cetoole

I know what the Koss spec is, and I am wondering if it is simply wrong. Both my analysis and measurements of the E/90 I have right here show 300v. Pretty obviously this isnt a recent change, as my PCB is dated 7-11-90, and has no obvious modifications made to it. I tried adding in a 5M ballast resistor inline with the ESP950 driven off the Stax amp, no change. Its just fine plugged into normal bias. I wonder if just some drivers are able to handle the voltage and some arn't. Also explains why Smeggy didnt have catastrophic results when he ran his ET1000 off the E/90.

Not if my theory is that the ESP950 bias is ~300v, not ~600v. There are definitely construction issues in the headphones, so I really have no problem believing that there is something going on beyond just the bias voltage.

So, I know that it is pretty much public knowledge that the ESP950 bias is 600v, and Koss even says this, but has anyone actually looked at the bias circuit? I got my ESP950 back from RMA today, and noticed that is has the squeal that so many of us know just too well out of my SRM1/mk2, but is dead quiet out of the stock E/90. This has been really, really bugging me, so I finally went ahead and tore the E/90 open to get a look at the bias supply. Well, its pretty simple, a 10M resistor from the 600v (measured 612v) rail to the pin connecting to the bias, and another 10M resistor from that to ground, in parallel with a 0.022uf 630v film cap. My measurement of the bias voltage, using a DMM with a 10Mohm rated input impedance, gave me 202v, just what would be expected from a 10M-(10M||10M) divider. I dunno guys, this sure looks like the E/90 is really just putting out 300v bias, and if that is the case, it would really explain the all-too-common squeal these tend to develop and we have been attributing to dust. Thoughts?

Since the autocrat has decreed this the official day, happy birthday Head-Case!

Have a great one, Dan.

They have workshops for diapers? Just do it a few times, its really easy. As for me: flew home today.

I would just buy a whole new DAC instead of going with the audiotuning mods, as IIRC, they are really no less expensive than getting something like a DAC 1100HD. Anyways though, the PCM67 outputs 1.2mA centered around something like 3v (not looking at the datasheet right now), but also provides a reference voltage equal to that offset which the I/V opamps are almost certainly using for their + input instead of ground, which cancels the offset. You should measure, but coupling caps are probably not needed at all here. I would upgrade the opamps used, or change to some other I/V, but I wouldnt just pull and bypass the opamps entirely, unless you like how aliasing sounds. DACs like these need a LPF to properly reconstruct the original waveform.

Very nice Brent.

South Africa sounds horrible! At least it is a balmy 45 here right now.

Yes, but why?

That looks like excellent work, nice job Fitz.

Pretty uneventful day, gonna go out for dinner though tomorrow. Thanks for all the well wishes, and for Simone pics.

CDs, aren't those the things one rips upon purchase and then just stores on one's ipod when one must carry them around?

NYC meet.

Cool. I too have read just enough to be interested, looks like I may get a chance to hear them though in a few weeks.

Nice Al, have you heard them yet or just bought them on a whim? Curious to see what you think.

Looks to be fully removed, so not in that pic.

Happy Birthday Dr. Wood!

https://www.antekinc.com/pdf/CA-xxx.pdf

Antek dual 18v 600VA transformer, dual 250v 100VA transformer, dual 300v 100VA transformer, and 100VA cover.

Just finished clearing off the driveway here near Boston, probably around 4" so far and still falling. Roads are a mess.

Ouch. Methinks Nate needs a set of thermal teflon strippers.

No way you can just have film caps from the dac to the outputs, wont work. PCM67 has a 1.2mA output.

2-4" here north of Boston. Hopefully it turns out like the last time they predicted this much.