Karl, thanks for the reply. You are correct. My mistake. I'm obsessed with precision rectifiers so I breadboarded your circuit late one night after watching your video. I was the one who reversed the diodes and, of course, your diagram is perfectly correct. Sorry for the confusion. I can verify that the circuit doesn't work if you wire them backwards and works fine if you don't. :-) All in the name of science.
Hi Karl, can I use this scheme to output from the amplifier? I need to connect VU meters to the turntable. Can you please advise me? Thank you and you are doing a good job 👍
Hi Mario, thanks for your support. Probably the biggest challenge in adapting this circuit would be the fact that it's designed around a split +/-15V power supply (since the circuit is DC-coupled, it's not so easy to adapt to a single-ended power supply.) In terms of input voltage swing, you could use it with any line-level output, and probably with a speaker output from a low-powered (say less than 50W into 8Ω) amplifier (limiting factor is that the input voltage shouldn't swing beyond the power rails of the input op-amp). A traditional turntable output would probably be at too low a level, and would need the RIAA equalization curve applied in order that the meter reading would accurately follow the content (otherwise the high frequencies would move the meter much more than low ones) - although a modern turntable with line-level outputs would be fine, of course.
First, thank you for the answer. Of course, I already have output after RIAA equalization, then the signal goes to the amplifier. But if I use a test vinyl with a 1kHz signal, it can be a different level output than a digital output such as a CD.
They're from the eBay seller 'jims_audio' - you can search for the title "VU meter huge size + warm back light for recording !" and that should locate them for you.
Karl, check the schematic linked above. I believe you have reversed the polarity of both D1 and D3. on the schematic. Obviously, you have them right on the board.
G'day Ralph, I've looked into this but I'm still not seeing it. The curious thing is that the linked schematic was rendered out of Diptrace, so it really should match the board layout (rightly or wrongly) if nothing else. Maybe not the clearest way to draw that part of the schematic (with the op-amps oriented that way) but I did keep it consistent between the simulation (the schematic in the video) and the Diptrace schematic capture, as transcription errors in that process have caught me out several times before. I'm happy to stand corrected of course, but both schematics look the same to me with regard to the orientation of those diodes.
I used a function generator to create a square wave at around 1.6Hz, so that the level was high for 300mS, then low for 300mS. By wiring a trimpot in series with the meter, I could adjust the amount of damping, (so long as I compensated with the output level and DC offset adjustments on the function generator as well) Eventually (with much jiggery-pokery) I got it to just reach full scale before it started to sweep back in the other direction, where it would just reach the end-stop before moving back the other way again. If the needle reaches the end and waits there for a bit, it's moving too fast - and if it doesn't quite get there before changing direction, it's too slow.
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Karl, thanks for the reply. You are correct. My mistake. I'm obsessed with precision rectifiers so I breadboarded your circuit late one night after watching your video. I was the one who reversed the diodes and, of course, your diagram is perfectly correct. Sorry for the confusion. I can verify that the circuit doesn't work if you wire them backwards and works fine if you don't. :-) All in the name of science.
Hi Karl! Love your microphone preamp project. Love to see more video's!
Hi Karl,
can I use this scheme to output from the amplifier? I need to connect VU meters to the turntable. Can you please advise me? Thank you and you are doing a good job 👍
Hi Mario, thanks for your support. Probably the biggest challenge in adapting this circuit would be the fact that it's designed around a split +/-15V power supply (since the circuit is DC-coupled, it's not so easy to adapt to a single-ended power supply.) In terms of input voltage swing, you could use it with any line-level output, and probably with a speaker output from a low-powered (say less than 50W into 8Ω) amplifier (limiting factor is that the input voltage shouldn't swing beyond the power rails of the input op-amp). A traditional turntable output would probably be at too low a level, and would need the RIAA equalization curve applied in order that the meter reading would accurately follow the content (otherwise the high frequencies would move the meter much more than low ones) - although a modern turntable with line-level outputs would be fine, of course.
First, thank you for the answer.
Of course, I already have output after RIAA equalization, then the signal goes to the amplifier. But if I use a test vinyl with a 1kHz signal, it can be a different level output than a digital output such as a CD.
thanks for the scheamtic...
but also - where did you get the Vu meter from ?!
They're from the eBay seller 'jims_audio' - you can search for the title "VU meter huge size + warm back light for recording !" and that should locate them for you.
Karl, check the schematic linked above. I believe you have reversed the polarity of both D1 and D3. on the schematic. Obviously, you have them right on the board.
G'day Ralph, I've looked into this but I'm still not seeing it. The curious thing is that the linked schematic was rendered out of Diptrace, so it really should match the board layout (rightly or wrongly) if nothing else. Maybe not the clearest way to draw that part of the schematic (with the op-amps oriented that way) but I did keep it consistent between the simulation (the schematic in the video) and the Diptrace schematic capture, as transcription errors in that process have caught me out several times before. I'm happy to stand corrected of course, but both schematics look the same to me with regard to the orientation of those diodes.
Nice! Came from Dave's....
Cheers!
How did you test the speed of the needle indicator? Thanks.
I used a function generator to create a square wave at around 1.6Hz, so that the level was high for 300mS, then low for 300mS. By wiring a trimpot in series with the meter, I could adjust the amount of damping, (so long as I compensated with the output level and DC offset adjustments on the function generator as well) Eventually (with much jiggery-pokery) I got it to just reach full scale before it started to sweep back in the other direction, where it would just reach the end-stop before moving back the other way again. If the needle reaches the end and waits there for a bit, it's moving too fast - and if it doesn't quite get there before changing direction, it's too slow.
The diodes are correct on the schematic in the video but note my next comment...
can you drop correct schematic? please
At this stage I don't believe there's a problem - the linked schematic was the one used to create the PCB, so it should be fine.
my bad)
where did you source your actual vu meter from?
www.ebay.com/itm/VU-meter-huge-size-warm-back-light-for-recording-/321236001999