[amb]

Quote:

Originally Posted by johnwmclean /img/forum/go_quote.gif I take it on those grounds, you’ve ditched the concept of monoblock design? Just curious...

No. The monoblock concept has other merits beyond separate power cords (in fact I don't consider the separate power cords a big advantage per se, it's just a "given" since true monoblocks are in a separate chassis per channel). Also, monoblock design make more sense for high power speaker amps rather than headphone amps due to the large currents involved.

Some of the benefits of monoblock that I consider useful:
- Allow placement of power amp close to the speaker, minimizing the length of the speaker cables and their resistive and reactive effects. This of course assumes a preamp with very low output impedance, and could drive a long, more capacitive interconnect cable without ill effects (unbuffered passive preamps need not apply here). Such placement usually also means that the power amps are located far away from the preamp and sources, so the large power transformers will have little chance of inducing hum/noise into the small-signal circuitry.
- Each monoblock amp has a separate power supply and ground which are not shared anywhere except at the input common ground (through the interconnect cable, where there is miniscule current). Allows for maximum channel separation. Of course a dual-mono construction in a single chassis could be made to do this, but chassis grounding needs to be common in the latter case.

 

[johnwmclean]

Thank you Ti for such a thorough explanation - very much appreciated.

 

[nkk]

Thank you all for your responses. I am going to do this over the summer (hopefully), and am just planning now so that I can spread the parts expenditure over a longer time period.

Hearing this, I will go with a single s11 and two 3ch boards, probably only one populated with the ground for a SE option. Maybe I will upgrade later to the other one, but I see no real use for it now.

Thanks again,
Nkk

 

[grawk]

The one cetoole built for me was 1 sigma 11, 2 3 channel boards, selectable gain on a 4 position switch (1,3,5,7), cinemag cmli 15/15b input transformers, with 2 rca and 2xlr inputs, xlr and rca preamp outs, xlr combo jacks and 4pin for balanced and unbalanced headphone outs. We ran one of the unbalanced outputs off the + channel and one off the - channel, so the load wasn't impacted by having 2 headphones or 1 plugged in at a time.

 

[bidoux]

Quote:

Originally Posted by grawk /img/forum/go_quote.gif cinemag cmli 15/15b input transformers,

Sorry for the noob question, is the transformer for unbalanced to balanced conversion ?

 

[grawk]

yes

 

[Steve Eddy]

Just a note, if the CMLI-15/15B is going to be used for unbalanced to balanced conversion, it should be used backwards, i.e. the secondary is used for the input and the primary for the output, with the can and shield connected to the output side signal ground.

se

 

[Jaypee]

Hi everyone, new m³ bulder here!

I'm planning on building a balanced (or "bridged) setup mainly to drive speakers. Just curious, is having two separate PSU beneficial only if you're building a monoblock design for headphones? In other words, for mainly speaker use, there's no point in building two σ11:s, but just one with enough power to do the job?

 

[johnwmclean]

Jaypee, refer to post 16 from AMB.

 

[Jaypee]

So in my case, two PSU's would be a waste of money, since I really don't need a true monoblock design, I'd use 2 bridged m³ boards ONLY to have more power to drive the stereospeakers.

 

[Beefy]

Quote:

Originally Posted by Jaypee /img/forum/go_quote.gif I'm planning on building a balanced (or "bridged) setup mainly to drive speakers. Just curious, is having two separate PSU beneficial only if you're building a monoblock design for headphones? In other words, for mainly speaker use, there's no point in building two σ11:s, but just one with enough power to do the job?

Quote:

Originally Posted by Jaypee /img/forum/go_quote.gif So in my case, two PSU's would be a waste of money, since I really don't need a true monoblock design, I'd use 2 bridged m³ boards ONLY to have more power to drive the stereospeakers.

No. Driving speakers is the one time when you would want to consider two PSU's. The heat production from a single S11 would be too high at the higher currents.

 

[amb]

There is another point to consider. When you use the amp to drive speakers, the amp will need to deliver a lot more current into the load than with headphones. This is because not only are speakers a lot less "efficient" than headphones, they are also much lower in impedance. In a bridged configuration, the speaker load impedance "seen" by each of the "hot" and "cold" amps is half the real speaker impedance, increasing the current further (this is why you get theoretically four times the maximum output power bridged, the voltage swing is doubled, and the current is also doubled due to halving of the impedance).

All this extra current has to come from the power supply, and one σ11 will have to work very hard to deliver all that current (the MOSFETs will get very hot when you turn up the volume). Using two σ11s, one per stereo channel, splits the current up and allows each one to bear only half the load.

EDIT: beefy beat me to the punch!

 

[johnwmclean]

If the build was purely balanced and the ground channels were left unpopulated, would this place less current demand on the psu?

 

[Beefy]

Quote:

Originally Posted by johnwmclean /img/forum/go_quote.gif If the build was purely balanced and the ground channels were left unpopulated, would this place less current demand on the psu?

A little less, but not much. The ground channels would only be running their quiescent current, as they aren't connected to the speaker. So less 80mA per board, compared to up to an amp for the other channels.

But yes, for speaker use, it makes little sense to populate the ground.

Quote:

Originally Posted by amb /img/forum/go_quote.gif EDIT: beefy beat me to the punch!

I've gotta be on the ball at least once in my life

 

[johnwmclean]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif The ground channels would only be running their quiescent current, as they aren't connected to the speaker. So less 80mA per board, compared to up to an amp for the other channels.

Thanks heaps Beefy