Yamaha A-1 for modding?

What a great amp! between Kenwood KA8100 recapped, Technics SU8080 recapped and Yamaha A-S500, the A-1(unserviced) sounds best. It has sparkly highs, good mids and what sound to my ears as high quality bass, meaning: not boomy or to restrained but with a good spread on the low range, not overtaking the mids and still have punch in the areas where it is needed.

But my problem is the lack of PRE OUT/MAIN IN outputs and I need those for bi-amping so, can I split the PRE from the main internally and divert the pre signal to the PRE OUT output in the back(it has one but different) and use the output "tape pb"(cancel it) for the MAIN IN? Can the preamp section in the A-1 handle a active crossover with 2 final amp sections?
My goal is to bi amp using 2 Yamaha A-1 and one of them as a preamplifier also.

Way too complicated. Why not get a M-4 for easy bi-amping? You get more power and even better bass control.

What I don't know is the impedance mismatch between the active crossover and the final stage amp. I don't know how to deduct impedance values from schematic...

I wouldn't frankenstien and A-1.

OK, then I wont, but I will do a recap, change trimmers...
I want to change in the voltage regulator board this 2, because they get too hot:
2SB566 with TIP32C is that a good choice?
and
2SD476 with TIP31 A, C or CG (the motorola book says TIP31B) but A, C,CG I can find at my supplier, which one should I take?

verde57 said:

OK, then I wont, but I will do a recap, change trimmers...
I want to change in the voltage regulator board this 2, because they get too hot:
2SB566 with TIP32C is that a good choice?
and
2SD476 with TIP31 A, C or CG (the motorola book says TIP31B) but A, C,CG I can find at my supplier, which one should I take?

Click to expand...

The new transistors are going to run just as hot in the regulator circuit. Thats why they have heatsinks.
TIP31C /CG would be the one to use.

IMHO unless your A-1 sounds really ugly i would leave it alone !

It sound good but someone before me changed some of the tr's on the drive board and MJ15003G , MJ15004G on one channel, and a few other...
Later I will ask for advice here if they need replacing or not, just need to identify them.
And also if I'm recapping the power board it is better to replace all that needs replacing, in terms of a clean power source and not make too many shopping runs. For example I want to change the fusistors and VD1212 diodes, as per suggestion on the forum.