67mike
Well-known member
JCA are cool amps. Wish I still had my 22H, that was a real firey little guy after I swapped out all the stock tubes.
Shask
Well-known member
I have a JCA100HDM that I modded completely into a SLO, and I also moved the loop to the normal spot and added a master volume. Thing sounds awesome, and also makes a great poweramp for other preamps.
RedPlated
Well-known member
I’d have to go through schematics again but there are some differences in the Rectifier preamp.
The difference I think of first is the 5000pf capacitor from B+ to ground off of the second stage plate resistor. Really cuts highs.
Recto also has a 20pf snubber cap from the second stage grid to ground.
Recto orange treble cap is 500pf vs 470pf in SLO. It does make an audible difference. And red channel treble cap is 680pf.
Rectifier has 30uF preamp filtering. SLO is 10uF.
Orange channel in vintage mode is closest to SLO. It adds negative feedback with a 47k NFB resistor. SLO has a 39k NFB resistor. Recto uses 8 ohm tap. I forget which tap the SLO is using but that can make a difference as well.
Modern mode lifts the NFB so it’s brighter, louder and more raw.
The difference I think of first is the 5000pf capacitor from B+ to ground off of the second stage plate resistor. Really cuts highs.
Recto also has a 20pf snubber cap from the second stage grid to ground.
Recto orange treble cap is 500pf vs 470pf in SLO. It does make an audible difference. And red channel treble cap is 680pf.
Rectifier has 30uF preamp filtering. SLO is 10uF.
Orange channel in vintage mode is closest to SLO. It adds negative feedback with a 47k NFB resistor. SLO has a 39k NFB resistor. Recto uses 8 ohm tap. I forget which tap the SLO is using but that can make a difference as well.
Modern mode lifts the NFB so it’s brighter, louder and more raw.
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fusedbrain
Well-known member
I was hoping you would chime in lol!
As that 5000pf cap goes from the B+ side of the plate resistor to ground, and is not connected to the tube side of the resistor, I was expecting it to be a B+ ripple cap, and not a high frequency snubber. I'll have to experiment with this.
The 20pf snubber is the other component I mentioned in my first post. The low pass filter created by the 470k resistor and the 20pf cap has a center frequency of 16.9Khz, so I considered it insignificant to the tone of the amp. Again, I'll have to experiment with this.
The craziest thing about the recto's in my mind is the total absence of negative feedback in modern mode.
As far as I know, every other high gain amp uses rather large amounts of NFB in the power section.
The recto's in modern mode have NONE, and it sounds F'n great!
Go figure....
BABMusic
Well-known member
Randall Smith said this year that he wanted to change the preamp section but everyone else at Boogie liked it the way it was with the power amp. So in other words, he didn't deny it and gave credit to Mike. I know that later on it did change more and more, but it still has that recto thing.
RedPlated
Well-known member
I was hoping you would chime in lol!
As that 5000pf cap goes from the B+ side of the plate resistor to ground, and is not connected to the tube side of the resistor, I was expecting it to be a B+ ripple cap, and not a high frequency snubber. I'll have to experiment with this.
The 20pf snubber is the other component I mentioned in my first post. The low pass filter created by the 470k resistor and the 20pf cap has a center frequency of 16.9Khz, so I considered it insignificant to the tone of the amp. Again, I'll have to experiment with this.
The craziest thing about the recto's in my mind is the total absence of negative feedback in modern mode.
As far as I know, every other high gain amp uses rather large amounts of NFB in the power section.
The recto's in modern mode have NONE, and it sounds F'n great!
Go figure....
Yeah that 5000pf cap does definitely cut high end out. I usually reduce the value. Too large for my liking.
The lack of NFB sure is wild sounding. I add a a NFB control that functions on orange/ vintage only. I use a decent sized pot so you get close to no NFB with the control all the way up.
stephen sawall
SEMI ERECT MEMBER
Mike offered to modify my Tremoverb 30 years ago. We talked about this back then. He mentioned he had borrowed from Mesa first. He didn't mention what he borrowed. He really liked the sound of the Tremoverb. Randy offered to modify my Tremoverb 10 years ago. He mentioned he was looking into copyright of sounds.
The Tremoverb is still stock. I have done more gigs with this amp than any otheŕ.
The Tremoverb is still stock. I have done more gigs with this amp than any otheŕ.
