[jlefley]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif The JT controller has an onboard voltage rectifier and voltage regulator. Why do you feel the need to feed it DC?

I would think that it would not be a good idea to send ac into the enclosure housings the b22s, where the attenuator relay driver board will be located. (I am planning on placing the amp boards and power supplies in separate enclosures)

 

[Beefy]

For a transformer sized for the JT, say 5-10VA, the effect will be negligible. But I see your point.

 

[linuxworks]

one thing I was considering - what do you guys think? in a setup where you feed ac into the b22 box (so the s22 is inside the same box as the b22), you have 60v p-p in ac form that you *could* tap into and step this down to 7v (to allow for drop to get to the target 5v). you won't be drawing that much from that 60v rail (both sides of the 30v rails) and so if you assume a US current of 120vac, you could take a trafo that is rated at 2x your target and when running it at 1/2 input you'd get your target (5v) out. would that work? I think so, but what do you guys think?

it would keep the wiring simpler (for my setup, at least) having *just* the 30, 0, 30 vac wires come in and then break that 60v diff down into a control voltage for my digital stuff.

comments on that idea?

 

[Beefy]

Quote:

Originally Posted by linuxworks /img/forum/go_quote.gif comments on that idea?

Only that a 5-10VA transformer at the correct secondary voltage is surely going to be a crapload easier

 

[linuxworks]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif Only that a 5-10VA transformer at the correct secondary voltage is surely going to be a crapload easier

what I was hoping for was to simplify things. if I have to carry the 30/0/30 AC from the PS box to the amp box, that's fine. that's 3 wires and its easy on the connector and the cable bundle. then if I can derive the control voltage, while things are still in AC, down to 5v and put a very small trafo off in the corner of the amp box, that seems like a win to me. even more if you needed a local 12/-12 set of rails. again, running the big old 30/0/30 AND a 5 AND a pair of 12's thru umbilical? no thanks! that is clumsy. I'd rather send the 'bulk' (dual 30) thru and derive the rest. if possible. you don't like this idea?

 

[amb]

Aside from what others have already posted, if you use one of the two σ22s to power the JT (and assuming that the JT would indeed draw 400mA), then that σ22 will run significantly hotter than the other one, and you'll need to account for the extra current requirement into your choice of transformer. Also, since the JT needs only a single supply rail, and the σ22 is a dual-rail regulator, it would create current draw asymmetry in two ways -- between the positive and negative rails on one σ22, and between the two σ22s. Not that this is inherently a bad problem, but it just seems out-of-whack in an otherwise beautifully balanced architecture.

 

[linuxworks]

that would be another reason why I'd want to straddle the 2 ac lines and steal power from that with my mini step-down trafo idea. you are keeping things 'balanced' that way (both rails get equally 'hit' for the lower control voltage). I would not want to tap into just one of the sides; that would ruin the symmetry.

 

[Beefy]

Quote:

Originally Posted by linuxworks /img/forum/go_quote.gif I'd rather send the 'bulk' (dual 30) thru and derive the rest. if possible. you don't like this idea?

No, not really. I would rather run a second umbilical.

 

[linuxworks]

I guess we differ in approaches, then

2 cords from box to box seems unprofessional to me; and I'd like to keep it to 1 semi-thin cord instead of 1 big 'garden hose' or even 2 cords.

I'll have to try it to see. but is there anything technically wrong with using a 120/14 v trafo and powering at 1/2 so that it gets 60 in and 7 out? I think that's fine (?).

 

[Pars]

How about using something like this as the connector?
Digi-Key - 670-1133-ND (Manufacturer - SRCN2A16-7S)
7 x #16 contacts rated at 10A, you could run both the 30-0-30Vac and your 7V or whatever on it. Reasonably priced and well made.

 

[linuxworks]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif How about using something like this as the connector? Digi-Key - 670-1133-ND (Manufacturer - SRCN2A16-7S) 7 x #16 contacts rated at 10A, you could run both the 30-0-30Vac and your 7V or whatever on it. Reasonably priced and well made.

cool! added to my cart along with its mate

have not seen/used that one before. sure, I'll give it a try.

but still, I do have to question if its better to have local trafos in the amp box (off in a corner, literally) and reduce the complexity and thickness of the box-to-box wire? in fact, you could still use the same connector and just parallel the key rail voltages (in this case, both, lol) on the pins, making the connector effectively 'thicker, electrically'.

taking the devil's advocate on myself (lol) one advantage of putting both the 'big' and 'control' trafos in the same remote box would be that you could power switch the big one on/off (via SSR on the 110vac side) and still leave a constant 5v for control. that would be a very nice and clean way to power off the remote 'floor box'; you'd have a control wire from the amp to the PSU box (that's 1 wire) and 2 wires from the PSU to the amp for 5v/gnd, for controller use. the controller would send a logic 0/1 over that control wire and the PSU would SSR-control, on or off, the big 30/30 trafo. and by keeping the 5v control voltage always on, the unit can fully be controlled by the 'non-floor' box

it can even pre/post mute things since it will know about the 30/30 trafo coming on/offline. things like that.

maybe I should just put them both in the same PSU box and run a thicker umb. cable. just seems less elegant to me, though, overall.

 

[pila405]

Does the B22 hiss? From HD800 to very sensitive phones like Denons.

 

[m1abrams]

Quote:

Originally Posted by pila405 /img/forum/go_quote.gif Does the B22 hiss? From HD800 to very sensitive phones like Denons.

I do not have one, but would think that the only reason a B22 would hiss is if it was improperly built. I have a M^3 and it is dead silent even with sensitive IEMs. I would expect the B22 to be as quiet as the M^3 if not more.

 

[amb]

There is no such things as a noiseless amp. The trick is to build it with an appropriate amount of gain for the type of headphones you'll be using it with. Too much gain and the noise floor will become audible, too little gain and you won't be able to get loud enough with the volume control maxed. Since headphones span a wide range of impedances and sensitivities (K1000s to IEMs at both extremes), it's almost impossible to have one gain setting that works well with all of them. Throw in differing sources with different output levels and things get even more complicated. But, usually, a gain of 5 is a good compromise and allows the amp to work with a wide range of sources and headphones.

 

[pila405]

On what gain will you recommend for using the HD800 & K701 with Gamma2?