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Old 28th September 2008, 02:47 PM   #681
Gyuri is offline Gyuri  Hungary
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Old 28th September 2008, 04:40 PM   #682
MRupp is offline MRupp  Germany
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Quote:
there is no need for complicating ...
I would hardly call two resistive dividers a complication unless you are ultra-orthodox; the question is really does the proposed method bring any advantage, such as cancelling out common mode signals, or does it not work. If you are going balanced you might as well try the best alternative.
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Old 28th September 2008, 06:09 PM   #683
Gyuri is offline Gyuri  Hungary
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Default van der Post

Touchdown Grey, I have to say it you have truth!

This is a better variant possibly here. The original book possibly is for you?

Regards,

Gyuri
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Old 28th September 2008, 08:16 PM   #684
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Quote:
Originally posted by Zen Mod
there is no need for complicating ;

one stereo B1 per channel , and that is balanced B1

if simplicity is goal , one can't make it much different

Is it really this simple? So each half of the balanced signal could go through this buffer, without say a negative rail voltage needed for the side the negative signal goes through?

If I just have to make two of these, that is easy.
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Old 28th September 2008, 09:05 PM   #685
Tolu is offline Tolu  Germany
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I would like to use the DS1802 digital pot in front of the B1 (or B3 ). NP uses the DS1802 in INT-150 and XP-10.

The main issues. More than 5V Vcc drives the pot into clipping. Proposal of Maxim: A wheatstone bridge!

The following stage should have a high impedance cause the DS1802 has 45kOhm impedance.

So, what solutions would be best to fit these two issues? How can I increase the input impedance of B1?

Perhaps NP could lift a little secret?
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Old 28th September 2008, 10:33 PM   #686
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Tolu
I........... How can I increase the input impedance of B1?

.......

hardly

input imp. of B1 AFTER the pot is well near 1M , so you really don't need to increase it
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Old 29th September 2008, 01:56 AM   #687
wct is offline wct  United States
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New subject maybe:

Hello All

Can someone tell me what a typical measured vgs is, when you do the test on LSK170's type "B" N FETs as outlined in Nelson Pass's article on matching?
These devices are headed for duty in the B1 buffer.

Ive measured about 20 of these devices now and I'm getting anywhere between .220V and .240V.

Does this sound correct?

I just want to make sure Im doing the test correctly by seeing if the results sound right.

I set up a little test setup based on Nelson Pass's device matching article and think I've followed it exactly as laid out in the article.

I used a 15 volt regulated supply, and a 2.2 K source resistor. The only way that I changed the procedure was to put a DC ammeter in series with the power supply.
I get a measured 6.67mA with just about every device.

So, is this in the ballpark? Thanks for the help.

Curt
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Old 29th September 2008, 02:48 AM   #688
EUVL is offline EUVL  Europe
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LSK170 is JFET and not MOSFET. For details, including matching you may read :

http://www.borbelyaudio.com/adobe/ae599bor.pdf

Excellent article.


Patrick
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Old 29th September 2008, 07:12 AM   #689
MRupp is offline MRupp  Germany
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Quote:
I used a 15 volt regulated supply, and a 2.2 K source resistor.... I get a measured 6.67mA with just about every device.
Small wonder, a 2,2K source resistor will, at 6,67 mA, have 2200 * 0,00667 = 14,674 Volts across it, that allows the JFet barely to turn on and sets the limit for the current you can measure. First, a 100 Ohm resistor would be more appropriate for this JFET, at, say 10 Volts. Secondly, some basic reading on electronics would be in order, you should at least be able to calculate voltage/current/resistance.
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Old 29th September 2008, 07:29 AM   #690
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Quote:
Originally posted by Zen Mod



hardly

input imp. of B1 AFTER the pot is well near 1M , so you really don't need to increase it
so for an inpedance variing relay attenuator like Joshua (realatively low 2k to 3k typical) it would be most suitable to place it after B1? As long as the ground(s) of the different inputs is shared, it won´t produce earthquake Plops when "hot pluggin´" rca- connects, i guess.
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