Small form factor, budget DACs?

Yes Bombaywalla the 10x factor works OK. I'm not sure this is written in stone though. After listening to the differences of the average CD player or DAC output impedance (which is around 3000 ohms)verses using a separate buffer(100k ohm input and 16 ohms output at the moment) to alleviate the load of the interconnect and the amplifier. There is more dynamics,deeper tighter bass and the images are more defined. It's almost like some one took the governor off and let the engine run without it being held back.

This is using a 25K passive volume control in the loop.I should have mentioned passive volume controls. You can hear the differences very easily.

I'm not as technically oriented as you are my friend. In layman terms, it's like using a CD player that is designed to run directly into an amplifier. Then running it through a linestage/buffer before the amplifier. Most would prefer the linestage/buffer to just the straight connection. Even though there's an additional component in the loop..it sure sounds better with that buffer in between.

One means to measure output impedance of a CD player, with close results, is to have a test CD with a 1Khz signal, play it and measure the open unloaded, output signal on a good AC voltmeter. Then add a variable resistance across it, adjust it until the value is half of the open measurement, remove this resistance and measure its resistance with a standard ohmmeter. That value should be very close to the source impedance, at least at 1Khz.

I've tried the BVaudio SR10 buffer unit in the past.This was done using analog outputs not as high grade as your Wadia. The difference was noticeable. When I moved to a more substantial buffer. The difference was unbelievable! Maybe this website can explain it better than I can BVaudio . By the way my TDA1543 based DAC doesn't use Op amps at all.

Howdy mates...I also have a non os dac- the Scott Nixon Tube + ...Love it..not bad for $500, seperate power supply-a buck and quarter...Old School :)

congrats Hudsonhawk

Gmood1,
yes, 10K input imp of the next stage vs. the driving stage is not written in stone. Usually the rule of thumb is 5X-8X. However, I've found that is not high enough & that 10X works 99% of the time successfully.

OK, from your 2nd lengthier post I think I understand better where you are coming from. Let me see if I can summarize: Hudsonhawk & I were musing why these non OS DACs based on TDA1543 DACs sounded (really) bad on bad recordings. He & I were hypothesizing that it's the lousy jitter performance from the recovered clock.

NOTE: both Hudsonhawk & I have non OS DACs that use a Burr-Brown opamp buffer that drives the RCA outputs. From the spec sheet of this opamp, it has very low harmonic distortion over 20Hz-20KHz + it can drive large capacitative loads - we are talking 5nF & still have a gain-bandwidth product greater than 1MHz + it has very good settle time. So, it seems that this buffer does the job of the BVAudio SR10 & similar after-mkt buffers. Thus, I see very little advantage in further attaching an after-mkt buffer. If there is an improvement in these 2 specific non OS DACs, I surmise that it is most likely to be very little. I wish I had one on hand to give your theory a try (I would be double buffering).

Now, in your Audio Sector Premium non OS DAC that uses passive buffering, the ball-game is entirely different. As an aside, if you look @ the TDA1543 data sheet, you'll see (in Fig 1) that they have suggested the use of buffer opamps that have some bandwidth limiting (that parallel cap in the feedback). It is not the only way to "terminate" the TDA1543 output i.e. one could also use passive buffering. However, the passive buffering will rely on the TDA1543 to drive the interconnect parasitic C + the preamp input. It'll do the job (as your ears have discovered) but you know that the sound could be better (again, as you have discovered). In your particular case, the BVAudio SR10 & similar products work & show the difference since the passive buffered TDA1543 has to drive 100K & very little parasitic capacitance of the active circuitry, a much easier load. I do not think that it'll be quite the same for my SN DAC or the DAC-AH.
There is nothing magical about the 50Ohms output impedance of the BVAudio SR10. It is a standard impedance used in test & measurement equipment & by the RF engineers. It is low enough where it'll work w/ 99.9% of the equipment in the market-place no questions asked. For that matter, 600 Ohms would have worked just as well (would have been an easier load actually) as it would have been low enough to work w/ all the preamps out there.
So, you have to pay the Piper - now (opamp buffer as part of overall DAC in the same chassis) or later (use after-mkt buffer).
So, in your particular case, it appears you have 2 issues affecting the sound: insufficient drive from the Audio Sector DAC & poor jitter performance from badly recorded CDs. IMHO.

Bombaywalla,
all your theories and hypothesis are great.But you really need to hear it to understand where I'm coming from. The Audio Sector DAC has sufficient drive. Probably more than many players. I've never heard a player or DAC make a garbage recording sound good. It is what it is. I can assure you jitter performance is excellent with this combo. I do use a Superclock 3 in the transport.

There maybe nothing magical about the BVaudio SR10 output impedance but it's better than most players on the market o/p. The output impedance and voltage of the analog outputs do attenuate the signal in interconnects if not sufficient correct?

Maybe we're talking about two different things here. I'm talking about the addition of a buffer for people using passives or changing the preamp to one with a higher input impedance. Also the impedance does matter when driving long interconnects or passives. I would rather have more drive than not enough in any case. I wish you were closer ..I could quickly prove your hypothesis wrong. Anyone that has tried this knows what I'm talking about.

You must ask yourself. Why use a preamp between your Wadia and amplifier? Besides the need for other inputs. After all you are double buffering already. What do you gain when using the preamp/buffer than not using it between the Wadia?
I suspect you use the preamp because it sounds better to you than running the CD player direct to the amplifier...correct. So because you do this the Wadia must not have sufficient drive...correct? Ok I was being sarcastic with that one. :-)

What I'm doing is no different than you using the CAT preamp in the loop. Now do you understand?

There's a reason why APL,RAM and other modders concentrate so much on the output stage of their players. Which includes doing away with the negative feedback opamps in some cases. I noticed most of them use single ended designs with no negative feedback and powerful output transformers in their top players. I added the same thing ..just in a different chassis.LOL

I can imagine handling interconnect interactions is a walk in the park for such players. Never heard the APL..but just from what's used, the output impedance(should be quite low using a tube and output transformers) and high voltage should make one powerful sounding player! There's no denying it, the presence of power in the right place makes one hell of a difference in sound!

Oh yeah..the piper is one happy camper! ;-)

Gmood1,

>> You must ask yourself. Why use a preamp between your
>> Wadia and amplifier?
the answer is very simple: Wadia's digital gain control is the absolute pitts! Sonically, it stinks! I know I'm an owner but I will not prop up this unit just 'cuz I spent money on it. What I do is put the volume control to 100 thereby bypassing it. Now I have totally lost control over adjusting the volume. That is where my preamp comes in. Inside the Wadia they provide a set of DIP switches to adjust the buffer outputs from 4.25V all the way down to 0.25V for each channel separately. I believe that the user adjusts this output depending on the amount of voltage gain in his/her preamp.
Wadia claims to have a patented I-->V conversion technique & I wonder if these buffers are doing double duty of I-->V + buffering? I don't know enough about the Wadia design (& the DAC control PCB is multi-layered thereby making wire tracing nearly impossible) to make a useful comment.

>> There's a reason why APL,RAM and other modders
>> concentrate so much on the output stage of their
>> players. Which includes doing away with the negative
>> feedback opamps.
well, even if I try the BVAudio SR10 external buffer, there's no getting rid of the negative feedback opamps inside the SN DAC.
OK, I can understand negative feedback in the opamp-based output stage is less sonically than those outputs stages not having any.

>> Also the impedance does matter when driving long
>> interconnects or passives.
agree! How long is long tho? Not 1m interconnect! I think long would be in excess of 5m.
I would agree that output impedance is very imp when driving passives. A CDP having an output imp of 3K (as written in your orig post) would likely be an issue when driving a passive preamp. I agree!

>> I can imagine handling interconnect interactions is a
>> walk in the park for such players.
I believe that this would also be a true statement for a DAC using a Burr-Brown OPA627.
When I plug this SN DAC into my preamp, I have so much gain from this DAC that I have to crank down the volume knob atleast 3 clicks from where I listen to the Wadia. In the CAT that's quite a gain reduction.

>> I wish you were closer ..I could quickly prove your
>> hypothesis wrong.
well, my hypothesis is, for the SN Saru DAC+ which uses a strong enough output buffer than can drive my 1m interconnect + my preamp input capacitance, that badly recorded CDs sound terrible thru it 'cuz the dominant effect is poor jitter performance in the recovered clock from the input data stream. The poor jitter performance xlates to poor DAC performance as the DAC uses this jittery clock to perform a D-->A.

(Were I to additionally remove the negative feedback in the output buffer would I get even better sound? probably!
I think that in my DAC the jitter performance dominates over the negative feedback in the output buffer).