The Phonoclone and VSPS PCB Help Desk

[needlz]

Thanks rjm... The DC voltgage reading from the bridge was sweeping from 0 to 14v. I did have it wired incorrectly until I downloaded a datasheet to see how each of the 4 posts were supposed to be wired. I blew a few fuses until I figured this out and might have damaged it. I swapped in the new one at it gives a strong consistant DC reading. The problem now is that the circuit is dead quiet... not a buzz, not a squealch, not a peep... nada from either board/channel. I just noticed that the voltage regulators I am using are 12V negative. Were these supposed to be positive?

[rjm]

I just noticed that the voltage regulators I am using are 12V negative. Were these supposed to be positive?

The negative regulators go in the position marked 79xx, the positive in the position marked 78xx. The dot denotes pin 1.

I should apologise, that's not as clear as it perhaps should be.

Worse, on the beta version the regulators are unmarked. The two negative regulators go on the edge with the V- pad, the two positive regulators go on the edge with the V+ pad. Again, the dot marks pin 1.

Also, in the diagram, I show bridge rectifiers with the AC connections side-by-side. I do this because its easier to draw the connecting wires this way. Of course on most bridges the AC connections are opposite on the diagonal. You are responsible for correctly wiring whatever configuration you happen to to use, simply because there are far too many options for me to cover individually.

As more people get into building the power supplies, its becoming clear to me that to assume the distiction between a 7812 and a 7912 would be obvious to everyone was a mistake on my part. I'm not quite sure what to do about it ... the only advice I can give is if unsure, ask first here for clarification before plugging it in and blowing things up.

needlz, your regulators are most likely still ok, just replace the two on the positive rails V+ of each channel with 7812's.

-rjm

[needlz]

Don't sweat the rectifier or regularor thing. Your directions are great... I was only mentioning it because I found out my newbie problems. The funny part is I always seem to figure out what happened after I post a question. There must be something internally that happens after asking for help. I have always used 4 diodes (or tube) for rectification and never used the all-in-one box. I have some 7812s handy and will replace them now.

[needlz]

voila... that was it (and when I mean it, I mean there were no other issues ) and it works.

thanks... I'll post pics in a bit.

[needlz]

I didn't have a large enough enclosure for both boards but I did have a bunch of smaller ones from my stompbox makin' days. Each enclosure has it's own mic unbilical coming in. The seduction sitting next to them is sweating... might get religated to the other room.

[rjm]

Ooooh. That's pretty neat to think that you got even one Phonoclone PCB stuffed in there! Those twisted pair CAT5 interconnects and Hammond boxes, that's a build close to my heart, indeed.

When you get the chance, could you report on the noise level, with and without the inputs connected?

Thanks,

-R

[rjm]

Now that I think about it, I'm curious what you did with the turntable ground wire what with having a separate box for each channel...

[needlz]

The enclosures are mechanically tied together (will have them on stand-offs if they sound good post burn in). I was going to connect a twisted pair from the TT and split them between the two but it seems going to one from the TT and connecting the two enclosures did the trick.

The den shares a wall with my neighbor's bedroom so I will need to wait until manana before I can resume the listening.

[needlz]

I do get a good amount of RF hum through the phonoclone. Adjusting the position of the input cables changes the amount of hum from deafening to mildly annoying.

[rjm]

If its basically quiet with the inputs disconnected, switching to a shielded phono interconnect might be a good idea, combined with putting as much distance between the input signal cables and potential noise source (Phonoclone power supply, turntable motor, other power transformers.) as possible. Since you didn't have the problem before, the Phonoclone power supply is an obvious suspect.

If its really RF interference (radio stations, rather than hum), you could try connecting a 220 pF cap over the inputs (pin2,3) of the input op-amp, as per the earlier post by cjunk.

Sounds to me though like you've got magnetic field coupling from a power supply transformer into the interconnect cable. The Phonoclone circuit, having zero input impedance, may be more sensitive to this than other topologies, or it might just be that the high gain makes the noise more obvious.

-R