Mezmerize DCB1 Building Thread - Page 28 - diyAudio
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Old 27th February 2011, 03:59 PM   #271
Salas is online now Salas  Greece
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Quote:
Originally Posted by qusp View Post
awfully dry,
The dryness is first to go with the Auris in RevB. Expands and layers also. So the Buffalo can be keeping happy an F5 even without gain in the line pre as I gather from you guys. Convenient.
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Old 27th February 2011, 04:51 PM   #272
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cool, well that would make it altogether more listenable, as that was my main complaint and brought a slight digitalis with it.

thats the plan, i'm planning running a pair of ackodacs with opc's d1 for sabre straight into an f5x and ajx using digital volume. i'll try out the balanced dcb1 on the cables to my workshop still, but for the main rig i think it should work well without it.

the project is gonna take me a little while, parts for ajx should be here this next couple of weeks, but still need to build the speakers. hopefully everything will be ready to warm the cockles of my soul and perhaps my actual terrestrial body in the southern hemisphere winter months
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Old 27th February 2011, 10:55 PM   #273
ramallo is offline ramallo  Europe
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Today I had some time free......

More at more level.


200kOhm

Crosstalk:
+6dBu (1,55V)
Click the image to open in full size.
+12dBu (3,09V)
Click the image to open in full size.
THD+N
+6dBu
Click the image to open in full size.
+12dBu
Click the image to open in full size.

Freq response

+6dBu
Click the image to open in full size.
+12dBu
Click the image to open in full size.

600 Ohm

THD+N

+6dBu
Click the image to open in full size.
+12dBu
Click the image to open in full size.

Freq response

+6dBu
Click the image to open in full size.
+12dBu
Click the image to open in full size.

Crosstalk:

+6dBu
Click the image to open in full size.
+12dBu
Click the image to open in full size.

Enjoy

Last edited by ramallo; 27th February 2011 at 10:56 PM. Reason: bad image
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Old 27th February 2011, 11:18 PM   #274
Salas is online now Salas  Greece
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It has 270 Ohm output impedance, you tortured the poor guy on 600 Ohm.
But on load it can handle stays cool enough for THD with level I see. Thanks for your extra time.
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Old 28th February 2011, 09:22 AM   #275
AndrewT is offline AndrewT  Scotland
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It's not the output impedance of the DCB1 that is the issue when feeding a low impedance load.

It is the output current capability.
A 8mAIdss jFET biased to 8mA has a range of output currents of -7.9mApk to +7.9mApk.

The absolute maximum driving voltage from the jFET into a 600r+270r load is 6.87Vpk. Only 69% of this driving voltage is across the 600r load.
4.7Vpk across the 600r hits the absolute current limit. The amplifier current clips.
+12dBu is ~4.4Vpk. The circuit has been driven into current clipping.
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Old 28th February 2011, 11:43 AM   #276
Salas is online now Salas  Greece
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+6dbu is 1.55VRMS, should have had the current for the low load? Still it shows the same trend as in +12dbu (3VRMS).
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Old 28th February 2011, 12:19 PM   #277
AndrewT is offline AndrewT  Scotland
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Single ended amplifiers generate distortion as they approach clipping. It's probably this that valve/tube folk like.

That increase in distortion can be avoided by ensuring the clipping voltage or current is 10dB to 20dB above the maximum normal signal that can pass through the stage.
Expect great performance when Iout <0.7mA to 2mApk
Expect gradually increasing distortion when 2mA < Iout < 7mApk.
Don't expect the SE amp to perform at all well when Iout >7mApk, for an 8mA bias.

Most pre-amps and the voltage amp stages operate in SE ClassA. That's why I try to adopt a clipping to max signal overhead of ~+20dB.

+20dB on a CDP signal is 22Vac. I can't and haven't tried to achieve that. +10dB to +12dB is certainly achievable for CDP replay.
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Last edited by AndrewT; 28th February 2011 at 12:37 PM.
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Old 28th February 2011, 12:24 PM   #278
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Yes, that is the B1 likeable thumbprint in a sense. We have referred in the past also I think. A JFET + BJT cascode or a JLH compound would hold differently with level. B1 maybe ''enamours'' digital sources dynamically its my guess. Reminding of analogue sources peaks. I would call it bridged loaded above 3kOhm. Beyond 10kOhm its dynamic THD signature is milder non the less (as in high load charts, post#250).
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Old 16th March 2011, 11:15 AM   #279
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Out of 100pcs of 2SK170BLs I was able to pull these 2 strings for a balanced build:

7.05/7.03 - 7.09/7.08 - 7.14/7.14 - 7.26/7.26

or

8.08/7.94 - 8.05/8.05 - 8.21/8.22 - 8.36/8.38

Which set is more desirable? And am I right in thinking the closest value pairs should be chosen per board.
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Old 16th March 2011, 11:23 AM   #280
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The 7ish set is tighter as a whole. But both sets are very good. Just don't mix the sets in any board, so to keep them tracking THD between phases alike. Use stepped fixed resistors pots, else the levels aren't going to match well, compromising CMRR.
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