PSU for Caiman with Pics

[Dave Hewitt]

Martin,I think you run the possibility of having a shorted turn on the tranny in your psu with the earth cable connected to the mounting bolt,just connect to case,dont make a continuous circuit thro the centre of the tranny.
Regards Dave.

[MartinT]

Hi Dave

That's a good point. I shall re-route the earthing locally. Look out for a new posting as 'PSU for Caiman' when I rework it tonight.

[MartinT]

Martin - do you know what is the optimum input voltage for the Caiman? I see that it states 15v to 18v on the back panel.

I have been thinking about just that today. The newer Caiman PSU puts out 15.5V and I was going to try up to 18V but before I do that I shall have an internal inspection and ensure that there are no 16V (a common value) electrolytics on the PSU rails.

[HighFidelityGuy]

I have been thinking about just that today. The newer Caiman PSU puts out 15.5V and I was going to try up to 18V but before I do that I shall have an internal inspection and ensure that there are no 16V (a common value) eletrolytics on the PSU rails.

From what I remember the main reservoir cap in the Caiman and standard 7520 are 16V. There is however a diode just after the power input that causes a voltage drop of about 0.5V. There's also a resistor which drops the voltage a bit more but I'm I can't remember if that's before or after the reservoir cap. So I would have thought you'd be ok supplying the Caiman with up to 16V but I'd be very cautious above that as there's very little safety margin.

I've been wondering about swapping the diode in my Caiman for a Schottky to reduce the voltage drop. I've done this successfully in my 7520 and that seems fine but that's only getting 12V.

With the standard diode in place in my Caiman the 12v Murrata reg is getting about 14.5V on it's input which is below the recommended 15V input. So a Schottky should bring the supply closer to 15v.
14.5V is still above the dropout voltage for that reg but the spec sheet says it provides the cleanest regulation from 15v+. So it makes sense to me to try and achieve that for completeness.

So I guess there's scope for supplying a bit more voltage, swapping the diode or both. I'm not sure if either of those on there own would make an improvement or whether simply using a quality linear regulated supply would overshadow these. Who knows. I guess these are all things you could experiment with. I'd be interested to hear how you get on as these are all areas I'm interested in exploring.

[UV101]

Whats the diode in the circuit for? If you are supplying the unit with DC, I can only "assume" its for protection. In which case, its not really needed unless something goes wrong with the PSU and it outputs AC.
*** purely educated speculation as I don't have a unit to look at or the diagram


With respect to the input voltage to the reg being 14.5v and not 15v, I wouldn't worry about that at all! So long as the Murata can supply the required 12v constantly and cleanly (the cleaner the better!) all will be fine. I intend to fairly soon take a look at one of these dacs as I'm really interested to see what I can do with it. Given the rocky start that Stan and I got off to, I'm hoping that he doesn't mind me taking a look and making my own suggestions here in the open!

[leo]

Yes, the diode on the DC input is mainly for protection.

[leo]

None yet - all I could glean from Dave is that he is going to put a much larger energy store (i.e. reservoir capacitor) in it.

He seemed to be quick to mention it on the first page of this thread so I thought he maybe keen to give some circuit details etc

Anyway let us know how you find the STR goes with the Caiman, I never tried the TR's with the Caiman but did try them with the analogue stage for the TDA1541 based dac and Sabre dac, tbh I thought it softened dynamics and made the bass loose some tightness even after adding CRD's on the output to give it more of a constant load, it may go much better with the Caiman though, of course only way to know these things is try it Its reported these regs are an excellent match with Naim pre-amps

[HighFidelityGuy]

Yes, the diode on the DC input is mainly for protection.

That's what I thought too. My idea of swapping it for a Schottky was simply to reduce the negative effect it has on the DC voltage to a negligible amount. You could of course just replace the diode with a wire link but then you'd loose the protection. Personally I'd prefer to keep the protection to be on the safe side.

As I said before, according to the spec sheet the 12V reg will work fine at 14.5V but 15V input will make sure it's output is as clean and accurate as possible right up to it's full output current rating. So it may be worth trying to see if it makes a noticeable change to the sound. Yes it's probably a bit overkill but then if you're going to fit fancy regs you may as well try and get the best out of them I think.

[MartinT]

I've redeployed my PSU project for the Caiman DAC with very promising results. Some pics first:







This project uses the Superteddy circuit described here http://www.teddypardo.com/. It features a discrete voltage regulator (rather than the LM-317T used in the Teddy) followed by a filter gyrator circuit. In experiments I have found this circuit to feature good, but not great, voltage regulation, slow start-up, some drift but settling after about a minute, very fine control over output voltage, high current (2.5A) capability and very low noise indeed. This latter is what attracted me to the circuit in the first place.

In addition and not shown in the pic above, I added another Nichicon 2200uF Fine Gold electrolytic on the DC input to beef up the reserve charge. The transformer is a 9-0-9V AC toroid providing about 23V raw DC into the regulator. I have set the output to exactly 16V to prevent damage to the Caiman's electrolytics but provide as much voltage as possible into the Dexa 12V regulator in my modified Caiman.

For safety I have also connected the earth to the chassis rather than via the toroid mounting bolt as shown in the pic.

Feeding the Caiman, the PSU barely gets lukewarm so there is no heat dissipation issue.

Listening to the Caiman on CD source from this PSU (using my Blu-ray player as transport) has moved it up from very good indeed to touching on the performance of my Ayre SACD player. I am hearing a wealth of micro detail, very natural and clean treble, extended, deep and tight bass and excellent spatial placement. The background is deep and black. I haven't yet performed the additonal electrolytic mods to the Caiman so there is more performance yet to be had. Soundtracks from Sky HD are very impressive, especially programming on HD channels, again with that natural placement of fine detail distinguishing it from the standard 15V Caiman PSU.

I believe the low noise performance of this PSU is responsible for enhancing the DAC's sound, however the 16V feed may just be helping the Dexa regulator perform in its envelope too.

This is good!

[leo]

Glad to hear it finally went well in the end with this psu.
so you get the good filtering of the STR and the low output impedance of the Dexa's