[jdkJake]

I agree. I took delivery of the par metal 12x12x3 last week. Started the layout and then got disrupted due to that most bizarre cold solder joint issue with my Alps/epsilon combo.

Started laying out the front panel tonight. I am trying to do something somewhat interesting and hopefully somewhat creative. We shall see.

 

[runeight]

Quote:

I'd use two no matter what due to the fact that the e12 sums the offsets of each channel.  If the rails go south in opposite directions, the e12 will never notice.

OK. Definitely a corner case, even if both channels went in opposite directions, but could happen.
 

 

[cobaltmute]

I know people who have had 2 drives simultaneously fail in RAID 5 arrays, and we just had a case at work where both drives in a RAID 1 array failed at the same time.
 
It is a corner case, but the cost of a second e12 versus the cost of my HD650s it is what I call insurance.

 

[jdkJake]

I have to agree with cobaltmute, when you start adding up the cost of the headsets (and in the case of the HF-2, availability), it becomes somewhat of a no brainer just to keep things somewhat under control.

Not to mention the inevitable upgrades that are sure to follow with an amp that can resolve this good. Certainly going further up the Sennheiser, Beyer and Grado lines is now more of a potential option than it might have been before building this amp. It is that good. And then there are those orthos to consider as well ( we hear you sachu ).

 

[runeight]

Sure, I understand. Unusual combinations of events do happen and if the risk is high enough it pays to protect against them.

 

[jdkJake]

Awful quite on the beta front. 
 
I know cobaltmute is awaiting a transformer, sachu is working the case and ujamerstand working a board trace short/defect.
 
Myself, I am working the casing. Need to pick up a new drill bit of a particular size and am awaiting a part for the front panel. Hope to have the case work finished by the end of next week if everything arrives as expected. Not sure where studeb or stringgz stand with their case work.
 
Amp continues to sound excellent. I also just received the parts to socket an swap the open loop/closed loop gain resistors. Looks like I am going to experiment with those settings after all.  

 

[ujamerstand]

I've fixed the board defect, but manage to damage a cap while soldering and melted its plastic encasing slightly. Just finished dealing with all the school work, so I hope to have everything running soon.

 

[sachu]

I need to test the boards. Will go over, check if everything is kosher tonight and maybe even bring them up. Heaters are rigged for 12.6V ( should be able to dial it in with 240R, 2k with a 200R trimpot) ..will report back when I test them out.

 

[ujamerstand]

Just wired up the transformer to the boards. The power sections works as intended. No magic smoke. (So far.) Some readings:
 
10.6V at TP3, 6.4V at heater output.
rails at +29.4V/ -30.4V and +29.6V/-30.0V 
before the regulator: (If I'm measuring this correctly) +46.7V/+46.9V and similar readings on the other side.
 
The power supplies are currently unloaded.

 

[runeight]

Those numbers before the regs are potentially dangerous, but they should pull down when you load the rails. If they get below 40V you're ok.

 

[ujamerstand]

I think so too. Let me wire up the amplifier section and see what happens.

 

[ujamerstand]

Okay, I've wired up the amplifier section, The voltage before the regulators are still above 40V prior to biasing. After biasing the mosfet to 220mV, the voltage before the regulator sits at +/-39.7~39.9VDC. 
 
DC offset reads at around 0.1mV on one channel, and 4.2mV~ 6.7mV on the other. (This is the board with the defect)

 

[ujamerstand]

Well, I got everything running now.

DC-offset on one channel stablizes at 6.3mV, while the other channel has it at less than 1mV. I might want to swap out the opamp or the V- reg to the servo, they might have been damaged while I took them out to figure out whats wrong. 
 
A short listening session with this amp proves to be quite an enjoyable experience. The EHHA has no problem driving the Hifiman HE-5. On the EHHA rev.A, it is almost as speedy as the STAX SR-404 on exstata, while packing a lot more punch than the 404s. Gotta love planar headphones.

It also runs quite warm. I don't think I'll need to turn on the heater in my room during the winter anymore. 

 

[runeight]

Great!!! You've probably done this, but make sure to re-bias when the heatsinks get to temperature.

 

[jdkJake]

That's great news ujamerstand!

FWIW, the DC offset on both of my channels always floats around 0V, so, replacing those parts seems like a logical next step.

What is your measure at TP3 once under load? Also, what is you AC line measuring on the primaries? Your values seem a touch higher than mine as I usually come in around 38V at the rails with 122VAC on the line.