Salas hotrodded blue DCB1 build - Page 291 - diyAudio
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Old 8th March 2013, 01:48 PM   #2901
stajo is offline stajo  Sweden
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Originally Posted by mantha3 View Post
Hi, I'm back
Speed hollidaying?
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Old 8th March 2013, 02:21 PM   #2902
Salas is online now Salas  Greece
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Originally Posted by mantha3 View Post
Hi,

I'm back to thinking I'll run my DCB1 with a Pot on the input side of the DBC1. I was thinking of the Khozmo 25K to keep the input impedance a little higher and friendlier on the way into the preamp I'm building.... I think the 25K is a little on the higher end of the recommended range with that recommended range being more 10K - 20K.

Is the 25K ok?
Its OK.
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Old 8th March 2013, 02:22 PM   #2903
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I ve been using 25k on mine without issues. I have not used a smaller one though to compare.
Higher is friendlier on the sources, but I believe dcb1 likes smaller ones.
It s a bit of a compromise
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Old 8th March 2013, 11:15 PM   #2904
mantha3 is offline mantha3  United States
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Thanks dimkasta. I know you are happy with the sound you get so this is nice to hear
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Old 9th March 2013, 01:26 AM   #2905
mantha3 is offline mantha3  United States
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I got the R Core from DIYGene 100VA Model: R80-53

That sucker is heavy!

I'm starting on a vacation this coming Monday and don't have time to do much with the build this weekend... Just a Assortment of nice parts... :-(
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Old 9th March 2013, 05:24 PM   #2906
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Originally Posted by mantha3 View Post
Thanks dimkasta. I know you are happy with the sound you get so this is nice to hear
Personal happiness is a weird deal... It has very much to do with personal experience.

The one thing that I learned playing with DCB1 is that you can be completely happy with it (even with higher standards) and then try a different component and get your mind completely blown by what you have been missing all this time.

So I can only say that 25k is not a problem. Ideally you should try different sizes and find out what better fits your system.

What my plan is for the attenuator (after a rather failed attempt), is to make quick tests with plain resistor couples on a comfortable attenuation level, lets say -30db

For example
  • 19K6R series and 634R shunt giving 20K impedance and -30,08dB
  • 14K5R series and 475R shunt giving 15K impedance and -30,09dB
  • 9K76R series and 316R shunt giving 10K impedance and -30,07dB
And see which impedance sounds better. Of course you can try in-between impedance values as well. The nice thing is that you should get a good idea of what fits your system better, even with cheap resistors, so that way trial costs are kept to a minimum as well.

I will then try different resistor brands and or models to see which one sounds better. Again, you are saving big bugs by buying only a couple of resistors from each kind.

And after that, I will build a full 24step ladder attenuator using the results from my tests...
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Old 10th March 2013, 01:24 AM   #2907
mantha3 is offline mantha3  United States
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dimkasta... I can't keep up with ya man. I def will be interested in your attenuator rolling adventure.
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Old 10th March 2013, 03:41 PM   #2908
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Originally Posted by dtses View Post
hi,

few quick questions regarding two 35VA pcb 15v transformers I have paralleled. The adjustment R is 2 ohms making it 1.77VDC and 1.92VDC on the rails. Wattage meter shows about 48VA of constant consuming. So as advised by Andrew I'm still in a safe zone

1. Trafos have 2x110v primaries, is it safe to use them? Checked the mains during the week and it varies from 218 till 228v.

2. I get quite audible hum when I'm close to them (about 10cm). Could that be reduced somehow? Will mu-metal be helpful here?
Quote:
Originally Posted by Salas View Post
Try separate them as much as you have space first. See if the mechanical hum softens with distance.
didn't help. Even tried to use one of them now, but still get same mechanical hum. Does it mean that I got a crappy trafo?! Could the voltage be the reason? It's 2x110v and I just measured 225-230VAC mains V.
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Old 10th March 2013, 03:58 PM   #2909
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That;s normal when the voltage is to high on primary.
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Old 10th March 2013, 04:33 PM   #2910
stajo is offline stajo  Sweden
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Originally Posted by dtses View Post
didn't help
Are you sure that you have connected primarys right?

First make sure you know which ends belongs to the same windings.

Then you need to connect the windings in series and they need to be in phase, meaning the "start" on winding number 2 connects to the "end" of winding number 1. If you connect the second winding the other way then the the first they work against each other and the trafo hums and gets warm very quick.

Staffan
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