Prosonic suppression cap excision

Discussion in 'Amp Central Station' started by jondanger, Dec 29, 2018.

  1. Wally

    Wally Telefied Ad Free Member

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    Jon, if I had a beater Pro Sonic, perhaps I would not mind drilling holes in the chassis. My Pro Sonic is pristine. If I did such a thing, I would want a separate switch for each cap.
    As for volume issues, that is where those three modes of operation available with that switch on the back could come in handy. Depending on whatone wanted the amp to do, one would select from those three modes. For 8nstance, unless I were looking for pure clean at volume, I might never get into that 60 watt mode. The distortion comes on so much earlier in that 30 watt mode that for lower volume situations, that is probably where I would run the amp. Ommv.
     
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  2. jondanger

    jondanger Poster Extraordinaire

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    I like using input 2 with hotter pickups as well. It’s pretty significantly attenuated.
     
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  3. Wally

    Wally Telefied Ad Free Member

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    Different strokes for different folks. I don’t like running the amp up just to hit that input stage with a weak signal.
     
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  4. JDB2

    JDB2 Tele-Meister

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    Lately with my Prosonic head I've been doing exactly that. Running gain 1 at about 3 and gain 2 between 3 and 5 (translation - a lot of gain) and rolling volume back on my guitar. I use the guitar volume and tone as additional gain controls ahead of the amp and have amazed at the tones I can cover with those two knobs. And like jondanger I often use input 2 with hotter pickups.

    As for brightness and sparkle I'm convinced for my purposes the Prosonic (head) is perfect as is. Lately I've been running a 1x12 open back cabinet with a Celestion Cream 90 watt alnico and found its a match made in heaven. I found there is a lot of high end information in the signal from my Prosonic once I was using a speaker capable of some precision in reproducing it.

    Also I have a second Prosonic head that was modified by the original owner to tame the gain and increase the treble and whenever I play it I find it sounds great at first and then soon I'm missing the subtleties of the stock unit.
     
  5. tonejam

    tonejam Tele-Meister

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    I'm using the Morley Effects Loop Correcter, and it does what's needed. No batteries, and I have it velcroed permanently on the back panel in the amp.

    Not cheap, but problem solved!
     
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  6. tonejam

    tonejam Tele-Meister

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    Does removing C103 affect clean and overdrive modes?

    Also, does removing C7 affect both modes?
     
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  7. Wally

    Wally Telefied Ad Free Member

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    C301...correction edit....is on the input stage and therefore is part of both modes. C7 is on the second added gain stage in the
    Gain mode and therefor is in the circuit only in the lead mode.

    JDB2, I have only been around one Pro Sonic Head. That Head was much different from the combos that I have owned or heard.....less low end. I didn’t get to open that head up to inspect it, so I don’t know if it was stock or not. I just knew that it was thinner sounding...and I did not like it.

    I got to playing through a few amps yesterday....Soldano Hot Rod 50, a build with the Marshall Md. 1987 circuit in a 2 x 10 tweed cab, and my Pro Sonic combo. The Soldano is dark compared to the Pro Sonic. The Pro Sonic is a great amp.....romps and stomps...or goes clean and sweet.
    I am going to run a lower gain tube in V1. I Amy already have a 12AY7 there. If so, I am going to break loose with one of my NOS 12AY7 or even a 6072 for this tube, which has a triode in the clean mode and the other triode in the Gain mode stages. There is plenty of gain everywhere in this amp, and a lower input stage will do it well, imho.
     
    Last edited: Jan 11, 2019
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  8. JDB2

    JDB2 Tele-Meister

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    There is a difference in the coupling caps before the PI that rolls off the bass at a higher frequency in the Prosonic head vs. the combo. That's clearly visible on the schematics. And its consistent with my observation that neither of my heads is what I would call bassy. However I wouldn't call them thin either - at least with right cab. The bass response ranges from almost anemic through rich and full depending on the cab. I've considered replacing the coupling caps to mimic the combo but with the right cab I've been happy with the sound of the stock configuration.
     
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  9. Wally

    Wally Telefied Ad Free Member

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    thanks for the feedback on that, JDB2. I knew there was a difference.....and I ran the amps through the same speakers for an accurate comparison. I have seen the Head schematic only one time and missed that difference.
     
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  10. tonejam

    tonejam Tele-Meister

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    Thanks Wally. Removing C103 sounds like an option, but I don't think I'd risk changing the gain mode.
     
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  11. Wally

    Wally Telefied Ad Free Member

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    Tonejame, I reversed two digits there. That cap is C301...not C103. Apologies.
    And.....C301 affects both modes since it is on the common input gain stage.
     
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  12. JDB2

    JDB2 Tele-Meister

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    jondanger, have you noticed any EQ imbalance between the normal and drive modes after the mods? I suspect Zinky took some care in designing that circuit to keep the drive mode sounding similar to the normal mode, EQ-wise.

    In my modded Prosonic head (with much more extensive mods than yours, though one similarity is C7 is gone), I find it necessary to change EQ when switching between modes, either on the amp, the guitar, or with an outboard EQ. Clean mode is bright and drive mode is much darker. By contrast in my stock Prosonic head, the drive mode sounds just like a distorted version of the clean mode. My hunch is that adding those gain stages and distortion would change at least the perceived EQ, if not the actual EQ necessitating some compensation elsewhere in the circuit. However I don't know enough about electronics to validate my hunch.
     
  13. Wally

    Wally Telefied Ad Free Member

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    JDB2, my stock Pro Sonic requires no EQ adjustments when going from one mode to the other. The Gain mode is brighter than the Clean mode.....as it should be and as all good amps that switch into high Gain do, ime. Low end has to be controlled to keep the ‘mud level’ down, imho. If the amp did not work this way, I would not still own one....one of three I have bought. I kept an LO from 1996 and sold two CR’s that were both built in April, 1997. All three amps had the updates at the factory....original circuits...and sounded exactly alike.
     
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  14. JDB2

    JDB2 Tele-Meister

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    I do hear that the drive mode is brighter and less bassy. Yet the perceived EQ - the character of the sound - is very similar between drive and normal - to me at least. Thus when the gains are set low, for mild to medium breakup, with the original circuit I don't hear a big change in the overall character of the EQ when switching from clean to drive. It sounds like a naturally distorted rendition of the same basic tone and EQ shape. The drive sound achieved is similar to cranking up the clean mode. That the circuit accomplishes that balance, while also achieving a bright and non-muddy drive sound, accounts for a lot of its quirks, and its genius, IMO. It is what makes this amp works so well with switchable clean and drive despite not having two completely separate signal paths. Its successor amps - the Super Sonics - had two separate signal paths, each with separate EQ, and a much more complex circuit, with a resulting increase noise, loss in depth and fidelity, and other undesirable traits, IMO.

    Sorry jondanger about the diversion - always a risk when bringing up the Prosonic . . .
     
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  15. horseman308

    horseman308 Tele-Meister

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    Just to add my $.02, I also find that the drive and clean sound essentially the same, which is one of the big reasons I bough this amp in the first place. Once I get the clean sound I want, I really just want that same thing in overdrive, too.

    Slightly different question, so I hope it's not too far off base: I've been experimenting with running the amp with the volume/gain controls way up, while leaving the EQ controls way down. Essentially, turn off all the EQ's, turn up the volumes to about 5-6 on the dial and then slowly crack the EQ's until I get the tone and volume I want. Usually that leaves treble and bass around 2-3 on the dial and mids around 1-2. I seem to get more flexibility in fine tuning the volume controls and warmth without it getting flabby. I wonder if this really does anything to drive the power section more, or if I'm just fooling myself.

    Sent from my SM-G930P using Tapatalk
     
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  16. Wally

    Wally Telefied Ad Free Member

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    IMe, one can run the tone controls anywhere on likes them at any volume/gain settings with no flab.
    That is the nature of the topography that was born in the 5F6A/5F8A Fenders. BF circuits don't act this way.....but any amp with the 2+1 topography does....the big Fender Tweeds, the Marshalls that were built on that basic platform, and all amps that evolved from that....Soldanos, Peavey 5150/6505, Boogie Triple rectifiers, Fender Blues/Hot Rods. Peavey modern Classics. Even when you drop in the extra two gain stages in the Pro Sonic...or three in the Soldano SLO/Hot Rods and the copycats of that design such as the Triple Rec...the tone stack follows all of the gain stages....and it acts differently than does the BF topography where the tone stack sits between the first two stages.
    So, find what gets it done for you and use it....right? The one exception on adjustments for this on the Pro Sonic is that Gain 2 knob, ime. I don't care for what goes on at the extreme end of that midrange boost circuit....it gets a bit out of hand for my ears past 7-8.....and by that time the amp is very overdriven and...as the manual says...compressed. that Gain 2 is not a tube circuit gain stage. It is a midrange boost using
     
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  17. JDB2

    JDB2 Tele-Meister

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    I've heard about that technique before. It has been awhile since I looked at the schematic and I'm no techie, but I will say that because both volume controls, the gains, and tone stack all come before the phase inverter I don't see how you could be driving the power section more by keeping volumes high and tones low. You are probably just shifting around the points within the preamp where the most gain is applied. But if you like the result, that's what what counts!
     
    Last edited: Jan 11, 2019
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