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Old 29th June 2010, 02:04 AM   #1621
Salas is offline Salas  Greece
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Quote:
Originally Posted by ClaveFremen View Post

Any problem with it?
Is it 50VA? I don't think that it will sag if so. If it is the R-Core from France, its going to be more than VAC nominal.
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Old 29th June 2010, 02:08 AM   #1622
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Wow Salas, blazing fast!

Yes, it's a 30VA R-Core, the one from France.

I've asked you about it in this post since 50VA were out of stock.
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Old 29th June 2010, 02:12 AM   #1623
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Still OK. That R-Core holds better than anything. And is silent both for field and buzz.
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Old 29th June 2010, 02:13 AM   #1624
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Great!

Thanks again Salas!
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Old 29th June 2010, 02:24 AM   #1625
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Andrew,
Forgive me if I've got this wrong - somewhere I thought you had written that the output Z of the B1 was 1kR but I can't find it - did I get this right and if so, is this for the standard single ended B1 or the Symmetrical B1?
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Old 29th June 2010, 08:56 AM   #1626
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the output resistor of the B1 is 1k0
The DCB1 uses a 220r instead.
Add the output impedance of the stage to get the total output impedance. I seem to recall a figure of <50r for the stage output impedance.
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Old 29th June 2010, 10:04 AM   #1627
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Ah, right - forgot - thanks for that.
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Old 30th June 2010, 12:05 AM   #1628
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Default A bit puzzled

I haven't written anything about my results with the DCB1 build for a while due to some unexpected results. Meaning that the frequency response is very different from the NAD C160 that this is intended to replace. In comparison the high frequency response is rolling off for reasons unknown to me as of yet.

Since I had bought one of the B1 kits off of eBay I went ahead and built that to compare it to. The results are pretty similar in that the frequency response is out of balance starting somewhere in the higher mid-range. I'm not sure what to make of this yet but am going to make a passive 50K volume control to see if this sheds some light on what is happening. I am not sure that this would be due to a poor mach between components. The B1 and the DCB1 are being driven by a Musical Fidelity A324 (output impedance of 50 Ohms) and are driving a Marchand XM-9 (input impedance of 25K). I may be able to acquire an oscilloscope later this week and perhaps that will be of some help.

I still have high hopes for this pre-amp and am not going to give up on it quite so easily. I have almost exactly the sound that I was looking for with my current stereo but felt that it was time to simplify the electronics as much as possible.

On a positive note, however, I can say the depth of the soundstage is very promising with the DCB1.

Last edited by Macronaut; 30th June 2010 at 12:11 AM.
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Old 30th June 2010, 12:39 AM   #1629
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How is it driven? Is there a pot before it? If yes, what value? What is the droop you have measured? -dB? Freq? Don't put more than 20k-25k pot.
Disaster scenario Sci-Fi:
Are your gate stopper resistors for the audio fets 220R and not much bigger by mistake? Can there be the 220k in series and the 220R shunt? That could create filters.
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Old 30th June 2010, 04:58 AM   #1630
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Quote:
Originally Posted by Salas View Post
How is it driven? Is there a pot before it? If yes, what value? What is the droop you have measured? -dB? Freq? Don't put more than 20k-25k pot.
Disaster scenario Sci-Fi:
Are your gate stopper resistors for the audio fets 220R and not much bigger by mistake? Can there be the 220k in series and the 220R shunt? That could create filters.
It is being driven by a DAC with a 50 Ohm output impedance.

I do not have a way to measure the frequency response. As best as I can describe it is the bass through low midrange is louder than the midrange through the treble. I would guess between 6 to 10 db difference between the bass and treble.

You might have identified the problem. I am using a 50K Ohm stereo potentiometer. I used the same pot on both the DCB1 and the B1 so that could very well be the mismatch. I do have a 20K pot ordered and should be able to try that soon. I checked the gate stoppers and they are carbon film, 220 Ohm resistors that I got from Mouser. I haven't attempted to use the LDR's yet because I felt more comfortable starting with a simpler volume pot, first. That and I had not ordered the power supply parts to run the Lightspeed attenuator.

Thank you for the advice. I'll check back in when I get the new pot.
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