TDM-1911 THD meter, any good? - Page 1
Forum section: electronics / testgear

author: TaylorD93
author_rank: Regular Contributor
timestamp: August 01, 2022, 12:48:57 pm
content: 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

author: Grandchuck
author_rank: Super Contributor
timestamp: August 01, 2022, 03:24:49 pm
content: Also, you could look at using a PC and software. I have an HP 8903B and find some software to be comparable.

author: macboy
author_rank: Super Contributor
timestamp: August 02, 2022, 11:28:20 am
content: 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).

author: Inside21
author_rank: Contributor
timestamp: August 02, 2022, 12:04:12 pm
content: I also considered TDM, but ended up buying Rohde & Scwharz UPA +B8 optionDistortion measurement - 0.0001% - 100%I have user manual and service manual for it.

author: TimFox
author_rank: Super Contributor
timestamp: August 02, 2022, 03:47:01 pm
content: 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.

author: wasedadoc
author_rank: Super Contributor
timestamp: August 02, 2022, 07:39:31 pm
content: Quote from: macboy on August 02, 2022, 11:28:20 amIf a measurement floor of 0.01% is not adequate for audio work then what loudspeakers come anywhere close to that?

author: Grandchuck
author_rank: Super Contributor
timestamp: August 03, 2022, 02:52:40 pm
content: Like volt-nuttery, another gear-head obsession?My guess is that testing A/D converters properly requires low distortion signals, which is easily justified. In audio applications, not so much. Also, isn't intermodulation distortion a better measure?

author: Arts
author_rank: Regular Contributor
timestamp: August 04, 2022, 12:57:18 am
content: Quote from: Inside21 on August 02, 2022, 12:04:12 pmDoes your UPA service manual have the schematics?

author: jonpaul
author_rank: Super Contributor
timestamp: August 04, 2022, 05:19:05 am
content: Industry standard is Audio Précision System one or two, needs a PCOlder Tektronix TM500 modules by same designer'sAA501 AnalyzerSG505 generatorJon

author: Inside21
author_rank: Contributor
timestamp: August 04, 2022, 07:56:35 am
content: Of course, comrad!https://disk.yandex.ru/i/U_biHNBNzH5sBAhttps://disk.yandex.ru/i/Hc8XN8LBXIGYxA

author: Arts
author_rank: Regular Contributor
timestamp: March 22, 2023, 11:08:15 pm
content: Quote from: Inside21 on August 04, 2022, 07:56:35 amI realize that this reply is extremely late. I lost track of this thread until today, and had never seen your reply. Thank you very much for the information, it is much appreciated, and answers several questions I'd had re my UPA. My sincere apologies!!Thank you very much,Art