The Phonoclone and VSPS PCB Help Desk

[rjm]

This is the fourth phonoclone I've put together, the last three of which have been using the PCB. Of the three that I've sat down and listened to, this is the most neutral. Its a little on the soft side, but at least it doesnt have the slightly intrusive treble of the original prototype. I put this down mainly to the filter caps, which were all low impedance types (ELNA and Panasonic) on the protoype, and regular Nippon Chemicon KMGs or equivalent on the later versions. The mica RIAA caps, for as far as I can tell, are sonically transparent ... I cant hear them at any rate. The bulk of the resistors are Riken ohm, with a couple of Panasonic carbon films in the RIAA since I cant get Rikens in these values, and a good old Allen Bradley for R8.

I recycled the old VSPS case (Hammond 1590D) and just managed to squeeze the two PC boards in there. Stuffing the board and hooking it up took less than 2 hours.

/R

[Franz G]

Richard

Many thanks for this great and very simple circuit!

I made one amp for me last week, for my DL103. This couple together really starts singing! It beats my formerly NAD PP2 without any discussion.

My amp is based on two OPA2227. No resistors between +input and ground. External, filtered, regulated and switchable PSU. Ferrite Beads direct before the bypass caps to filter any RC.

I prefer some voltage about 10V, concerning noise / sound.

Apropos noise: 10cm nearby my >95dB/W speakers, there is some very slight noise. No hum, when the psu is about 30cm away from the amp.

I am excited, now for more than 4 days listening to the amp.

Franz

[Panelhead]

Originally posted by rjm
This is the fourth phonoclone I've put together, the last three of which have been using the PCB. Of the three that I've sat down and listened to, this is the most neutral. Its a little on the soft side, but at least it doesnt have the slightly intrusive treble of the original prototype. I put this down mainly to the filter caps, which were all low impedance types (ELNA and Panasonic) on the protoype, and regular Nippon Chemicon KMGs or equivalent on the later versions. The mica RIAA caps, for as far as I can tell, are sonically transparent ... I cant hear them at any rate. The bulk of the resistors are Riken ohm, with a couple of Panasonic carbon films in the RIAA since I cant get Rikens in these values, and a good old Allen Bradley for R8.

I recycled the old VSPS case (Hammond 1590D) and just managed to squeeze the two PC boards in there. Stuffing the board and hooking it up took less than 2 hours.

/R

Richard,
I take this to mean that you prefer the sound using standard type caps. Is it more relaxed than the more expensive types?


George

[rjm]

My hypothesis is that a low ESR cap right after the voltage regulator causes a certain amount of stress, hardening the sound.

I've been kindly given a set of Rubycon ZAs so I will try to get around to a definitive test, until then though its no more than a hunch.

/R

P.S. Speaking of tests, using some of the equipment at work I will try to at least put PC no4 through some basic tests: measurements of the frequency response and noise spectrum are planned.

P.P.S. Franz, when I get the chance I'll replace the 7x12s with 8 or 9 V versions and see if I can get an improvement. I just cant figure out why this should happen...

[Franz G]

P.P.S. Franz, when I get the chance I'll replace the 7x12s with 8 or 9 V versions and see if I can get an improvement. I just cant figure out why this should happen...

I think it is a matter to optimize between headroom and noise. The higher the voltage, the higher the headroom but the same time noise is increasing eg. the S/N ratio is getting worse.

So, it could be an advantage to drive the first stage by a much lower voltage than the second stage. Maybe 5-6V for the first stage, 10-12 V for the second stage.

I cannot test it, as I used dual opamps

Do you still use LM7xnn? Aren't they to noisy? I prefer LM317/337.

Franz

[rjm]

I dont follow why the output noise of the op-amp should increase with the supply voltage. What is the rationale behind that?

I'm still using my humble 7812s. I've got a lot of mileage from these chips and I'm still interested in seeing just how far I can carry them up the hifi totem pole.

-rjm

[ran_ph]

Maybe it's more of the noise of the regulator?

LM317/337 RMS Output Noise is 0.003% of Vout (National Semiconductor datasheet). So as you increase the voltage you also increase the noise.

Fixed voltage regs output noise from NJR datasheets:

NJM7808 = 55uV
NJM7809 = 60uV
NJM7812 = 75uV
NJM7815 = 90uV

[ran_ph]

Some say that a low esr cap after regulator is not a good thing. Here's one:

Originally posted by Jocko Homo
All of those 3-terminal jobs have a feedback loop, and just throwing any old cap......especially with low ESR is asking for problems. It affects phase margin, and can easily make an oscillator. As you have found out.

Those of you with access to a spectrum analyzer.....here's what you do.

Look at the noise vs frequency with several different value and types of caps. You will see how the noise will peak at some frequency if you pick the wrong one.

If you don' t have an analyzer, but do have a 'scope and a square wave source.............drive the output with the square wave, and see if it rings. If it rings a lot, you have stabilty problems

Jocko

[Franz G]

I dont follow why the output noise of the op-amp should increase with the supply voltage. What is the rationale behind that?

I should have write: "imho"

It was just a hypothesis of me, not beeing an electronic engineer. Maybe I was wrong?

In the meantime I could buy very cheap two 15V military batteries and I just tested my amp with it.

The result: the (very little) noise is in fact induced and amplified as soon as I connect the TT to the input.

I do not remark any difference between the battery operated amp or LM317/337 based psu (at the same voltage).

Here a picture of the battery setup.

Franz

[Panelhead]

A couple amplifiers I built lately use a dropping resistor, zener to ground, and a bypass pass cap to make a simple regulators for the input stage.
I do not have a scope, but people who do claim this is a cleaner supply than a three pin reg. Whether 78/79XX or 317/337.
I built a phonoclone last night, need to build the boxes to check. I used LM320/340. From specs this is inbetween the LM78/79 and the LM317/337.
If I hear some hash, may bypass the regs and install the zener circuit. The available current is adjustable, what is max current pull for the phonoclone?

George