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  #21  
Old 9th February 2017, 09:30 PM
Richard Richard is offline
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Default Re: Klp1

John, if it's any further help, K5881 is 240mV sensitivity for its 20W output.
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  #22  
Old 9th February 2017, 09:53 PM
bikerhifinut bikerhifinut is offline
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Default Re: Klp1

How do you intend to use the new 845 amps? I shall assume they are monos?
If so you have the option of placing them very close to each loudspeaker and have the benefit of extremely short speaker wires. This is how I am using my power amps at home now. The downside is you need a pre amp that will drive a long cable to the power amps. This can be something as simple as a basic cathode follower. Bob O has a lot of experience here. I have had success with the basic CF design using an ECC82 type (other variants are available). The basic need is to have a low resistance output and ability to drive a long cable with a bit of capacitance, hence the LOW resistance output.
The other option, and one which I hope to explore soon, is a transformer output stage such as the WD Pre3, Extremely lo Z output and really good "drive" and the icing for me is the option of using the transformers to provide a balanced output which should cancel out common mode noise and hum which a long cable run can suffer from. A bit of gain isnt always a bad thing as long as the volume is controllable over a long part of the travel and also if attenuating an input signal doesnt contribute to overall noise in the output signal.
Andy.
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  #23  
Old 9th February 2017, 11:10 PM
vinylspinner vinylspinner is offline
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Default Re: Klp1

Hi Andy,

I forgot about the balanced out on the pre3, may give it a try into my 300B to check what it sounds like. How would you configure the cables? Would be using mic cable, 2 core plus screen, the length is 2.5mtrs.

Nigel
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  #24  
Old 9th February 2017, 11:34 PM
bikerhifinut bikerhifinut is offline
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Default Re: Klp1

Decent mic cable and wire as normal i.e. screen to common/CT and the two inners for the signal.
The cocnundrum is what to do at the power amp? Do you build a fullybalanced one or use a transformer or active device to restore single phase operation?
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  #25  
Old 10th February 2017, 09:29 AM
bob orbell bob orbell is offline
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Default Re: Klp1

Quote:
Originally Posted by vinylspinner View Post
Hi Andy,

I forgot about the balanced out on the pre3, may give it a try into my 300B to check what it sounds like. How would you configure the cables? Would be using mic cable, 2 core plus screen, the length is 2.5mtrs.

Nigel
What I understand is, that your power amp also needs to balanced, unless this is so, you are wasting your time, you can find more about balanced signals on the web. BOB
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  #26  
Old 10th February 2017, 10:27 AM
John Caswell John Caswell is offline
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Default Re: Klp1

The simplest way is to balance the input of the power amplifier with a 10K:10K 1:1 transformer terminated in 10k across the input phone.
It can be temporarily mounted externally screened with aluminium cooking foil suitably isolated but earthed, but keep it some distance from the power amplifier power tx. Until lots of ICs came along that is how we did it professionally. PreII and III will drive it very well.
Try it and see.

John
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  #27  
Old 10th February 2017, 07:00 PM
Chris Chris is offline
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Default Re: Klp1

something like this?

http://www.sowter.co.uk/specs/3293.htm

Chris
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  #28  
Old 11th February 2017, 12:45 PM
bikerhifinut bikerhifinut is offline
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Default Re: Klp1

Quote:
Originally Posted by Chris View Post
something like this?

http://www.sowter.co.uk/specs/3293.htm

Chris
That could work, I'm a bit confused about where you'd wire the common (earth) on the balanced side of things. I can only assume you either leave it floating, connected at the preamp output as its really only for screening and returns of common mode noise? The secondary you'd wire normally, and depending on the phasing you require you'd take one end of the matching transformer secondary down to 0V.
Have I got that right JC?
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  #29  
Old 11th February 2017, 02:08 PM
John Caswell John Caswell is offline
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Default Re: Klp1

Hi Andy,
Yes that will do very nicely. The screen wire goes to amplifier chassis.
You must use twin screened between the pre and amp and the screen of the cable I suggest you earth at the preamp end to chassis,via the XLR. Depending on your earthing arrangements you can either earth the cable screen at the amp end or leave it floating. Try it both ways to see what gives the best results.

John
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  #30  
Old 12th February 2017, 10:17 AM
JohnG JohnG is offline
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Default Re: Klp1

There has been another option presented, after my initial inquiries into a Passive Preamp.
The suggestion has been made by my friend who kickstarted my return to HiFi a few weeks back.
He has referred to my potentiometer on the Monoblock, he has pointed out this can be exchanged for a very good Stepped Attenuator. This can be fed by a high quality RCA Female socket, then use OCC internal wiring. The exact attenuator model would need to be worked out, he feels this would remove the need for a off board pre amp, so a saving can be made , and a saving can be made by removing the need for another set of quality interconnect cables.
At the moment I spent a bit of time looking at mono stepped attenuators,
DACT, Khozmo, Acoustic Dimensions 41 Step. I also have the option of having one made to be a perfect suit to the monoblocks.
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