Info on Melos MA-111?

[neddyboy]

I know it's a tube/SS hybrid design but that's about it. Can anyone tell me more? Specifically, how do the tube section and the transistor section work together? I'm wondering if the tubes preamplify the mids and highs and the SS deals with the lows.

I just bought a maybe broken/maybe not one on eBay for not much and I'm having trouble finding anything about it.

Neddyboy

[SY]

Preamp?

I don't have a schematic, but I'd doubt that it works the way you speculate. More likely, the silicon is used in support functions, at the bottom of a cascode, or as a follower.

[neddyboy]

Sorry, forgot that important bit of info. I kinda made up that bit about separating the frequencies between tubes and solid state. Wishful thinking.

Buying the Melos is my attempt to simplify my system a bit. I currently have a restored Knight tube preamp driving a Hafler DH-200 for midbass, mids and highs, plus an NAD 1240 driving the subwoofer. The lows are a bit flabby on the Knight, but not bad for midbass, but the sub end of the signal just goes to mush, hence the NAD. Anyway, I'm hoping the Melos will deal with both ends of the range so I can use one preamp.

[SY]

It couldn't hurt. The vast majority of old preamp designs were gnarly: high distortion, high source impedance, inability to drive cables and power amp inputs unless coddled. IIRC, the Knight-Kits all used variations of the two-tube 12AX7 circuit (or worse yet, 12AU7), cascaded common cathode with feedback tone controls and no buffer.

[neddyboy]

Thanks.

My Knight uses two 12AU7s and one 12AY7 per channel. It was a kit and is held together with spit and baling wire. Sweet sound, but hell yes, noisy.

[neddyboy]

I finally got the Melos on my bench and can get down to figuring it out. Again, I'm relatively competent with the mechanics of electronics repair, but woefully ignorant of theory.

First, there's a missing part. You can see the space in the photo, marked "K". It looks like a space for a metal case output transistor like the ones in my Hafler DH-200 -- maybe a power regulator? It does seem to be part of the power end of the circuit. There's no heat sink in place now, but there were traces of heat sink grease on the PC board.

I don't have a schematic or the chops to recognize what it might be by looking at the circuit. All I can tell you is the circuit is entirely non-op, not even a pilot light. The fuse is good and the PT seems okay.

Does anyone out there have a working MA-111 hybrid preamp they could open up and ID the part for me?

[honinbou]

hi neddyboy,
do you happen to have the assembly manual or the schematic of the knight tube preamp?

looks like both the filaments and the HT share the same secondary... tubes do not light up on my unit so i think the dropping resistors might be out of spec

[udailey]

Did you figure this out? I have one open in front of me and can identify missing parts if you still need.