Prototypers wanted

[n_maher]

that's my fault Nate. The two heat sinks are available at Digikey, I'm not sure about Mouser. Make sure you don't get that crappy version that TPA uses that has the three holes in in, one of which is conviently placed right in the middle of the device Anyways, the recommended parts are:

8 1 HS346-ND HEATSINK TO-220 W/PINS 1.5"TALL 0 1.49000 $1.49

9 2 HS216-ND HEATSINK TO-126 VERT MNT SLIP-ON 0 0.41000 $0.82

Yeah, it's such a hassle that you only took care of 98% of the parts for me. Sheesh. [/sarcasm]

I need some pot from Digikey anyway so I'll drop a small order today and put the choke on order too. Our friends from across the pond are taking their sweet time with my caps so evidently I'm not in a rush.

[edit]And I actually had the sink for the Vreg part, leftover from Millett days gone by. It's the crappy too many holes version but should still be sufficient given that I plan to do more than the typical amount of ventilation on this chassis. And looking at the HS216 part I'd swear I have a few of those kicking around too somewhere so I should probably have a good look before needlessly ordering more and adding to the already stupid # of spare parts on hand.

Edited July 6, 2010 by n_maher

[dsavitsk]

A quick note, it looks like distortion drops a ton with higher current. I'll post more details later, but upping CCS current to ~18mA (replacing R4R and R4L, the 75R resistor, with a 56R one) seems to drop it by an order of magnitude.

[kevin gilmore]

here are some pictures, don't read too much into them.

high impedance is 300 ohms, low impedance is 32 ohms,

you can figure out which is which.

This is before changing the CCS currents

http://gilmore.chem.northwestern.edu/dsav1.jpg

http://gilmore.chem.northwestern.edu/dsav2.jpg

http://gilmore.chem.northwestern.edu/dsav3.jpg

http://gilmore.chem.northwestern.edu/dsav4.jpg

http://gilmore.chem.northwestern.edu/dsav5.jpg

http://gilmore.chem.northwestern.edu/dsav6.jpg

http://gilmore.chem.northwestern.edu/dsav7.jpg

http://gilmore.chem.northwestern.edu/dsav8.jpg

http://gilmore.chem.northwestern.edu/dsav9.jpg

http://gilmore.chem.northwestern.edu/dsav10.jpg

http://gilmore.chem.northwestern.edu/dsav11.jpg

http://gilmore.chem.northwestern.edu/dsav12.jpg

more pictures friday or saturday after i change the ccs resistors.

thd measurements from above, well over 1%, IM approaching 2%

[n_maher]

Got home, found some heat sinks, found caps in the mailbox, found that my basement is about 15 degrees cooler than the rest of the house so I soldered the last of the parts in. Time to watch some TV with the wife but I expect to flip the switch later tonight.

[n_maher]

It's on and making music. Testing so far with HD201s (go ahead, blow me up headphones) so no comment on sound yet, it's too damn hot to do any critical listening tonight.

Q2L/R do run pretty damn hot though, even with the little heat sinks that I have. I don't think the infrared is getting a good reading so tomorrow night I'll try to break out the thermocouple and get something better than the ~110F that doesn't seem nearly hot enough. I can't lay a finger on them for a half second before pain.

[dsavitsk]

Q2L/R do run pretty damn hot though, ... I can't lay a finger on them for a half second before pain.

Please don't touch high voltage parts.

[n_maher]

Please don't touch high voltage parts.

Not even with my tongue?

[luvdunhill]

Please don't touch high voltage parts.

what's the fun in having insulated parts then?

[Nebby]

Tinkering with my IR thermometer is showing 180-ish on Q2L/R, they sure are toasty.

[luvdunhill]

Tinkering with my IR thermometer is showing 180-ish on Q2L/R, they sure are toasty.

with heat sinks?

[Nebby]

with heat sinks?

Yes they have heatsinks but I think I was picking up the heat off the tubes; pointing it up close it shows ~145.

[luvdunhill]

Yes they have heatsinks but I think I was picking up the heat off the tubes; pointing it up close it shows ~145.

my cheap IR thermometer is amazingly inaccurate it's more of an ambient temperature meter if anything...

[n_maher]

what's the fun in having insulated parts then?

This was kind of my thinking, along with the whole 'one hand in the pocket approach.

[dsavitsk]

This was kind of my thinking, along with the whole 'one hand in the pocket approach.

Even if that part is insulated, there is plenty of stuff around it that isn't. Didn't you just get a nasty shock recently?

[dsavitsk]

Here are some distortion + noise plots for normal listening levels. The first is from the 32 ohm tap, the second is from the 300 (both loaded with resistors). THD of the first is ~0.144%. THD of the second is about 0.047%. As you push the volume, THD will go up into the 1 to 2% range -- seems to be the limit of the tube. When I get a chance, I'll post distortion at particular power levels.

Also, we aren't sure if the 60Hz and other LF noise is magnetic coupling between the PT and OPTs, or if it is PS noise. Probably the former which means probably adding an inch of length to the thing.

Oh, most of the the higher (4th and 5th, etc.) harmonic components are an artifact of the sound card.

[n_maher]

Even if that part is insulated, there is plenty of stuff around it that isn't. Didn't you just get a nasty shock recently?

I did get a nasty wack from the Exstata, so you are certainly correct to preach caution and I appreciate it.

[luvdunhill]

action shot

[ATTACH=CONFIG]3347[/ATTACH]

Doug: With respect to the noise, you could try a low ESR cap for C5 (tantalum) perhaps?

[luvdunhill]

Tom:

What's the height of the PCB that you used to layout the panels? I need to get the y coordinate of the center of the red switch, to make sure it fits.

I double checked all measurements on the diagram and they look good. The one measurement that was a bit off was the x coordinate of the pot and the antirotation nub. This could be due to slop in the slot, but I get about 1.5mm less than the numbers you have. Could anyone double check one of these two for me?

[n_maher]

One recommendation I would make so far would be to see if it's possible to make the PCB thicker (and still fit the slots of course). The poor proto boards wilt under the weight of the various iron bits and I don't even have the choke on there yet.

[dsavitsk]

I did get a nasty wack from the Exstata, so you are certainly correct to preach caution and I appreciate it.

My wife refers to me as the safety inspector ...

Doug: With respect to the noise, you could try a low ESR cap for C5 (tantalum) perhaps?

Hard to imagine that that's heater noise. Worth a try I suppose.

One recommendation I would make so far would be to see if it's possible to make the PCB thicker (and still fit the slots of course). The poor proto boards wilt under the weight of the various iron bits and I don't even have the choke on there yet.

Once in the case and with standoffs in all the holes in the center, it is definitely more stable. But, particularly if it grows a little in length, a slightly thicker board might be prudent.

[luvdunhill]

Hard to imagine that that's heater noise. Worth a try I suppose.

bigger caps in the CLC? I have a small bit of lessemf I can send your way that you can drop in and re-run your tests. Just PM me your address if you'd like to try it out.

[n_maher]

My wife refers to me as the safety inspector ...

Errrrmmmm....

Once in the case and with standoffs in all the holes in the center, it is definitely more stable. But, particularly if it grows a little in length, a slightly thicker board might be prudent.

I'm not worried about the long-term health of the board, I agree that once in the case it's more than adequately supported. It's during the build process that has me concerned. I also think it'd be fun if you could hack the board in half and separate the PSU and amp sections but I digress and understand the design decision.

[luvdunhill]

have you guys tried using a 6N15P, ECC91?

[luvdunhill]

I get 60C on the PT and 60C on the regulator heat sink 105C on the tubes and 50C on the BJTs. This is with the lid off and being on most of the day...

[n_maher]

Dang, that's pretty hot for a PT or at least seems it to me. I've only known one to run that hot and it was a fully potted and shielded version. 50C on the BJTs sounds right to me too.