Over the years, I’ve managed to accumulate a few more cards than I need for repair inventory purposes. Specifically, I have several Equalizer cards for sale. They are fully restored, tested, and guaranteed. While I have some other cards as well (to be offered at a later date), they are not yet refurbished.
Trying to be fair, I’ve set a price of $30 each plus shipping, which is about what I charge to refurbish one. If you need one, please send me an email at admin at dap310.com. First come, first served.
I am looking for a circuit with modifications to the equalizer card. I found one made by Dana Puopolo but the part numbers don’t match up and I haven’ had any luck finding him. His modification looks to be better for AM.
Here is the article with Dana’s recommended value changes. While I don’t agree with him, do what works for you. Remember, these filters are only 6dB per octave.
https://steampoweredradio.com/pdf/dorrough/Modifying%20a%20DAP%20310%20for%20Optimum%20AM%20Modulation.pdf
As far as the values are concerned, the stock value for C3 was 0.1 uF. I don’t know where he got .03 uF.
I’ll email you his email address. You can ask him.
You don’t think that the factory curves are not beyond AMs frequency response? What would you recommend?
Phil
No, I don’t. The filters are very broad. When I rebuild them, I return them to stock. Mike and Kay Dorrough got it right the first time.
The fact that the curves on The Equalizer are beyond the accepted pass band of am transmission, is irrelevant. The idea is to have a nice smooth transition across the frequency bands for the entire audio spectrum. So that it is processed evenly. Trying to tailor the unit specifically for am broadcast. Was where the second generation Clipper limiter card came into play. That provided a preemphasis circuit and a low pass filter. But attempting to jostle around the filter board frequencies too far, can get you into trouble. The only suggestion I have is not to replace the capacitor with a wire jumper in the ground leg of the low frequency filter. There is a slight bit of roll off that occurs. To get rid of extremely low frequency rumble. And that is actually something you want to keep. As the low frequency is not intelligible below 50 cycles. And would cause excessive gain reduction and disturbing the spectral balance even further. I have tried probably almost every modification there is for the 310. From playing with Filter frequencies, attack and release times running them in parallel even taking and having one chassis act as nothing but three compressors and then having another chassis act as three separate clipper cards.. look at the processor in the time it was invented and the theory used behind its invention. To improve the sound of AM radio and not to destroy the carefully balanced mixes of the recording studios. That was the original intention. As they say do what you want it’s your equipment. But I find that a correctly operating 310 without the expander cards. That has had each compressor adjusted to have a linear gain reduction. In my opinion it’s probably the cleanest and most inaudible compression system available. Where every other multiband that’s been made since has tried to copy some part of the 310’s operation or spectral process.