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Azimuth meter |
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Fatmangolf
Moderator Group Joined: 23 Dec 2009 Location: Middlesbrough Status: Offline Points: 8958 |
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Posted: 22 Apr 2013 at 9:35pm |
Just wanted to share a bit of DIY: I am building a stereo crosstalk analyser using the AD8302 RF/IF chip. I based the schematic on the datasheet and adapted it to work at audio frequencies not Mega Hertz.
In short I've breadboarded a device that will be in a box later this week as follows:
2 phono sockets to connect my turntable via the phono preamp Analogue meters for left channel separation (LED comes on), right channel separation (different LED comes on), and phase difference. The range is +/- 30dB (adjusted to 20 or 40dB with a switched attenuator on one channel only) for measuring crosstalk and 0-180 degrees on phase difference. If anyone's looking at the datasheet I wired the left meter from Vmag to Ground and the right from Vref to Vmag. The 1.6V low current LEDS block the reverse current flow to protect the meters and bring them in from about 20dB when the diode conducts. And they look pretty. The phase meter is wired from Vref to Vph. The AD8302 is 14 pin SMD needing few external parts, I used 22uF caps for the input and offset decoupling, giving about 100Hz as the corner frequency. After construction and calibration for +30dB FSD on each meter I plan to use the meter to fine tune the azimuth on my turntables using a test LP that has test tracks with 1kHz on only the left and right, respectively. I will note the changes to maximise and equalise the L-R and R-L separation, whilst minimising and matching the readings for phase difference. I will also be listening carefully to ensure aligning the coils coincides with aligning the stylus. If anyone is interested I will post a schematic and some photos? |
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Jon
Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC. |
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BackinBlack
Senior Member Joined: 05 Feb 2012 Location: Hinton, N'hants Status: Offline Points: 2020 |
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Sounds interesting. A novel application that could prove really useful. Cartridge set up is something akin to a black art, this should counter some of the apparent magic (ie guesswork!).
More info would be good, I look forward to seeing the development and your results. Ian. |
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tg [RIP]
Moderator Group Joined: 19 Jan 2008 Location: Sydney Status: Offline Points: 1866 |
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A sort of DIY Fosgometer then. Bit beyond my DIY skills (or electronic knowledge FTM) but certainly interesting. Piccies are always good :) |
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Fatmangolf
Moderator Group Joined: 23 Dec 2009 Location: Middlesbrough Status: Offline Points: 8958 |
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A bit like it but the phase measurement is different. Balancing that as well should improve the stereo.image with stable positioning and width.
I'll draw a schematic and photograph the pcb. |
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Jon
Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC. |
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JamesD
Senior Member Joined: 05 Nov 2012 Location: Bolsover Status: Offline Points: 246 |
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Sounds interesting, will have a look at your schematics if you post them. Always good to have some means of confirming what you think your ears are telling you!
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Aren't ears brilliant
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Fatmangolf
Moderator Group Joined: 23 Dec 2009 Location: Middlesbrough Status: Offline Points: 8958 |
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This is the datasheet:
AD8302 datasheet On page 16 you'll see the schematic. For 1kHz test LP tracks the input caps C1/4/5/6 are all 22uF polarised and I used a spare 470uF for C2. For the left signal separation I wired a 250uA meter in series with a 1.6V LED and a 1k preset pot, connected from Vmag to 0V. For right the same but wired from Vref to Vmag. Please note that +30dB (approx. 200mV ac on L/6mV ac on right) and -30(6mV and 200mV, both ac) give 1.8V and 0.03V. I adjusted the presets to full meter deflection at +/- 30dB. +35dB or more overshoots the 1.8V stated limit on Vmag to give about +1.95V. It's the phase difference on crosstalk (i.e. from the active left channel to the almost silent right channel, or vice-versa) that adds another dimension to azimuth adjustment. If you've done this with a dual channel oscilloscope (or software equivalent) you'll know why! I will draw the schematic I've built and photograph the circuits at the weekend. This is simply using a production IC and schematic but for a different use. Once I spotted the potential application I did search online to see if someone had already done the fine tuning. Edited by Fatmangolf - 24 Apr 2013 at 10:24pm |
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Jon
Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC. |
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Fatmangolf
Moderator Group Joined: 23 Dec 2009 Location: Middlesbrough Status: Offline Points: 8958 |
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The unit does work but the metering on L and R channel separation is less linear than I would like. In reality connecting one digital voltmeter to the Vmag (channel level difference) and another to Vph for the phase difference is more precise.
After trying various resistors in series with and in parallel to the level meters, I am reconsidering a larger meter with the midpoint. The aim was to design a self-contained unit for level and phase so I will persevere when I next have time. I can confirm that the IC works fine at audio frequencies and works with only a few extra parts. I ran a 22k resistor from each phono socket to the dc blocking capacitor on that IC input. That took the 300mV coming from the phono preamp down into the log detector's midband, see the datasheet for more details. |
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Jon
Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC. |
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