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-   -   Monoblock amplifiers - any significant (dis)advantages? (http://www.diyaudio.com/forums/aksa/221123-monoblock-amplifiers-any-significant-dis-advantages.html)

supernet 8th October 2012 12:41 AM

Monoblock amplifiers - any significant (dis)advantages?
 
My amplifier (LF 100) need a decent case and while thinking about visual WAF friendly apperance, I have noticed that having two monoblock cases would make some asthetic and sonic benefits...better separation, placement amplifier close to speakers...but on the other hand, I am a bit worried about grounding issues. Each mono amp should have his own central grounding point, that means that both grounds meet together at extension main cord, compared to stereo amp where both channels meet each other at one central point with short (low impedance connection).

So...have anybody made practical test if monoblock amps are really better or this is just another audio myth?

andyr 8th October 2012 02:26 AM

Quote:

Originally Posted by supernet (Post 3193269)
My amplifier (LF 100) need a decent case and while thinking about visual WAF friendly apperance, I have noticed that having two monoblock cases would make some asthetic and sonic benefits...better separation, placement amplifier close to speakers...but on the other hand, I am a bit worried about grounding issues. Each mono amp should have his own central grounding point, that means that both grounds meet together at extension main cord, compared to stereo amp where both channels meet each other at one central point with short (low impedance connection).

So...have anybody made practical test if monoblock amps are really better or this is just another audio myth?

I presume you have a "standard" LF100 ... which has 1 x PS PCB connected to 2 power transformers? So to move to monoblocs, you will have to cut that PS PCB in half.

I implemented my LF100/55/55s as monoblocks - so that's what I did (cut the 3 x PS PCBs in half). I can assure you there is no grounding issue when separating the 2 channels - as long as you drill a new hole in each half of the PS PCB, so you can implement a new "star ground" in each.

How do I know there is no "grounding issue" ... because my system is dead quiet - ie. no ground hum. :D

And the big advantage is that, as you noted, you can put the monobloc case right behind each speaker. (In my case, I have 3 amp modules, 1 active XO and 4 complete PSes in the one custom-designed case, sitting right behind each speaker. :) )

Go for it! :)

Regards,

Andy

supernet 8th October 2012 06:30 PM

1 Attachment(s)
Thx...Yes I have LF100, but with separate PSUs which were designed by myself. So no cutting here :D


Did you connect central ground point to mains earth(chassis) too? Probably you use insulated RCAs...

andyr 8th October 2012 10:29 PM

Quote:

Originally Posted by supernet (Post 3193934)
Thx...Yes I have LF100, but with separate PSUs which were designed by myself. So no cutting here :D

Did you connect central ground point to mains earth (chassis) too? Probably you use insulated RCAs...

OK, so one problem solved. :)

Yes, I use insulated RCAs - so mains earth never touches signal earth anywhere in my system. Mains earth is there solely to earth the chassis.

Regards,

Andy

supernet 8th October 2012 11:50 PM

Quote:

Originally Posted by andyr (Post 3194222)
Yes, I use insulated RCAs - so mains earth never touches signal earth anywhere in my system. Mains earth is there solely to earth the chassis.


That`s a point that bothers me:xeye: Wouldn`t be better if each mono amp central ground would also be connected with mains earth and insulated RCAs?

andyr 9th October 2012 12:17 AM

Quote:

Originally Posted by supernet (Post 3194314)
That`s a point that bothers me:xeye: Wouldn`t be better if each mono amp central ground would also be connected with mains earth and insulated RCAs?

Not IMO. ;)

Mains earth is dirty - it should never touch signal earth. So I use insulated RCAs to keep signal earth separate from the chassis (which is connected to mains earth).


Regards,

Andy

stvnharr 9th October 2012 03:48 AM

Quote:

Originally Posted by supernet (Post 3194314)
That`s a point that bothers me:xeye: Wouldn`t be better if each mono amp central ground would also be connected with mains earth and insulated RCAs?

For safety's safe it is best to connect mains earth to the psu star earth.
On the LF board the signal ground is connected to power ground with 2 diodes and a 10R resistor, so signal ground is not directly connected to power ground, which is directly connected to star earth on the psu.

Not connecting the mains earth to psu earth is fine as long as nothing catastrophic ever happens.

stvnharr 9th October 2012 05:43 AM

Quote:

Originally Posted by supernet (Post 3193269)
So...have anybody made practical test if monoblock amps are really better or this is just another audio myth?

I meant to include this in my earlier post, so I'll just add it here. I used to have a pair of Aksa 55's each in their own case near the speaker so as to run short speaker cables, as Andy does. The drawback to this is you need an extra power cable.
Given that Aksa's and LF's are designed to be dual mono, with each channel with a separate board, power supply and transformer, it makes little difference if they are in one case or two.
As to the audio myth of monobloc configuration automatically being better, well, the new Naksa 70's are not dual mono and sound great, a step up from the LF series for sure.

jcx 9th October 2012 05:44 AM

safety rated "double/reinforced" insulation for xmfr, proper internal construction allows for floating electrical equipment: "Class II" - the 3 A mini 2 pin plug may be OK for a 100 W monblock amplifier

stratus46 9th October 2012 05:59 AM

Quote:

Originally Posted by supernet (Post 3194314)
That`s a point that bothers me:xeye: Wouldn`t be better if each mono amp central ground would also be connected with mains earth and insulated RCAs?

You're asking - no, begging - for a nasty ground loop. Why would you want monoblocks and then connect the output grounds together via the power ground? The signal grounds should come back together via the RCA cables at the preamp. Any slight ground variances due to signal currents won't make an iota of difference as the output ground is 'floating'.

Please remember that any voltage drops in a cable happens in both conductors. 'Ground' (earth if you will) is not the same at the load as it is at the source. You MUST obey Ohm's law. You can try to force your way with ground straps or larger gauge wires but there is always resistance whatever you do. Don't fight it, work within the limits.

G


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