The Phonoclone and VSPS PCB Help Desk

[rjm]

The two black wires connect together to AC neutral, the two red wires connect together to AC live (for N. America).

Here's the likely problem, the transformer manufacturer has poorly chosen the wire colors for the output windings, you can't tell which blue wire and which green wire connect to a common winding, but you can easily check for connectivity with a multimeter.

The blue and green wires from one secondary winding go to the ~ terminals of one of the rectifiers, the blue and green wires from the second secondary winding go to the ~ terminals of one of the other rectifier.

Again: the blue and green wires connecting to a rectifier must be connected inside the transformer, check resistance using a meter/tester. If they are from separate windings things will not be good.

After that it's easy: + if one rectifier goes to - of another (arbitrary), defining COM. The remaining + is your V++ and the remaining - is your V--.

[davidfmartin]

Hi RJM,

Originally Posted by rjm

The two black wires connect together to AC neutral, the two red wires connect together to AC live (for N. America).

This is how I wired it. No issues there.

Here's the likely problem, the transformer manufacturer has poorly chosen the wire colors for the output windings, you can't tell which blue wire and which green wire connect to a common winding, but you can easily check for connectivity with a multimeter

Yes I used this method for determining the winding pairs after seeing it somewhere in this forum. Before I checked continuity I was blowing fuses this is because I had crossed a green and blue wire from the secondaries, after I did a continuity check and verified that I had the right blue/green pair and connected to ~, no more blown fuses but read on.

The blue and green wires from one secondary winding go to the ~ terminals of one of the rectifiers, the blue and green wires from the second secondary winding go to the ~ terminals of one of the other rectifier.

All good after continuity check.

Again: the blue and green wires connecting to a rectifier must be connected inside the transformer, check resistance using a meter/tester. If they are from separate windings things will not be good.

After that it's easy: + if one rectifier goes to - of another (arbitrary), defining COM. The remaining + is your V++ and the remaining - is your V--.

Now I have made a "Y" adapter that goes from + of the first rectifier to - on the second creating my "COM". This is where the problem starts, no blown fuse, but I am getting close to 30v on the remaining + (v++) and - (v--) terminals.

Btw, I get close to 12v AC when I check the secondary windings and when I connect a single winding pair to one bridge rectifier I see about 15v DC on the +/- terminals.

Thanks for all you help!

[davidfmartin]

So I wired just one secondary to one bridge rectifier and have com going to chassis ground. I get about 15v at the v+/v- terminals on the pcb and around 12v at the opamp. I am listening to Blue Train right now and it is working, but I would still like to now why I get double the voltage with two rectifiers? Please bare with me I am a total electronics noob.

[rjm]

After reading your detailed reply (thanks, that makes my job easier) I'm pretty sure everything working as it should. The hard part is how to convince you this is indeed the case.

Voltages and how to measure and report them:

"I get about 15v at the v+/v- terminals on the pcb" is poor wording as it can mean two totally different things:

1. There is 15 volts measured between the positive (V++) and negative (V--) terminals on the PCB

or,

2. both terminals measure +/-15 volts above/below ground(COM).

Whether one rectifier or two, you should have the same result:

The voltage measured between V++ and COM is about 15 V.
The voltage measured between V-- and COM is about -15 V.
The voltage measured between V++ and V-- is about 30V.

If that's what you measure then you can safely connect the circuit board.

If you only measure 15 V between V++ and V-- then there is a problem, but the circuit will still power up and play music. If you measure 60 V between V++ and V-- then do not connect the circuit board as all the electrolytic caps will blow since they are only rated for 25 V.

[protos]

A few remarks about sound quality.

Everything worked normally from the start.However on first audition I did not like the sound at all.Despite good dynamics the mid/high-range was very hard and unnatural (compared to Naim phono boards).I am not a huge believer in break -in effects so I was initially disappointed.
However 48 hours later everything is much better .Although I am still not 100% sure of the midrange I clearly have much better bass , micro and macro dynamics as well as very good soundstaging.
One remaining problem is that of high buzz and hum.I put in some C0 Rf suppressors since I did notice some rf breakthrough and everything is grounded as per schematic and the PS is in a different case.But this circuit must be very sensitive to noise issues -any ideas?.

Of course not to forget to congratulate rjm on an excellent piece of work and general and generous support to the diy community.

[northernsky]

Hi,

a couple of days ago I just reported in the thread "Phonoclone 3" the same RF interference problem with my phonoclone. Please read there some suggestions I received. I still had not the time to check if they work

Renato

[davidfmartin]

Thanks RJM! All is good now. Sounds great! May I make a suggestion that you add a section on the construction guide about testing voltages after assembly to validate that everything is working as expected?

Regards.

[rjm]

@protos

I'm still not sure exactly why, but the phonoclone circuit takes a couple of weeks to settle down. I've seen that myself time and time again, and many others have observed the same thing.

Also, statistically about 4-5% of phonoclone builders seem to experience problems with RF and noise. For the VSPS it is 0%. Unfortunately (in a sense) I have never had such a problem, so I've been unable to look at the issue myself directly. Gain set too high, incompatibility with tonearm grounding scheme (seems to affect people with DIY tonearms/turntables/phono interconnects more than others), noisy RF environment (near radio towers, cell phones, or even WiFi routers)... there are many factors. Perhaps the best thing is for you to email me directly and we can go through things step by step.

[[OK, "never had a problem" isn't quite true: my phonoclone was not happy sitting next to my wireless router, and turning off the lights in the room can generate audible ticks from the speakers. ]]

One thing to try: 50ohm carbon resistor from COM after the rectifier diodes to the power supply case. The other thing is a 330pF between the op amp inputs. The last thing (if you have a dual mono power supply) is do disconnect COM from the phonoclone chassis and reconnect it at the input RCA jacks of both channels by removing the insulating washers from the back for example.

@davidmartin

Glad to hear it works, and I'll keep your comments in mind.

[protos]

Actually I was naughty and never connected PS com to PS AC ground lug so the PS is not AC grounded (the ps case is grounded of course) to avoid ground loops.Of course the com is then grounded on the phonoclone chassis.The C0 is 220pf and cures the rf problem.The hum problem is not really unacceptably bad .At normal/average listening levels you can just about hear from the listening position when the music stops but of course at louder levels it is more obvious .

[rjm]

That level of hum is not normal.

Nice to learn that C0 200 pF (across IC1 in+ and in-) gets rid of the RF at least. There are actually a number of things you can do to "RF proof" your phonoclone. I've been reading up on them:

1. 1-10 nF cap between the insulated RCA shields and the chassis, for both the inputs and outputs, and also for COM to chassis at the power supply connection.
2. 100-1000 pF cap between the input wires (IN+ to IN-), but don't do this for the outputs (out- to out-) as the driving op amp may not like it.

Just to be clear, normally COM is not connected to AC earth ... ie you have it as I have it, and how I tell people to do it. There may be some advantage in connecting COM to AC earth via the power supply chassis, but not directly ... use a 47 ohm resistor and say 10 nF in parallel, to avoid ground loops.

re. the hum issue, just for reference please let me know which cartridge and arm, and what value of R2... thanks!

/rjm