Need B22 S22 EHHA help

[Smeggy]

For the moment I have the beta and the EHHA amps, two boards each but only one Sigma.

Until I get another sigma they are going to share. The sigma has four outputs, enough for the boards. Now, if I want to run both amps together is there any reason not to?

I can switch on the heaters before the amps to warm up the EHHA.

Any problems so far?

Not ideal but I'm not worried about ideal at this point, just functionality.

There's also the option of running the sigma output pairs through switches to turn one or the other pair off.

Any thoughts on the best and safest way to do this or is what I suggested first fine?

[Smeggy]

Piccy of setup

[dBel84]

would you ever want them running at the same time? ..dB

[Mister X]

Why wouldn't you?

[Smeggy]

Well, yeah, one running my dyanamics, one with my stats in them. People seem to think it'd overheat the S22 regulators or whatever.

[dBel84]

this was my concern too, both those amps can suck good juice. Switching the rails between the 2 amps would work but you effectively lose one active amp with this configuration ( not that that was obvious at all ) . Are you averse to dropping a second S22 into the case ( is there enough room? - i don't see the torroid in there , could be stacked but still very tight and from Nates experience, the B22 can pick up noise like this ) ..dB

[Smeggy]

There is room for a second S22, the toroid is external.

[dBel84]

and your torroid is the mutha load iirc , so it would handle both S22's without any concerns? seems the sensible thing to do then ..dB

[Mister X]

Well, yeah, one running my dyanamics, one with my stats in them. People seem to think it'd overheat the S22 regulators or whatever.

People?

Can't you just measure the current draw of each amp board and figure the rest out by yourself?

[dBel84]

The voice of reason

I am embarrassed to say that I fell into the same trap too, just looked at the 2 amps under consideration, figured both running full tilt would draw more that the S22 heatsinks would tolerate and abandoned the idea.

The truth iabout the S22

No current-limiting

* The high-current MOSFETs are not normally the limit of how much current the σ22 PSU could supply, as long as they are adequately heatsinked.

* The maximum current limit is determined by the rating of the power transformer, the rectifier diodes (the specified MUR820 devices are rated at 8A), and the AC line fuse.

* The AC line fuse rating should be selected to protect the power transformer from overcurrent damage.

* There is otherwise no current-limiting circuit in the σ22, which allows it to supply peak currents of many amperes. High transient bursts of current are always available, which some amplifiers require to avoid clipping and distortion.

Come on Smeggy , I am sure you want to see how much moar power you can push

The rethink

I have not done the math but a ballpark for the EHHA pushing headphones is a max of about 1-2W ( my boards idle at a bias current of about 200mA ) , I suspect the B22 is about the same. Thus, driving headphone loads, both amps should be able to work happily with a single S22 in a well ventilated case.

I was just scanning the B22 information and Ti says the following "The current draw from the β22 board is approximately 200mA per board as a headphone amplifier ... 5A peaks driving speakers" and I recall a comment about a single S22 being able to power 4 B22 in balanced mode quite comfortably.

I am not sure if the on board S22 heatsinking would be adequate , we would have to do the real math for that one

..dB

[digger945]

I am sure with a large enough transformer, say minimum 100VA, you won't have any problems. I have run both EHHA boards and two Dynahi boards from one Sigma22 with an 80VA transformer with no problems(HP's plugged into both while playing music). The transformer does get moar warm this way but not stinking hot.

What size toroid do you have Smeggy.

[n_maher]

I would recommend doing the real math before firing up both amps at the same time. I have no idea how much current the EHHA draws but it makes me uncomfortable to think about the tube heaters and what they must be drawing (if 6GM8s that's .33A each).

[dBel84]

the tubes have their own supply , so it is just the amp rails that need to be considered - I will go back and work it out but my suspicion is that it will not be more than 300mA per board..dB

[digger945]

The heaters on the EHHA are on a seperate PS.

For the pair of EHHA boards all plugged in and running I get 350mA per rail (that's 2 boards together).

[Smeggy]

You're all talking to one of the worlds mentally challenged here, I wouldn't know what to measure and as to the math... bottom in class 3 years running.

Yes, it's a miracle I can walk and breathe at the same time

[Smeggy]

Heh, sitting here with Kelviz having our mini meet and I'm listening to the HD800 )

[dBel84]

and you never invited us???

Well I was just looking at the EHHA and idling for each board ( set with a MOSFET idle current of 100mA ) will be about 220mA. I am not sure what bias your boards are set to digger but your measurements suggest that you are idling around 75mA - all within spec ..dB

[digger945]

I haven't had time to do much with the EHHA lately. I remember adjusting until I had .23V across the output resistors. I can plug it in again and do some measuring if you guys want, can't seem to find a certain pink baggy for another project atm.

[dBel84]

I remember adjusting until I had .23V across the output resistors.

well that will give you 104mA per mosfet = 208mA per board . There is about 10mA in the VAS stage and about another 4mA in the mirror ( I allowed 20mA all in for good measure ) So in theory , your amp should be drawing about 230mA per board ( unless I am missing something here )

How did you measure current draw for your amp? The easiest way is to use a dummy load and check the voltage drop , calculating the current from that..dB

[digger945]

I put a DMM in series with each of the rail supply lines and measured the current drawn from the sigma. It was about .35A per rail to supply both boards with the heaters on to make sure everything is conducting properly. I let them sit on for about 2 minutes to see if anything would drift.

[luvdunhill]

I am not sure if the on board S22 heatsinking would be adequate , we would have to do the real math for that one

that would be very wise

[digger945]

True. I have 2" Aavids on mine as opposed to the stock 1.5".

Still they get only warm even when hooked up to the Dynamite via umbilical and having the EHHA tapped directly to the board.

[dBel84]

no questioning that then

..dB

[Smeggy]

cool, not sure of sink size on my S22 but I can order bigger ones. I also need to get one of those 3 screw slot board connectors for the fourth output, which is currently empty. I only have the twin ones. I suppose I ncoud use external connectors as it's not likely to come out any time soon.

Digger, my toroid is 160vA.. big hairy monster

Bugger it, couldn't wait...

Now we'll see ig it overheats.

The S22 sinks get hot, no doubt about that but not much more than either set of boards alone. It's too hot to hold my hand on the inks for more than a couple of seconds but that's about the same as the EHHA sinks and I upgraded those. Hot little bugger.

Great hearing both together!

Edited June 29, 2009 by Smeggy

[dBel84]

talk about a big hairy monster - that is one beast.

Did you by any chance hook he HD800s up to the EHHA - i suspect this union to be nothing short of a revelation..dB