Marantz PM66 KI tweeks

[SimontY]

I knew you'd like the 2nd tx

[Ben Hanke]

Blissfully unaware as I am of any mysterious electromagnetic restrictions on my placement options, I've secured the second transformer orthogonally on the back plate of the chassis using the original mounting bracket.

[Fidelity Audio]

Nice work!

I think you are now officially the second person to do the tx mod. Very worth while it is too

Brent

[Ben Hanke]

Oh man, so worthwhile. It's a huge improvement. My 805s are loving the extra juice and revealing more crisp details and producing deeper and tighter bass than I could've imagined (and I used to have a sub!). I joined DiyAudio in '07 because of this thread and I've wanted to get to this point for all that time. Even with that long build-up, this mod has surpassed my expectations :-)

[Fidelity Audio]

Yes very big gains. This is why when I upgraded from the Marantz I had to buy the ATC amp as most 'very good' amps were not as good as the Marantz

Brent

[Ben Hanke]

Hey guys, any opinions on whether I should bypass my 10,000uF Black Gates with some good film caps?

I was thinking of running some Mundorfs across them but I'm not sure of the best values or whether I should do it at the PCB or cap terminals. I've heard rules of thumb quoted of 0.1%, 1% and 10% or even all three.

Also, is it worth bypassing the 1000uF filter caps?

Cheers,

Ben

[Fidelity Audio]

It may be beneficial to bypass the main smoothers with 0.1uF & 1uF 2% Mundorfs.

Brent

[SimontY]

Brent, I think Ben means 10% of the main cap value in uF, ie. 1000uF (not capacitance tolerance).

I think the problem with the typical 100nF sort of range bypass caps is a) their impedance is too high for them to work properly and b) they only act at very high frequencies causing an uneven impedance curve - this can be alleviated with a series resistor, something like 1-5R. There is a thread on here showing scope measurements of different bypass caps.

I would suggest 100uF or 1000uF BG to try. And if you can get a film cap right up next to the transistors that is also a good move.

[Fidelity Audio]

I knew what he meant!

I was suggesting the 2% Mundorfs as they work very well in those positions and have a good ESR figure that will no doubt be much better than the BG. I would not want to strap a cap across a decent BG like those and add something worse in terms of esr and ripple rejection

Brent

[Ben Hanke]

Thanks guys. I looked at what was available to implement Brent's suggestion and ended up trying Mundorf 1uF/1000v SO and 0.1uF/1200v SGO in my shopping cart for size. Overkill? They're pricy, but so were the BG. I think I can get more certain gains elsewhere for that kind of investment.

As per Simon's suggestion - well, I don't have many Black Gates left (who does?), but I do happen to have a couple of 100uF/50V "K" to hand... which is interesting! (Are K as good as FK? I can't remember). They're just lower than the 56v specified rating for the smoothing caps. What do you think?