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Post by maq3396 on Mar 5, 2017 21:37:45 GMT -6
Hello all,
Posted this on the other site but it didn't seem to stimulate any interest so...
I have assembled a CAPI FC526 and am about to start on Volker's LA2A.
I am not fluent in electronics and the calibration instructions for these are a bit confusing.
I have reviewed Mike's video from Hairball Audio on using a DMM and DAW generated sine wave.
Have also reviewed Jeff's calibration instructions.
There seem to be a number of options.
Looking for some guidance in terms of what is a "preferred" or "best" or easiest way to do this.
Can I use the XR2206 chip kits to generate the signal for calibration or am I better off using Pro Tools (or something else)?
DMM vs scope?
All comments appreciated!
Thanks
Mac
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Post by johneppstein on Mar 6, 2017 8:54:22 GMT -6
Hello all, Posted this on the other site but it didn't seem to stimulate any interest so... I have assembled a CAPI FC526 and am about to start on Volker's LA2A. I am not fluent in electronics and the calibration instructions for these are a bit confusing. I have reviewed Mike's video from Hairball Audio on using a DMM and DAW generated sine wave. Have also reviewed Jeff's calibration instructions. There seem to be a number of options. Looking for some guidance in terms of what is a "preferred" or "best" or easiest way to do this. Can I use the XR2206 chip kits to generate the signal for calibration or am I better off using Pro Tools (or something else)? DMM vs scope? All comments appreciated! Thanks Mac To do it right you really need hardware test gear - a decent sine wave generator, and RMS reading voltmeter, and a real (not DAW) scope with accurate voltage calibration. Most DMMs are NOT true RMS. If it's not true RMS your readings will be off at all frequencies except 60Hz. I don't trust DAW based tools because there are too many variables in the chain that could affect the calibration. Also, most inexpensive DMMs don't really have very good resolution. If you're going to be doing DIY you really need a basic set of decent test gear anyway. |
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Post by rocinante on Mar 6, 2017 23:41:34 GMT -6
For volkers dual la2a you are gonna want a nice meter at the least and a scope is nice to have if your planning on doing any other diy. It'll cost more than free but in the end you'll be better off and will have built some of the nicest compressors ever- period. The D-la2a was also one of my favorite projects as i learned a ton from it.
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Post by maq3396 on Mar 7, 2017 14:49:51 GMT -6
Thanks for the answers.
Need to pick up a quality DMM then...mine is an old Radio Shack one from some time ago.
Fluke seems to be highly regarded but they have quite a line up.
Recommendations?
As far as scope goes was considering the Rigol DS1054Z.
Would that be satisfactory?
Thanks
Mac
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Post by indiehouse on Mar 7, 2017 15:24:02 GMT -6
I'd like a recommendation for a decent scope to calibrate the FC526 as well.
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Post by johneppstein on Mar 7, 2017 15:40:01 GMT -6
Thanks for the answers. Need to pick up a quality DMM then...mine is an old Radio Shack one from some time ago. Fluke seems to be highly regarded but they have quite a line up. Recommendations? As far as scope goes was considering the Rigol DS1054Z. Would that be satisfactory? Thanks Mac One of the Fluke models that reads true RMS and has a high resolution readout would be a decent choice. Not all Flukes do. Interestingly enough a good RMS reading VTVM (vacuum tube voltmeter) is actually a better choice provided it's in calibration and you know how to read the analog scale correctly. Analog is more accurate than digital because analog doesn't quantize. For example, if you're good you can accurately read resistors to .001 ohm on a good analog meter with a large scale. Most good DVMs won't do better than .01. |
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Post by indiehouse on Mar 8, 2017 8:52:26 GMT -6
Thanks for the answers. Need to pick up a quality DMM then...mine is an old Radio Shack one from some time ago. Fluke seems to be highly regarded but they have quite a line up. Recommendations? As far as scope goes was considering the Rigol DS1054Z. Would that be satisfactory? Thanks Mac One of the Fluke models that reads true RMS and has a high resolution readout would be a decent choice. Not all Flukes do. Interestingly enough a good RMS reading VTVM (vacuum tube voltmeter) is actually a better choice provided it's in calibration and you know how to read the analog scale correctly. Analog is more accurate than digital because analog doesn't quantize. For example, if you're good you can accurately read resistors to .001 ohm on a good analog meter with a large scale. Most good DVMs won't do better than .01. Oh geesh, so many choices. What about the Fluke 123? I don't know jack about these things. I'm just looking to pick up something basic that will get the job done and not cost me $1500. I'm looking on eBay and see some of the Fluke 123 models for around $500. |
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Post by indiehouse on Mar 8, 2017 9:03:44 GMT -6
One of the Fluke models that reads true RMS and has a high resolution readout would be a decent choice. Not all Flukes do. Interestingly enough a good RMS reading VTVM (vacuum tube voltmeter) is actually a better choice provided it's in calibration and you know how to read the analog scale correctly. Analog is more accurate than digital because analog doesn't quantize. For example, if you're good you can accurately read resistors to .001 ohm on a good analog meter with a large scale. Most good DVMs won't do better than .01. Oh geesh, so many choices. What about the Fluke 123? I don't know jack about these things. I'm just looking to pick up something basic that will get the job done and not cost me $1500. I'm looking on eBay and see some of the Fluke 123 models for around $500. svart EmRR any recommendations, man? |
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Post by rocinante on Mar 8, 2017 10:39:20 GMT -6
This is not an insult and I'm not trying to dissuade you but you might want to try something a tad easier than the d-la2a which is not only a very involved project which requires you to source your own parts but deals in high voltages as well. And trust me those voltages hurt. You can literally feel the power upon start up of the d-la2a.
Knowing a little bit more than color by numbers is pretty essential for the d-la2a. That said just building the la2a will teach u a ton about electronics.
The gssl is a great starting point and you end up with an awesome compressor to boot.
But that's just my opinion and really I'm sure you can do it, its just not going to be very easy.
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Post by kcatthedog on Mar 8, 2017 12:43:11 GMT -6
You know you are reading too many Facebook political threads, when, you read this thread's title as "Best way to recalibrate your congressman"  |
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Post by johneppstein on Mar 8, 2017 13:28:15 GMT -6
One of the Fluke models that reads true RMS and has a high resolution readout would be a decent choice. Not all Flukes do. Interestingly enough a good RMS reading VTVM (vacuum tube voltmeter) is actually a better choice provided it's in calibration and you know how to read the analog scale correctly. Analog is more accurate than digital because analog doesn't quantize. For example, if you're good you can accurately read resistors to .001 ohm on a good analog meter with a large scale. Most good DVMs won't do better than .01. Oh geesh, so many choices. What about the Fluke 123? I don't know jack about these things. I'm just looking to pick up something basic that will get the job done and not cost me $1500. I'm looking on eBay and see some of the Fluke 123 models for around $500. The 123 is a scope meter and costs over $1500 new. Way overkill, plus an analog scope is actually better unless you really need field portability. And you'd probably find a scope meter a bit confusing to use. The Fluke 115 DMM is adequate unless you need to read things like emitter resistors on power amps, because low ohms resolution is only .1 ohm, inadequate for checking if a 5% .33 ohm resistor is within spec. it's about $170.00 new. To get better low ohms resolution you'd need to go to a Fluke benchtop meter for over $1,000. Rather than do that I'd look for a good Simpson analog meter for those measurements, or a VTVM. The Fluke 115 should be fine for everything else. For a scope I'd look for a bench model analog scope - you don't really need anything really fancy and the resolution of a real CRT display is a lot better than on a digital handheld. Tektronics is the best but a typical serviceman's scope from a company like Leader or Sencore will do fine and for analog audio you don't need anything above 20MHz. You do want dual trace for the ability to compare waveforms. You won't find anything new in an analog scope. Make sure you get a guarantee or the right to return it if there's a problem. Should be able to find something for a couple hundred bucks or less. |
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Post by johneppstein on Mar 8, 2017 13:39:16 GMT -6
Oh, one other thing regarding that LA2A project - bear in mind that voltages in tube gear are DANGEROUS. You can easily kill yourself if you're not careful. Power supplies can store high voltages in their filter caps for a significant time after being turned off, even if unplugged. Always remember to discharge the power supply caps before sticking your hands in the chassis. When taking measurements on a live piece of tube gear it's a good idea to take Nicola Tesla's advice and work with one hand in your back pocket, so that when (not if) you do get a jolt it's not applied across your heart.
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Post by indiehouse on Mar 8, 2017 14:38:04 GMT -6
Oh geesh, so many choices. What about the Fluke 123? I don't know jack about these things. I'm just looking to pick up something basic that will get the job done and not cost me $1500. I'm looking on eBay and see some of the Fluke 123 models for around $500. The 123 is a scope meter and costs over $1500 new. Way overkill, plus an analog scope is actually better unless you really need field portability. And you'd probably find a scope meter a bit confusing to use. The Fluke 115 DMM is adequate unless you need to read things like emitter resistors on power amps, because low ohms resolution is only .1 ohm, inadequate for checking if a 5% .33 ohm resistor is within spec. it's about $170.00 new. To get better low ohms resolution you'd need to go to a Fluke benchtop meter for over $1,000. Rather than do that I'd look for a good Simpson analog meter for those measurements, or a VTVM. The Fluke 115 should be fine for everything else. For a scope I'd look for a bench model analog scope - you don't really need anything really fancy and the resolution of a real CRT display is a lot better than on a digital handheld. Tektronics is the best but a typical serviceman's scope from a company like Leader or Sencore will do fine and for analog audio you don't need anything above 20MHz. You do want dual trace for the ability to compare waveforms. You won't find anything new in an analog scope. Make sure you get a guarantee or the right to return it if there's a problem. Should be able to find something for a couple hundred bucks or less. Cool, thanks. Didn't mean to hijack the thread. I'm not building the LA2A, but I need a scope to measure dBu and THD+N in order to properly calibrate my CAPI FC526 and EZ1290 pre's. |
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Post by johneppstein on Mar 8, 2017 22:09:56 GMT -6
The 123 is a scope meter and costs over $1500 new. Way overkill, plus an analog scope is actually better unless you really need field portability. And you'd probably find a scope meter a bit confusing to use. The Fluke 115 DMM is adequate unless you need to read things like emitter resistors on power amps, because low ohms resolution is only .1 ohm, inadequate for checking if a 5% .33 ohm resistor is within spec. it's about $170.00 new. To get better low ohms resolution you'd need to go to a Fluke benchtop meter for over $1,000. Rather than do that I'd look for a good Simpson analog meter for those measurements, or a VTVM. The Fluke 115 should be fine for everything else. For a scope I'd look for a bench model analog scope - you don't really need anything really fancy and the resolution of a real CRT display is a lot better than on a digital handheld. Tektronics is the best but a typical serviceman's scope from a company like Leader or Sencore will do fine and for analog audio you don't need anything above 20MHz. You do want dual trace for the ability to compare waveforms. You won't find anything new in an analog scope. Make sure you get a guarantee or the right to return it if there's a problem. Should be able to find something for a couple hundred bucks or less. Cool, thanks. Didn't mean to hijack the thread. I'm not building the LA2A, but I need a scope to measure dBu and THD+N in order to properly calibrate my CAPI FC526 and EZ1290 pre's. THD+N is a bit of a different thing but a scope with good screen resolution should get you going, at least kinda. For a real THD+N measurement you need a distortion analyzer. They tend to be on the expensive side. The one I had on my bench at FM Productions back in the day was a Sound Technology ST 1701 (I think, maybe an ST1710, I don't remember for certain.) The thing about a distortion analyzer is that in addition to the analysis circuitry it must incorporate an ultra low distorttion signal generator - a typical troubleshooting bench generator won't do because your distortion measurement is only as accurate as your generator. HP has also made good distortion analyzers. I find none of the Sound Technology units on Ebay at present but there are quite a few HPs of various age and condition. You don't want a really old one and you don't want one that is not in good working order and calibrated. You also should check some of the used electronic test gear dealers. You should be able to get good dBu measurements with a properly calibrated VTVM. |
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Post by maq3396 on Mar 10, 2017 20:18:07 GMT -6
Thanks for the comments every one.
Also thanks for the warnings about the high voltage that can be encountered when working with tubes.
The LA2A wil not be my first build...have had the pleasure of building six preamps (of which two were tube designs), 51X power supply and rack, two tube based microphones with power supplies and Jeff's compressor.
It is always wise to review safety procedures and am glad to do so. However, I do feel comfortable with tube gear and am looking forward to the LA2A.
Although I have been looking, haven't really seen a good description yet...do you recommend a good DMM and a scope or one of the other?
Thanks again
Mac
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