Gain Question

Marshall Amp Discussion

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lpd
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Gain Question

Post by lpd »

On a Marshall 50 watt Plexi build I noticed the bright/normal gain seems to max out at about 10:00 on the pot from there on no more gain just a little compression. Is this typical of a 50 watt circuit?

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M Fowler
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Re: Gain Question

Post by M Fowler »

Maybe those mixer resistors are loading it down?

220k verses 470k.
pdf64
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Re: Gain Question

Post by pdf64 »

I dont see how that layout could be a plexi? It looks more like a mid 70s 2204 with a single input and switched channels http://schems.com/schematicheaven.net/m ... _2204u.pdf
A schematic would save a lot of effort in trying to work out exactly what you've got there.

Gain, overdrive, compression and power output are different things.
Can you review your terminology and re-phrase?
sluckey
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Re: Gain Question

Post by sluckey »

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pompeiisneaks
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Re: Gain Question

Post by pompeiisneaks »

I was gonna say "That sure looks like one of Steve's amazing layouts" :P

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lpd
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Re: Gain Question

Post by lpd »

pdf64 wrote: Thu Oct 26, 2017 11:11 am I dont see how that layout could be a plexi? It looks more like a mid 70s 2204 with a single input and switched channels http://schems.com/schematicheaven.net/m ... _2204u.pdf
A schematic would save a lot of effort in trying to work out exactly what you've got there.

Gain, overdrive, compression and power output are different things.
Can you review your terminology and re-phrase?
Good question. Lots of volume on this amp and on Plexi input compressed decent. What I do notice is with the gain pot all of the crunch is given up at 9:00-10:00 on the pots. After that not much more gain or volume for that matter just a little more compression. This amp has a double master (pre Pi and post) if I drive the pi beyond 10:00 on the pot the amp gets hazy or hallow like in tone (no matter how I adjust the post master pot). At loud volumes both masters at about 5-6 on volume it has great tone just not a lot of gain like a jcm800.
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Littlewyan
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Re: Gain Question

Post by Littlewyan »

For the plexi sound you need to dime that pre pi master. Have you definitely used log taper pots? You should notice the plexi channel being a bit thin at lower gain levels and getting fatter as you crank it.

Also if you leave the JCM800 channel connected it might take some of the high end off. Try disconnecting it temporarily to see how it sounds. Might get brighter.
lpd
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Re: Gain Question

Post by lpd »

Littlewyan wrote: Sat Nov 04, 2017 4:09 pm For the plexi sound you need to dime that pre pi master. Have you definitely used log taper pots? You should notice the plexi channel being a bit thin at lower gain levels and getting fatter as you crank it.

Also if you leave the JCM800 channel connected it might take some of the high end off. Try disconnecting it temporarily to see how it sounds. Might get brighter.
I figured this out...pi has huge impact on overall tone and gain on this amp. I noticed that on the pre pi master the amp gains up quickly and after four on the pot it gets abit ragged.
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Littlewyan
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Re: Gain Question

Post by Littlewyan »

Ragged in a bad way?
lpd
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Re: Gain Question

Post by lpd »

Littlewyan wrote: Wed Nov 08, 2017 11:53 pm Ragged in a bad way?
May be unrealistic expectations here. I drop post master to next to mother omg and pre Pi master is good up till 4 ish then gets hollow sounding if I bring in postbox master it becomes more defined and of course louder :) I’m assuming the two masters have a relationship with how they interact with each other :)
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sonicmojo
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Re: Gain Question

Post by sonicmojo »

I made a higher gain Marshall 18W amp with both masters. I had the same blow out problem with the Pre-PI-Master.

Then when I was experimenting with the Friedman Dirty Shirley values, I found that the voltage divider on the first lug of the pre-PI-Master really smoothed out the sweep and made it more useable all the way around. In fact, I really don't use the Post PI Master at all now on that amp.

You could try it. I think it was (ground/PI) 1M/220K for the 40Watt and 220K/560K for the Mini but you can experiment with different values. I'd start with the 1M/220K and move from there. I don't know what value pots are on the Friedman but I was using 1MA for the pre-PI-Master.
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Littlewyan
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Re: Gain Question

Post by Littlewyan »

I think you need to play that amp flat out like you would a normal plexi. If it sounds good like that, then we need to look at your Post PI Master Volume Control.

Turn both master volumes up to 10 and see how it sounds then.

I personally don't like the Post PI Master Volume Control in my amps. I tried it once and couldn't get it to sound right. So I use an attenuator instead.
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