Caiman passive output mod revealed

[lemon]

Comparative Table with Capacitor of 2.2uF



Frequency Response with Capacitor of 2.2uF


Τhe data tell the truth ... we must have enough attention to the selection of the capacitance whith a low input impedance preamplifier.

[HighFidelityGuy]

Excellent work Manolis!
That illustrates the relationship very clearly and should help people choose what capacitance value to aim for. Thanks.

[MartinT]

But watch the vertical scale: -1dB is a very small amount, barely discernible, and how many active preamps do you know with an input impedance of less than 47k ohms? Coupling caps are not for passive preamps anyway.

[HighFidelityGuy]

But watch the vertical scale: -1dB is a very small amount, barely discernible, and how many active preamps do you know with an input impedance of less than 47k ohms? Coupling caps are not for passive preamps anyway.

Could you explain a bit more about why coupling caps are not for passive preamps? I have a passive preamp and I've been told that because it uses a 10K Alps potentiometer the input impedance is 10K, so surely that would make using a higher value coupling cap (in the DAC output) rather important. Or am I missing the point you're trying to make. That's quite possible. Cheers.

[MartinT]

Yes, you could use a higher value coupling cap into a 10k ohm pot, but you might start hitting the drive limits of the DAC chip and your gain remains low. I personally far prefer an active preamp that doesn't have so many gain/noise/frequency compromises.

[Reid Malenfant]

I have a passive preamp and I've been told that because it uses a 10K Alps potentiometer the input impedance is 10K, so surely that would make using a higher value coupling cap (in the DAC output) rather important. Or am I missing the point you're trying to make. That's quite possible. Cheers.

Yes, you'd need a capacitor approximately 5 times the value of one that'd produce the same low frequency rolloff as with a 47 or 50K potentiometer

I have just had a thought, i'm not sure whether you'd like to try this but i think a PM to the Caiman designer might well get you more information. In theory the Caiman will output zero volts with no signal, the only reason DC blocking caps are used is because of the op amp output which can & often indeed does have a DC offset. No op amp is perfect so you'll get a bit of DC which will cause a bit of noise if it's allowed to conduct through the volume pot.

You might be able to get away with doing away with the coupling cap altogether if using the passive mod. Again i'd suggest a PM to the man himself. Assuming the DAC output to be zero with zero input i see no need for the cap at all, it might be able to be replaced with a bit of wire

Just a thought

[MartinT]

You might be able to get away with doing away with the coupling cap altogether if using the passive mod. Again i'd suggest a PM to the man himself. Assuming the DAC output to be zero with zero input i see no need for the cap at all, it might be able to be replaced with a bit of wire

You can't. As I remember it, the Wolfson DAC chip has about 2.6V on its output, which is why you need a coupling cap.

[Reid Malenfant]

Ah, yes indeed you'd need a coupling cap. Sounds like it uses a 5V & ground rather than +/- supplies

[MartinT]

Sounds like it uses a 5V & ground rather than +/- supplies

Yep, thus the favourite mod of replacing the +5V standard 7805 regulator with something better.

[Jonboy]

These are subtle differences, guys, not night and day!

The ClarityCap ESA sounded very clean with transparent midrange, extended highs and a non-harsh overall sound but slightly light in the bass. Note that I was using 1uF 600V but into a 47k load so plenty of bass extension. They were better than the Rubycons but not by so much that the Rubycons are embarrassed.

The AuriCaps better the ClarityCaps by a small amount of midrange transparency and liquidity (female voice is truly beautiful), very wide soundstage and a very tight but extended and slightly weightier bass. Note that mine are 2.2uF 200V but I don't think the value differences account for the difference in quality of the bass.

Does that help? I say again, SUBTLE differences. All of these caps are good!

Thanks for your breakdown Martin, thats helped me a lot
I'm going to give it a go with some non polar caps i have had given to me and go from there