Rocktron Plexi afterburner feature - Tried something new

mourguitars

Platinum Supporting Member
Messages
322
Havent had time to look over the Plexi schematics due to work but i do plan on playing this weekend . I have the unit dialed in great and like the sound but i may try swapping a 7025 in there ...have plenty of those. Thats pretty easy

I really dont use the afterburner on the Plexi at all so, I use my JMP-1 for more a compressed gain , i do use it on the Black Plate tho on the suggested settings in the manual. Im going to try the Kingsley Jouster into the Back plate for a little more gain...other than clean i havent played around with that pre amp that much....Break out the Strat

Mike
 

okgb

Member
Messages
27
Well, I was busy and did just finish drawing out the Black Plate's schematic.
Those of you who also have the Black Plate: Are you also kind of not being satisfied to get a good Fender sound as I am? I tell you the reason why ...

Believe it or not: The Black Plate's schematic and signal flow is absolutely the same as the Plexi o_O
The circuit-bord is the same, the designation of the components is the same, and so on.
The only difference are some lightly different values here and there - for example 1,5 kOhms instead of 2,7 kOhms.

The Black Plate is far away from being a Fender schematic. The EQ sits at the end of the signal chain as it is in a Marshall (or early Tweeds). In a Blackface Fender the EQ sits usually after the first gain stage, which is an important thing.

Once again, both preamps are basically the same, except a few value differences, which results in a different behavior.

Now knowing about this, it is funny to watch that Namm-show video again, where that guy talks about "everything from Tweed to Deluxe to Mesa" ... :(

Yup Having both of them and after looking inside and seeing only the slope resister change and a couple caps added to the plexi I wondered if they had the gall to try to pass this off. it's like someone calling you stupid.
Although I couldn't tell where the tone controls were they looked in the same place, maybe they would say it's an old bassman circuit! . Maybe thats why the Vox one never came out?
 

okgb

Member
Messages
27
Let us know if you have any success with moving the Black plate tone stack , it appears to be on a separate pcb so doable? One thing that bothered me [ and tipped me off ] was that the black plate has too much gain, or not enough clean range on the gain control. It's annoying because I have to switch outputs if I'm trying to get a clean sound out of it. moving the tone stack would cut some of the gain off the top, if the boost stage is not in front of it.

If someone has " official " Rocktron schematics should be ok to post those ? [ or sent to me please ]
 
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DirtyHarry

Member
Messages
26
Let us know if you have any success with moving the Black plate tone stack , it appears to be on a separate pcb so doable? One thing that bothered me [ and tipped me off ] was that the black plate has too much gain, or not enough clean range on the gain control. It's annoying because I have to switch outputs if I'm trying to get a clean sound out of it. moving the tone stack would cut some of the gain off the top, if the boost stage is not in front of it.

If someone has " official " Rocktron schematics should ok to post those ? [ or sent to me please ]
Yes, I had success with moving the Black Plate's tone stack from the end of the schematic to after the first gain stage - like it is in the Blackface or Silverface schematics.
It doesn't requier a separate pcb. Just changing the signal flow by moving some cables.
The sound goes much more in a Fender direction than before.
The gain is quite less compared to before, but still enough to crunch it up. I don't expect more gain from a Fender.

I will rework my raw drawings and then post them here.
 

okgb

Member
Messages
27
As dirty Harry mentions the master is before the last gain stage, not a bad way to do as the output impedance remains constant but plenty of companies pedals & amps tack on output pots on the end of the circuit as more or less standard. One could use a duel concentric pot in the master position or relocate the power switch and use that hole for an over all output master. Maybe the extra drive will not be that dramatic or make a big useable difference but in my case It will allow me to stop having to switch outputs from line to Instrument [ especially on the black plate ] When I get a little more info I'll start a general valvesonic " Mods " thread. Thanks D.H.!
 

okgb

Member
Messages
27
Yes, I had success with moving the Black Plate's tone stack from the end of the schematic to after the first gain stage - like it is in the Blackface or Silverface schematics.
It doesn't requier a separate pcb. Just changing the signal flow by moving some cables.
The sound goes much more in a Fender direction than before.
The gain is quite less compared to before, but still enough to crunch it up. I don't expect more gain from a Fender.

I will rework my raw drawings and then post them here.
Excellent! You wonder why Rocktron [ or whoever ] didn't simply do that themselves in the first place since there's a ton of jumper wires and separate pcbs and it seems like a modular concept anyway. Look forward to seeing that mod!
 

DirtyHarry

Member
Messages
26
As dirty Harry mentions the master is before the last gain stage, not a bad way to do as the output impedance remains constant but plenty of companies pedals & amps tack on output pots on the end of the circuit as more or less standard. One could use a duel concentric pot in the master position or relocate the power switch and use that hole for an over all output master. Maybe the extra drive will not be that dramatic or make a big useable difference but in my case It will allow me to stop having to switch outputs from line to Instrument [ especially on the black plate ] When I get a little more info I'll start a general valvesonic " Mods " thread. Thanks D.H.!
BTW: The difference between line and instrument outputs are just 2 resistors. Life is easy ...
 

okgb

Member
Messages
27
right, I'm thinking for my black plate I replace that second resister to ground with a pot for the over all master?
[ which would be on the line out only ]
 
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DirtyHarry

Member
Messages
26
right, I'm thinking for my black plate I replace that second resister to ground with a pot for the over all master?
[ which would be on the line out only ]
The resistor to ground at the inst output is R49 (2,7k). When replacing it with a pot, the pots value should be the same. Otherwise it will have an influence to the line output level also.

But why not deciding for an outboard master pot in a small alu case?
You'll save some work, keep the unit untouched without additional drill holes and it has no value lost in case of selling it.
 

El Rey

Double Platinum Member
Messages
2,231
I admire all you great minds that have the curiosity and patience to run all those rabbit holes.

I marvel even more that all that can make enough difference to stay at it.

Interesting thread........good stuff. :aok
 

DirtyHarry

Member
Messages
26
Ok...
Well, I have reworked the original schematics of the plexi and the black plate with the right/real values of components. I also have a separate schematic of the black plate with the mods I did.
As I don't know how to attach files at this forum, everbody who is interrested can give me his email and I will send the schematics directly
 
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mourguitars

Platinum Supporting Member
Messages
322
Ill see if this works below Dirtyharry ...if it works ill put in my dropbox for you...cool

Test...Rocktron Schematics Original below


 

mouzer

Member
Messages
1,139
I haven't seen those schematics available anywhere else, that would be a great resource for us Valvesonic users!
 




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