Always Wanted to do this...

[hpsenicka]

That's a bummer.....

FYI... According to my KA-9100 service manual, the specs for that unit are 1.0V/50 kohms, although I suspect that it would be a huge stretch to presume that the specs would be similar.

 

[Velocewest]

As they say -- the only stupid question is the one you don't ask, so -- what does the above accomplish? Both the jumpers and the other mod?

Point of reference -- I don't own any true integrateds, I have 2 sets of pre-amp/amp separates and a receiver amp.

Thanks,

 

[hpsenicka]

The simple answer.... I can use the pre-amp and power amp stages separately!

How useful is this? That depends on what you want to accomplish.

I initially hesitated to spend the extra $$ on these mods out of concern for the practical value... and did on a whim more than for any specific requirement, but it has been fun to mix and match components as a result.

I hope to have an opportunity soon to try the KA-7100 amp with a tube pre-amp..... that will be interesting!

 

[ferninando]

EW, anychance for a schematic of the in/out buffer?
or just use a standard unity buffer from the national appl. hndbk?

 

[jpdylon]

Yes, I'd be interested as well. I've got a quad receiver I'd like to turn into a preamp for my adcoms.

 

[nosirrah]

Jumpers

EW, I am interested in how you made the jumpers. I made some from brass but they did not come out with a really smooth U shape like yours.

Very Nice.

Nice job Glenn, having the option of preout/main in is also
an aid when trouble arises and you want to isolate an issue.
I make my own jumpers from sterling silver, and buy 1/8 rod from Rio Grande jewelry supply....in the 3 or 4 years since I made my first set to replace missing jumpers for a 8080 receiver they have been trouble free.
Cut the rod to about 2 1/4 length, chamfer the ends, and bend it around a socket extension to get the proper radius, if you use a little care you won't scar up any surfaces, but if you do it's a simple task to sand away any dings.
Casey:thmbsp:

 

[gonzothegreat]

Thanks for posting this EW. A while back I found a dead 7100 (output stage issues and battered cosmetics) and I think it might get this mod to drive my 700m.

 

[Digital_Llam]

This is a very interesting thread given that I just picked up a KA-7100 yesterday

 

[johnda]

Wow. VERY nice. It looks like the amp came from the factory with them. Super job!

 

[EchoWars]

EW, anychance for a schematic of the in/out buffer?
or just use a standard unity buffer from the national appl. hndbk?

Yes, I'd be interested as well. I've got a quad receiver I'd like to turn into a preamp for my adcoms.

Someone should have tapped me on the shoulder and told me I missed this thread getting bumped.

The OPA2604 was used in the simplest of bonehead ways...as a unity gain buffer: http://www.facstaff.bucknell.edu/mastascu/eLessonsHtml/OpAmps/OpAmp3Note1Buffer.html

All the surrounding circuitry was to knock down the voltage (stolen from the large PS caps) to +/-18 or 19V with a zener and a resistor. There's a couple of 47µf 25V caps after the zener, and a couple of small film caps to act as a supply bypass. That's it.

The 2604 has fallen out of favor with me a bit...I like the National Semiconductor LME49860 nowadays.

 

[thefragger]

Sorry if I missed it; what's the point of the buffer?

 

[EchoWars]

Post #10 of the thread.

 

[thefragger]

So the buffer is used to bring down the impedance of the pre?

 

[EchoWars]

The buffer lowers output impedence, yes. The stock 7100 has no use for it, but if the 7100 is to be used as a stand-alone preamp it is necessary for the reasons detailed in post #10.