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Old 27th March 2009, 04:09 PM   #1
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Default Monoblock Vs Stereo

Hi guys, after build a few amps and search many times about mono vs stereo conf, i want to let you please help me to create a thread about just this topic, so can be used as reference thread.


Any fix will be welcomed, as my english and Knowledge are not good.

Stereo Amp = Two Mono Amplifiers on one Chasis, sharing PSU.
Monoblock = One Amplifier on one Chasis, with dedicated PSU. Monoblock can use 2 diferent Chasis, one for PSU and other for Amplifier.
Channel Separation = refers to the measurement in decibels of the amount of channel leakage from one channel to another.


Good about Monoblocks
- Superior Channel Separation
- Possible better power supplier
- Possible power output
- Short speaker cables


Bad about Monoblocks
- Earthing Arrangement
- Price
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Old 27th March 2009, 04:15 PM   #2
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Default Re: Monoblock Vs Stereo

Quote:
Originally posted by samsagaz

Bad about Monoblocks
- Earthing Arrangement

What's wrong with the earthing?
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Old 27th March 2009, 04:26 PM   #3
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well i found this

"
A stereo power amp has both channels tied to the same earth point. Monoblocks don't have this since they're separate. A difference in earth potential can make the amps sound slightly difference and can even introducec mains-borne noise
"
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Old 29th March 2009, 03:53 AM   #4
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My Kenwood/Trio mono blocks ( LM 7s ) provide a linking point to tie both amps together if this proves to be a problem so the fix has been around since at least 1970
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Old 29th March 2009, 07:57 AM   #5
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They are already tied together at the source (i.e. the preamp) through the shielding of the interlinks. Connecting the housings of both monoblocks (if they are connected to signal ground) with a separate wire introduces a groundloop because then you have a full circle (PA<->MB1<->MB2<->PA). To prevent the groundloop, the middle "<->" should not be there.

I know I cannot hook up my DAC and CD-player to my (stereo) integrated amp with both digital (coax) out and analogue out of the CDp connected. It will create a groundloop (audible hum) because now the housings are connected full circle: DAC<dig>CDp<ana>AMP<ana>DAC. This results in a current trying to eliminiate the differences in ground potential. And you know a current can only exist if a circuit is "full circle".
A difference in ground potential will not harm the sound, a current surely will! Reason: a potential does not create a magnetic field, but a current does.
How bad the groundloop becomes depends on the size of the loop and the sensitivity of the amp. A bad one will be very audible at normal listening levels!

To visualize what I mean you should "bend" the above line in a circle so that both "DAC"s (or "PA"s in the other line) become one (they're actually one and the same).
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Old 29th March 2009, 09:30 AM   #6
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I didn't say I did it, just that the connections were there if needed
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Old 30th March 2009, 07:51 AM   #7
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And I didn't say you did it, just that you probably shouldn't, but you didn't, so I didn't have to tell you shouldn't . The reply was also intended as an answer to post #3 to clarify that:
- difference in ground potential is not bad persť;
- ground potentials are equalized by the fact that the grounds of MB1 and MB2 are connected anyway (through the preamp);
- introducing a groundloop is the real culprit...
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Old 30th March 2009, 09:44 AM   #8
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When I got the manuals for those amps the connection was actually touted as a good option by Trio/Kenwood, to be honest i never considered the introduction of a loop, the amps worked fine as is.

I like mono blocks personally; as they can make great sub-woofer amps, in fact I got 3 of the Kenwood amps, one as a singleton; as nobody seemed to be interested in a single amp I got it reasonably cheaply.
Mono blocks also have greater WOW!! factor
Mono blocks are dearer of course as you have to pay for 2 chassis buy I don't think they offer any great sonic advantages in these days of good quality and reasonably cheap speaker wire with low DCR

Regards
Ted
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Old 30th March 2009, 12:09 PM   #9
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Default Re: Monoblock Vs Stereo

Quote:
Originally posted by samsagaz
Bad about Monoblocks
- Earthing Arrangement
- Price
- Weight
- Portability
- Need room for them

Cheers!
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Old 30th March 2009, 07:39 PM   #10
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Quote:
Originally posted by Moondog55
When I got the manuals for those amps the connection was actually touted as a good option by Trio/Kenwood, to be honest i never considered the introduction of a loop, the amps worked fine as is.
I find it a bit strange that Kenwood would facilitate the creation of a groundloop. Then I realized that maybe the GND terminals on the back of the monoblocks are not connected to common ground of the circuit.

I found a Kenwood brochure on the L-07C (pre) and L-07M (power). A passage in it about the GND terminals:

Quote:
Originally written in Kenwood brochure of L-07C/L-07M
How to use the "GND" Terminals

The power amplifier has one "GND" terminal, while the Control Amplifier has two. The latter two are not common, one connecting directly to the common ground of the circuit, and the other to the amplifier's chassis (body).

Hum or external noise pickup through turntable connectors is complex, but it can be eliminated by connecting the turntable "GND" to one or the other of the Control Amplifier's two different "GND" terminals. Use the connection that is most effective. Be careful not to short the two "GND" terminals of the Control Amplifier.

The "GND" of the Power Amplifier can normally be left unconnected. However, if a low hum is encountered from the speakers when some component or aplliance is connected, it may be eliminated by connecting the "GND" terminals of both Power Amplifiers together.
Sadly it doesn't say if the GND terminal of the power amp is connected to common ground or to the chassis, but my guess is to the chassis. If that's the case, a groundloop cannot be introduced by connecting the two together.
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