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Thread: fender prosonic output transformer

  1. #1
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    fender prosonic output transformer

    Hi all

    Ive been asked to change a output transformer on Fender Prosonic ( USA model 110v customer using a stepdown transformer ) Customer has given me all the parts inc a and some info

    Speakers were wired in series 16ohm now rewired for 4ohm ( as request)

    The info sheet ive been given seem to be that you change the wiring of the transformer in the unit at present.Not replace it, But its badly worded

    Black
    green
    yellow/green
    Yellow ( Not used )

    Now i have a repalcement output tx ( ZOT 60 9961104 ). The customer wants it changed. as he has been told it will change the sound!
    Black
    Purple
    Green
    Yellow

    The info sheet also says that i got to change 1 x filter cap .. but dont say what one!! any ideas?

    The amp still has stock filter caps in which i will try and get him to pay for a cap change.

    While it is on the bench any other parts worth changing/Upgrading

    many thanks

    BBB

  2. #2
    Senior Member Enzo's Avatar
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    Um... Just what is happening?

    The guy asked you to change his output transformer? Was the old one defective? Or did he want a "better" one? In which case he was HOPING for a better sound, ie different sound. But now he DOESN'T want a new one because it will change the tone? What am I missing?


    I am guessing you did not get an actual fender Prosonic output transformer and are instead using some sort of aftermarket type?

    If you replace a transformer with a different brand, they may use different color wires. So you may have to change the wiring colors, but the plate lerads still go to the tube plates, the 4,8,and 16 ohm taps would wire to the same places. etc.

    I genuinely have no idea why you would need to change a filter cap to replace a transformer. WHy would that be needed? Perhaps if you posted or linked us to that data sheet...

    I don't "upgrade" parts for no reason. I do it with a specific goal in mind. What specific issues would you want to address in the amp by changing parts?
    Education is what you're left with after you have forgotten what you have learned.

  3. #3
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    Hi Enzo

    Im unsure where he got the tx from but the box it came in came from the us post service. I think he's been sold the tx when he dont need it. The info sheet just talks about making it usable with a 4 ohm load. Nothing about changing the tx. I didnt have a clue on the filter cap either. I will speak to him tomorrow about this.
    When i was helping him bring in the amp to the workshop and he said it will change the tone. I did think WTF... But i was busy giving bass guitar lesson. Didnt want to discuss it
    When i said changing/upgrade. I was refering to any parts that is worth changing as i think the amp was make in either 1990 or 1999. I just read posts on here about other fender combos. anyway its 1am over here in freezing south of england..( Should be warm, but it aint ) I'm off to bed to dream of anything but valve amps

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    I often dream of amps... For better or worse Sometimes it's because I have a new idea. And sometimes it's because I'm pressed on a paid project. But I digress.

    Like Enzo, I think it's important to be clear about the customers goals. If the customer wants improved tone, but doesn't want to change the tone, they need a shrink, not a transformer. And you probably don't want to be the tech involved as this persons illusions disintegrate into reality. You might get paid, but you'll feel like you need a shower afterward.

    I've read about guys seeking out Prosonic OT's for personal builds. It's my understanding that it's a very good sounding and reliable transformer. Bruce Zinky (the Prosonic designer) thought that the weak link in that amp was that it only sounded good with certain speakers. Well what amp doesn't? If the amp is in good working order I think there may be more benefit to experimenting with different speakers than in changing the OT. I did have a Prosonic combo for a time when they were new on the scene and I DIDN'T like the speakers that came stock in the amp. The speakers that seem to work well seem to be somewhat boxy with other amps. I played mine through a sealed back 2x12 with a pair of Celestion G12M70's. Not the best speakers with many amps. But great with the Prosonic. Something like the Eminence 1058 is a boxy 10" speaker but with good bottom end. The extra bottom would work well for a combo type amp. And they're fairly efficient. Which seems to add a little dynamic feel IMHE. Your customer sounds confused and befuddled by hype and desire. Good luck.
    "I should have been born sooner. Of course, if I had been, I might be dead now." trem

  5. #5
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    Hi all
    Ive spoken to the customer about this and he said that the info he has been given has come all the way from Bruce Zinky himself. Ive been forwarded an email from him
    Both the speakers are celestion One has been replaced for a G10 the other is the original
    Customer did also say that he has tried one with an upgraded transformer and it was much better sounding, Thats all he said. He wants me to go ahead with the change. so ill have to do it.
    I advised him not to have it done. But He's paying.. Did say he would be better off replacing the bad set of o/p tubes and all the filter caps as its was made in 1990

    He has agreed to the recap and revalve. But still wants the tx changed along with a few other mods that bruce advised
    He also has brought a Zinky blue velvet amp in for check and a couple of mods.

    email from Bruce

    I would change the stock transformer to our Zinky unit, model
    ZOT604816. This transformer will give much better bass response than
    the original, AND the overdrive will not have any of the "Buzzy" or
    "Fizzy" character you may hear with the stock one (Especially at low
    volumes. Clean tones will be bright and airy, the big changes will be
    on overdriven tones). Does not fit the standard bolt pattern (Slightly
    larger), so you'll have to drill. $150 but well worth it. Has 4/8/16
    Ohm taps. Will give you the liquid overdrive even at highest gain
    settings, even with high treble settings. Get dynamics AND tone....

    Bruce Zinky

    thanks again for your help on this. Its the weekend here and the sun is shining a rare thing in the uk at the present. Amps can wait til monday

    BBB

  6. #6
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    I met Bruce at the 2009 NAMM show. He's a little odd. But I really like the Prosonic design so I overlooked that. It may be that the production amps had puny transformers. I had a custom shop amp and I seem to remember reading something about that.

    Quote Originally Posted by blindboybenton View Post
    Its the weekend here and the sun is shining a rare thing in the uk at the present. Amps can wait til monday

    BBB
    I hear ya. Spring is opening up SLOW here in costal Washington state. Looks like another drizzly day for me. So I'll be working on amps. Enjoy the sunshine.
    "I should have been born sooner. Of course, if I had been, I might be dead now." trem

  7. #7
    Supporting Member Jazz P Bass's Avatar
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    Alright.
    I'll bite.
    What is "liquid overdrive"?
    It's a friggin guitar amp for crying out loud.

  8. #8
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    Quote Originally Posted by Jazz P Bass View Post
    What is "liquid overdrive"?
    Rehydrated powdered overdrive.
    "I should have been born sooner. Of course, if I had been, I might be dead now." trem

  9. #9
    Supporting Member Alex R's Avatar
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    Quote Originally Posted by Jazz P Bass View Post
    Alright.
    I'll bite.
    What is "liquid overdrive"?
    It's a friggin guitar amp for crying out loud.
    Quite. It's probably creamier and browner too. So is bullshit.

  10. #10
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    Ok, ok... Let's be fair. Bruce is a pretty well respected designer with some very eloquent and effective circuits to his credit. By "liquid overdrive" I interpret that all the attributes of the EQ post clipping, sag vs. dynamics, crunch vs. smooth, etc. blah, blah, should compliment rather than oppose each other. That is, Bruce wouldn't consider a clipped tone that is spikey and harsh "liquid". C'mon guys. We all use terms that don't have specific definitions sometimes. That's because there aren't any specifically designated and layman understood terms to describe clipping. But I'll hope to be enlightened by any offerings.

    Words that seem to be consistently understood might be limited to: compressed, bright, dark, buzzy and farty. After that you see a lot of words that are even more subject to personal interpretation like: smooth, chunky, creamy, searing, gritty, ugly, thin, harsh, boomy, crunchy and dynamic (whatever that's supposed to mean to a clipped signal!?!).

    When trying to describe how one feels about what they hear a reference to asymmetry, cold biased stages, peaks, recovery times or waveforms are basically useless. So it's easy to bash someone for not committing to technical accuracy when communicating to a lay person, but frightfully hard to achieve it for ones self.

    Let he is without sin cast the first lead clippings, solder drops, wire bits and insulation strippings.
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    Well mamy thanks on all your words of wisdom

    I will be revalving and doing the recap when parts arrive tuesday.and ill do the tx change then too. I will update you all with the feedback from the customer when he comes over to pick it up
    Im hoping all the mods ive been asked to do and tx change is to the customers liking.. Oh well they were all his idea

  12. #12
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    Hi all

    Just thought i would give you all an update

    The customer was happy with the sound though his prosonic with a new output transformer. Sounds alot better. The old transformer had been wired up for a 4 ohm output,
    But the speakers were still wired for 16 ohm. Rewired speakers and repalced tx and replaced all filter caps and all the 100uf 100v. Will the other mods he asked me to do it sounds great !
    Oh well he's paying. I think it sounds better more because it has had a service !!!!! instead of a new and better output transformer

    BBB
    Chuck H likes this.

  13. #13
    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by blindboybenton View Post
    The old transformer had been wired up for a 4 ohm output,
    But the speakers were still wired for 16 ohm.
    What a shaggy dog story!

    You have to wonder whether the customer would have been satisfied had this minor matter of mismatch been resolved. But he bought the Zinky story (and transformer + shipping to old Blighty) and spent way way more than he need have. Nonetheless it looks like it's smiles all around. Zinky sold a transformer, you made some money, and the amp owner is a lot happier with his tone.

    Hope your weather reports improve to 25C, light breeze and fine fine fine.

  14. #14
    Supporting Member Dave Curtis, dB AudioTech's Avatar
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    FWIW, I replaced the OPT in my '76 Pro Reverb with a Pro Sonic OPT which was a bit bigger and more versatile (4-8-16Z). Much better bass response.

  15. #15
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    +1
    But... Did Prosonics come with different transformers? Mine was a custom shop made amp from the early production. Did products from other locations have a different tranny? I don't know. But I do know that Prosonic transformers have been somewhat popular with people building other amps. So the stock OT, if all things are created equal, are considered good.
    "I should have been born sooner. Of course, if I had been, I might be dead now." trem

  16. #16
    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Dave Curtis, dB AudioTech View Post
    FWIW, I replaced the OPT in my '76 Pro Reverb with a Pro Sonic OPT which was a bit bigger and more versatile (4-8-16Z). Much better bass response.
    +1 more now. I always recommend to those who have amps with the A6A transformer to replace it. It's the one Fender transformer I've replaced more frequently than any other, due to failure. They're in Pro Reverbs, Vibrolux Reverbs, Bandmaster, Bandmaster Reverb, maybe some others. Usually I use a universal Bassman/Super-Reverb 4/8/16 from either Magic (Ruby) or Hammond. Similar improvement to using a Pro Sonic OT I'm sure.

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