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Old 23rd July 2004, 11:24 PM   #1
RJEL is offline RJEL  Norway
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Question Attenuator on my Aleph P 1.7?

I have build me an Aleph P 1.7 and the preamplifier is working
very good. I will buy a DACT CT1 4-decks (stereo,balancert) to use as a volum controll.
http://www.dact.com/html/attenuator_datasheet.html
I will connect the attenuator to the output on the preamplifier.
It exist 6 values of this attenuator : 10k, 20k, 50k, 100k, 250k
and finaly 500kohm.
Is there anyone who has a idea what will work best?

If I choose wrong I will problery get max. volum at "ten o`clock"
on the attenuator, or maybe to much gain beetween steps
or something like that.
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Old 24th July 2004, 02:49 PM   #2
Kermit is offline Kermit  Norway
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Chose a value that is equal or less then the input impedance, and you should be fine. If the volume is to high at low settings you can always add a L-pad to tune it to fit your perfect listening level.
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Old 24th July 2004, 05:21 PM   #3
RJEL is offline RJEL  Norway
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I not shure I understand what you mean ny L-pads.
Can you explain som more?
You said the attenuator shoud be equal or less then the input
impedance. But I mean to connect the attenautor to output.
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Old 24th July 2004, 10:54 PM   #4
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Best it would be some 4-5Kohm,but they just don't produce the one.With 10K it sounds worse than with 5K in my expirence but among the ones they produce it would be the best.

Bartek
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Old 25th July 2004, 11:12 AM   #5
Kermit is offline Kermit  Norway
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If placed at the output, the value is idealy that of the input impedance of whatever amp your conecting it to. If your only going to use it with one amp, then it's not a problem, simply chose a value equal to the imput impedance of the amp. Otherwise go for the 10K like zygibajt says. Less then the input impedance is far better then more.
L-pad is simply two resistors connected to form a voltage divider placed before the attenuator. The values of the two resistors is selcted to give the desierd attenuation and keep the same impedance as the attenuator itself. I have a excel sheet somewhere to calculate the values. I can try to dig it up if you need it.
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Old 28th July 2004, 09:52 PM   #6
RJEL is offline RJEL  Norway
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Thanks for all comments.
I gonna buy a 10 k DACT attenuator from Denmark.
Have try to call NL Elektronikk in Denmark in two days now but they dont answer the phone. Maybee they all are on holiday.

Anywey Kermit, if I need your excel sheet I send a reply.
It will go some weeks before I can test my preamplifier.
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Old 28th July 2004, 09:56 PM   #7
RJEL is offline RJEL  Norway
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My amplifier is Dynamic Precision 6.52 HP.
This amplifier has 100k input impedance.
Do you mean 100k attenuator is the best way to go?
(Was meaning to by a 10K)
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Old 29th July 2004, 07:23 PM   #8
Kermit is offline Kermit  Norway
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Well, 100k might sound better… or worse then 10k. A higher value is easier for the preamp to drive so it might give less distortion, but it’s somewhat unlikely to be noticeable. But if the value is too high you risk hf roll-off.
If you’re still in doubt, you could get two decent low priced pots and try out witch value you like best before you buy the dact.
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Old 30th July 2004, 07:37 AM   #9
AuroraB is offline AuroraB  Norway
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Go for the 10k..............

If your DP has100 k, this impedance will modify your attenuator resistance, so that the step values will no longer be correct !
The attenuator is effectively a switchable L-pad, and the lower resistor will be parallelled by the amp input impedance.

For 10K or 100K, the load on the preamp output is of no concern!
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