Pars

I had hoped to enjoy this show, but really didn't and wound up making no effort to watch it (was usually watching a DVR-delayed Lie To Me instead).

The only time in the past that I have touched the volume control on an amp under test is if I can't get the input level low enough for RMAA. It wants to see as close to -1dB IIRC as possible. I don't know what the gain is on this amp, but it doesn't seem particularly high, at least from listening.

Doug and Tom, Thanks, I'll play around with it some more and see what I can find. I did already turn the volume down on the amp, but maybe not enough.

I think I will socket either one or both (paralleled) CCS resistors to make changing them easier. That way, my brother can decide what he likes the best and go with it. Doug: yes, I'm aware that RMAA is just a tool. Running it on my Counterpoint tube preamp resulted in much much lower distortion numbers, but it is an entirely different tube architecture. Volume (and gain) were at max for that testing as I used the THD values to bias the tubes in the line stage. Here's a sample. The M-Audio FW Audiophile is an external box, but yes, functions as a sound card. RMAA has to have a certain level range in order to function. I have control via the control panel of input levels (I presume this is input coming back from the M-Audio, so it is the output of the DUT), and output levels (I presume this is the output of the M-Audio into the DUT). I can of course also vary the volume pot on the amp. Normally, amps are tested turned all the way up (at least to my understanding). Speaking of the Counterpoint, would you be willing to take a look at it sometime Doug? No hurry, maybe this winter or something if you are up for it. Still having a slight hum problem. RMAA_test_ SA5.1_32_192k_80407_4.pdf

Yes, when I looked at the previous numbers, I thought I would see the 56 ohm numbers much higher based on RMAA bitching at me. The channel imbalnce with equal input levels (the 56 ohm CCS numbers) is ~0.7dB for the high impedance and 1.7dB for the low impedance. BTW, for 120 ohm phones, would the high impedance be the setting most likely to produce good results? Or just listen and see which you prefer? EDIT: Also, does anyone have dimensions for center on the tube holes in the top? I think I am going to use a 1 1/4" holesaw for these. I may have access to a unibit big enough as well.

OK. I got around to grabbing the two RMAA runs I saved last week, as well as running a couple more today. Last week's runs were done with 75 ohm CCS resistors. I also tried to balance the input levels between channels so these will not show the channel imbalance to the full extent. Bias (PR / PL) was 110Vdc / 130 Vdc. Runs at both 32 ohm setting (33 ohm load) and 300 ohm setting (330 ohm load): RMAA_test _ l'esp_330_load_up.pdf RMAA_test _ l'esp_load_33_down.pdf I paralleled 221 ohm resistors to the existing 75 ohm for 56 ohm CCS. I also matched the BJTs in the CCS as well. When I went to run RMAA, it was complaining that there was too much distortion. I played around with the volume control on the amp, input and output levels to/from the M-Audio box, etc., but could not get rid of it. Bias is now at 148 Vdc (PL) and 129 Vdc (PR)... yes, it got worse. RMAA_test _ l'esp_330_load_up_56.pdf RMAA_test _ l'esp_32_load_down_56.pdf I've never had anything distort so much that RMAA complained about it. THD levels don't look too good. I may pull one end of the 221 ohm and run some and see how it behaves that way. Any other suggestions?

Happy Birthday Pete!

New series on A&E. Caught the premier two episodes of this last night, though I think it is slotted for Sunday nights. Seems promising; I am going to target watching this. Rubicon - AMC

Happy Birthday Todd!

A couple of reasons: Countersunk is teh sex, at least from looking at Nate's. Check page 169 IIRC in the Amp Build thread here. These are for mounting the pair of 0.25" standoffs under the PCB in a slide-in case. Normally I would run a 1/2" or so screw up from the bottom and fasten the PCB with a nut, but since the board slides into the case, this would be difficult. Since flathead screws apparently are measured from the head, it would be easier to come up with short enough screws. 2x 1/4" panhead screws are too long; you really need something like 3/16" which aren't easily found. I ground some 1/4" down for now.

Just a crappy one from Harbor Freight. I wouldn't recommend it as it tends to lift up at the adjustable head when tightened, thereby angling your work for you Like this one 6" Jaw Capacity Drill Press Vise

^ I have a drillpress vice which can hold it. Otherwise, I usually don't have problems holding stuff by hand on a piece of wood.

I've never done this before, but partly due to seeing a pic of an amp that Nate had built, I was thinking of countersinking two screws on the bottom of the l'espressivo torpedo prototype that I am building for my brother. So, a couple of questions: [*]Is a Hammond 1455 case such as what is used thick enough to countersink a 4-40 flat head machine screw in? [*]Countersink bits: do you need one for each size you are doing? I would be most likely to use 4-40 or 6-32. [*]Angle: I see 82

Jeff: Maybe you should send those pics to Dan Hesse of Sprint

Happy Birthday to the motley lot of yez!

Agreed on temp... 55-60 deg. C seems fine. When they get up to 70 I start getting concerned. Once I put the top on, I may need to do something. The power transformer does not feel warm or measure above 35 or so. I may use the heatsink for the top over the BJT area instead.

Thanks Tom. Is there an optimal voltage, or does higher = better in this case (measured at PR / PL to ground)?

I thought these tubes were matched? As for increasing the bias, while I was running RMAA, the temps on the BJTs were ~60 deg C. The voltage regulator was around 55 deg C, heatsink was uncomfortable to touch, but case wasn't hot anywhere I felt (top is not on or drilled currently). It's no problem for me to replace the 75 ohm resistors, though I'll have to see what I have laying around. Off the top of my head, I have some ratshack carbons (I think) from a variety pack I may have some RN60s or something around also, or as you say, I can parallel something. I could put 100 ohm pots in also, but since this isn't intended to be a play amp, probably not. Again, if anyone needs another end panel or two, you can have them. Out of the US I might have to charge postage, but free otherwise.

I started running RMAA on the amp tonight. There does seem to be a channel imbalance with the higher bias tube having a slightly higher output. The delta appears to be greater at low impedance. I have a load box (Amb's design) that I was using, but also ran unloaded measurements. I am using an M-Audio Firewire Audiophile box for the test. I was adjusting the input levels (I assume coming out of the amp) with the M-Audio control panel and had to compensate for the level imbalance. Not sure whether I should do that or just lock them at an equal position. The CCS 75 ohm resistors are Draloric 0.5%, but I did not measure or match these. I'll take some voltage measurements of the drops across the L and R, as well as the LED voltages tomorrow. I'll try to pdf the RMAA test results and post tomorrow also.

Also, I got some extra end panels, so if anyone wants one for redos, let me know.

Is there any particular heatsink grease anyone would recommend? I used a silpad on the regulator, but only had some really old ratshack thermal grease for the BJTs. Arctic Silver? Other?

Thanks, that is helpful. It has probably been stated in the thread already, but which switch position is which? If from the schematic, pin 1/4 of the switch should be the higher impedance and pin 3/6 the lower? For this amp, is it 300 ohm and 32 ohm taps?

Thanks Nate. I'll run RMAA on it, and also some test tones and look with joe scope to see how things are doing. I would certainly expect sand state to be better than this j/k

Doug (or anyone): Will the bias imbalance between channels that I am noticing at PL/PR have any negative effects on performance? I am guessing that a better matched tube pair is the only way to fix this? Or is it a non-issue?

Congrats on the mill usage and on the job switch proceeding as planned Nate. I'm sure that was a bit odd on Thursday. Vicki: glad that the NSAID is working; that is good news. When I was going thru my hip(s), I was taking diclofenac sodium, and it helped, but wasn't what I would call awesome. I looked into resurfacing but my ortho recommended against it; these things seem to come into/fall out of favor. And Brent, congrats on the job.