Sessionette 75 ILP 'brick'

[TheUnWiseOne]

I do also get a horrible loud crackle when I put a lead into the FX send

[J M Fahey]

IF you are going from Preamp Out (FX Out) in the Sessionnette or most any am p into another amp's normal (guitar) input you may easily overload it, that is not a defect but misuse.

Try again but go from Eff Out to the other amp Eff In or Power Amp In, that should match levels.

[Mick Bailey]

Or use the 'Monitor' output and set the level with the monitor output control.

[J M Fahey]

Some repair shop. Maybe a good living can be had from charging Ģ20 a pop to tell a customer you can't fix something. Not much job satisfaction, though.

In the early 80's , definitely *before* Internet or even personal computers, there was this Tech guy, nicknamed "El Digital = the digital one" who was both famous and hated.

No "normal" Tech took digital or complex stuff, think keyboards, MXR 1 second digital delay, DBX compressors/limiters, harmonizers, etc. but him.
We couldn't because of absolute lack of data (remember, no Internet and averything was on paper , period) , no service manuals, no access tomparts even if problems successfully identified, an absolute desert.
No big deal , even lacking info, to repair any tube amp, or 70s 80s technology SS amps such as Peavey/Ampeg/etc. but the above stuff was impossible.

So any such dead or malfunctioning stuff went straight to him.
He had a rented 2 room office, you left stuff in the front one, explained the problem, he had some house amp for you to demonstrate the problem , his Lab was in the second room, nobody, I mean NOBODY was allowed inside.

I once visited him and he told me: I'll let you in, I know we think alike and won't betray me.
I expected to find complex digital analyzers and testing equipment, multichannel high bandwidth scopes, pulse signal generators, the works ... all he had, no kidding, was a needle (analog) meter.
My jaw dropped and that's an understatement.
He explained: I receive the dead stuff and don't let jobs stack up, I open it at once when customer leaves and have a good look, then:
* reseat plug in boards, way back then instead of dedicated connector to connector they used plain copper "fingers" etched in the board edge , best case said fingers were nickel or gold plated, in any case grime took its toll.
He pulled the board, cleaned its edge, sometimes with a rubber eraser or fiberglass tip pen and reseated, that alone cured 20% of problems.
* pull and fully reseat ribbon connectors , most partially unplugged by device shaking and transport: another 20%
Not bad, huh? .... already 40% real repair success.
* used his trusty needle multimeter to check for +/-15V and +5V where approppriate all over the board.
Say another 10/20% .
For the others, which were over his head at component level, he detected which was the bad board, pulled it, and sent it to USA by his hot Air Hostess girlfriend who mailed it from Miami, LA or NY to original factory, think Moog, Oberheim, Kurzweil, UREI, DBX, etc. which, remember, were located in Continental USA ... and if German/Austrian/whatever certainly had an official service and representative center in, say, NY , think Gotham Audio and such.

When the repaired module came back, he reinstalled it and charged twice what he had spent, or more if possible.
His success rate was impressive, customers grunted and hated his high prices but nobody could argue his efficiency.

[petertorro]

Hello mick ,

Is this the powermodule for the sesionette 75? Do you have a shedule and/or where do you buy these?

[petertorro]

Sorry for not introduced myself.

I am Peter a 60 year old guitar player from the Netherlands that like the sound of the sesionette, special the upgrade one.
I buy a poweramp in parts 40 W, because my brother thought that the wattage has split.
Thats what he measered
I am not a technician like my brother.
We put the poweramp in and the fuse burns.
I have only one fuseholder.
I have seen that normaly that are two fuseholders

Hope someone have some good advice?

greeting Peter

[J M Fahey]

Looks that the power amp your brother bought is not compatible.

You need something like what Mick made, which does the same as original module:

1) has 100W capability , and works with available rail voltages, which if I donīt remember wrong were about +/-45V

2) has power transistors mounted to an aluminum L shaped heatsink so it can be bolted to back panel as original one.

3) its connections will be just 5:
+45V
-45V
Ground
Signal input
Speaker output

And of course must fit in the available space.

Many similar amps are available, only slight problem could be that TO3 (metallic fried egg shaped) power transistors are not popular nowadays, so they should be somewhat harder to find, today most use plastic power transistors , which are fine anyway, the main point being the L shaped aluminum extrusion, so you can mount it .

Small world, I am just finishing a similar mounted 300W module

I had to adapt it to use plastic MosFets (IRFP250) because thatīs whatīs currently available, but kept then old PCB design and L shaped aluminum extrusion so I can repair my own "80's Sessionnettes" , in this case 300W Bass amplifiers which used TO3 metallic 2N3773 ... today practically extinct.



EDIT:a far cry from the über complex Roland power amp shown in another thread: just 4 transistors as the main amp, driving 4 power MosFets , plus another TO92 one for Bias .
Oh, board also includes +/-63V power supply, +/-15V for preamp, an Opto limiter and 15mA supply for Led.

Minimalism at its best.

Almost forgot: after mounting Iīll kludge there also the 12V fan supply: a single 1N4002 and a 2200uFx25V cap.

[nosaj]

Thanks for this

I've heard back for the 'repair' shop chap he tells me the power amp is working - but the some thing on the pre amp has failed - but he cannot tell me what it is.

I had one these a few months ago that was brought back stateside, nice little amp variety of sounds.. Dirty pots and what looks like footswitch problems, but the issue came down to the 15v supply only putting out almost 9v(barely enough to light the LED's in the footswitch) replaced 2 caps in the 15v supply brought the 15v rail back. Footswitch works fine after that.
nosaj

[Dave H]

Could one of these - Power Amp be made to work with a suitable heatsink?
The build instructions look good and there's a schematic.

Edit: I've just noticed it's also available ready built.

[J M Fahey]

Could one of these - Power Amp be made to work with a suitable heatsink?
The build instructions look good and there's a schematic.

Edit: I've just noticed it's also available ready built.

That Vellemann is an excellent amp and very suitable as general purpose replacement or "plate amp" to build or repair a powered cabinet, but unfortunately does not fit in the *tiny* space allowed inside the Sessionette.
In this particular case, itīs too long (or wide, depending on how you see it)

You need no extra heatsink, Sessionette uses the thick aluminum chassis for that, so you bolt there (with some thermal grease in between) either the original ILP brick or a **same width** power amp, which usually means one with an L shaped aluminum extrusion so transistor heat can be transmitted to aluminum backpanel.

See that space is so tight that a "window" was cut in the PCB itself :



this picture is very unusual, because it shows an *open* (non encapsulated) module, it might be a prototype or perhaps some dedicated amateur designed and built his own replacement
Or maybe Mr Awards himself built a homemade replacement when ILP supply dried down.
IF that specific aluminum extrusion were available, the module could possibly be reproduced, from what I see circuit is tha straight Toshiba datasheet example .
Those huge dual bolt transistors are NOT available any more, for decades now.

Same but with original fully encapsulated brick.
Notice it needs only 5 wires: +52 , -52 , In , Out , Gnd.
Any replacement must be able to use those.



************************

Plan B: somebody replaced the original power brick with a new Class D power module which barely fits in the available space:



No need to thermally join it to back panel, since it has its own heat sink.

read all about it in: http://www.smpartizan.com/?page_id=3002

[nosaj]

That Vellemann is an excellent amp and very suitable as general purpose replacement or "plate amp" to build or repair a powered cabinet, but unfortunately does not fit in the *tiny* space allowed inside the Sessionette.
In this particular case, itīs too long (or wide, depending on how you see it)

You need no extra heatsink, Sessionette uses the thick aluminum chassis for that, so you bolt there (with some thermal grease in between) either the original ILP brick or a **same width** power amp, which usually means one with an L shaped aluminum extrusion so transistor heat can be transmitted to aluminum backpanel.

See that space is so tight that a "window" was cut in the PCB itself :



this picture is very unusual, because it shows an *open* (non encapsulated) module, it might be a prototype or perhaps some dedicated amateur designed and built his own replacement
Or maybe Mr Awards himself built a homemade replacement when ILP supply dried down.
IF that specific aluminum extrusion were available, the module could possibly be reproduced, from what I see circuit is tha straight Toshiba datasheet example .
Those huge dual bolt transistors are NOT available any more, for decades now.

Same but with original fully encapsulated brick.
Notice it needs only 5 wires: +52 , -52 , In , Out , Gnd.
Any replacement must be able to use those.



************************

Plan B: somebody replaced the original power brick with a new Class D power module which barely fits in the available space:



No need to thermally join it to back panel, since it has its own heat sink.

read all about it in: http://www.smpartizan.com/?page_id=3002

The one I worked on was not covered either. I was the only to work on it. Guy bought it in England when he was in the military.

nosaj

[J M Fahey]

The one I worked on was not covered either. I was the only to work on it. Guy bought it in England when he was in the military.

nosaj

Originhal ILP were all potted, of course, that was the key of ther product line.

They must have sold thousands, so when original Company disappeared I bet a small cottage Industry must have developed and thrived for a few years just on the replacement market.

The circuit IS known, in the 80īs Toshiba and similar MosFets were still available, so only somewhat hard to source component must have been the aluminum extrusion.

Now that my interest refreshed I might search for a suitable extrusion (commonly available) and make my own, go figure.

Stay tuned

[dmeek]

For what it's worth here are a couple of schematics of ILP amps I've hacked into, not guaranteed 100% accurate of course.

https://music-electronics-forum.com/...1&d=1549036979

https://music-electronics-forum.com/...1&d=1549036979

[J M Fahey]

For what it's worth here are a couple of schematics of ILP amps I've hacked into, not guaranteed 100% accurate of course.

Thanks, very interesting and afaik look good.

Were they open or you had to submerge potted brick into some ungodly liquid?

That said, this is reinforcing my idea of building some similar brick, with screw-in wiring, so Musicians can replace their own.

Freight costs in Argentina went through the roof , it IS a large Country (superimposed on Europe would stretch from Germany to Lybia, on North America from mid Canada to mid Mexico ) so for me itīs cheaper (or same cost) to send a brick one way than full amp (or head) both ways.

[dmeek]

I use toaster oven to heat them up to about 300F then pick away while it's hot. The epoxy they used is very tough even then as you can see. Components get broken.
This method works very well sometimes, depending on the type of epoxy.

On the left are two HY364s, on the right is an HY124 that I never traced out - not worth the trouble.

https://music-electronics-forum.com/...1&d=1549140784