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| TDM-1911 THD meter, any good? |
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| TaylorD93:
Hi everyone, I am looking at getting a THD meter for doing some testing on an audio amplifier circuit. Maybe also for repair or testing of some HiFi amps etc too. I was looking at a broken HP 8903a on ebay for a repair project, but listings for TDM-1911 meters also came up too. There are multiple rebranded units all with the same model number, on both ebay and aliexpress, so I was curious to know if anyone had bought one and what they had thought about it? Admittedly I have just a home gamer setup so not typically something I'd calibrate, just more for comparison or at least a wet finger in the air to assess if one audio cct design is less distorting than another. Or if anyone is aware of a homebrew cct for something equivalent, I'd be really interested to know, I have seen a post on DIYaudio about a TL074 based THD circuit but the thread seemed to have died back in 2011. Looking forward to seeing if anyone has any experience with these TDM-1911 units, Thanks |
| Grandchuck:
Also, you could look at using a PC and software. I have an HP 8903B and find some software to be comparable. |
| macboy:
The TDM-1911 seems to be spec'd to measure 0.01 to 30%. I don't know how low it will actually measure (what is the output to input self distortion) but if the measurement floor is actually 0.01%, it is not really adequate for audio work. The 8903B goes much lower. The self distortion can be lower than 0.002%, and if using a better external oscillator, The measurement section alone can measure 0.0007% or lower. I sold my 8903B and got a Panasonic VP-722A, whose self distortion measurement goes as low as 0.00008% (less than 1 PPM). |
| Inside21:
I also considered TDM, but ended up buying Rohde & Scwharz UPA +B8 option Distortion measurement - 0.0001% - 100% I have user manual and service manual for it. |
| TimFox:
I have been happy with my old-school -hp- 339A THD analyzer, with internal generator. Normally, on the 0.01% full scale, the residual distortion (generator connected directly to the analyzer input) is < 0.002%. When set properly, the percent distortion automatically scales to the analyzer input. |
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