Need Advice - Page 1
Forum section: electronics / general

author: tony3d
author_rank: Frequent Contributor
timestamp: August 03, 2014, 05:56:22 am
content: Hi All, I have this Topping TP21 Tripath Amp.http://www.parts-express.com/topping-tp21-class-t-digital-mini-amplifier-25-wpc-with-headphone-output--310-310I thought it would be kinda fun to hook up vintage VU meters to it just for show. Found this on EBAY.The input Left, and Right only has one common ground, the amp has a ground for each channel. So, I can just use the ground from either left or right correct?

author: mij59
author_rank: Frequent Contributor
timestamp: August 03, 2014, 06:16:27 am
content: Hi,The link doesn't work.Probably the grounds are connected, you could check it with a ohm meter.What are you using as power supply for the VU meter ?

author: tony3d
author_rank: Frequent Contributor
timestamp: August 03, 2014, 06:29:23 am
content: Try the link now. Think I fixed it. I'm just going to use a DC BRICK ADAPTER. So, if there is no continuity between the left, and right grounds of the amp, then I can't use this driver board? I'll check it tomorrow with my Fluke. Just by looking at the top of the amps board, it looks like the grounds are connected.

author: mij59
author_rank: Frequent Contributor
timestamp: August 03, 2014, 06:53:26 am
content: Quote from: tony3d on August 03, 2014, 06:29:23 amLooks like a class D amplifier using a Texas Instruments chip.The speaker connections are both 'live', so you have to get the ground connection from some where else.Do you have a multimeter ?

author: tony3d
author_rank: Frequent Contributor
timestamp: August 03, 2014, 06:59:48 am
content: Yes, I have a Fluke.

author: mij59
author_rank: Frequent Contributor
timestamp: August 03, 2014, 07:16:37 am
content: Quote from: tony3d on August 03, 2014, 06:59:48 amConnect the speakers to the amplifier, no input signal, power the amplifier up, and measure the dc voltage of one of the speaker terminals to ground (e.g. the outside of the input plug).What voltage do u measure ?

author: tony3d
author_rank: Frequent Contributor
timestamp: August 03, 2014, 07:19:19 am
content: I'll have to check it tomorrow. It's getting very late here. I'll let you know.

author: tony3d
author_rank: Frequent Contributor
timestamp: August 03, 2014, 12:20:45 pm
content: Quote from: mij59 on August 03, 2014, 07:16:37 amOk, so you want me to measure let's say the right positive speaker output to the right ground of the RCA input terminal?

author: mij59
author_rank: Frequent Contributor
timestamp: August 03, 2014, 12:35:11 pm
content: Quote from: tony3d on August 03, 2014, 12:20:45 pmYes

author: rob77
author_rank: Super Contributor
timestamp: August 03, 2014, 12:46:44 pm
content: what about using the headphone output for the VU meter ? it has a common ground for both channels for sure

author: David Hess
author_rank: Super Contributor
timestamp: August 03, 2014, 01:41:47 pm
content: The speaker outputs are bridged so they do not share a common terminal.Either use the headphone output to drive the VU meters or use one speaker terminal from each channel and the amplifier's power supply ground.The TS2021 datasheet gives a pretty good idea about what is going on:http://pdf.datasheetcatalog.com/datasheet/Tripath/mXyzxwwv.pdf

author: tony3d
author_rank: Frequent Contributor
timestamp: August 03, 2014, 01:50:40 pm
content: Quote from: David Hess on August 03, 2014, 01:41:47 pmThat sounds good. Probably use the the two positives, and the amps PS Ground. Thanks everyone, and thanks for the data sheet.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 03, 2014, 02:03:08 pm
content: DO NOT connect that VU meter board to the speaker outputs of that amplifier!The speaker outputs are NOT ground referenced and any attempt to connect something other than a speaker is unlikely to work at best, and very possibly will damage the amplifier and/or the meter board.There are TWO DIFFERENT issues here:1) The output from that amplifier is NOT ground-referenced, so it is suitable only for connection to a floating load like a speaker cabinet. Atempting to connect ground to Either side of the speaker output will almost certainly damage the amplifier! And attempting to connect something to one side or the other, and assuming a ground reference is also highly unlikely to be successful and is strongly discouraged.2) The input to that meter board assumes ground-referenced, line-level input If you want to use that meter arrangement, then connect it to a line-level signal such as the signal going INTO the amplifier. Or perhaps to that headphone output which IS ground-referenced. The headphone signal is roughly equivalent to line-level and I would expect that it would drive the meter board properly.DO NOT MAKE ANY CONNECTION BETWEEN THOSE SPEAKER OUTPUT TERMINALS AND THE METER BOARD!!!!!If you want to actually meter the OUTPUT level of the amplifier, then use a more traditional passive meter solution which is effectively "self-powered". i.e. the speaker signal actually drives the meters directly with no electronic circuit inbetween.

author: tony3d
author_rank: Frequent Contributor
timestamp: August 03, 2014, 05:13:10 pm
content: Quote from: Richard Crowley on August 03, 2014, 02:03:08 pmI see, thanks! I'll probably use the headphone jack connections then since this is only for show.