Oh and don't forget to properly bias the driver transistors to class A, otherwise it may work "funny" such as nothing, then suddenly jump high. then connect to the meters, it will probably work. You could always duplicate the onboard meter driver circuitry (including the rectification circuit, the voltage divider network and the driver transistors), put onto a small project board, and then source it from a preamp level audio signal source found by using a signal tracer on the record bar pins. I don't know how badly you want to make this happen. Several things are probably switched at the same time including meter function from batt/tuning to VU and also function which could also cause the record bias to activate (which turns on the erase head) reverses the audio signal from the heads (reading to writing). If that's the case, then the switch is probably the record bar. Without it, it will be very hard.Īs for record mode, are you saying that the VU meters don't even work during playback? That's unusual. Every boombox is different so how one boombox does their meters could be entirely different on another so the circuit diagram is very important. I think the RS Pannys were not released here in USA and I don't have a schematic or service manual for it. Of course if you modify the circuit in this way, I hope your boombox has an ALC for recording, otherwise, you won't be able to set the proper recording level anymore. Probably the easiest solution for you is to purchase a pre-made needle meter driver off eBay and connect the source to your speakers. Oh, and of course don't forget to factor in the voltage drop naturally present in the rectifiers. Computing that with the max expected rectified voltage of the audio signal at the tap, and the meter top range voltage, you can design a proper voltage divider to ensure that the range is correct. Instead, you are better off with a voltage divider network. A simple resistor in series won't work well as resistors only limit current, and doesn't reliably limit voltage. It's for rectifying the audio signal, which is AC. If you look at any boombox service manual with needle meters, you will see that there are always diodes in that part of the circuit. So in order to get the meter to respond, you'll first need to rectify the signal. You'll first need to consider if the needle meter is a low level AC meter or a DC meter. Secondly, most needle meters aren't just powered through a resistor. Most audio circuits have many layers of audio signal levels which get amplified or attenuated along the way. If your meters are calibrated to the low level record signals, just jumping it directly to a different part of the audio circuit might not have results you expect because you don't know the level of the signal at that part of the circuit. Firstly, although needle meters seems like simple thing but in reality, you need a proper driver. Actually, I don't want to throw water on your project but I suspect that it's not going to be nearly as easy as it would seem.
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