Rowland Research Amplifier Help!

[ungie]

Hello,

I am wondering if anyone has experience with any of the early Jeff Rowland amplifiers? I have a line on a pair of Model 7 amplifiers but only one of them is functional. The other is complete and the power supply is working correctly but there are a few bad output devices. Rowland is not willing to supply a schematic and I would like to investigate repairing it myself.
If it's not worth it the chassis would always make a nice platform for a DIY amp!
Thanks!

[jacco vermeulen]

Eeer, the front end in your Model-7 isn't a totally thermal resin encapsulated module ?

[ungie]

Originally posted by jacco vermeulen
Eeer, the front end in your Model-7 isn't a totally thermal resin encapsulated module ?

Ummm...I'm not sure as I don't have access to the amplifiers right now. What does that have to do with an issue with the output stage?
Someone out there must have a schematic or an idea where to start troubleshooting?
How about approporate replacements for the output devices?

[The golden mean]

Don´t know if they had started to use chip-amps as output devices with this model. But they should at least be willing to answer what they actually used in my opinion.

[ungie]

Originally posted by The golden mean
Don´t know if they had started to use chip-amps as output devices with this model. But they should at least be willing to answer what they actually used in my opinion.

Nope, these were Rowland's first commercial amplifier.
It uses TO3 cased BJTs.
From my own contact with the company they do not support "non-qualified" people to work on their products and will not supply much in the way of technical information.
The reply is the usual "Ship back your 100 lb amp to us and we will fix it...for a price". Fair enough.
The issue I am having is that I'm sure that this amplifier can be repaired for minimal cost as the "big ticket" items like the power transformer and power supply caps are good.
I guess from the lack of available information I will have to start digging around inside the functioning unit and start signal tracing and measuring section voltages.
Alas life is much easier with a schematic to follow, but it's not the end of the world.
Anyone familiar with Rowland's early amplifier topologies have any ideas what could have caused blown output transistors?
From what I understand these designs are well protected against most fault conditions.
Thanks!

[jacco vermeulen]

The front-end of the all-discrete 80's models is in a flat plastic box with round edges, resin-filled.

That black sandwich box is soldered on the main board that connects to the TO-3 Motorolas, which are mounted on the heatsink flanges, 2 rows of 12 TO-3s per channel.
The Models 1, 3, 5 and 7 all had the same layout with the lunch box.
You could unsolder the encapsulated gain module and check to see if it is undamaged, there's no way to repair it.

[ungie]

Originally posted by jacco vermeulen
The front-end of the all-discrete 80's models is in a flat plastic box with round edges, resin-filled.

That black sandwich box is soldered on the main board that connects to the TO-3 Motorolas, which are mounted on the heatsink flanges, 2 rows of 12 TO-3s per channel.
The Models 1, 3, 5 and 7 all had the same layout with the lunch box.
You could unsolder the encapsulated gain module and check to see if it is undamaged, there's no way to repair it.

So essentially if those modules are toast the amps are boatanchors?
I'm not sure it would be worth the investment of a new module.
But the chassis could still be put to good use.

[jacco vermeulen]

Yep, basically that's the idea but i don't want to be the one with the advice to hack up such beauties.

If you know where to look/ask, there are contemporary designs available that suit the chassis and powersupply of the Model 7 very well.
(the toroid in the Model 7 is a 2400VA monster, IIRC)

[ungie]

Originally posted by jacco vermeulen
Yep, basically that's the idea but i don't want to be the one with the advice to hack up such beauties.

If you know where to look/ask, there are contemporary designs available that suit the chassis and powersupply of the Model 8 very well.
(the toroid in the Model 7 is a 2400VA monster, IIRC)

That's really unfortunate.
Surely there is nothing special going on inside those modules?
Maybe it's worth un-potting them and designing a new front end?
So where would you suggest I ask about a contemporary design that would make use of these nice chassis and power supplies?
Thanks!

[The golden mean]

I own a Rowland Synergy II in which the remote control stopped working many years ago. I can live with this or fix it in some creative way e.g. with a model plane radio control, not that hard.

There are many options if you want to reuse the chassis etc.
Aussie amplifiers? Ground Sound? Or this:

http://www.shine7.com/audio/bpa300.htm

BTW, someone in Hong Kong provided a schematic (and a kit) of what was said to be an early Rowland power amp. I kept it for a while but probably trow it away as I decided to go in a different direction. From memory it wasn´t a particularly complicated construction. Medium I would say.