The Phonoclone and VSPS PCB Help Desk

[rjm]

I'm not sure exactly what your DC protection circuit is, or why you even need it, but apart from that the plan looks okay to me - except for one thing:

If you break the signal and power grounds within the VSPS the op-amps bypass capacitors are connected to the signal ground back in the preamp via some long lengths of wire and this might cause a problem. Just so you are aware in advance.

Good luck.

/R

[LHMAudio]

rjm - Success! I made the changes as suggested and the VSPS is nearly dead quiet. There was some hum picked up by the output leads from the VSPS to the preamp selector switch. Repositioning the leads made the hum go away, so I will look at shielding the wires with the shield connected only at the VSPS.

The tube/mosfet hybrid line stages are not stable with respect to DC offset. They tend to drift over time. I want to be able to listen without an output capacitor so I added the DC protection. The protection circuits are a modded version of the Epsilon12 associated with the M3 head phone amplifier. The cicuit is here:

http://www.amb.org/audio/epsilon12/

I modified it to use a real ground rather than a virtual ground. This eliminated the top portion of the circuit. I added a resitor to the negative leg for regulation stability (there wasn't enough current draw for the negative regulator to work). I have two protection circuits, one for each channel since the circuit sums the offset.

Thanks for all your help on this! I will be listening to vinyl all weekend.

[LHMAudio]

rjm - by the way when you say:

If you break the signal and power grounds within the VSPS the op-amps bypass capacitors are connected to the signal ground back in the preamp via some long lengths of wire and this might cause a problem.

What type of problem? Would I be looking for oscillation? I don't have an oscilloscope, so how would I tell if there was a problem? So far it appears to work correctly, but I haven't checked to see if anything is getting excessively warm. One ground wire is about 25 cm and the other is about 10 cm. Is this too long? Is there any modification I can make if there is a problem as I don't think I can shorten the ground wires by much?

Thanks.

[rjm]

I've had trouble with this, which is why I brought it up. Come to think of it though, it was having the capacitors attached too far away from the opamp power pins that cause the problem, not the long return to the load.

If your setup is now hum-free and sounding as you expected it to, I'd forget about it. Chances are high that its not remotely an issue. There's no way you can do it any better than you have done anyway, not without completely rebuilding everything.

Glad to hear it worked out.

/rjm

[LHMAudio]

Well my wife is home and the house did not burn down so it is either fine or blew the fuse. I'll find out when I give it a listen tonight.

Thanks for all your help.

[rjm]

Reminder that the deadline for ordering Phonoclone and VSPS PCBs is Saturday, June 25.

VSPS $20
Phonoclone mini $20
Phonoclone BE $45

price per pair, includes shipping worldwide.

-rjm

[Original Burnedfingers]

Just saw this thread......are there going to be any extra VSPS boards? If so I would like to purchase a pair.

[rjm]

I'd like to ask for suggestions regarding the PCBs.

The twice yearly batch order mechanism is a compromise. It's annoying for you, having to wait for months, and to be honest, its still all too frequent from my point of view.

Not that I've lost interest, its just that I cant really justify the time investment given that both VSPS and Phonoclone projects are now mature.

So, there are a couple of different options:

1. Just sell the PCBs, no kits or parts, and have enough stock kept so that orders can be sent without delay.

2. Make the Eagle board files available to download, so you can go and order your own from Olimex or wherever.

3. Make the Olimex phototools ref number publicly available, so you can go to them and order the board from the files they have made from my Eagle files. This way you avoid any processing charges, though whether you'd be given the discount for a repeat order I can't say. (Their current policy is a 20% discount for every identical board (10x16cm) after the first.)

Since the VSPS and PC mini are quarter eurocard size, you'd be looking at a minimum order of 4 boards. Its rather inefficient to order individually, especially if you dont get the discount.

The PC BE works out to about the same price whether you order it by yourself or through me, again depending wither the discount is made available.


At present, I am leaning towards putting the eagle files into the public domain. Hopefully, people here at diyaudio could then advance the project as a group effort: making the Gerber files available, for example, or creating new varients for differnt voltage regulation circuitry, etc.

I'm Ok with making the Olimex phototools ref no. available, but I'd have to confirm with them first.

-Richard

[rjm]

Go forth and prosper!

[franksmith]

I finished my version of the phonoclone yesterday late at night.

It use the phonoclone be boards made by a 1 hour etching service near here. I have 2 transformers with 2 seperate 13vac tap each so I'm using 4 diode bridges. The casing is made of an old 10base-t network switch (cisco) with an added plexiglass front pannel painted at it's back with black spray paint. I modified the 1.5k / 220 ohms resistors combo on the regulators to a potentiometer / 220 ohms so I can adjust accuratly the voltages.

It's used with a dl-103, sme 3009 (rewired in cardas) on a modified thorens td-125. The preamplifier is based on tx-102 s&b mkIII transformers and my 4 channels amplifier based on lm3875 and line level cross-over. My speakers are 96 db efficient using fe206e on decware hdt cabinet and great heil tweeters.

At first I had problems with opamp oscillation by my fault (used opa637 at the second stage). Now I use opa27 in first stage and opa627 on the second stage. Until I resolved the oscillation problem the sound was nasty and noisy. Using the scope the problem was easy to solve.

The phonoclone is pretty silent in my configuration, the gain is just perfect to match my digital source and more than enough in my global configuration.

I made it out of cheap (not accurate) resistors but used nice polystyrenes matched capacitors in the riaa section. Now I will improve the component since I really like the result.

I have to finetune the loading (the dl-103 like high loading resistors), I want to get rid of the 4.7uf capacitors if the dc ofset is low enough and try different opamp configurations.

Thanks Richard for the design and the files you sent me !

Sylvain

Here some pictures :