Fender Prosonic SERVICE Manual / Components List sought

[SeveBC]

I am shortly to begin sorting and modding my '96 Prosonic Combo (as yet untouched beyond new cryo valves, high quality leads to the speakers and reverb plus designing effective vibration isolation of the Accusonics reverb unit (screwed to an 18 mm plywood board) using coil spring & rubber pad vibration isolators).

So, of the many owners and techs / engineers on this forum anyone willing to email a Fender Prosonic Service Manual / Components List? N.B. I have all the Prosonic tech bulletins, circuit diagram revisions D & E and owner's manual, Bruce Zinky's mod suggestions (some questionable - blindly cut out ceramic caps on pre-amp valves?? )....e.t.c.

I have not yet removed the amp as space is limited and I prefer to prepare thoroughly before tackling a project. I will be replacing the electrolytics as the amp has stood unused for 12 years prior to my purchasing it locally via ebay. I will be upgrading some the the noisier components but will not be replacing either the transformers or the speakers. I will probably sand the cones by hand to reduce the paper thickness as that was one of the principal shortcomings highlighted by Bruce Zinky.

I have read all the previous threads on Ampage, Music-electronics etc so if Trace, Doc, Grindell, Enzo et al read this I am especially open to information / advice. My amp suffers from a particularly noisy reverb, the typical channel relay pop and hot effects loop signal (which is fine for my rack units but limits use with pedals). Until I recap I can't make a balanced assessment of levels of noise. I have done extensive reading to date to increase my meagre valve amp knowledge beyond C&G 6958 Electronic and Electrical Servicing: RDH 3rd & 4th Eds, Weber's Hip Vintage, Tube Amp Talk and Tech & Service combined DVD, Jones Valve Amps & Building VAs, Tino Zottola Vacuum Tube Guitar and Bass Amplifier Theory and T G & B A Servicing. I am currently awaiting delivery of Kevin O'Connor's LONDON POWER/POWER PRESS The Ultimate Tone 1 & 6.

[booj]

Prosonic - 11x17.pdf:
Your file of 2.15 MB bytes exceeds the forum's limit of 1.95 MB for this filetype.

PM me

[Enzo]

The service manual consists of those schematics and a fender part number list. WHat else are you hoping to find there?

Here it is.

[Chuck H]

Originally Posted by SeveBC

I will probably sand the cones by hand to reduce the paper thickness as that was one of the principal shortcomings highlighted by Bruce Zinky.

I think you may have misread some information. Bruce Zinky actually felt that the Prosonic only sounded good with the issued speakers and thought that the specific cone weight was an important part of the amps tone. I personally disagree as I owned a Prosonic and ran it through other cabs and it sounded fine to me. But I want to make sure you understand what you read. I read an article where Bruce actually stated that the specific cone weight of the stock speakers was kind of unusual and that the Prosonic only sounded good with those speakers. In the same article Bruce said that the Prosonic wasn't really a marketable amp because of this as most available speakers didn't fit the criteria. I'm sorry I can't reference the exact article now, but I am sure of what I read. OTOH Bruce is a bit of a crank. Meaning that he's eccentric and strange to some degree. So it's possible he has said things that are contrary at times. When I met him at the 2009 NAMM show he was strangely removed and inaccesable, as geniuses often are. After the encounter any inconsistencies with his statements wouldn't surprise me.

Don't get me wrong. Bruce is a minor hero of mine. I owned a Prosonic and still consider it a benchemark of tone. Selling it was an unfortunate nessecity but my memory is very clear on that amp. I had a very early model reported to be straight from the Fender Pro shop that Bruce himself worked at. And I have a very early schematic for that amp. I have payed close attention to peripheral info about it.

Originally Posted by SeveBC

I have read all the previous threads on Ampage, Music-electronics etc so if Trace, Doc, Grindell, Enzo et al read this I am especially open to information / advice. My amp suffers from a particularly noisy reverb, the typical channel relay pop and hot effects loop signal (which is fine for my rack units but limits use with pedals). Until I recap I can't make a balanced assessment of levels of noise...

If you haven't checked out the Blue Guitar website (run by Steve Ahola, who we don't hear from much anymore) you should. There are some good writings from Bruce Zinky listed under "Prosonic notes". He (Bruce) covers the channel switching "POP", the noisy reverb and the clipped caps you referenced.

As for the hot effects loop, well, at least he had the good sence to make it a low impedance drive by running it from a cathode follower circuit. You can't really change much about that without a major rework of the amp, such that it would change the tone too much IMHO.

JM2C

Chuck

[SeveBC]

First I want to thank Ed Treat from Fender Musical Instruments who responded to my email the next day with a pdf Prosonic service manual.

I had little chance to play my OS serial number '96 Black Tolex Prosonic as I was too concerned by the loud hum, pops and crackles emanating from the amp and decided that it needed servicing before something let go.

I hoped to assemble a component shopping list and thereby reduce delivery costs and speed the service by having all parts to hand. Also to prepare a schedule that I could work through systematically to simplify the whole operation and avoid oversights.

My main Prosonic concerns were:
1. The spec of the relays as Bruce Zinky mentioned lousy relays as a major cause of the channel switching pop. Other similar era Fender amps e.g. Vibrosonic appear to have used 12v relays but the Prosonic used 24v items as listed in the service manual. I am very interested to hear of any successful modifications to the Prosonic relay circuit that address the pop noise. Perhaps simply replacing the relays? I'm reading up on relay switching circuits to see if that provides any feasible mods.

2. To garner any information relating to successful mods that removed the channel switching pop and addressed the reverb noise without sacrificing tone.

3. An interest in using SPICE and TextWrangler to simulate the Prosonic amp's circuits as designed and then plug in component variations and see what came out. The pdf text greatly reduces the coding work for a newbie like me.

Regarding the speakers I may well have it round the wrong way. I had understood that the speaker paper used in some units was too heavy or too heavily doped. However it may be the inverse: I am still not sure. Gerald Weber writings, Weber Speakers and Tone Tubby speakers websites and others suggested to me that paper got heavier it later Celestion models speakers and tone can be significantly adversely affected by heavier doping on some speaker cones. However, I was not going to do anything to the speakers until I have a clean playable amp.

Q & A with Bruce Zinky Archives
At Fender, the Prosonic combo was a good sounding amp, but it was absolutely speaker dependent. By this, I mean the combo sounded good, but change the speakers out and it was disappointing. I became aware of this when the speaker vendor used cones made from a different type of paper, then every amp sounded bad. There was only one speaker that ever sounded good with that amp. We had to wait for more than a month before we could ship Prosonic amps in quantity......The problem with the Prosonic speaker was traced to a cone that was less than 2 grams heavy. It was the wrong paper formulation, and the tone was 100% wrong. This happens from time to time with every large speaker company. But, the density, flexibility and hardness of the paper cone is very important to the tone. The Kurt Muller company still has the paper mill that was formerly owned by Celestion in the 40s, 50s and 60s, so you can still get those original Celestion paper cones from them.

I am currently away so all the information resources stored on my external hard drives are unavailable to me at present.