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Equipment for bench testing

BinaryMike said:
I'm looking pretty hard at a Stanford Research Systems model SR1 audio analyzer to replace my old Sound Tech analyzer. Here the link: http://www.thinksrs.com/products/SR1.htm

Would you happen to have an opinion on the relative merits of that product?
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That SR box looks really good, but I have never used one. I did have an SR 2-ch FFT that might have been an early precursor, and it was excellent.

-k
 
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TPI 1P20B x1 x10 Switchable 100 MHz Oscilloscope Probe
$48 on fleabay

I got a couple and they are very nice ...
 
Jon_Logan said:
Hi Ken,

Yes, Julian Dunn. A sad story. I didn't buy into all of his theories about the impact of jitters, but I respected him and am sad that he's not around. I agree that the Prism's didn't have that great interactive feel of the AP's.

Yup, still in the Bay Area. Hayward. It gives my wife and I about an equal commute. She works in the city, I work in the south bay.

I was going to drop by your place in Berkeley when I dropped by Meyer Sound a few months ago, but I had a rented truck and blew it off. You still have a lab there?

At the D, we looked at a lot of soundcards. Lynx, Creative, M-Audio, RME, etc. Many were not bit perfect in the digital domain. Lynx and RME were, but were sometimes finicky with their software and/or clock settings. There was a card that was cheaper than either, bit perfect and had great analog sections, CardDeluxe. I don't know what's available now, but a CardDeluxe with a good (software controlled?) attenuator in front of it would be a great core to a card based test instrument.

Do you remember a guy named Brian Elliott? I used to do some part time work for him. He's a buddy of Seigfried Linkwitz, both doing the open baffle designs. Brian was buying some NHT 12" for a sub. He really liked'm.
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Oh, it all just clicked in my addled brain. Of course, we swapped details before. I didn't connect you and you, until you mentioned Brian again. Sure, I knew/know him. Got him a deal on some 12" woofs. Drove a Maserati. Bit of a nut about the walls vibrating, right?

We are on the same page about I/O. I had a CardD through CardDeluxe in my home studio, upgrading a Turtle Beach. Replaced it with an Antex, which fell to a Frontier+Yamaha Board. Then I moved, and stopped frequent recording. Chose a Lynx 2 as the wrapper for my DSP development hardware. Bit of a pain, but clean.

Anyway, stop by the still extant, though messy, lab sometime. I'm just a few blocks from Meyer. (No theater, though, sorry.)

-k
 
whoaru99 said:
I'm not sure if this is the exact unit I saw in those review tests, but it appears to have the same/similar functionality. Certainly not necessary, but looks like fun.

http://www.audiograph.se/standalone.html
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Whoa! Cool (literally). I've never heard or seen one of those. Looks expensive. AP was selling a filter designed for use testing Class-D/Switchmode amps. I think B&O/IcePower put out some tech note on how to fab your own Switchmode amp filter. You really need some filter if you want to get good numbers on Switchmode stuff. The ultrasonic artifacts will infect your THD and noise measurements. I'm using standard power resistors from a BPI load setup. I can do 4, 8, and 16 ohms @250W with both channels driven, or 2,4, 8 @ 500W with one channel driven.

It does look like fun. I'll have to add a room to my bench.:scratch2:
 
ken kantor said:
I don't have any idea what the "White Oak/ Phase Linear conversions" are, but if you basically need THD, then I'd recommend just getting a good soundcard I/O and PC. Something like the TASCAM US144. Then you can use any one of about a million freeware or payware apps that do all kinds of audio measurements, including THD. Sure, the AP is perhaps a little better, but not significantly, for this kind of thing. Certainly my current portable laptop rig can do far better distortion measurements than the HP gear I relied on 15 years ago, at a tiny fraction of the price.

-k
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Ken, Joseph King at White Oak Audio Design has come out with a new driver boards for the old Phase Linear amps. Does away with mosty of their bad traits and is a hell of a lot quieter. I have been converting these and doing crude power tests. THD & N testing was not necessary but a lot of folks who own the equipment would like before and aftert testing, can't say as I blame them, I would too.
 
laatsch55 said:
Ken, Joseph King at White Oak Audio Design has come out with a new driver boards for the old Phase Linear amps. Does away with mosty of their bad traits and is a hell of a lot quieter. I have been converting these and doing crude power tests. THD & N testing was not necessary but a lot of folks who own the equipment would like before and aftert testing, can't say as I blame them, I would too.
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OK, thanks for the explaination. Makes many things more clear. What is it about those amps that makes them a good platform for an ambitious upgrade? This is a sincere question. Jensen owned Blaze while I was there, and I have a very high regard for Bob Carver's abilities. But, I don't know that much about the details of the designs.

Anyway, if you just need to verify the performance of the mod, I would think you only need to test 2 or 3 of them. So, you could probably borrow gear to test them with, or find someone to do it. In fact, why can't you just use the data from the guy who did the new design? Of course, he would have detailed performance measurements. Don't know your location, but you are also very welcome to spend an afternoon at my lab running some reference curves. Of course, if you want to test each unit individually, then you probably need your own rig.

Are you at liberty to say how many units a month you have to test? That would help me think about cost-effective test gear, if that would be helpful.

-k
 
jdurbin1 said:
Not sure they were the only ones, but Rockford Fosgate used the PowerCube method to rate their car amps for some period of time.

John
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I read their brochure and all of the clients they listed were Car Audio power amps. They (the PowerCube)go down to 1 ohm with inductive or capacitive loading.
 
Ken, I suppose the cost per watt is a driving factor. Plus Joe's day job, he heads an engineering department at a major corporation designing servo amps, as I've got to know him, a very capable and personable engineer. Joe has published the THD & N specs weighted at 80KHZ at 1 watt and the ol PL 400 and 700's with MJ 15024's as drivers and MJ 21196's as outputs are now at .008% THD & N. Quite an improvement over the stock item. The board is completely redone as a 2 sided solder masked premium grade PCB. They will no longer "latch up" to the positive rail on power up nor oscillate with the modern drivers and outputs.
I would like to test each unit for S/N, THD & N, Frequency response and power to clipping, and send a copy of the test rersults.
This is a hobby for me and my day job is a partner in a small oil and gas production company in Gillette, Wyo that I co-founded in 1996. A few thousand in test equipment is doable. Thank you for continuing this conversation.
 
jdurbin1 said:
Not sure they were the only ones, but Rockford Fosgate used the PowerCube method to rate their car amps for some period of time.

John
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Jon_Logan said:
I read their brochure and all of the clients they listed were Car Audio power amps. They (the PowerCube)go down to 1 ohm with inductive or capacitive loading.
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That's what I saw on their site too, but I'm positive I saw tests using something of the same name and producing the same/similar type of 3D output plot on some home gear. Can't remember who was doing it though.
 
laatsch55 said:
Ken, I suppose the cost per watt is a driving factor. Plus Joe's day job, he heads an engineering department at a major corporation designing servo amps, as I've got to know him, a very capable and personable engineer. Joe has published the THD & N specs weighted at 80KHZ at 1 watt and the ol PL 400 and 700's with MJ 15024's as drivers and MJ 21196's as outputs are now at .008% THD & N. Quite an improvement over the stock item. The board is completely redone as a 2 sided solder masked premium grade PCB. They will no longer "latch up" to the positive rail on power up nor oscillate with the modern drivers and outputs.
I would like to test each unit for S/N, THD & N, Frequency response and power to clipping, and send a copy of the test rersults.
This is a hobby for me and my day job is a partner in a small oil and gas production company in Gillette, Wyo that I co-founded in 1996. A few thousand in test equipment is doable. Thank you for continuing this conversation.
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Interesting, thanks! This sure sounds like a job for an Audio Precision System One. I got mine from a large used test equipment broker for well under $5K. Guaranteed and calibrated. Not sure how often they come up, though. This would give you everything you need, and then some. Plus, you would have confidence that the gear could measure .008% THD accurately. You could probably reach this level of precision with a soundcard-based solution, but it would take a fair amount of care in the selection and connection of the test gear to avoid mitigate noise at such low error levels.

I surely don't recommend that cube thingy, for all kinds of reasons. For one thing, it seems to be made for pilot and mp applications, rather than for development work. Sure, it would have >some< use in development, but its not very flexible in terms of the signals and loads one might want on the bench.

-k
 
Jon_Logan said:
Awesome. I shall! Thanks
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A post script: I just ran across a photo of my last "high end" AP. It was a 2722, or similar, after all. We got a great deal from AP by buying their field demo unit. It was loaded. I tried really hard to wind up with it personally, but it got away.

-k
 

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ken kantor said:
A post script: I just ran across a photo of my last "high end" AP. It was a 2722, or similar, after all. We got a great deal from AP by buying their field demo unit. It was loaded. I tried really hard to wind up with it personally, but it got away.

-k
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Great deal from AP? Did they knock $1000 off? LOL 50% off is getting way closer to my financial abilities.
Yeah, I think my last machine at the D was a 2722. It had their digital interface thingie ((PSIA?) too. It was a great setup (sigh!). It was primarily used for digital domain tests, even though it was outfitted with the analog section too. I can't even remember if the 2700's were available without the analog sections. At Dolby, there were a lot of System 2's without analog sections fitted. Just the digital sections were there. kind of a shame.
 
Mr. Hogue won't get into trouble now, so I can say: Yes, I got it for exactly 50% off. It was a heavily used unit, of course. This is why I really wanted to buy it myself when the company shut down the lab. It might have maxed a credit card, or two, but it was a once in a lifetime deal. Alas, it went to a broker that bought all the lab stuff for a lot price. Damn!

-k

PS- there seems to be an active and technically sophisticated group of AP fans over on LinkedIn. Williams participates frequently, as do others ex and present AP folks. Much of the stuff is over my head, like rolling your own BUR cards or re-writing DLL's to allow better bus control, etc. But, its a good resource.
 
You can always build a metered variac, indispensable on the bench. This one even has a built-in isolation transformer. Only good for about 5 or 6 amps due to the transformer, but if something is drawing that much current it is either broken or you are trying to test output, and if it is the second you could just plug it into a normal outlet.
Only $100 in parts into this one.
DSC_0822.jpg
 
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