Using burson opamps on an old Sumo nine

[omc]

Hi,

I am thinking of getting one of these old amps, and doing a full rebuild on it. I was checking out the schematic and it looks like the opamps will have a lot to do with the sound that comes out. Has anyone used these in an application like this? I have used the bursons in a DAC before, and they were worlds better than an OPA2604. I often find older amps have a grainy edge, where the bursons are very fluid sounding.

[omc]

How about I word it this way; has anyone tried changing the opamps in this old amp. If you have how did it work out?

[jackies]

So omc, you ever tried changing these opamps?
I have a Sumo Nine too, and was thinking to swap the opamps, but I'm not so sure if I can put bipolar input opamps (LME49860) in there, since they also serve as servos (pun?).

[ticknpop]

It is not good to use Bursons or bipolars for servos .
Fet input opamps are what you need for servos.
Use Bursons and LME for the signal path.

It's easy to update preamps and DACS with them and check for oscilation and better local power supply decoupling. In power amps the compensation may be tied into using an older slow opamp so you need to be carefull and do some testing as you go along so you don't blow it all up and have to sell me the Sumo chassis for not a lot of money.........

[evette]

I,ve owned 3 of the sumo,s nines before not worth the worth the effort. However if you blow it up I,ll buy it from .

[llwhtt]

The opamps in the NINE are NOT servos they are the gain stage for the entire amp. They also need to be able to run on + and - 20VDC, I have the OPAs in mine now. The output transistors are set up as emitter followers, as in no voltage gain. I'm not sure if the Circlotron configuration has gain or not. As far as the Bursons go I don't think there is enough room for anything but a regular 8 pin DIP. Also the alignment of the NINE is very involved and requires the use of a distortion analyzer with a balanced input. I just went to visit James Bongiorno last week and got the entire alignment process from him. He wouldn't even talk to me until I had the correct instrumentation, a Sound Technology 1700B in my case. Remember if this is a NINE not a NINE+ the output transistors are made of unobtainium, if you blow it up that's it.

Craig

[jackies]

Hey Craig, thanks for the very informative post!
I read somewhere that opamps are also maintaining the 0 on the outputs somehow, that's why I assumed they also serve as servos...

[djk]

The caps in the feedback loop are only 0.1µF, you better have a J-FET input or you will need a much bigger coupling cap. Also the input bias resistors are 10M on the inverting inputs, and 1M on one non-inverting input, and 0 on the other input, so you need an opamp with no input off-set current (J-FET).

JB recommends a selected AD825.

[jackies]

Thanks everybody! I suppose I can start with ordering OPA2604 and AD825 and see what happens...

[djk]

I meant the AD823 (dual), not the AD825 (single), and it has to be selected to run on 40V (it's only rated for 36V).