Mezmerize DCB1 Building Thread - Page 18 - diyAudio
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Old 28th January 2011, 09:50 PM   #171
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Originally Posted by Salas View Post
That gives 73mA. The other side gives 71mA. You are finely set. Also that output DC offset you mentioned was in mV right?
Yup, mV. I'll give it a listen to make sure everything's 100% before I attempt hotrodding.
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Old 29th January 2011, 01:39 AM   #172
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Originally Posted by johnwmclean View Post
Yes still going for balanced (of course), but have have switched back to the new Hyno boards from the recent GB, saw youíre down for 5?? My builds going something like this sumR transformers, Nichicon KZ for the 4700uF, Silmic II for the 100uf, 0.22uf auricap (thanks qusp) for the ref bypass, Takman Carbon for the 470R, Mills 10R 5W for current, PRP for the rest, Iím aiming for hotrodding up to 300mA.
I did put myself down for (5) blue hypno's. I've already got the blue mez's populated, so I'm committed to finish that one. I figured I might want to try an all out balanced hypno (super hot-rod style) in the future with a lightspeed attenuator. Bought a few extra boards for shunt power supply purposes.
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Old 29th January 2011, 02:41 AM   #173
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I just plugged the DCB1 into my F5, it's making beautiful music as I type. The passive pre I was using before never sounded quite right with the F5, probably because it used a 100k stepped attenuator, but the DCB1 is just as clear and more tonally "correct" to my ears. Seems to have more kick to it, too.

Next up is a Pearl 2 phono. Firstwatt is rapidly taking over my whole audio chain!
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Old 29th January 2011, 08:49 AM   #174
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Default Balanced DCB1 Diagram

Hereís a wiring diagram for a balanced DCB1 Iím planning, I would appreciate any feedback as whether this would work or not. Iím not sure whether a zobel is necessary or not.

Click the image to open in full size.

Beyond the default and hotrod configurations are there any board changes or parts that need to be addressed for this to work?

Cheers
John
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Old 29th January 2011, 10:09 AM   #175
AndrewT is offline AndrewT  Scotland
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Hi john,
your use of adjustable attenuators at the front end of the balanced receiver completely wipe out any hope of maintaining a balanced connection.

All the input impedances must be matched very accurately. This includes the capacitors, not just the resistors. Similarly all the output impedances must be matched very accurately.
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Old 29th January 2011, 01:35 PM   #176
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Hi Andrew,

Although the diagram shows separate attenuators for input and grounds, it will actually be one conventional 4 channel volume pot.

Balanced impedance, I have a feeling that’s a big spanner coming my way, I can probably match the resistances for better than 0.1%, and may have some success with balanced voltage but exact impedance matching, my eyes are glazing over. I don’t have the know how (yet) or equipment needed (I’m guessing), silly question here goes - is this a very complex undertaking?
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Old 29th January 2011, 02:02 PM   #177
AndrewT is offline AndrewT  Scotland
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Hi,
a pair or a quad of potentiometers cannot be made such that Rupper and Rlower are always exactly matching at all positions of the potentiometer. The total of Rupper + Rlower can easily be selected to match to sufficient accuracy, but that is totally irrelevant as soon as the balanced attenuator is moved away from infinite attenuation.
A switched attenuator could be made to sufficient matching accuracy, but it will cost a fortune, i.e. even more than the $50 to $200 seen as asking prices for a normal stereo switched attenuator.
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Old 29th January 2011, 02:47 PM   #178
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What about something like the balanced shunt attenuator the guys over at K and K Audio use for their balanced linestage? It's stated, "no change in common mode rejection as different volume settings are used..." I realize that stepped control is expensive, but is this a reasonable and "correct" way to handle balanced attenuation?

K & K Audio - Lundahl Transformers, audio DIY kits and more
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Old 29th January 2011, 02:59 PM   #179
AndrewT is offline AndrewT  Scotland
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The example on the left still has the balanced resistor value problem.
The example on the right was my suggestion, but apparently is technically flawed. One of our Forum Members linked to a D.Self article that discussed why it was wrong.
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Old 29th January 2011, 04:36 PM   #180
Horio is offline Horio  United States
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Quote:
Originally Posted by AndrewT View Post
Hi,
a pair or a quad of potentiometers cannot be made such that Rupper and Rlower are always exactly matching at all positions of the potentiometer. The total of Rupper + Rlower can easily be selected to match to sufficient accuracy, but that is totally irrelevant as soon as the balanced attenuator is moved away from infinite attenuation.
A switched attenuator could be made to sufficient matching accuracy, but it will cost a fortune, i.e. even more than the $50 to $200 seen as asking prices for a normal stereo switched attenuator.
So would something more like TPA's Joshua Tree attenuator be a better solution if you were to closely match all the resistors between the (4) boards?
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