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    Test Equipment and Measurements?



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    Test Equipment and Measurements?

    Post by GP49 on Mon Dec 12, 2011 12:38 pm

    A question to the membership as a whole (I KNOW Bob can do it!): how many of you have the equipment and the ability to do rudimentary measurements on equipment? It has always been my procedure, after completing a modification, to check frequency response, even if only by looking at a sine wave on an oscilloscope at 50Hz, 1KHz and 10KHz, and checking proper signal level and power output (if the unit is a power amplifier). Rather than relying on ears, this is a better means of verifying proper circuit behavior, and more than once has revealed an error in a "wonderful-sounding" modification featured in a print magazine article or on a Internet site.

    One such was a "wonderful-sounding" Dynaco Stereo 70 modification which was shown to output about seven watts. After verifying that the circuit had been built correctly, I took it to the next level on the test bench and found it produced gobs of low-order harmonic distortion, nearly 10%; but that wasn't necessary to reveal that something was seriously wrong with the "wonderful-sounding" design.


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    Re: Test Equipment and Measurements?

    Post by captn on Mon Dec 12, 2011 6:13 pm

    I use a Tektronix 466 Scope and an HP 204 Audio Generator which are quite old but work well enough to do the type of basic testing you describe. I agree that some simple testing can reveal things your ear might not.

    I've tested my own Latino ST-70 and it has very clean output throughout the audio frequency range. A quick power test into 8 ohm resistive loads show mine starts clipping at just over 40W per channel at 1KHz. My listening tests validate that my ST-70 is performing very well and the sound is fantastic.

    Regards, James

    Bob Latino

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    Re: Test Equipment and Measurements?

    Post by Bob Latino on Mon Dec 12, 2011 9:33 pm

    I only have a scope here. I don't have a distortion analyzer or more sophisticated test equipment. I have put all the VTA amps on a scope and have pumped sine waves and square waves through them to confirm what I hear. GP49 does have a point here though. Sometimes a tube amp will sound good but won't measure well. Solid state amps are just the opposite. Sometimes a SS amp will measure well but won't sound good. One of the WORST sounding solid state amps I ever heard was Dynaco's original Stereo 120 from the mid '60's. IMHO it sounded bad ... sort of "hard" or "brittle" sounding. I guess Dynaco can be excused as the Stereo 120 was one of their first solid state efforts.

    About 2 1/2 years ago, Russell Knize, who built one of the VTA ST-70 amps from a kit, put the amp through it's paces. Russ has all the proper test gear. His results are at the link below ...

    Testing the VTA ST-70 amp kit



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    DSO Nano oscilliscope

    Post by baddog1946 on Wed Dec 14, 2011 8:33 am

    Good thread:
    I got one of these for my birthday from my son in law who is a tech type and math teacher. It is amazing for such a small unit and around $100.
    It took a while to get over the learning curve but after that it was easy to use it for the basic tests I did on my amps and looks like it is very accurate in this video.
    It is actually a real oscilliscope in your hand and good for all the basics Bob mention here.
    Check out the link of a comparison demo on You Tube.


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    Re: Test Equipment and Measurements?

    Post by sandy on Wed Dec 14, 2011 2:58 pm

    I would agree with how it sounds is more important that how it looks Wink

    I have picked up a few bits of gear from EPay and have had mostly good luck getting working equipment. Good scopes and distortion analyzers and related signal generators show up a lot. I picked up a bunch of the Textronix test gear for a good price (The modular stuff) and works well. That being said I have never used the digital distortion analyzer as the speakers are good for me. A good scope and probes are your best friends, I have a Fluke scope meter and a HP Scope and mostly like the HP scope but the portable Fluke is nice and does a lot of stuff but it's expensive. I have not tried any of the newer PC based scope/labs and I'll bet they are pretty good and have tons of slick features since it's more software these days.



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    Re: Test Equipment and Measurements?

    Post by j4570 on Fri Dec 16, 2011 8:53 pm

    I have stuff from Ebay. I do have a few bits and pieces, a scope, variac, frequency counter (only because it was like $10), and a function generator. If you keep searching, you can get stuff cheap that works well. Just takes a while. Not everything came from Ebay.



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    Re: Test Equipment and Measurements?

    Post by cartek on Mon Dec 26, 2011 1:07 am

    I've got my own test/ repair/ building facility in my garage. Not too elaborate, BK 2021 scope, BK sig gen., BK DVM, ESR meter, Combo DVM/ freq counter/ capactiance meter, test amp/ speaker setup, power supplies,variac,etc etc. Been into electronics since my teens... I stopped repairing stuff for others, now it's just one of my crazy hobbies. More funner that way!

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