Please check my box

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  • oneoldude
    Senior Member
    • Apr 2005
    • 203

    Please check my box

    Hi all,

    I need help. I am getting back into building again. But I am not looking for a therapist. At least not yet.

    When I looked at my box full of audio measurement stuff I remembered the pia it is to drag cables and amps and pre-amps around. So I decided to come up with a simple test box that includes a chip amp and a mic pre-amp. I checked the web and found a bunch of complicated projects. I want simplicity at my advanced age. So I have come up with a simple design I'd like you to peek at and check for errors. Heck, make suggestions too.

    I am going to use a chip amp to drive the DUT and I have a couple mic pre-amps on perf board I can use for dynamic mics. But I also want to use my ECM 8000 with its pre-amp. I will use an out board resistor for impedance measurements. That makes things much simpler. This design uses only two switches and two pots. I will be using ARTA. Hopefully the attached schematic is clear.

    Thanks

    Click image for larger version

Name:	Speaker Testing Jig.JPG
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ID:	871177
    oneoldude :later:
    ----------------------------------------------------------------------------------------------------------------------------
    "The race is not always to the swift, nor the battle to the strong, but that's the way to bet" - Damon Runyon
    ----------------------------------------------------------------------------------------------------------------------------
    "De Gustibus Non Disputandum Est" (There is no disputing taste) - Ancient Roman Saying
  • TacoD
    Super Senior Member
    • Feb 2004
    • 1078

    #2
    Looks fine to me (if you build this as depicted ).

    Thus you have
    - two l-pad inputs with 47k/ 10k
    - mic preamp
    - line in without resistors.

    With switches you can select 2x l-pad, 1x l-pad + line-in, 1x l-pad + mic pre.

    Comment

    • oneoldude
      Senior Member
      • Apr 2005
      • 203

      #3
      Thanks
      oneoldude :later:
      ----------------------------------------------------------------------------------------------------------------------------
      "The race is not always to the swift, nor the battle to the strong, but that's the way to bet" - Damon Runyon
      ----------------------------------------------------------------------------------------------------------------------------
      "De Gustibus Non Disputandum Est" (There is no disputing taste) - Ancient Roman Saying

      Comment

      • BobEllis
        Super Senior Member
        • Dec 2005
        • 1609

        #4
        Can your sound card handle 5.2V without damage? The zeners might need to be lower voltage to actually provide protection. Another option is a pair of antiparallel diode strings using 1N4007s. They have a forward drop of 0.6V, so just string 4 together to get 2.4V protection, etc. Why 1N4007? They are dirt cheap and used in almost everything, so I bought a box of 1,000. you can use any similar diode low current that you have on hand. Switching diodes are also an option, but speed is not required.

        If you plan a lot of use, consider adding a circuit to allow you to switch in reference resistor(s) for impedance testing rather than connecting three leads. Resistors if you want to measure higher impedance components such as capacitors for active crossovers.

        Comment

        • JonMarsh
          Mad Max Moderator
          • Aug 2000
          • 15261

          #5
          AS devil's advocate around here, I'll point out that simplicity is using a Smith and Larson woofer tester for impedance measurements




          And a decent Firewire or USB audio interface with both line inputs and balanced TRS mic inputs for audio send/receive




          or



          (I have an Impact twin but am actually still using the older TC Konnekt 8, which often can be found online)

          TC Electronic Konnekt 8 FireWire Audio Interface. IMPACT preamps. True Hi-Z guitar inputs. Full feature stand alone mode.



          One caution if you use a low power chip amp, is that if you use a program that uses an actual MLS test signal instead of a chirp sine sweep (the latter used by Fuzzmeasure and Praxis), the peak to average ratio for an MLS signal is VERY high- you'll have to be careful not to over drive the amp. I test with signals for both SPL frequency response and distortion, and usually use 100W or better amps, like a Sony HT power amp or an Aragon X3. If your completed speaker system has funny things going on in the impedance range, due to design, having a high current amp may save you some grief in testing.

          I used to use a custom personal built test box like you're planning back in the 70's and 80's, but it it's been sitting on the shelf for, umm, 25 years now. Building and debugging it is not the path to simplicity. Just my contrarian thought, from someone who is also an old dude.

          But if you just like building a test box, then your design looks like close, but lacks things like line level adjustable gain (you'll likely need that with the ECM800- it's not an instrumentation mic, and you need to be careful not to overload it, either- optimizing the gain structure in test is important at all times, even more so with limited dynamic range microphones. (the ECM 8000 has rather low dynamic range compared with a 200V DC powered instrumentation mic like an ACO Pacific test mic and preamp. )
          the AudioWorx
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          Resistance is not futile, it is Volts divided by Amperes...
          Just ask Mr. Ohm....

          Comment

          • oneoldude
            Senior Member
            • Apr 2005
            • 203

            #6
            Originally posted by BobEllis
            Another option is a pair of antiparallel diode strings using 1N4007s. They have a forward drop of 0.6V, so just string 4 together to get 2.4V protection, etc.
            I have a bunch of 1N4001s and 1N4002s. But I do not know what an "antiparallel diode string" is. Can you enlighten me. I sure would like to use up what I have before I end up on the wrong side of the grass.

            Thanks
            oneoldude :later:
            ----------------------------------------------------------------------------------------------------------------------------
            "The race is not always to the swift, nor the battle to the strong, but that's the way to bet" - Damon Runyon
            ----------------------------------------------------------------------------------------------------------------------------
            "De Gustibus Non Disputandum Est" (There is no disputing taste) - Ancient Roman Saying

            Comment

            • oneoldude
              Senior Member
              • Apr 2005
              • 203

              #7
              JonMarsh,

              Thanks for the input. Excellent point on the use of MLS. I have ARTA and can choose my poison. I will remember.

              I have an M-Audio Transit as an interface device. It is an oldie but a goodie. And it is small enough to put right into the test box eliminating more cables. Just a USB out. More simplicity.

              I do not do a lot of TS measurements. I don't have that many new drivers. When I need to, I will handle it outboard. I am basically into active crossovers and dipoles anyway except for subs.

              I am pondering a level control for the MIC. Probably a buffer amp in the test box. All of my MICs are the hobby type and I do not do high level distortion tests like you do. Shoot, you are a pro.

              As you said, debugging is a drag. I will probably follow the old school and float all my inputs from the chassis then use shielded cable and rely on a star grounding system. Hopefully, that will keep the ground loop demons away.

              BTW, my project does not look like the image above any more. As usual, things get more complex rather than simpler over time. To paraphrase an old expression, "Things have to get more complex to stay simple."

              Thanks
              Last edited by oneoldude; 03 July 2013, 22:34 Wednesday.
              oneoldude :later:
              ----------------------------------------------------------------------------------------------------------------------------
              "The race is not always to the swift, nor the battle to the strong, but that's the way to bet" - Damon Runyon
              ----------------------------------------------------------------------------------------------------------------------------
              "De Gustibus Non Disputandum Est" (There is no disputing taste) - Ancient Roman Saying

              Comment

              • craigk
                Member
                • Dec 2007
                • 59

                #8
                reverse electrical flow stopper, like a triac but with diodes

                Comment

                • oneoldude
                  Senior Member
                  • Apr 2005
                  • 203

                  #9
                  Triac? I guess if I knew what a triac was and how it worked I would know what an "antiparallel diode string" is. :roll: You guys are way more knowledgeable than I. :T

                  Show me a picture of how to apply them to work as a protective zener and I will be real happy. So will my diodes. They will be given a chance to do something useful.

                  Let me guess. Put two in series cathode up and two in series cathode down. Now parallel the two series diode pairs. Result, ummm, clamped at +-1.2V? Is that the way it works? Three in series on each side and +-1.8V? :huh:

                  If I guessed right, then what clamp would be ideal for a sound card line in? If I guessed wrong, please show me the way. ;x(

                  Thanks.
                  oneoldude :later:
                  ----------------------------------------------------------------------------------------------------------------------------
                  "The race is not always to the swift, nor the battle to the strong, but that's the way to bet" - Damon Runyon
                  ----------------------------------------------------------------------------------------------------------------------------
                  "De Gustibus Non Disputandum Est" (There is no disputing taste) - Ancient Roman Saying

                  Comment

                  • JonMarsh
                    Mad Max Moderator
                    • Aug 2000
                    • 15261

                    #10
                    Originally posted by oneoldude
                    Triac? I guess if I knew what a triac was and how it worked I would know what an "antiparallel diode string" is. You guys are way more knowledgeable than I.

                    Show me a picture of how to apply them to work as a protective zener and I will be real happy. So will my diodes. They will be given a chance to do something useful.

                    Let me guess. Put two in series cathode up and two in series cathode down. Now parallel the two series diode pairs. Result, ummm, clamped at +-1.2V? Is that the way it works? Three in series on each side and +-1.8V?

                    If I guessed right, then what clamp would be ideal for a sound card line in? If I guessed wrong, please show me the way.

                    Thanks.
                    An anti-parallel diode is a diode connected across a device or load that with the normal polarity of operation does not conduct; it's in the blocking mode. When the polarity of voltage reverses, it conducts, acting as a clamp and providing a current path for protection.

                    Standard MOSFETs have an anti-parallel diode built into them, as part of the MOS device structure (actually, it comes from the p doped islands in which the N source element is created; the P-doped region to the n-doped epi drift region forms a diode... this is what I do for my day job, by the way, power semiconductors and power conversion applications engineering.

                    What they are suggestion is stringing together normal diodes to create a forward reverse clamp- I wouldn't really recommend that, cost wise or for avoiding sub threshold conduction below the desired clamping voltage. Just use slightly lower voltage zeners- say, 3.3V. I would also suggest adding a schottky blocking diode in series with each zener so that in the reverse connection it's more completely out of the circuit- even small zeners have pretty substantial capacitance.
                    the AudioWorx
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                    In Development...
                    Isiris Mk II updates- in final test stage!
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                    Resistance is not futile, it is Volts divided by Amperes...
                    Just ask Mr. Ohm....

                    Comment

                    • oneoldude
                      Senior Member
                      • Apr 2005
                      • 203

                      #11
                      As always Jon, thank you for your erudite comments.
                      oneoldude :later:
                      ----------------------------------------------------------------------------------------------------------------------------
                      "The race is not always to the swift, nor the battle to the strong, but that's the way to bet" - Damon Runyon
                      ----------------------------------------------------------------------------------------------------------------------------
                      "De Gustibus Non Disputandum Est" (There is no disputing taste) - Ancient Roman Saying

                      Comment

                      • BobEllis
                        Super Senior Member
                        • Dec 2005
                        • 1609

                        #12
                        In the name of simplicity, why do you need anything other than your sound card, an amp and a mic if you are only going active? Your "measurement jig" can be a Y cable to send the signal to the amp and the reference input. Driver impedance doesn't matter if they are connected directly to a low output impedance amp.

                        Jon hit it well, but yes, a string cathodes up and one cathodes down is what I meant. I didn't realize that there were low level conduction issues. Guess I'm going to rework the input protection on my DIY amps.

                        EDIT: I missed that you were using a transit for your sound card. all you need to do is set the audio output to mono, and use make a Y cable taking one output to the reference input and select the microphone for the other channel. With my FW-410 I use the left channel for driving the amp and microphone in and use a standard 1/4" patch cord running from the right channel out to right channel in for the reference signal.
                        Last edited by BobEllis; 04 July 2013, 09:07 Thursday.

                        Comment

                        • oneoldude
                          Senior Member
                          • Apr 2005
                          • 203

                          #13
                          I have a WM61A mic capsule calibrated by Kim Giardin, so my testing is built around it. Most all my amps weigh about 35 pounds (I haven't weighed them but thats what it seems) and I do not want to move them around any more. After all I am oneoldude.

                          My M-Audio Transit has line in but no mic in. So I believe it does not provide the phantom power needed by my capsule. Previously, I had a mic pre in a box that supplied phantom power and ran it with 9V batteries a la Linkwitz. That is another cable and an additional box. It would be better if my pre was in my mic wand and power was supplied from my test box. That would eliminate more cables and a box.

                          I use the two channel method that looks at the signal to the voice coil and adjusts for that nonlinearity against the FR of the speaker thereby taking the amp's nonlinear behavior out of the measurements. More cables and y-plugs for that.

                          If I use my ECM 8000, I need its mixer with more cables and another box. If I can supply phantom power from my box, I can eliminate another cable and another box.

                          By the time I am done, it looks like a spaghetti factory explosion with stuff all over the place. I would like to simplify cause I do not do 115 dB SPL measurements or look at distortion at those levels.

                          Most of my measurements are at around 90 dB SPL and for the drivers I use that means about 1W to 4W are all I need (N.B. Jon's earlier warning).

                          I would love to use a T-Amp like this http://www.ebay.com/itm/MKll-Tripath...item3cbf347b53. Some have told me that they use this amp with no problems. Others tell me not to use them caus they could damage your equipment. The folks at ARTA say, "not tested, not recommended".

                          Another alternative is an analog amp like this http://www.ebay.com/itm/370759055327...84.m1439.l2649. See this very nice blog on it http://atoomnet.net/tda2030a-amplifi...ldering-howto/ Its not as easy as a T-Amp cause of the heat sink. But easily doable and inherently safe. But this board can be run BTL and then comes the risk of damaging equipment. Or does it?

                          I have both boards so its mox nix to me.

                          Any suggestions re BTL amps and equipment safe measurement?

                          Anybody got a nice design for an in wand mic pre with a buffer/amp with level control in the test box?

                          This is what I have in mind. I would like to make it as simple as possible. But this is starting to get too complex purely to simplify measurement. And as Jon suggested, troubleshooting the design is a pain. So i will review what BobEllis suggested. Well here is where I am so far, one switch and two level pots. Suggestions, comments and criticisms are all welcome.

                          Thanks

                          Last edited by oneoldude; 04 July 2013, 16:49 Thursday.
                          oneoldude :later:
                          ----------------------------------------------------------------------------------------------------------------------------
                          "The race is not always to the swift, nor the battle to the strong, but that's the way to bet" - Damon Runyon
                          ----------------------------------------------------------------------------------------------------------------------------
                          "De Gustibus Non Disputandum Est" (There is no disputing taste) - Ancient Roman Saying

                          Comment

                          • BobEllis
                            Super Senior Member
                            • Dec 2005
                            • 1609

                            #14
                            Here's my theory: As long as you observe the precautions that Jon noted earlier virtually any amp can be used for FR measurement. Since you are just using a driver and no complex crossover, that helps keep the minimum load reasonable. If your testing environment is quiet you need less signal to get an acceptable signal to noise ratio, so low power works. If your amp has low distortion, you can take the reference signal from its input and the amp's internal configuration doesn't matter. That brings T-amps back into the picture s long as you can get a decent SNR.

                            Understanding that you already have the Transit, an M-Track plus is under $100 and includes a mic preamp and phantom power so you can use your ECM-8000, guitar and line level signals, too. The only time you'll need the L-pads if you decide to take impedance measurements. Unless you're looking to verify box tuning, it's not needed in my book. http://m-audio.com/products/en_us/MTrack.html

                            I fight the urge to build stuff that I can buy for less than my time is worth all the time. My version of the above is the amp (or something inexpensive like http://www.parts-express.com/pe/show...number=302-601) and the M-Track interface and a custom built patch cable, splitting the signal to the amp and looping back to the reference input. It could be made with store bought cables and adapters, but where's the fun in that?

                            EDIT: The PE amp is bridgeable, which implies the one of the speaker terminals is grounded and therefore suitable for impedance measurements.

                            Comment

                            • oneoldude
                              Senior Member
                              • Apr 2005
                              • 203

                              #15
                              Yea,

                              I have been fighting the urge to build rather than buy for as long as I can remember. But now that I am retired, my time has no monetary value and I enjoy the building anyway. Unlike you, I would rather buy y-cables and the like and build the more complex stuff. But only within reason. I have built Class A amps and on one occasion Nelson Pass sent me some matched mosfets and the schematics to build one of his commercial designs. Many years have passed so I now can say that he did that gratis. He even paid the postage. Nice guy.

                              I am not without amplifiers. I have a few channels of amplification. Its just that I don't want to move those heavy guys around. It gets my scoliosis.

                              I never considered taking the sense at the T amp input. But I do not trust them or any of the other little guys I am considering. So its analog for me and sense the output.

                              I am thinking about your y-adapter version (what I have always done) but with a box with an amp and the mic phantom power and a little mic amp with level control. That will allow me to leave my mixer for the ECM 8000 on the shelf. Really though, if I go that far, I may as well go all the way and build the thing. Ahhh, what would life be without equivocation!

                              Oh, BTW, anybody got a decent single supply OP Amp mic preamp design for an unmodified ECM? Mine are not cut in the Linkwitz tradition.

                              Thanks
                              oneoldude :later:
                              ----------------------------------------------------------------------------------------------------------------------------
                              "The race is not always to the swift, nor the battle to the strong, but that's the way to bet" - Damon Runyon
                              ----------------------------------------------------------------------------------------------------------------------------
                              "De Gustibus Non Disputandum Est" (There is no disputing taste) - Ancient Roman Saying

                              Comment

                              • BobEllis
                                Super Senior Member
                                • Dec 2005
                                • 1609

                                #16
                                Yes, Nelson Pass seems to be headed for audio sainthood, with all that he has given DIYaudio and the DIY community before the web. I know what you mean about how beastly his amps can be, my back protests moving them. I'd rather build more complex stuff, too. I sometimes use simple things to placate my need to build something. I haven't been able to build much lately, but I am setting up to build another set of amps and an enclosed version of my crossovers.

                                Linkwitz' preamp should be fine for the ECM, just raise the supply voltage to 15V. (the ECM minimum) You may need to adjust the 10K that limits phantom power current. Check the current requirement. The effect of the Linkwitz capsule mod is to increase dynamic range, it doesn't effect the jfet's capability.

                                Comment

                                • JonMarsh
                                  Mad Max Moderator
                                  • Aug 2000
                                  • 15261

                                  #17
                                  Originally posted by BobEllis
                                  In the name of simplicity, why do you need anything other than your sound card, an amp and a mic if you are only going active? Your "measurement jig" can be a Y cable to send the signal to the amp and the reference input. Driver impedance doesn't matter if they are connected directly to a low output impedance amp.

                                  Jon hit it well, but yes, a string cathodes up and one cathodes down is what I meant. I didn't realize that there were low level conduction issues. Guess I'm going to rework the input protection on my DIY amps.

                                  EDIT: I missed that you were using a transit for your sound card. all you need to do is set the audio output to mono, and use make a Y cable taking one output to the reference input and select the microphone for the other channel. With my FW-410 I use the left channel for driving the amp and microphone in and use a standard 1/4" patch cord running from the right channel out to right channel in for the reference signal.

                                  It's not a bad idea to test any proposed clamping circuit on a distortion analyzer! I figured that out in the 70's after spending too much time trying to hunt down the source of a low level distortion that wasn't actually in the amplifier circuitry itself! Picking up an older model HP analyzer on eBay can be pretty useful if anyone is doing DIY audio- great for trouble shooting the origin of problems when you look at the distortion waveform. (we do all have scopes, don't we? :W)
                                  the AudioWorx
                                  Natalie P
                                  M8ta
                                  Modula Neo DCC
                                  Modula MT XE
                                  Modula Xtreme
                                  Isiris
                                  Wavecor Ardent

                                  SMJ
                                  Minerva Monitor
                                  Calliope
                                  Ardent D

                                  In Development...
                                  Isiris Mk II updates- in final test stage!
                                  Obi-Wan
                                  Saint-Saëns Symphonique/AKA SMJ-40
                                  Modula PWB
                                  Calliope CC Supreme
                                  Natalie P Ultra
                                  Natalie P Supreme
                                  Janus BP1 Sub


                                  Resistance is not futile, it is Volts divided by Amperes...
                                  Just ask Mr. Ohm....

                                  Comment

                                  • oneoldude
                                    Senior Member
                                    • Apr 2005
                                    • 203

                                    #18
                                    Yep, I do have a scope. But I'll be darned if I can find the probes for it now.

                                    From what I have read, SL's preamp is specifically designed for the modified capsules. I have not cut my calibrated capsule and am not going to.

                                    I am no engineer. So when it comes to matching impedances in a circuit, minimizing resistor noise, designing for optimum current flow, setting the proper gain in each stage and the like, I am in deep water. I have the ancient Audio Op Amp Cookbook and could cobble up something. But am concerned re: proper gain in each stage. SL used low gain in his pre cause he had improved dynamic range due to the capsule mod. With a standard capsule, what should the first stage gain be to allow for mic sensitivity vs 0 dB at line in? With an unmodified capsule what should be bias V be and how does one properly set the front end impedances so the mic is most efficient? I guess maybe 10 dB for the second stage would be OK for level setting. Deep water for me.

                                    BTW, check this out

                                    WM-64PNT MICROPHONE OMNI 6X2.2MM W/CAP Panasonic - ECG datasheet pdf data sheet FREE from datasheetz.com Datasheet (data sheet) search for integrated circuits (ic), semiconductors and other electronic components such as resistors, capacitors, transistors and diodes.


                                    And this



                                    I foolishly gave away my extra WM61A capsules years ago. Well, here are some cheap replacements with even better FR. I bot some. Hopefully I can calibrate them against my calibrated mic just in case.

                                    Later
                                    oneoldude :later:
                                    ----------------------------------------------------------------------------------------------------------------------------
                                    "The race is not always to the swift, nor the battle to the strong, but that's the way to bet" - Damon Runyon
                                    ----------------------------------------------------------------------------------------------------------------------------
                                    "De Gustibus Non Disputandum Est" (There is no disputing taste) - Ancient Roman Saying

                                    Comment

                                    • BobEllis
                                      Super Senior Member
                                      • Dec 2005
                                      • 1609

                                      #19
                                      The preamp portion of the "microphone with 10 dB preamp" http://linkwitzlab.com/sys_test.htm#Mic would be good for your ECM, since its sensitivity is virtually identical to the WM60AY, at 8.06 mV/Pa (with 24V phantom power, probably a little bit less at 15V) http://www.content.ibf-acoustic.com/...000-sample.pdf Makes you wonder what capsule they used. No engineering required. If you find you want to adjust the gain, just change the 10K between the output and inverting input. I think SL made a mistake calling the gain 10 dB, since it looks like it has a voltage gain of 2x, only 6 dB.

                                      Digikey had the WM-64 in stock, part number P11966-ND Significantly more expensive than that ebay auction. Buy some soon it you think you need them, production was discontinued in 2011.

                                      Comment

                                      • oneoldude
                                        Senior Member
                                        • Apr 2005
                                        • 203

                                        #20
                                        10/5+1=3
                                        oneoldude :later:
                                        ----------------------------------------------------------------------------------------------------------------------------
                                        "The race is not always to the swift, nor the battle to the strong, but that's the way to bet" - Damon Runyon
                                        ----------------------------------------------------------------------------------------------------------------------------
                                        "De Gustibus Non Disputandum Est" (There is no disputing taste) - Ancient Roman Saying

                                        Comment

                                        • BobEllis
                                          Super Senior Member
                                          • Dec 2005
                                          • 1609

                                          #21
                                          ops: Used the wrong equation. Should have known better than challenge SL.

                                          Comment

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