this isn't my hot rod Marshall--this is very close to a stock amp. I think this amp is really sweet. But, like I said, I am a bit biased. It would be cool if some other member could play it and give an unbiased review--Mark? are you there? We don't live that far apart--I can drive them over one afternoon.
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LeftyStrat
- Posts: 3117
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- Location: Marietta, SC, but my heart and two of my kids are in Seattle, WA
Re: New Amp Build
That truly is a work of art!
I'm off to learn cable lacing...
I'm off to learn cable lacing...
It's never too late to have a happy childhood.
Re: New Amp Build
Thanks Lefty!
Re: New Amp Build
Ha!Jana wrote: What do you call that red stuff? Paint!
I remember when I was in my Marshall phase and hung out at the Metro forum, there is indeed a special thread locker that Marshall used but I can't remember the trade name.
But I'm sure any lacquer based paint or even finger nail polish would work.
As well as some Lock-Tite products.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: New Amp Build
I'm in Minnesota so I'm safe.
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Reeltarded
- Posts: 10189
- Joined: Sat Feb 14, 2009 4:38 am
- Location: GA USA
Re: New Amp Build
It is an amazingly clean build, and I bet it does sound very good.
I want to do one with some Angela caps, and Takman or Dales.. or something different.. not Rikens though! They hurt my eyes.
I want to do one with some Angela caps, and Takman or Dales.. or something different.. not Rikens though! They hurt my eyes.
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
Re: New Amp Build
Jana,
Great looking build and I'm glad your enjoying that amp!.
I would love to see the amps but it will have to be when I feel better, not sure if the flu is justing continuing or if I have other problems, docs don't know.
I love the tone of a 2204 one of my favorites. The next favorite is the JTM50 EL34's.
Mark
Great looking build and I'm glad your enjoying that amp!.
I would love to see the amps but it will have to be when I feel better, not sure if the flu is justing continuing or if I have other problems, docs don't know.
I love the tone of a 2204 one of my favorites. The next favorite is the JTM50 EL34's.
Mark
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The New Steve H
- Posts: 1047
- Joined: Mon May 30, 2011 11:24 pm
Re: New Amp Build
I think it would be worth it to get a big piece of aluminum and put a bunch of holes in it and use it for "breadboarding" new amps. Seems smarter than taking a chance on ruining a new chassis every time. Actual breadboards don't seem too useful for tube projects.
You could put five or six noval-size holes in it, plus at least five octal holes, and you'd be ready for nearly anything.
You could put five or six noval-size holes in it, plus at least five octal holes, and you'd be ready for nearly anything.
Relax. It's SUPPOSED to smoke a little.
Re: New Amp Build
Mark,
Let me know when you are feeling better and feel like a doing some amp sniffing. I am curious to check out some of your creations as well.
Let me know when you are feeling better and feel like a doing some amp sniffing. I am curious to check out some of your creations as well.
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martin manning
- Posts: 14308
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: New Amp Build
Jana, can you tell me more about the lower B+ voltage- what did you use for a PT? Looking over Mark Huss' 2204 schematic with voltages I saw 468V for a 1983 production amp. Replacement PT's are 345-0-345 which would more or less square with that. The reported 3k6 Zpri and that voltage seems like it would be pretty hard on the EL34's.