Preamp wont drive Monoblocks to full power

[Shad29]

Hello all this is my first post.
Hoping you can please assist with the following conundrum:
I’ve recently purchased a Denafrips Athena 12th Preamp (Unity Gain).
I’m having issues with sound levels and driving the monoblocs to high power via the Athena.
With reference to the diagram, I’ve a Cambridge Audio CXN100 media player providing 4V via XLR to the Athena, which feeds three preamp outputs,
two via XLR (4V) to four Audiolab 8300MB’s (250W) and the other RCA (2V) to two Audiolab 8000M’s (125W), all with an input sensitivity of 1.5V and gains of 29dB,
these then drive ATC SCM 40 speakers.
The Athena digital volume range is 0 to 60, nothing much happens until a setting of 20, however it only produces medium volume before clipping at around 55.
Any help would be greatly appreciated.

Cheers

 

[staticV3]

Try measuring the output voltage of your media player, preamp, and power amps to confirm that you're getting the expected voltages and gains.

A basic $15 multimeter is more than enough.

Attached below is a 60Hz 0dBFS test tone which your can play on loop for measuring.

Please make sure you plug out your speakers before you play it.

Edit:
Calculating the gain is really easy.

20*log10(output voltage/input voltage)=gain in dB

 

[DVDdoug]

It SEEMS like you should have enough gain unless you have low-level digital files so you're not getting the full 4V out of the DAC.

A unity gain preamp should NEVER clip unless you over-drive the input. IMO a unity gain preamp is a little silly. Most preamps have gain and can go up to around 12 or 20V.

 

[Shad29]

Try measuring the output voltage of your media player, preamp, and power amps to confirm that you're getting the expected voltages and gains.

A basic $15 multimeter is more than enough.

Attached below is a 60Hz 0dBFS test tone which your can play on loop for measuring.

Please make sure you plug out your speakers before you play it.

Edit:
Calculating the gain is really easy.

20*log10(output voltage/input voltage)=gain in dB

Thanks for that info and the test tone, I’ll take some measurements and check. Cheers

 

[Shad29]

It SEEMS like you should have enough gain unless you have low-level digital files so you're not getting the full 4V out of the DAC.

A unity gain preamp should NEVER clip unless you over-drive the input. IMO a unity gain preamp is a little silly. Most preamps have gain and can go up to around 12 or 20V.

Thanks for the response, very good point hadn’t really considered low level files, everything I’ve thrown at it are high res files from Qobuz so should be ok. Right ok I see what you mean, (re clipping) so it’s clipping from elsewhere then.
I did some experimenting last night and disconnected the phono connection preamp outputs to the 8000A’s and fed the tweeters from the mid range 8300MB monoblocks.
This seemed to increase the sound levels. Still not right but better.
Not sure why that would affect it though?
Anyway taking some measurements and calculating gains next.
Thanks for the help guys much appreciated.

 

[antcollinet]

two via XLR (4V) to four Audiolab 8300MB’s (250W) and the other RCA (2V) to two Audiolab 8000M’s (125W), all with an input sensitivity of 1.5V and gains of 29dB

Something wrong there - you cant' have amps with the same gain, but different power having the same sensitivity. Higher power needs more output volts - which means if the amps are the same gain, then you need higher input volts.

 

[Sokel]

Something wrong there - you cant' have amps with the same gain, but different power having the same sensitivity. Higher power needs more output volts - which means if the amps are the same gain, then you need higher input volts.

On top of that,if I got the scheme right,these four amps are used for bi/tri-amping (?) but two of them are fed with 2V and the others with 4V.
Something amiss here.

 

[antcollinet]

I did some experimenting last night and disconnected the phono connection preamp outputs to the 8000A’s and fed the tweeters from the mid range 8300MB monoblocks.

Do I understand from this you are bi-amping (or even tri-amping) the speakers? With the lower power amps driving the tweeters? If so, what are you using for crossovers (presumably built into the speakers) and also how are you matching the woofer/tweeter voltage given the woofers are driven from 4V XLR, and the tweeters from 2V RCA? That will result in a 6dB mismatch between Bass/midrange, and treble.

If you do have such a complex setup it is probably worth providing us a connection diagram (sketch will do) so we can better understand.

Also an understanding of your listening environment, especially speaker distance will be useful.

 

[Sokel]

Do I understand from this you are bi-amping (or even tri-amping) the speakers? With the lower power amps driving the tweeters? If so, what are you using for crossovers (presumably built into the speakers) and also how are you matching the woofer/tweeter voltage given the woofers are driven from 4V XLR, and the tweeters from 2V RCA? That will result in a 6dB mismatch between Bass/midrange, and treble.

If you do have such a complex setup it is probably worth providing us a connection diagram (sketch will do) so we can better understand.

Also an understanding of your listening environment, especially speaker distance will be useful.

The strange thing is that even if the XLR 's 4V output level is reduced to 2V (by what?) to match the RCA outputs (as it should) it should still be enough to drive the 1.5V inputs of the amps.
Something is VERY off here.

 

[Leeken]

You’ve done what I’d have suggested,disconnecting the RCA and that amplifier,which then leads to a what is going wrong question.
I’ve got scm40s,driven from a Rme via rca into a nad c298,which is around 29db of gain,it’s ridiculous how loud it can go with no clipping,my next step if I was you would be to go to one pair of amps,take the pre amp out of the equation and see if the problem still persists,if it’s ok put the pre back in with one pair of amps,and see what happens.

 

[Roland68]

Thanks for the response, very good point hadn’t really considered low level files, everything I’ve thrown at it are high res files from Qobuz so should be ok. Right ok I see what you mean, (re clipping) so it’s clipping from elsewhere then.
I did some experimenting last night and disconnected the phono connection preamp outputs to the 8000A’s and fed the tweeters from the mid range 8300MB monoblocks.
This seemed to increase the sound levels. Still not right but better.
Not sure why that would affect it though?
Anyway taking some measurements and calculating gains next.
Thanks for the help guys much appreciated.

Have you checked whether the "Volume Limit" function is set in the CXN100?
Have you deactivated the Preamp Mode?

 

[Shad29]

Hi they are both deactivated thanks.

 

[Shad29]

You’ve done what I’d have suggested,disconnecting the RCA and that amplifier,which then leads to a what is going wrong question.
I’ve got scm40s,driven from a Rme via rca into a nad c298,which is around 29db of gain,it’s ridiculous how loud it can go with no clipping,my next step if I was you would be to go to one pair of amps,take the pre amp out of the equation and see if the problem still persists,if it’s ok put the pre back in with one pair of amps,and see what happens.

Hi thanks for all of your assistance and comments gratefully appreciated. It’s definitely the 8000A Monoblocks connected by RCA, feeding the tweeters shown in the diagram I posted at the start. With the tweeters fed from the mid monoblocks again the volume level is more than adequate now.
I thought that was the way to go using the 8000A’s, but with the power miss match mentioned previously I see now.
Anyway I’ll upgrade to two more 8300MB’s and connect via XLR. Thanks again everyone!

 

[antcollinet]

in the diagram I posted at the start.

Sorry - I missed that.

power miss match mentioned previously

The power mismatch is not the problem.

The pre-amp output voltatge mismatch definitely is. You need to match the amplifier output voltage for all drivers - which means you need same input voltage (which you don't currently have) and same gain - or different gain can work, but then you have to adjust the relative input voltages to compensate for gain difference.

If the amp gains are all the same as you stated, then you need to put 6dB attenuators in line with the XLR connections.

 

[Shad29]

Sorry - I missed that.



The power mismatch is not the problem.

The pre-amp output voltatge mismatch definitely is. You need to match the amplifier output voltage - which means you need same input voltage (which you don't currently have) and same gain - or different gain can work, but then you have to adjust the relative input voltages to compensate for gain difference.

If the amp gains are all the same as you stated, then you need to put 6dB attenuators in line with the XLR connections.

Ah right I understand now, thanks very much.

 

[Sokel]

If Audiolabs for the tweeters can accept XLR too you can just use two XLR splitters and multiply two XLR outputs (L-R) into four.