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Footling with phono cards

RichardH

RichardH

Bodging pleb
Having been pleased with the results of popping some 323/3 S boards into a separate box and feeding them from their own hicap, I'm going to try tweaking the boards themselves. Now I'm no electronics guru, and am much more in the "monkey see monkey do" mould, so forgive the questions.

Looking at the London Live DIY hifi mods page (which relates to the 523 rather than the 323, but there are a lot of similarities), the first thing I notice is that they recommend improving the voltage regulator, which seems to drop the voltage for the rest of the card down to 20v. Now, am I missing something, or would it be possible to lose that whole chunk and just feed the card 20v to begin with?
This brings me to the second query - the 323 cards have the two 47uF decoupling caps, which are recommended to be replaced by oscons. Now the oscons I can find don't come in 25v 47uF - either they're lower voltage, or lower capacitance. Any experiences here? Is this another good reason to drop the input voltage down to 20v?
 
Richard, I have replaced the 47uF power rail decoupling capacitor with 56uF, 25V SP OSCONs. I don't think size really matters for this cap, within limits of course. Certainly there has been a 'smoothing' of the overall sound (a bad pun?), a little coarse edge to the sound removed. Personally I like the sound.

Also, I've trying a couple of Les's BC128(?), solid Alu caps in place of the tants, both input and output. Again a smoother sound, but the bass certainly takes a long while to come back on song.

I've replaced the two polyester caps with polystyrene, the 22nF and 6n8F. Hunting down a couple of 68nF polystyrene caps rewarded me with an email from LCR asking £20 for four! So I have a SMR10 PPS in there at the mo. I found the sound with the cap changes were remarkable, cleaner, leaner, more focused, less 'smudgy' (if there is such a word).

Once upon a time I did remove the regulator (zener diode+resistors+ZTX384), but now the SRs are back in the PSU I put the cct back for stability, as recommended by Neil. I have read good things about the improvement in sound quality though. I believe Andy has something up his sleeve!

Les also recommends replacing the 5xZTX384 ladder with 2SD786s (from memory!) Tracking these down at a reasonable price has not yielded any fruit yet.

Lots to tweak and try... I should really take a picture of the moded boards, quite colourful they are!
 
Cheers Chiily. After your post I went back to the Farnell catalogue, and found some 47uF 25v Oscons straight away (duh!) from the SC-SA series. Might you, they're £2.60 odd each. Ahhh - just found the 56uF SPs you must have used - the CD catalogue lists things in a funny way sometimes, so I hadn't notieced they went down that far.

I was going to try both oscons and the BC128s to replace the tants, and see which worked best - the pig is letting things burn in and then comparing....

I did pick Les's brains the other day re that ladder - he commented that you can cut down the ladder with a single low noise jobbie, so I may try that when suitable transistors come available.

I'll have to try that PPS jobbie - looks like a sensible thing to give up at the 22nF level on the polystyrene front... Les suggests polypropylene as an alternative to polystyrene, I think.

Have you tried upgrading any of the resistors, at all?
 


Also, I've trying a couple of Les's BC128(?), solid Alu caps in place of the tants, both input and output. Again a smoother sound, but the bass certainly takes a long while to come back on song.
Click to expand...

Black Gates are also an option for the in/out position.



Once upon a time I did remove the regulator (zener diode+resistors+ZTX384), but now the SRs are back in the PSU I put the cct back for stability, as recommended by Neil. I have read good things about the improvement in sound quality though. I believe Andy has something up his sleeve!


Just to clarify - are you saying that the zener circuit produced a better result than a Superreg feeding the board direct?

Thanks
 
Originally posted by Jo Sharp
Just to clarify - are you saying that the zener circuit produced a better result than a Superreg feeding the board direct?

Thanks
Click to expand...

Jo, the concern here is that if the SRs are too 'far' away from the phono cards then additional regulation is required, hence when I moved the SRs to a separate box I had to reinstate the zener diode regulation cct on the MC cards. I'm not sure about the sound quality gains, but removing a noisy zener diode from a particular senstive cct must be a 'good thing'. Though the problems I was having with sound quality, see thread on 18v in a 32.5, were probably masking any improvements due to removing the zener diode cct.

Oh, which BGs type would you recommend for i/o?

Richard. Yep, the SPs were expensive. I've now replaced all the power rail decoupling caps on the unity gain and 12x final stage boards with SPs. Quite a sweeter sound, though dry and lean (I like dry and lean).

I have tried SGs replacing the tants. I midband was superb, treble quite sparkling but the bass was lost to a distant rumble

And I couldn't find any SPs at 47uF, 25v to replace the second cap on the boards, hence my orginal idea of running the SRs in the pre-amp below 20v. I have left the ROEs in place. I'm not sure of the qualities required of this cap in what looks like a filter.

On the resistor side I followed Les's advice and replaced the 15Rs with ones by NEOHM, RS order number 148-051, 1% tolerance and 50ppm temp co. I just couldn't find anyone in the UK who sold RC55Ys at 15R. The value is in the range. Also, working from Neil cct diagrams on his site I did trace the signal and feedback paths through the MC cct and replaced these resistors with RC55Ys. Not sure if this has really bought any gain and it has meant I had to replace a 470R with a 475R, in parallel with the 68nF. I will swap it back once the boards and SRs have burnt in a little more to gauge the different.

I have tried, and failed, to model the MC cct in PSpice, first time I had used this package in my life. I was hoping to mess with some of the component values, but it is all in the listening.

As to a single low noise jobbie to replace the 5 transistors, I would be very interested in anything you try or fancy trying

Any help, part numbers etc drop me a line at garf at roadum dot org dot uk.
 
Garf,

From the Audionote website :


The Black Gate™ C Type

Designed for coupling between circuits with a direct current potential difference. Features better leakage and distortion characteristics than tantalum film capacitors. Lead lines fixed with resin for resistance against shock noise. Capable of transmitting signals at a high level of performance in a physically very small electronic package, suitable for use in high gain pre- and power amplifiers, small audio systems and video applications.


The N and Nx types are also recommended. Full details here.

http://www.audionote.co.uk/kits/cap_black_gate.htm


I understand that Audionote have stopped selling individual components now, but you can get BGs from Audiocom.

Jo
 
Right, I've been a busy boy. Am taking the mods slowly, and have so far just swapped out the 3 polyesters so far.

However, I have traced the circuit diagram through, from the circuit on Neil Mc B's site. Have a look at my lovely "inneractive" phono board page....
 
Jo, the concern here is that if the SRs are too 'far' away from the phono cards then additional regulation is required, hence when I moved the SRs to a separate box I had to reinstate the zener diode regulation cct on the MC cards. I'm not sure about the sound quality gains, but removing a noisy zener diode from a particular senstive cct must be a 'good thing'. Though the problems I was having with sound quality, see thread on 18v in a 32.5, were probably masking any improvements due to removing the zener diode cct.
Click to expand...

Just some improved decoupling is all your likely to need here, rather than add that awful Zener reg.

Try a 3.3 - 4.7u Polyester film cap in place of the 47u, and 1R in place of the normal 27R feed.

Andy.
 
Andy,

Just for clarification; are you talking about removing the 47uF power rail cap and replacing it with a smaller polyester film type? Wouldn't that reduce the regulation?

Confused I am...
 
Just for clarification; are you talking about removing the 47uF power rail cap and replacing it with a smaller polyester film type?
Click to expand...

Yes, but you must reduce the value of the resistor feeding the circuit, from the normal 27R to 1 - 2.2R (use 1R if the reg only feeds a single circuit, 2.2 if it feeds 2 circuits).

As an example, at an LF frequency of say 100Hz, the rail impedance using the conventional Naim circuit will be (assuming a perfect PSU) 27R in parallel with about 34R, so the circuit sees around 15R.

Using the above arrangement the circuit sees 1R and the cap has little effect - a 15x improvement in rail impedance.

The cap only then starts to work at much higher frequencies, reducing its sonic imprint. The Oscon's are a lot better, as I think you've found, but even these aren't a match for even an inexpensive film cap.

This only works with super-reg's BTW, the performance of conventional reg's isn't sufficient to do the above trick, an Oscon / 27R would be better here.

Andy.
 
I have just bought a Denon DL103. Which has load impedance of 100ohm and output impedance of 40ohm.

I have a 323/4 K and a 323/2 S.

Given that the /4 is probably a lot better than the /2, I intend converting the /4 K to a /4 S.

However, I found the following information in a review for a phono stage

Flipping the DIP switches to 100ohm load, 0pF capacitance, and 50dB gain, the VPP-1 was ready to be used with the Denon DL103 low output moving coil cartridge. Options where, (100ohms or 47kohms), (0pf or 100pf).

Would it be better to swapping the 560ohm resistor for a 100ohm resistor and not replace the 1n0 cap?

Or is it the 40ohm-output impedance that determines the resistor value.

Or should I use the values used in a 323 S
 
The DIP switches in your quoted review are to do with MM-MC conversion.

I'd leave the Naim stage alone and see how it sounds.

Paul
 
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