DS DAC Amp matching question


#1

Just pondering… I’m replacing an amp that has input impedance of 12K ohms with another that specs 100K input impedance.

In theory, that should be a better match for my DS DAC running balanced cable direct to the amp, if I’m not mistaken, and should result in less stress and voltage sag in the output circuits of the DS, and thus perhaps a more dynamic sound ?

Please note the question mark. Comments to expand my understanding appreciated.


#2

The DS isn’t affected much by resistive loads - for example the 20dB attenuator is a 15 Ohm shunt to ground and the mute is a short of the outputs, neither of which causes any significant heat or other stress. Also the difference in output voltage changing the load from 12k to 100k is less than a 1/10 of a dB.

Perhaps the bigger differences would be caused by rejection of interference, etc. which can be a bigger function of amp quality than might be implied by just the input impedance spec.


#3

Thanks, Ted. I’m replacing a Classe Omega Stereo with a pair of Parasound JC-1 monoblocks - should be here this week. Specs are very similar, but I’m hoping for a bit cleaner sound from the JC-1s.


#4

A related question, if I may: does the DS DAC’s transformer output stage guarantee 0 volts DC output bias at all times? (This is relevant to amplifier matching in respect to the different DC bias protection methods different amplifiers employ.)


#5

Yep, the output of the transformer and follow on circuitry are symmetric (relative to ground) and passive - there’s no DC offset. The 20dB attenuator switches in 15 ohm shunts to ground on each leg and the mute is a short to ground on each leg.


#6

With this particular amp, DC offset on the output is spec’ed at zero using unique circuitry, if that is the concern.


#7
EldRick said Thanks, Ted. I'm replacing a Classe Omega Stereo with a pair of Parasound JC-1 monoblocks - should be here this week. Specs are very similar, but I'm hoping for a bit cleaner sound from the JC-1s.
I hope you are very happy. I love mine.

Out at dealer recently, and heard them driving the new B&W 803D’s (apparently all new inside), fed by an old analog Reel to Reel source.

Previously didn’t enjoy the old B&W’s with either Devialet or PS Audio DAC (and different amplifiers).

No digital in the path this time around, and the JC-1 + 803D’s were very nice.


#8

Hoping to hook them up today, driving my Apogee flat-panels thru bi-wired 12" jumpers. Should be a good fit, as the Apogees are very revealing and like a lot of current.


#9
EldRick said With this particular amp, DC offset on the output is spec'ed at zero using unique circuitry, if that is the concern.
I had no concern about your amp, sorry if I gave that impression. Just you started a topic which prompted me to actually ask a question I'd been pondering for my own reasons for a while, related to a further modification I might get done to my power amp.

#10

No issue - they sound really good, although I’ll never be able to get my sig line changed to reflect the changes on this forum - a bug in the code…


#11

EldRick, is this the sig above what you would like?


#12
EldRick said No issue - they sound really good, although I'll never be able to get my sig line changed to reflect the changes on this forum - a bug in the code...
Glad you are enjoying. Mine were 2nd hand and therefore already broken in. Read that about 400 hours is required on the JC-1's.

Peak instantaneous current is 135 A, if the 132k of output capacitance can supply. Have also read that the JFETs cause a ‘softer’ sound. Although I have no idea if this true. I do know that I enjoy the sound.

My one reservation is the negative feedback (apparently poorly implemented back in the 60s) vs open balanced circuit of the BHK mono’s. Soulution amps have massive negative feedback, but is complete within a few nanoseconds, which supposedly limits (not eliminates?) timing differences on the inverted cancellation.

Here is an interesting article interviewing 9 amplifier designers including Pass, Curl, and a Soulution guy:

http://www.moremusic.nl/pass_labs/Brochures/TAS_AmpDesignerRoundtable2012%20.pdf


#13

Further, interesting to note that after Curl discusses his preference for Class A and need for Class AB for practicality, he suggests transition to hybrid Class A / D designs is inevitable.

Devialet of course doing a 1W Class A + Class D hybrid. The second iteration of which is due out with the upcoming Devialet Zero.

Without any evidence, I suspect Curl figured higher than 1W of Class A output power would be specified.


#14
Elk said EldRick, is this the sig above what you would like?
It's close enough - still mystified why changes in Preferences don't work.

#15

I have no idea.

If you would like a different sig, send me a PM with what you would like and I will change it for you. While the process is a bit squirrelly at times I seem to be able to get it to work.


#16

I bought the JC-1s used also. Seller stated that they were two years old, but had very limited use, as he was mostly traveling. I’m assuming that a month of power-on will complete any break-in process.

So far, though, they already sound excellent, and much different frequency balance than the outgoing superamp.


#17

Hi, I just bought a Directstream Junior dac to use directly feeding mi Parasound jc1’s amps. Connected directly through the amps I have a lot of noise through the tweeters, even when the dac has the volume ser to 0. I tried connecting the dac to a preamp and the noise lowers significantly, even it is not dead quiet as I would expect. My speakers are Paradigm Signature S8, which are very sensible, but tried with dynaudio speakers which aren’t and have the same problem if running the dac directly to the amps. I wonder if this could be some mismatch between my amps and the Directstream Junior, so I would appreciate Eldrick any information regarding how does the same match sounds in your case. Thanks in advance


#18

The 20dB attenuator can help with sensitive systems. It will lower the output level by 20dB which will also lower the noise by 20dB. Tho you can get to it on the menu with the knob… it much easier to use the remote: the FILTER button toggles the 20dB attenuator.


#19

Ted, I tried the attenuator in and the noise still there. It also reduces too much the volume, at almost full volume I only get a decent volume, not high. Looks like a hardware issue…


#20
Fmaspero said Hi, I just bought a Directstream Junior dac to use directly feeding mi Parasound jc1's amps. Connected directly through the amps I have a lot of noise through the tweeters, even when the dac has the volume ser to 0. I tried connecting the dac to a preamp and the noise lowers significantly, even it is not dead quiet as I would expect. My speakers are Paradigm Signature S8, which are very sensible, but tried with dynaudio speakers which aren't and have the same problem if running the dac directly to the amps. I wonder if this could be some mismatch between my amps and the Directstream Junior, so I would appreciate Eldrick any information regarding how does the same match sounds in your case. Thanks in advance
Hi Fmaspero, I had the exact same issue with my Luxman L-505u int amp, I am using Focal Sopra N2. Please share your solution if you find one. Paul mentioned that he used DS to directly feed amps from PS Audio, Audio Research, Sonic Frontiers, etc. I assume that he didn't have any noise problem.