pre power gain matching for Audiolab + LM4780 kit

[dakku]

Hi,
I am considering getting the Audiosector LM4780 kit from Peter and looking to use this with my Audiolab 8000s (pre amp mode)

I have no idea about gain matching etc etc, I have tried to read up a number of times but I am afraid I am still confused.

Basically, can someone please tell me if this LM4780 dual mono kit from audio sector work with my Audiolab 8000s preamp?

Manual for Audiolab can be found here:
http://www.avrevolution.com.au/SiteMedia/w3svc1114/Uploads/Documents/8000S.pdf

 

[AndrewT]

It depends on your Source signal level and the Audiolab's gain and in/out impedances.

I suspect the Audiolab pre outs are passive, i.e. no added gain.
The tape outs are usually highish impedance.
You can measure these before you commit to choosing the gain and input impedance of your new power amp.

 

[dakku]

Hi AndrewT,
Thank you for the reply. According to the Audiolab 8000S manual:

Pre Amp Out
PRE OUT 1 and PRE OUT 2: Output Impedance 100 W
Maximum Output >7.3 V RMS

Would that be sufficient for LM4780 you think?

 

[sreten]

Hi,

Of course it will work with the preamp output.
For biamping you need to match the 29dB gain.

FWIW there is utterly no point is trying to upgrade
the power amplifier section and use it as a preamp.

The power amplifier section should eat chip amps
for breakfast and do ~ 100W rms into 4 ohms.

rgds, sreten.

 

[dakku]

Hi,

Of course it will work with the preamp output.
For biamping you need to match the 29dB gain.

FWIW there is utterly no point is trying to upgrade
the power amplifier section and use it as a preamp.

The power amplifier section should eat chip amps
for breakfast and do ~ 100W rms into 4 ohms.

rgds, sreten.

Thank you Sreten for the response.

I am just confused if Chipamps and T-Amps are an improvement on the Audiolab sound. I have a new arrival tomorrow, Topping TP20.. Lets see how the sound compares to Audiolab (irrespective of power), before I jump to a 100% DIY option

 

[sreten]

Hi,

Buying or building stuff isn't the best way of clarifying a confusion.

rgds, sreten.

 

[AndrewT]

output impedance is 100W, should read 100w, where little w is the lower case version of omega, or ohms.

The 100ohms indicates the pre-out is not passive. There must be a Buffer after the vol pot.
Does the "S" have tone controls? Are the tone controls before, or after the Pre-outs?

 

[Mark Whitney]

The pre-amp has a gain of 9dB and the power-amp of 29dB.

 

[AndrewT]

That combination of gains (9+29 = 38dB) comes to 80 times voltage gain.
This gives a full power (60W?) input sensitivity of 274mVac
For 1W of output, the input sensitivity is 35mVac.

I would be inclined to bypass the pre-amp gain for most sources and feed direct from vol pot to Power Amp.

 

[dakku]

Hi Andrew.
There are no tone controls on the Audiolab 8000S.

That combination of gains (9+29 = 38dB) comes to 80 times voltage gain.
This gives a full power (60W?) input sensitivity of 274mVac
For 1W of output, the input sensitivity is 35mVac.

Would that cause any issues to use Audiolab 8000S in preamp mode with the
LM4780 kit?

I would be inclined to bypass the pre-amp gain for most sources and feed direct from vol pot to Power Amp.

I am not sure if it is possible to bypass the gain with Audiolab.

 

[AndrewT]

The minimum gain for some of these chipamps is 10 times (+20dB)
If you add on the pre-amp gain at +9dB you end up with a manageable +29dB
.

But most of these chipamps perform better with the gain set to between +26dB and +30dB
Now add on the +9dB of the Pre-amp and you have as much gain as the "S".

Many sources can manage with just a Buffer (+0db) into chipamps.
A few Sources might need an extra +6 or +12dB, BUT !!!! ONLY apply that to the Sources that need that much gain.
Read the article on System Gain on the diyaudio front page.