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Old 6th March 2010, 02:20 PM   #1031
Salas is offline Salas  Greece
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Default Tweak to test

For all of you tweak inclined DCB1 owners, I have a an idea to test. If you happen to have a pair 0.1-1uF axial MKT or MKP that can fit upright replacing the 100uF 5X LEDs filter caps (the pair behind the transformer connector), give it a try and evaluate subjectively. Due to the node's impedance of the LEDs Vref, there will be no averse effect with the regs very low frequency gain & phase. Its a trade off between much noise filtering or little filtering and adequate or better cap distortion. Since the LEDs are good enough for self noise, and we have line level audio here, lets see what it may subjectively matter more to you. Don't destroy the 100uF caps, you may want them back or not. Let us know your evaluations.
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Old 6th March 2010, 02:23 PM   #1032
massimo is offline massimo  Italy
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MKT p 5 mm are available up to 4,7 uF/50V..... and I have a lot of 3,3 uF/50V from Ero
The bigger the better in that position?

Are you experinmenting V1.2 in the DCB1?
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Old 6th March 2010, 02:46 PM   #1033
Salas is offline Salas  Greece
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The bigger axial film cap it can fit upright, the more the filtering too. Positive suggestion then. But maybe better if smaller but MKP. V1.2s are proving excellent on phono for now, a friend here evaluates a double on his 57dB MC, he is chuffed head to head with V1.0s. Line level is less demanding, but Bill in Sydney is chuffed on op amps too. He will let us know with them on DCB1 point to point soon. I will integrate special LED ref V1.2s only if I can find a way to relatively simply nail the B1's Achille's heel manifesting in any package guise first, namely its tendency to up THD with level. Although pleasant (N.P. knows his stuff VERY well), its still what a so simple 2 Jfet circuit has to trade off. Not objectionable as a max number, but still a non linearity trend that has to do with 2SK170 Ciss.
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Old 6th March 2010, 02:52 PM   #1034
massimo is offline massimo  Italy
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I'm talking about tiny radial caps p 5 mm that fit nicely in the pcb.... MKPs AFAIK aren't available bigger than 0.33 uF I'm afraid.

Axial MKPs are generally 250V.... that means quite big stuff.

he is chuffed head to head with V1.0s Sorry, I don't undesterstand: means he's ultra happy with V1.2 over V1.0?

Last edited by massimo; 6th March 2010 at 02:55 PM.
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Old 6th March 2010, 02:56 PM   #1035
sugden is offline sugden  Singapore
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Quote:
Originally Posted by AndrewT View Post
Hi Sugden.
The voltage across the current setting resistors should not change. There is slight drift with temperature.

I think your 12Vac transformer is not giving sufficient voltage before the regulator and that's why you see a lower volts drop across the triple 68r, cf. the double 68r.
Do you have a 15+15Vac transformer to try?
I do not have any 15+15Vac transformer, but I connect DCB1 to my PS audio power plant which I can get adjust to 250VAC main power supply. Now voltage after rectification are +16.15V & -16.22V, volt at 3 parallel 68R are 1.547V & 1.666V. Look like not much different to the CCS. These all can do untill now, if necessary I will buy one 15+15VAC transformer to test it.
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Old 6th March 2010, 03:04 PM   #1036
Salas is offline Salas  Greece
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Quote:
Originally Posted by massimo View Post
I'm talking about tiny radial caps p 5 mm that fit nicely in the pcb.... MKPs AFAIK aren't available bigger than 0.33 uF I'm afraid.

Axial MKPs are generally 250V.... that means quite big stuff.

he is chuffed head to head with V1.0s Sorry, I don't undesterstand: means he's ultra happy with V1.2 over V1.0?
Whatever fits.

Yes, chuffed means very happy, well satisfied.
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Old 6th March 2010, 03:06 PM   #1037
Salas is offline Salas  Greece
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Originally Posted by sugden View Post
I do not have any 15+15Vac transformer, but I connect DCB1 to my PS audio power plant which I can get adjust to 250VAC main power supply. Now voltage after rectification are +16.15V & -16.22V, volt at 3 parallel 68R are 1.547V & 1.666V. Look like not much different to the CCS. These all can do untill now, if necessary I will buy one 15+15VAC transformer to test it.
You DCB1 is a healthy young man, told you before.
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Old 6th March 2010, 03:31 PM   #1038
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I have already finished my DCB1 and put it in a case. For that matter I used an old telecom equipment chassis. Old stuff has no plastics and is more robust than what is made today I will post some pictures as soon as I get a camera.
It works and sounds wonderful. I managed to have a very close match between leds (and I had the luck of finding matched pairs of jfets in my bag as close as 0.02% between them).
Here are the measurements, done with inputs shorted to ground and waited 2 hours after turning it on. 100-150h of burn-in already:

DC offsets: -0.86mv and -1.84mv
AC output: 0.01mv (less than DVM noise floor)

Tx voltage: 13.48vac
After rectification:17.4vdc
Positive rail: 10.748
Negative rail: -10.041
PSupply ripple: 0.00mv

Vdrop68//68: 2.456v (72mA) and 2.216v (65mA)

I'm thinking in rising the CCS to 200 or 250mA. I've done my calculations, and maybe I'm wrong, but I've found that you dont need 1W res. If you are passing 2.456v along 34 ohms, that is 72mA.
P=VI, so 2.456 x 0.072 = 0.176W. Wich is less than the standard quarter-watt resistor. So you don't even need to paralled them, neither making them 0.5W.

Am I wrong in something? Probably sure because you guys have thought of it before. As we say, don't try to teach your father how to make children
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Old 6th March 2010, 03:51 PM   #1039
sugden is offline sugden  Singapore
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Originally Posted by Salas View Post
You DCB1 is a healthy young man, told you before.
Thanks Salas, now I hook it up to my system. It make my system sound more lively, continue burn-in before my volume pot coming. Will report back the sound. Appreciate for all the advices.
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Old 6th March 2010, 03:54 PM   #1040
massimo is offline massimo  Italy
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Regiregi, when you calculate Pd, then multiply al least 3 times or better 4-5 times to chose a resistor that stay just warm.
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