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Old 17th March 2007, 07:22 PM   #1
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Default anyone tried up aleph x input impedance?

hello fellows, I have o problem feed directly tube dac( 2x 6922 not SRPP, which has lower impedance.)anybody tried to up input impedance for aleph x? from 20kohmbalanced to 40-47kohm balanced. as I understand this is not only changing input resistors to 10kohm resistors to 20-23kohm..

anyone tried?

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Rolandas
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Old 17th March 2007, 09:16 PM   #2
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anyone? is no one can anyone put me in right direction. I think many people would like to conect high impedanse sources(like tube dac) and have the same problem. I was very surprise that 10V rms(!) output (manufacturer claims 5V rms non HDCD and 10V Rms HDCD)are so weak comparing to 2V RMS low output impedanse ordinary opa amps dac. not speaking about muddy ,undynamic,not controled bass..
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Old 18th March 2007, 05:41 AM   #3
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Quote:
Originally posted by elviukai
anyone? is no one can anyone put me in right direction. I think many people would like to conect high impedanse sources(like tube dac) and have the same problem. I was very surprise that 10V rms(!) output (manufacturer claims 5V rms non HDCD and 10V Rms HDCD)are so weak comparing to 2V RMS low output impedanse ordinary opa amps dac. not speaking about muddy ,undynamic,not controled bass..

which schematic exactly?
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Old 18th March 2007, 08:32 AM   #4
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its my vesion of aleph x . looks like kristijan and grey 100W amps. I using 220kohm resitors instead 100kohm to have better input sensitivity.
lets say it is kristijan schematic, only 100kohm changet to 220kohm. what direction to go when replacing 10kohm input resistors with 20-23kohm?
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Old 18th March 2007, 09:07 AM   #5
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Quote:
Originally posted by elviukai
its my vesion of aleph x . looks like kristijan and grey 100W amps. I using 220kohm resitors instead 100kohm to have better input sensitivity.
lets say it is kristijan schematic, only 100kohm changet to 220kohm. what direction to go when replacing 10kohm input resistors with 20-23kohm?

input impedance is roughly sum of two series resistors (+ and - side);
you can up them to ,say, 27 K -but you must scale up 100K resistors for same factor (2,7x) . Also you must scale up (2,7x ) 10K resistors from inputs to gnd.

after that you need to scale down (2,7x) 10pF caps across (now) 270K resistors

try it like that-and if you have some problems with sensitivity, we will re-think what to do;
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Old 18th March 2007, 09:57 AM   #6
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thanks ,

so I marked resitors in schematic 1/2/3 respectively. so if I change R1 to 23kohm I will need also change 230kohm(which I already have 220kohm in circuit anyway) and also r3 to 23kohm??
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Old 18th March 2007, 10:04 AM   #7
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Quote:
Originally posted by elviukai
thanks ,

so I marked resitors in schematic 1/2/3 respectively. so if I change R1 to 23kohm I will need also change 230kohm(which I already have 220kohm in circuit anyway) and also r3 to 23kohm??

yup

1 and 3 to -you say-23K
2 you already have 220K

both 10pf to 3p9 if needed (best to see with CRO)

if you still need more sensitivity- increase 2 to 470K and decrease caps to 2p2............

in your boots-I'll make decent preamp
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Old 18th March 2007, 10:11 AM   #8
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hi, understad, will try this combination.thanks
as for preamps, I have few laying arround, but i hate preamps.
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Old 18th March 2007, 10:35 PM   #9
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Elviukai-

Do you have an oscilloscope?

I found using a high input impedence caused a phase variation between the channels of my aleph-mini amp. It was only a few degrees at 20kHZ, but could be seen very clearly at 100kHZ.

I don't know if it was from bad devices, or if this might be typical of all the amps, (unless someone took the time to match input devices in circuit).

If you do have a scope, once you have implemented Choky's resistor values, just feed the same signal to both channels and check the signal at the gates of the input devices to make sure it matches. Check both positives against each other at the same time, then both negatives.
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Old 18th March 2007, 11:34 PM   #10
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thanks, I do not have but I will bring amp to friend which have.
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