The Objective2 (O2) Headphone Amp DIY Project

[Shamharoth]

Yes, that's why I was asking if the ODA would be able to supply a little more voltage than that. Because if my calculations are correct (following your article on Inner Fidelity) the Sextett would need near 9V for 110dB.

[RocketScientist]

As of right now, the ODA will also have 7 Vrms. There are some options under consideration that would allow for 15 volt rails and more output. But being realistic, 7V vs 9V is only about 2 dB difference. 1 dB is the smallest change most people can even detect. So it would hardly be an obvious difference between 108 dB peaks and 110 dB peaks.

I'm not a vintage AKG expert so I really don't know how many people have them who might be shopping for a new amp? I get the impression it's a fairly small number. I know they no longer make them and the newer AKGs are easier to drive and within the O2/ODA's capabilities.

[dewasiuk]

I finished building the rest of the amp today and all the measurements seemed correct, however the regulators seemed pretty warm, almost hot to the touch. How warm should they get? I checked over the pcb and all the solder joints seem fine so what else could be happening?

[Shamharoth]

Originally Posted by RocketScientist

As of right now, the ODA will also have 7 Vrms. There are some options under consideration that would allow for 15 volt rails and more output. But being realistic, 7V vs 9V is only about 2 dB difference. 1 dB is the smallest change most people can even detect. So it would hardly be an obvious difference between 108 dB peaks and 110 dB peaks.

I'm not a vintage AKG expert so I really don't know how many people have them who might be shopping for a new amp? I get the impression it's a fairly small number. I know they no longer make them and the newer AKGs are easier to drive and within the O2/ODA's capabilities.

OK. I'm using almost exclusively my K701 these days anyway, so that was most by curiosity than a real request.

[agdr]

Originally Posted by lorriman

Are those pics of a completed board, agdr?

Yes - everything is on the board.

Also, I just now read your post about the solders. Somehow I missed that when I posted about the solder diameter a few posts back. I would echo what nezbleu said - definitely go for eutectic alloys. All the components of the alloy solidify at the same time. Just scan down the "eutectic" column here in the wiki for a yes or no on the various alloys:

https://en.wikipedia.org/wiki/Solder

I would also agree with RocketScientist that no fan is needed. I fixed TVs and stereos in a large shop for years while putting myself though the BSEE. I breathed in a ton of fumes, as did the others and the owner of the shop who had been doing it for decades - and I'm still kicking. Probably says that secondary x-ray emission off the back of CRT tubes isn't that great of an issue, either. I probably absorbed several chest x-rays worth every few months.

[dewasiuk]

Maybe just to double check, here's the measurements I recorded using the wau16-400 transformer:

Adapter output: 18.6 VAC
Battery terminals: 23.85 VDC plugged in with switch off and 23.42 VDC with switch on
C8 and C9: 11.75 VDC and 11.70 VDC
C2 and C3: Both 23.57 VDC
P2 DC: 0.004 VDC
J3 DC: 0.001 VDC
Input DC: 0.001 VDC
All ICs cool to the touch

I don't have batteries to test the MOSFETs and the current draw yet, but I did use a wrist strap and was very careful with handling them so I'm still unsure why my regulators are getting hot.

[MrSlim]

I've been using a Radio Shack (now "The Source" in Canada and most of the parts are disappearing from the stores) solder they call "High-Tech Rosin Core" that is 62/36/02 (silver) for a few years that I really like.. It's about $5 for 1.5 oz..

[MrSlim]

Originally Posted by rtos

Looks like Q1 and Q2 might be installed backwards...

They look fine to me..

[shadow419]

I think it's just a matter of perception. How hot is hot? Do you have to pull your finger of them as soon as you touch them for fear of getting burned, or are they just hot shower hot?

[MrSlim]

Originally Posted by dewasiuk

Maybe just to double check, here's the measurements I recorded using the wau16-400 transformer:

Adapter output: 18.6 VAC
Battery terminals: 23.85 VDC plugged in with switch off and 23.42 VDC with switch on
C8 and C9: 11.75 VDC and 11.70 VDC
C2 and C3: Both 23.57 VDC
P2 DC: 0.004 VDC
J3 DC: 0.001 VDC
Input DC: 0.001 VDC
All ICs cool to the touch

I don't have batteries to test the MOSFETs and the current draw yet, but I did use a wrist strap and was very careful with handling them so I'm still unsure why my regulators are getting hot.

If you're getting 18.6VAC out, I'm wondering if the 16V Adapters are too high for the un heat sinked 12V regulators. The extra voltage ends up as heat, so the greater the differential between the input and output voltages, the more heat that needs to be dissipated.