[Lil' Knight]

25 feet? Your cases must be huge.
Just try to keep the signal wiring as short as possible.

 

[linuxworks]

I would not use fancy 'silver' wire. its certainly not needed and since regular wire is known to work (and work well) why not try that first before assuming you need 'upgraded' wire?

 

[Beefy]

Quote:

Originally Posted by linuxworks /img/forum/go_quote.gif I would not use fancy 'silver' wire. its certainly not needed and since regular wire is known to work (and work well) why not try that first before assuming you need 'upgraded' wire?

pompon believes in audible differences between power cables. Enough said

 

[mhamel]

So, I'm getting close to embarking on a Beta22 adventure.

I've been reading and researching for a few weeks now... have made it all the way through this thread, 2-1/2 of the Headwize threads, Amb's Web site (multiple times) and a bunch of other assorted threads.

I've been going back-and-forth on whether to go with a 3-channel active ground build, or just go all out and build a balanced amp. I'm leaning heavily towards the 3-channel active ground config.

I've got what may be a stupid question about power supply configuration, but I'm going to go ahead and ask it just the same. Heh

I'm thinking of building the PSU with dual Sigma22 PSU boards, to spread the thermal load out, and to minimize future work if I decide I eventually want to upgrade to a 4-channel balanced config.

I know I could run 2 of the amp boards from one PSU board and the 3rd from the 2nd PSU board, but with the thought of keeping the power and thermal loading as even as possible, can the o22 outputs be run together in parallel?

Thanks,
-Mike

 

[oneplustwo]

My opinion.... size the enclosure, plan the layout and jacks (get an 8 pin speakon jack or something similar) for two sigmas and trafos but only install one. Then, if you go balanced later, it will be easy to add another sigma.

 

[johnwmclean]

Quote:

Originally Posted by mhamel /img/forum/go_quote.gif I know I could run 2 of the amp boards from one PSU board and the 3rd from the 2nd PSU board, but with the thought of keeping the power and thermal loading as even as possible, can the o22 outputs be run together in parallel?

Quote:

Originally Posted by amb /img/forum/go_quote.gif Also, never parallel the outputs of two σ22s. One σ22 will "see" the output of the other, which will appear as a short circuit and the two will fight. You'll have some blown parts as a result.

 

[nattonrice]

In addition to the suggestion above, I would also layout, cut vents and xlr jack holes, and drill mounting holes for a 4 board build.
That way when/if you make the decision to change to a balanced build it is as simple as dropping in the 4th board and wire.
... well you also need to make a handful of parts changes to the 3rd board but that will be trivial.

 

[amb]

You cannot parallel the outputs of two σ22s (or, for that matter, most regulators). One will "look" like a dead short to another due to its low output impedance, and the two will "fight" and both will likely be damaged.

 

[mhamel]

John/Amb - Thanks... sorry, I must have missed the discussion about parallel along the way... lots of info to digest.

I'm thinking I'll take oneplustwo's advice, build up the dual PSU and just use one side for now, that way at least that part of it is done and available for a later upgrade.

Thanks,
-Mike

 

[oneplustwo]

Another thought... depending on the likelihood of going balanced, you might consider going with a 2 channel at first. If a 4 channel is inevitable, this would make your life easier especially if you don't have to change the gain of the existing boards. (Remember, your effective gain will double once you go balanced.) This would also give you the opportunity to think about a truly mono-mono setup where you could have one sigma PSU and one 2 channel beta enclosure for the left and another for the right. I've never actually seen that done (for good reason I think) but for your situation where you could potentially build half a balanced beta at a time, that could work. Plus, if you decide 2 channels is good, you won't have these large enclosures with wasted space. Just a thought.

 

[aloksatoor]

The volume control on a dual mono would be complex at best. You either need 2 knobs or you need a digital attenuator controlled by a single knob or buttons. It works for power amps since we have a preamp to control the volume.

 

[mhamel]

Yes, I think a monoblock design with 4 chassis wouldn't work that well for a headphone amp. Whichever config I end up with, I'm going to keep it to a single PSU chassis and single amp chassis, but try to lay everything out so that upgrading later on won't be that bad, if I decide to go that route.

I've been playing around with panel designs and enclosure layouts just to get some idea of how feasible it would be, and I think I have something that would work... using Neutrik D-series jacks for the RCA inputs and headphone outputs, that way if I decide to go balanced, replacing those with the same series XLR jacks will be trivial.

The Ecomate power connectors come in a 6-contact version, so I'll plan on using that from the start, with a 6-conductor umbilical, and that keeps me covered later as well.

As far as gain goes, from what I've read, I think I'd need to change if I upgrade. I'm going to be ordering D7000s in the next few weeks, which would need lower gain, but will also be using the amp with 250 ohm DT-990s. I've settled on a gain of 5 for the unbalanced config, but if I go balanced, I'm thinking I'd need to drop that to a gain of 2 per board to account for doubling. Still, though, as long as I'm careful with the boards, swapping out the gain parts shouldn't be too bad after the fact.

I'm still deciding on which way to go for volume control. I've got some email out to TKD about their stepped attenuator - according to their data sheet, it doesn't come in a 50K version, and it's rated at "0-15KHz frequency" - I wasn't sure if that had any effect on using it for this, though from everything else I've read, it seems to be a good choice. If they don't have it in 50K, though, I need to decide on an alternate. They've got 10K, 20K and 100K listed in the data sheet.

Another potential downside - no quad version of the TKD. So if I upgrade, it also means a change of volume control, so I need to think about that for the layout as well.

Still time for decisions, though.. I'm not rushing into anything... I want to make sure I plan this out well before I start.

-Mike

 

[oneplustwo]

If you plan on having the balanced amp run unbalanced, you'll need the ground to go back to the sigma PSU. So you'd need the 8 pole ecomate if they have one to accommodate this. I used an 8 pole speakon from Neutrik which is awesome. I got a matching preterminated cable from ebay for super cheap too.

 

[aloksatoor]

Im on the lookout also for an 8 conductor cable can you point me to the ebay seller?

 

[FallenAngel]

Uhm... 8 cables, sleeve in nylon?