My Sumo appears dead....

[weinstro]

...or at least needs major restoration. It's in very rough shape.

It's an Andromeda I with BJT outputs, and I'm considering what to do with it. One idea is two replace the driver PCB's with Borbely Audio DC50 PCBs, while trying to retain the other parts as much as possible. But, I have some questions:

1. The DC50 is designed to drive an FET output stage. The Sumo has BJT's. Actually, it's a triple if I include the driver BJT's. What would I need to change in order to have the DC50 work successfully with these devices (2SA747A and 2SC1116A)?

2. Is the DC50 board likely to sound better than the original Sumo?

3. The Sumo is a balanced bridge ouput, kind of like an H-bridge. There are enough devices (8 per side) to split this into a 4-channel amp with ~100 Watts per channel. 4 DC50 cards would fit. Should I go for it?

Advice and discussion appreciated.

[jackinnj]

I have the utmost respect for Erno's work...the first MOSFET amp I built was one of his....but what part of the Andromeda is "dead" --

[weinstro]

A few points:
- Left and right driver cards don't match - one has mostly film capacitors, the other mostly ceramic disc capacitors.
- One board has had the input transistors replaced, but whoever did this didn't pick a device with the same pinout. This was addressed by simply crossing the leads - the touch now. These are also TO-220 cases, rather than TO-92.
- The boards are have a very high parts density, and I doubt these will withstand lots of desoldering/soldering.
- Cosmetically, many issues. I'm not sure that even a mother could love this one.
- I acquired it 2nd hand several years ago and never listened to it. I felt compelled to look under the cover and honestly, I'm afraid to hook a speaker and turn it on. A load resistor OK, but not a driver.

[h_a]

Reworking an amp like you intent is for the more experienced in my opinion. It would be a pity if you spend the cash on Erno's boards and find out that all the rework is no success.

Anyway, you're not in a hurry, so why don't you start with fixing the amp first? Seems replacing the input transistors on a single board will be sufficient for that. Otherwise it's also a nice experience.

If you're worried about hooking up speakers, let me tell you the feeling will be worse for your experiment with Ernos boards as you're fully responsible then

Just check offset (DC-voltage) across output connectors first before connecting speakers. If smaller than 100mV hook up some (test) speakers.

Have fun, Hannes

[weinstro]

Thank you for the suggestion. I may try to source the parts, but the board looks tricky to service.

I'd still like to ponder a replacement driver board for a bit, so back to the Borbely driver boards:

1. Any thoughts on changes that would be needed to drive a BJT output stage?

2. Mr Borbely offers and has offered several different boards over the years. The one I had in mind is intended for a 50 watt @ 8 ohms. What would I need to think about if I wanted to use this driver as a universal driver board for 100 WPC (or more)?

3. The Sumo has a ginormous transformer (approx 1.2kVA) with two supplies; +/- 48 vdc and +/- 42 vdc. Can I get there with this supply?

Thanks!