Input impedance of Multiamps

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aleph

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Input impedance of Multiamps
« on: 17 Jul 2004, 12:29 pm »
Does anyone know what the input impedance of the Multiamp is?

I have a pair running in active mode and am considering a passive line level control unit based on a transformer volume control (see http://www.stevens-billington.co.uk/page102.htm)

TIA

tkp

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Input impedance of Multiamps
« Reply #1 on: 17 Jul 2004, 02:26 pm »
The input impedance of the Multiamp is 22 Kohms.

aleph

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Input impedance of Multiamps
« Reply #2 on: 19 Jul 2004, 05:46 am »
Hi tkp,

Thanks for the info.

I found your posts about the Bent Audio TX102 compared to the IRD LLC-P and also the LLC-P with the the Multiamps in active mode.

Would you have any impressions/opinions about using the TX102 with the Multiamps in active mode? Any particular issues, constraints, things to watch out for?

I have a pair of Multiamps in active mode driving a pair of nOrh 7's (the first generation). CD source only.  I'm not able to get my hands on a TX-102 based unit to demo.

tkp

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Input impedance of Multiamps
« Reply #3 on: 19 Jul 2004, 01:16 pm »
Quote from: aleph
Hi tkp,

Thanks for the info.

I found your posts about the Bent Audio TX102 compared to the IRD LLC-P and also the LLC-P with the the Multiamps in active mode.

Would you have any impressions/opinions about using the TX102 with the Multiamps in active mode? Any particular issues, constraints, things to watch out for?

I have a pair of Multiamps in active mode driving a pair of nOrh 7's (the first generation). CD source only.  I'm not able to get my hands on a TX-102 based unit to demo.


You need to give me a bit more information so I can tell you whether or not it will be okay.  What CD player and what preamp do you plan to use with the MAs?

aleph

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Input impedance of Multiamps
« Reply #4 on: 20 Jul 2004, 03:10 am »
1. My current CD source

   Sony CDP-X33ES.  Manual specs say:

   Fixed line out output level: 2 V (at 50 kilo ohms)
   Load impedance over 10 kilo ohms

   Some other info on the Sony:

   http://cdp101.hp.infoseek.co.jp/cdpx33es/cdpx33es.html

   (in Japanese; I translated via http://www.systransoft.com/)


   I also use a DVD video player: JVC XV-E100SL - Analog out: 2 Vrms (10
   kohm)

   Future (life after the Sony: probably a computer source to external USB
   DAC)


2. Which pre-amp?

   I am considering the S&B TX102 based ones: DIY HiFi Supply's Django,
   Bent Audio's NOH

tkp

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Input impedance of Multiamps
« Reply #5 on: 20 Jul 2004, 04:48 am »
I cannot read Japanese and I will not even try to verify your translation :-).

I am a bit confused with the specs you translated.

The output voltage is 2V which is a good thing because the MA has a gain of 30 db so the output voltage is definitely can drive the MA to its max output power.  

However, the 2V output is for driving into 50 Kohms load?  I got confused because of the load impedance of higher than 10K spec right underneath the 2V (50 Kohms) spec.

In my experience, most CD fixed output level can drive 10 Kohms or higher load.  The variable, on the other hand, can not drive as low so most likely the spec you posted is.

Variable output: 2V  into 50 Kohms load.
Fixed output: 2V into load of 10 Kohms or higher.

Assuming the above is correct then we have the following situation.

The MAs in active amping mode will present a load of 11 Kohms (Two 22 Kohms in parrallele) to which ever source is driving it.

a)  If you plan to use the variable output of the CD player to drive the MAs directly then you might overload the variable output of the CD player because it specs 2V at 50Kohm load.  There is no information at 10 Kohms load.  You will have sound but the system probably will not sound good.

b)  If you use the fixed output with the Noh passive preamp then it will work fine because at the highest volume level on the Noh preamp the CD player will see 11 Kohms load from the MAs.  At lower volume level, the CD player will see even higher load impedance (ie...44 Kohms+) so this is even better.  This is one of the greatest benefit of using a transformer base passive preamp.

c)  If you plan to use an active preamp to drive the MAs then make sure it can drive 11 Kohms load without any problem.  I can give you more detail once you pick an active preamp.

d)  If you want to use a tube preamp to drive the MAs then PM me to discuss this offline.

aleph

  • Jr. Member
  • Posts: 6
Input impedance of Multiamps
« Reply #6 on: 20 Jul 2004, 07:09 am »
Hi tkp,

The Japanese stuff was just more descriptive stuff about the CDP including the specs.

Quote from: tkp
In my experience, most CD fixed output level can drive 10 Kohms or higher load. The variable, on the other hand, can not drive as low so most likely the spec you posted is.

Variable output: 2V into 50 Kohms load.
Fixed output: 2V into load of 10 Kohms or higher.


The specs I listed earlier are taken as printed from the English user manual. This is exactly what it says:

Code: [Select]
Outputs

LINE OUT (FIXED)        Output level 2 V (at 50 kilo ohms)
 (phono jacks)           Load impedance over 10 kilo ohms

LINE OUT (VARIABLE)     Output level max. 2 V
 (phono jacks)           (at 50 kilo ohms)
                        Load impedance over 50 kilo ohms



Sounds like it ought to be do-able with the Noh using the CDP's fixed output. Will send you PM.

Thanks very much for your time and patience.

Regards