advertisement


MDAC first listen (part XVIII)

Status
Not open for further replies.
JohnW said:
Harry,

This is certainly an odd issue - one I'd certainly like to understand - if only out of interest as to understand what's happening!

Couple of things spring to mind – maybe the amplifier’s input stage is being overdriven by the MDAC’s output level – or maybe Hi-Levels of Low or even High frequency energy is upsetting the amps input stage…

Have you tried with the MDAC set to -1dB, (I'm presuming you are using the amplifiers level control)?

If reducing the MDAC’s output level resolves the issue then it’s the input stage of the amplifier unable to cope with the MDAC’s output level (its about 2.3Vrms “Peak”)…
Click to expand...
Thank you for getting back to me John.

I normally have the preamplifier disabled, and just adjust the output on the Quad77. Having just reversed this process, I find that when I reduce the output to -1dB I almost get rid of all the clicking but it is only when I go to -2dB that it completely disappears. So both of our initial theories as to the cause of this problem stem from the possibility of the the output of the M-DAC being too high for the Quad77 (something that could be possibly rectified by altering the input sensitivity on the Quad77, although I do not own the remote control that would allow me to do this).

However this doesn't answer the much more interesting effect of changing the filter or even altering the macbook bit depth and sample rate to something higher then the actual bit depth and sample rate of the music file being played (ie from 16bit/44.1kHz to 24bit/96kHz). Either one of these changes will stop this issue.

How about this other strange phenomena too? The Quad77 integrated has 32 interval steps from zero output to maximum on the volume control, (admittedly not linear, with bigger incremental changes for each of the first half or so steps of those output power selections). When the volume is set between 1-10 is when these clicking/flicking noises present themselves (remembering this is only on a few tracks), at the same perceived volume level whether at 1 or 10. Suddenly disappearing at 11 or above. Possibly masked, although I am really listening intently to see if I can pick up these artefacts and I am struggling at 11 on the volume control. Also remember that with the headphones plugged in, this is a non issue too.

Weird.


Let me know what you think.

Kind regards,
Harry



Just to add, apparently the selectable Quad77 integrated sensitivities include 100mV / 300mV / 775mV. I'm not an electrics expert or engineer by any stretch of the imagination, so make do with those figures as you will.
 
haridhos said:
Thank you for getting back to me John.

I normally have the preamplifier disabled, and just adjust the output on the Quad77. Having just reversed this process, I find that when I reduce the output to -1dB I almost get rid of all the clicking but it is only when I go to -2dB that it completely disappears. So both of our initial theories as to the cause of this problem stem from the possibility of the the output of the M-DAC being too high for the Quad77 (something that could be possibly rectified by altering the input sensitivity on the Quad77, although I do not own the remote control that would allow me to do this).

However this doesn't answer the much more interesting effect of changing the filter or even altering the macbook bit depth and sample rate to something higher then the actual bit depth and sample rate of the music file being played (ie from 16bit/44.1kHz to 24bit/96kHz). Either one of these changes will stop this issue.

How about this other strange phenomena too? The Quad77 integrated has 32 interval steps from zero output to maximum on the volume control, (admittedly not linear, with bigger incremental changes for each of the first half or so steps of those output power selections). When the volume is set between 1-10 is when these clicking/flicking noises present themselves (remembering this is only on a few tracks), at the same perceived volume level whether at 1 or 10. Suddenly disappearing at 11 or above. Possibly masked, although I am really listening intently to see if I can pick up these artefacts and I am struggling at 11 on the volume control. Also remember that with the headphones plugged in, this is a non issue too.

Weird.


Let me know what you think.

Kind regards,
Harry



Just to add, apparently the selectable Quad77 integrated sensitivities include 100mV / 300mV / 775mV. I'm not an electrics expert or engineer by any stretch of the imagination, so make do with those figures as you will.
Click to expand...

Hi Harry

Pending John's reply.

If the MDAC output is 2.3Vrms peak I believe that equates to 230mv (not sure about the rms)

So given your three input sensitivity choices, I would go for 300mv or 775mv as 100mv would be 'overloaded' by the MDAC's 230mv output.

I'm no expert and this is just an 'educated' guess but may be worth trying.

NB: REMINDER suggest you switch off and unplug first.
 
finesensations said:
Hi Harry

Pending John's reply.

If the MDAC output is 2.3Vrms peak I believe that equates to 230mv (not sure about the rms)

So given your three input sensitivity choices, I would go for 300mv or 775mv as 100mv would be 'overloaded' by the MDAC's 230mv output.

I'm no expert and this is just an 'educated' guess but may be worth trying.

NB: REMINDER suggest you switch off and unplug first.
Click to expand...

UPDATE: Sorry, just noticed you don't have the remote. If Quad can't provide a replacement may be worth considering a Universal Remote such as one of the Logitech Harmony range.
 
finesensations said:
UPDATE: Sorry, just noticed you don't have the remote. If Quad can't provide a replacement may be worth considering a Universal Remote such as one of the Logitech Harmony range.
Click to expand...
Thank you finesensations.

I will call Quad to find out what my options are in regard to acquiring the remote control codes. I figured that this would almost certainly be my first port of call, however the fact that this issue is eliminated by the factors I mentioned earlier is what is really interesting. Hopefully Quad have a simple solution to help me out here.

Thanks again,
Harry
 
JohnW said:
I'll confirm with Dominik - maybe he's trying to test us all!!!

*I often Ask Dominik "double blind test me" - unknown to me he would swap the filter names etc - Then I'm greatfull to find I'm not going crazy or imagining things...
Click to expand...


Hi John,

I would actually like to propose such experiment with let's say firmware A10.
Let Dominik swap functions around and have people listen to it WITHOUT them talking about their preferences. Vote one's result on a page and after say 2 weeks post the results and the actual function vs A10 displayed function.
This would stop people getting biased by results of others and get very much in the direction of a blind test.
 
haridhos said:
Thank you finesensations.

I will call Quad to find out what my options are in regard to acquiring the remote control codes. I figured that this would almost certainly be my first port of call, however the fact that this issue is eliminated by the factors I mentioned earlier is what is really interesting. Hopefully Quad have a simple solution to help me out here.

Thanks again,
Harry
Click to expand...
Although one thing is throwing me. Unless I am making a massive school boy error, 'mV' is milli volt which is to the order of 10-3, so the 2.3Vrms peak value of the M-DAC is the equivalent of 2300mV. Am I being stupid here? Hence why I am not sure how relevant those Quad input sensitivity figures are. Either they are really relevant and the peak output of the M-DAC far exceeds the maximum input sensitivity of the Quad77 or I should hand back my A-level & GCSE physics certificate...........
 
haridhos said:
Although one thing is throwing me. Unless I am making a massive school boy error, 'mV' is milli volt which is to the order of 10-3, so the 2.3Vrms peak value of the M-DAC is the equivalent of 2300mV. Am I being stupid here? Hence why I am not sure how relevant those Quad input sensitivity figures are. Either they are really relevant and the peak output of the M-DAC far exceeds the maximum input sensitivity of the Quad77 or I should hand back my A-level & GCSE physics certificate...........
Click to expand...

I think it's me being stupid, and you are correct, so best to wait for John's reply!

My amp's input sensitivity/impedance is 270mV/47k Ohms with an Overload of 4v.

So maybe it's your overload figure you need to look at.
 
finesensations said:
I think it's me being stupid, and you are correct, so best to wait for John's reply!

My amp's input sensitivity/impedance is 270mV/47k Ohms with an Overload of 4v.

So maybe it's your overload figure you need to look at.
Click to expand...
Yes, let us see what John says. I am still quite unsure what the full picture is here.

John, some further info on the Quad 77 I pulled up from another forum:



Quad 77 int.

Signal Bus: Up to 32 77-Series productsInputs: Source 1, Source 2 and Tape
Inputs Source 1&2 Tape
Input sensitivity 100 or 300 or 775mV
Load Impedance 33kOhms 33kOhms
Signal/Noise >100dB >100dB
Outputs Preamp Out Tape Out
Output level 775mV same as input level
Source impedance 850Ohms 300Ohms

Interchannel balance:
+/-0.1 dB with volume control varied from maximum to -70dB
Maximum Power Output:
84W into 8Ohm <0.5% dtot 115W into 4Ohms <0.5% dtot
Maximum Current Output:
11A peak per channel
Distortion (total harmonic):
Continuous sine wave into 8Ohm resistive load
20Hz any level up to 70W <0.005% (22kHz bandwidth)
1kHz any level up to 70W <0.005% (22kHz bandwidth)
20kHz any level up to 70W <0.01% (80kHz bandwidth)
Output internal impedanceand DC offset:
1.5µH in parallel with 0.05Ohm, DC offset <20mV
Frequency response:
-0.3dB at 20Hz and 20kHz
(ref 1kHz): -3dB at 3Hz and 50kHz
Power response (ref 1kHz):
-0.75dB at 10Hz and 20kHz
Crosstalk:
<-90dB at 1kHz
Hum and Noise:
-105dB ref. 75W (22kHz measurement bandwidth unweighted)
Stability:
Unconditionally stable with any load and any signal
AC input:
110-120V or 220-240V, 30-350VA, depending on signal level
Weight:
6.3kg
Dimensions:
321mm wide; 65mm high; 300mm deep

Thanks again guys.
 
haridhos said:
Although one thing is throwing me. Unless I am making a massive school boy error, 'mV' is milli volt which is to the order of 10-3, so the 2.3Vrms peak value of the M-DAC is the equivalent of 2300mV. Am I being stupid here? Hence why I am not sure how relevant those Quad input sensitivity figures are. Either they are really relevant and the peak output of the M-DAC far exceeds the maximum input sensitivity of the Quad77 or I should hand back my A-level & GCSE physics certificate...........
Click to expand...

Its overload headroom you need to consider not input sensitivity - looks like the Quad has limited overload headroom.

Just to clarify, the MDAC's signal path is the same in DAC mode or PreDAC mode, its only a software change that enables the level setting or not - so NO difference in sound quality between the two modes.

Setting the MDAC level to 0dB is the same as "Dac Mode"

The solution is to attenuate the MDAC's output to -2dB if it solves the issue.

John
 
fusion5 said:
Have you tried disabling the upsampling on the 740C?
Click to expand...

Yes, upsampling is disabled. Can't see an option for enabling or disabling SRC, but then I am not sure what that is! Are we talking about Solomon-Reed correction?

Thought the 740C would be a good enough tranport while I wait for the MTRN. Doubt I'll change for the time being. Served me well as a DAC for the last three years too, but then I got the upgrade bug and the MDAC shows just how much things have moved on!

Out of interest is there an approx price in mind for the MTRN?
 
Hi John,

Thank you again for your reply. I can't say I know where or how to calculate the overload headroom but I will take your word for it. :)

Now, since it is only a few tracks that are presenting this issue, should I only adjust the output when playing those tracks so that when I play other music I am able to get the most out of the dynamic range? Or will this reduced overload headroom effect all my music, but only noticeable on certain tracks? And finally, would I be right to assume that perhaps with the optimal spectrum filter in use, I will tend to over the amplifier the most? I still can't quite grasp how altering the bit depth/sample rate output negates this issue either.

Sober, -3 it is!

Thank you both for all of your advice.

Harry
 
Wow, the new A.09 firmware is fantastic, such a large sound stage. Loving it. For me personally i`d like it a bit more crisp & raw sounding with the same wide sound stage.

Thanks to all for their time & effort in making a fab piece kit even better.

I'm using MP filter
 
finesensations said:
Will be interested to hear how you get on with A.09 as, atm, I appear to be alone in preferring A.05.
Click to expand...
It may not be A.05, but I've returned back to A.08 today. After listening to a lot more tracks, I can say that A.09 is great for classical music. It also (on OTXD) makes my guitar and piano tracks sound beatiful, but the bass on some others is way too distorted (low frequencies spanning most of the track). Also, it makes me feel like I'm 100 meters away from everything. Kind of like "remember how great this song sounded? .. it still sounds great - over there!".
I remember having similar problems on 0.96, but I don't think they were this exaggerated.

Some filters help a bit with the bass (non-OT ones), but not by much. They make the music at least listenable, though.

Maybe the bass on A.09 is so good that it moved beyond the distortion-free spectrum of my headphones, maybe not. Will stay tuned for future A.09 updates :)
 
sq225917 said:
Nice looking thing any similarities with upcoming Westlake products?
Click to expand...

Not really - apart from the OLED display and maybe the Epoxy / Rubber buttons - but we are very happy with the way it turned out!

We found a new vendor for the dispaly Window - looks so much better flush to the front panel IMO

Looking forward to the matching CD/DAC ;)
 
Status
Not open for further replies.


advertisement


Back
Top