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Amps for KEF LS50M, balanced, high gain, NOT class D

sergioiudicibus

Active member
Oct 1, 2020
9
1
25
Hey everyone,
Perhaps I'm looking for the impossible, but... would anyone be able to recommend a separate amp (standalone, not integrated) for the new KEF LS50M? Ideally, it should be:
-comfortable going down to 4ohms, but rated for 8ohms (i.e. solid-state, probably)
-class A or class A/B; I don't really like class D
-around or above 100W
-high gain (around 30dB) because my preamp is passive
-balanced design (XLR), not bridged
-not stratospherically priced (I wouldn't want to exceed the price of the LS50s by too too much)
I recently discovered Odyssey Audio's gear and thought I was saved, but - alas - their circuitry isn't balanced; otherwise, their premise is very interesting to me: small, unpretentious, well-made, local, etc.
Yours thankfully,
Sergio
 

Al ears

Moderator
Hey everyone,
Perhaps I'm looking for the impossible, but... would anyone be able to recommend a separate amp (standalone, not integrated) for the new KEF LS50M? Ideally, it should be:
-comfortable going down to 4ohms, but rated for 8ohms (i.e. solid-state, probably)
-class A or class A/B; I don't really like class D
-around or above 100W
-high gain (around 30dB) because my preamp is passive
-balanced design (XLR), not bridged
-not stratospherically priced (I wouldn't want to exceed the price of the LS50s by too too much)
I recently discovered Odyssey Audio's gear and thought I was saved, but - alas - their circuitry isn't balanced; otherwise, their premise is very interesting to me: small, unpretentious, well-made, local, etc.
Yours thankfully,
Sergio
You mention preamp and standalone. Do you mean stereo power amplifier?
You also mention balanced circuitry. Can you explain exactly what you have and what you want as your initial post is confusing.
 

shadders

Well-known member
Nov 19, 2009
148
87
18,670
Hi,
How about the Cambridge Audio Azur 851W which has balanced inputs, and has +1.5v/-1.5v RMS balanced inputs for full output.

It does depend on your source equipment maximum output, so perhaps mention that, as 30dB gain is not as helpful.

Regards,
Shadders.
 

sergioiudicibus

Active member
Oct 1, 2020
9
1
25
Thanks for all the feedback!

Perhaps you would be better off getting the active version of the LS50 then?
I would have thought so too, but most of my gear is analog and I'd hate to have the signal converted to digital (I'm under the impression that the amplified version does that)

So what is your pre amplifier?
It's a Promitheus TVC, a transformer passive preamp. Rather niche, but I've grown attached to it.

Hi,
How about the Cambridge Audio Azur 851W which has balanced inputs, and has +1.5v/-1.5v RMS balanced inputs for full output.

It does depend on your source equipment maximum output, so perhaps mention that, as 30dB gain is not as helpful.

Regards,
Shadders.
My main source (a phono preamp) says this on their website: Output Voltage: >6.0V RMS
 

shadders

Well-known member
Nov 19, 2009
148
87
18,670
It's a Promitheus TVC, a transformer passive preamp. Rather niche, but I've grown attached to it.


My main source (a phono preamp) says this on their website: Output Voltage: >6.0V RMS
Hi,
The system you have will drive any power amplifier, as they usually are less than 3volts peak for full output. So, i don't think you have to worry about the power amplifier sensitivity.

Regards,
Shadders.
 

sergioiudicibus

Active member
Oct 1, 2020
9
1
25
Hi,
The system you have will drive any power amplifier, as they usually are less than 3volts peak for full output. So, i don't think you have to worry about the power amplifier sensitivity.

Regards,
Shadders.
Really? That's very reassuring, thank you! This whole sensitivity/voltage/gain issue has always confused me. My current setup also includes a DAC which outputs 2V and it's never driven my amplifier very well, hence my concern. What sort of ratio between output voltage and "voltage peak for full output" - as you say - should I be looking for? Thanks again for everything :)
 

shadders

Well-known member
Nov 19, 2009
148
87
18,670
Really? That's very reassuring, thank you! This whole sensitivity/voltage/gain issue has always confused me. My current setup also includes a DAC which outputs 2V and it's never driven my amplifier very well, hence my concern. What sort of ratio between output voltage and "voltage peak for full output" - as you say - should I be looking for? Thanks again for everything :)
Hi,
OK - for the CD player, that will be 2.1volts RMS which is 3volts peak. I assume this is unbalanced connection.

Therefore, for your CD player, then it will need to be matched with the amplifier. A transformer can have gain, so does it have any voltage gain at all ?

Regards,
Shadders.
 

sergioiudicibus

Active member
Oct 1, 2020
9
1
25
Hi,
OK - for the CD player, that will be 2.1volts RMS which is 3volts peak. I assume this is unbalanced connection.

Therefore, for your CD player, then it will need to be matched with the amplifier. A transformer can have gain, so does it have any voltage gain at all ?

Regards,
Shadders.
Yes, the DAC is unbalanced. The transformers in my preamp have no gain, they merely attenuate.
 
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shadders

Well-known member
Nov 19, 2009
148
87
18,670
Yes, the DAC is unbalanced. The transformers in my preamp have no gain, they merely attenuate.
Hi,
The preamplifier does not seem to have a specification sheet - i checked the website. Are you using a mixture of balanced, and unbalanced inputs, and balanced output only for the preamp ?

Regards,
Shadders.
 

daytona600

Well-known member
Oct 5, 2012
251
127
19,070
Virtually all the active speakers are digital inputs these day ( convert analogue signal into digital )
for crossover / DSP etc & most only Rca inputs

LS50 with external integrated amp or pre/power
or look at Heed type 05/07 Analogue input ( no conversion to dogital ) & XLR inputs performance is world class
 

Simon 13th note

Well-known member
BANNED
Jul 27, 2020
183
72
170
I dont think you would. The driver matched to the amp is the issue. LSX are quite smooth when I tested them (baby brother). They use Class D in the case because class D runs cool in compact cases. I wouldn't make Class D an issue or not to OP. Go on overall sound.
 
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sergioiudicibus

Active member
Oct 1, 2020
9
1
25
Hi,
OK - do you know what the output voltage is (balanced) for the CD unbalanced input ?

(example, 2.1volts RMS CD output, appears as +1.05volts/-1.05volts RMS on the balanced output)

Regards,
Shadders.
The preamp certainly doesn't convert an unbalanced signal into balanced, it just bridges them together, so I assume that the voltage isn't split.
 

sergioiudicibus

Active member
Oct 1, 2020
9
1
25
Actually, I now realize that this preamp might be another can of worms; I just emailed its maker to ask how the unbalanced input is fed through to the balanced output. As I mentioned before, it's just two transformers that attenuate the signal, but the website says they run in "true balanced."
 

shadders

Well-known member
Nov 19, 2009
148
87
18,670
Actually, I now realize that this preamp might be another can of worms; I just emailed its maker to ask how the unbalanced input is fed through to the balanced output. As I mentioned before, it's just two transformers that attenuate the signal, but the website says they run in "true balanced."
Hi,
Unless you have an oscilloscope to test, then only the manufacturer can assist to state what the voltages are.

Regards,
Shadders.
 
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