Kenwood KA-2600

[adason]

Hi everyone,

I have a few questions about amp design. Before...here is the story. A friend of mine at work asked me to repair his beloved Kenwood KA-2600 for second time. First time we both worked on it because he wanted to learn how to troubleshoot dead amp. We found the amp protection circuit, one driver transistor and few caps dead, it was ok repair. He was happy again. He is musician with good taste for audio and he loves this amp. He has bunch other amps and receivers he likes less. First time I did not bother to listen to this amp, I just repaired it at work. Second time he brought it, I took it home. It was shorted power supply, bad insulation. Easy repair. This time I managed to listen to it. Man, it sounds great. I mean it. Now I know why he keeps it around. I compared it to two Onkyo audiophile amps I had that time and they did not even come close. They sounded boring in comparison to this one. This amp is sparkly clean, juicy, just fun to listen to. It reminds me good tube amp sound.
Anyway, I am not an expert, this is just my hobby, I just built and listen.
Could any of you circuit experts have a look at the circuit and tell me what makes it sound so great? Seriously, it so damn old and yet is sounds way better than today's mainstream media stuff.
My musician friend is curious too. He remains happy reunited with his Kenwood.

Thanks,
ed

[adason]

here is the schematics

[adason]

and few guts pistures

[bob91343]

Nothing special. Just a good, clean design. Uses NPN output transistors, capacitance coupled to the load. It's actually close to being a low end unit.

Maybe what's happening is that you are driving it too hard and just happen to like the sound of that clipping distortion.

[Mooly]

Originally Posted by adason

They sounded boring in comparison to this one. This amp is sparkly clean, juicy, just fun to listen to. It reminds me good tube amp sound.

You can take this basic design much further and develop an amp that just blows all the "designed by simulation/designed for best specs" stuff into the weeds... as I keep saying, what good are all these designs when you don't actually like listening to 95% of your music collection through it... but folk just don't seem to get it

You don't need class A either to achieve that.

On your amp , the "vital" bits are that the input stage is "single ended", which means the distortion produced rises far less sharply with frequency than the LTP used these days, it's also mainly even harmonic.
The output stage is a "quasi complementary", worse than the full complementary designs of today in respect of linearity, but again, the distortion produced is the "right kind".

[sakis]

what makes it sound greate is not the amp it shelf but the all thing together ... this type of circuits have a gozzilion errors compaired with todays hifi or high end standards ...

example of errors
limited bandwidth at both ends
capacitor coupled
no diferential LTP
absense of curent sources /sinks
terrible crosstalk figures
horrible tone control
generally amp like that will measure terrible

BUT !!!!

the all arangement will produce wonderfull sonics and add to the sound colours that dnt really exist but make the sound extremelly warm add to this that simplicity of most circuits makes it even better to listen and there you go ...

The problem is that you actually think that it plays well ....it sounds friendly.... it both plays and measure bad ... but friendly ...

do your shelf a favour and make construct any amplifier like the DX or the leach or the symasym or the P3A and use it just with a pot in the input and our favourite music and source ... it will be compaired next to nothing with any of your comercial equipment ...

kind regards sakis

[adason]

Originally Posted by bob91343

Maybe what's happening is that you are driving it too hard and just happen to like the sound of that clipping distortion.

That would not be the case, I was testing it with 97+ speakers and barely used few watts.
Thanks for the comment.

[adason]

Originally Posted by Mooly

On your amp , the "vital" bits are that the input stage is "single ended", which means the distortion produced rises far less sharply with frequency than the LTP used these days, it's also mainly even harmonic.

Thanks Mooly for this comment, I have seen it mentioned before quite a few times and there is lots of folks which seems to prefer the sound of SE to differential input.

[adason]

Originally Posted by sakis

do your shelf a favour and make construct any amplifier like the DX or the leach or the symasym or the P3A and use it just with a pot in the input and our favorite music and source ... it will be compaired next to nothing with any of your commercial equipment ...
kind regards sakis

Thanks for the comment sakis, but the kenwood is not my amp and I am not going to construct any more solid state amps, I did that in the past, have actually quite a few good ones sitting on the shelf without being used much...I use tube amps for their tone, solid state only to power woofers

I am not sure if it has horrible tone control. Can you explain what you mean?
Its tone control uses series of switches rather than pots, which might be better. Again it uses single stage before the tone control...which can give it certain pleasing tone. But I would not call its tone controls terrible.

By the way, I did not need to use much of tone controls, the amp sounded so good. Its one of the first things I noticed that with boring sounding amps one needs to use more tone controls to compensate.

[adason]

Originally Posted by sakis

what makes it sound great is not the amp it shelf but the all thing together ...
the arrangement will produce wonderful sonics and add to the sound colours that dont really exist but make the sound extremely warm add to this that simplicity of most circuits makes it even better to listen and there you go ...
kind regards sakis

sakis, your comment is is nicely put together...
it means that the sum of all part, no matter how inferior they may be, gives overal very pleasing sound

Is it possible that designers were simply listening to their design and kept adjusting, changing, modifying and so on, till the outcome was pleasing sound?