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?
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.
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
Thx...Yes I have LF100, but with separate PSUs which were designed by myself. So no cutting here
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
That`s a point that bothers me
Wouldn`t be better if each mono amp central ground would also be connected with mains earth and insulated RCAs?That`s a point that bothers me
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
That`s a point that bothers me
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.
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.
That`s a point that bothers me
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.
G²
Did you read my post on how the LF board is designed?
It's relatively easy to check for ground loop noise by just connecting mains earth to star earth, and seeing what happens. I've used LF amps for years, and find no ground loop issues with connecting mains earth to star earth.
Just noticed this thread, I have "monoblock" amps made in a mirror pair.
I have connected the chassis to star earth as I had a bit of noise in my "Soraya" boards, due to the fact that I had a large Mundorf silver/oil input cap fairly close to the board and therefore the output inductor. Dead quiet now. I did'nt have to do this on my original 100+n amps.
I tried this after I noticed that Hugh had done it on his commercial "Soraya", no problems at all.
I have connected the chassis to star earth as I had a bit of noise in my "Soraya" boards, due to the fact that I had a large Mundorf silver/oil input cap fairly close to the board and therefore the output inductor. Dead quiet now. I did'nt have to do this on my original 100+n amps.
I tried this after I noticed that Hugh had done it on his commercial "Soraya", no problems at all.
Then again, with my Soraya monoblocks (each module is in a custom-built case with 2 Lifeforce 55 modules plus an active XO), the star earths on all 3 modules are connected together but the chassis is not connected ... with zero noise.
But then, I only have the standard input caps.
Regards,
Andy
Rod Elliot to the rescue: "How to wire a power supply".
Power Supply Wiring Guidelines
Note the dotted box with the label "loop breaker" in Figure 2. That is "ground loop" breaker.
The connection (or otherwise) of the 0V to chassis ground is what the guys have been talking about above.
I prefer to have a direct connection but that can introduce ground loops. If you have a ground loop problem (causing hum) then add in the "loop breaker".
Rod's "loop breaker" is covered here:
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
It breakes the ground loop without compromising safety.
There, everything (and more) that you ever wanted to know about earthing and power supply wiring. Thank You Rod.
Cheers,
Ian
Power Supply Wiring Guidelines
Note the dotted box with the label "loop breaker" in Figure 2. That is "ground loop" breaker.
The connection (or otherwise) of the 0V to chassis ground is what the guys have been talking about above.
I prefer to have a direct connection but that can introduce ground loops. If you have a ground loop problem (causing hum) then add in the "loop breaker".
Rod's "loop breaker" is covered here:
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
It breakes the ground loop without compromising safety.
There, everything (and more) that you ever wanted to know about earthing and power supply wiring. Thank You Rod.
Cheers,
Ian
On the contrary, AFAIAC ... as the chassis should be connected to mains earth (for safety reasons), if signal earth is connected to chassis then it will be "infected" by hash on the mains earth line. Hence I do not connect signal earth to chassis.
If you mean by that statement ... having a separate PS & power trannie for each channel is no better than when both channels share the one PS/power trannie then IME, you are wrong.
A pair of mono Naim 135s always sounded better than a single stereo Naim 250 ... because each channel had its own dedicated PS. This is also the case with the amps I use.
However, if you are saying that a 'stereo' amp which has a PS+power trannie for each channel is no better than the same thing in 2 separate 'mono' boxes ... then I would agree with you. Except of course, the 2 monoblocs will enable you to locate the amps directly behind the speakers - so reducing considerably, the length of speaker cable required ... which is definitely a benefit.
Regards,
Andy
Assuming grounding is done right, I would expect having separate power supplies in a stereo poweramp for each channel to make about as much audible difference as using Jenlabs $12,000 speaker wire compared with 14AWG wire you bought at the hardware store. Any time you do comparisons, you have to look at any other variables that may be at play. Not everybody is knowledgeable and experienced enough to see some of the variables. Don't always believe what you think. It turns out that we are able to fool ourselves.
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