Byron, The datasheet calls for +12V, but it also shows examples of lower +Vcc. It's in the same class as the NE602/612 DBMs that function at +9V. As a solid-state balanced mixer used as a product detector, I can't image a performance hit by running the supply down to +10V.
When using the LM383/LM380, and TDA-series audio amp devices, my experience has been that hum/buzz rejection is greatly improved with wiring care, but residual hiss may be objectionable when using modern headphones. I couldn't live with it, so I looked for other solutions. Some options: 1) Through a coupling cap, bring the AF Control wiper arm out to a spare rear panel RCA jack (or pig-tail jack). Then use a high quality external amp like a used Marantz; 2) Construct a simple push-pull audio amp using low-noise transistors. For ultra-simplicity, I like the KK7B design that uses headroom boosting emitter caps. See http://www.qrp.pops.net/af-amp-2008.asp ; 3) Construct a low-noise, precision Class-AB amp using one of several designs. Generally, these designs use 2-3 biasing diode to allow a small amount of collector-emitter current to flow in the absence of an input signal. These designs have very low noise and distortion characteristics, owing to the use of the diodes and low noise figure transistors in the high-gain stages; 4) If you end up using the LM383 amp anyway, then consider using an in-line headphone attenuator and dial-in the amount of attenuation that reduces hiss to an acceptable level. Of course, as a trade-off, the LM383 is working harder and the source Z increases. Radio Shack and on-line sources sell these. I'm using the SM0VPO amp design. The circuit board is available from FAR Circuits and component values as well as the schematic are available on the SM0VPO website. If you primarily use stereo headphones, consider replacing the mono headphone jack with an enclosed Switchcraft or Neutrik Tip-Ring-Sleeve (TRS) stereo type. I would avoid open-frame jacks. Feed the Drake output audio to both L and R channels. Now, you'll never need a mono-to-stereo adapter. If you have an old set of phones with a Tip-Sleeve plug, that will require replacement with a TRS type plug -- or use an adapter in those rare instances. Paul, W9AC ----- Original Message ----- From: Byron Tatum To: [email protected] Sent: Sunday, March 31, 2013 9:53 PM Subject: [Drakelist] R-4C IC Product Detector Hello- I am in the process of installing some upgrades in my R-4C, an early one (18K SN range) that has the 6HS6's. The INRAD 8 KC 5645 KC first IF filter was in when I bought it, so at least I have a little bit of protection for that second mixer. I upgraded the power supply with the 7812 regulator and better electrolytic caps all around, per WB4HFN info combined with Sherwood info. Today I built the IC product detector using a TL442CN, installed it and appears all is well. I thought I would post this as I believe the TL442CN is an obsolete device. The TI SN76514 is an identical chip, it was used in the Mihuzo 9 Mhz SSB boards as the balanced modulator. One thing, I am powering mine fom the +10 VDC that is provided for BFO, as that terminal was very near the module. Is itnecessary to have the full 12 VDC on the chip? I wish to do the sudio amp upgrade, mostly to get rid of the heat, but also to have a little better audio. I am thinking of going with the LM383T as done by Sherwood, but saw a video of an R-4C sporting a "D-Labs" audio upgrade. I cannot find any additional info on this. Thought I would ask for advice before I proceeded with the audio changes. Thanks, Byron WA5THJ ------------------------------------------------------------------------------ _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
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