And this is the last step, the same LP track, showing a much smoother wave-form, and audibly pure. Job completed - another Quad Turntable rescued! As is evident, calibration of the CD4 PCB is impossible without an oscilloscope, but certainly possible without the Meguro CD4 generator, as long as the JVC Test disc is on hand.

So now, I put on my favorite CD4 LP to check the real-world signal cleanliness. I don't know why, but Enoch Light's Spaced Out has a couple of tracks which sound very slightly distorted, even after completing the full calibration according to the SM with the JVC test disc. Other CD4 LP's play right through without any distortion! So, I have

TR206 has 3 terminals - the Base, which has the Demodulator signal from Pin7 of IC202 (LM565), the Collector, which is the one showing the bad signal, and the Emitter. Not having the circuit diagram for this PCB (this one is a single-storey version, as opposed to the much more common two-storey version with a little daughterbosrd mounted on top), and

Gary To answer your question, the CD4 / RIAA amplifier is always powered, no matter the switch position. So, if you play a Stereo LP, it functions as an RIAA amplifier only, because the carrier signal is not detected by the amplifier (no matter the switch position). 2 line-level signals are delivered to your main amplifier. If you play a Quad LP (assuming

I've had a really interesting time with this CD4 demodulator - not finished yet, but it has been a real learning experience for me. This is the first time I've ever had one with such levels of defects. So, In the BeoGram section, I've put up a Workshop on this - I'm not finished yet, more to come! Menahem

But I'm not finished yet - there is another issue with the 30KHz carrier signal detection.... The symptom of this problem was reduced volume in the right-channel. This is the waveform off TR206 (right-channel) collector - nothing like the SM's picture, and look at the amplitude - less than 200mV p-p. See the next post for what the Left channel

So, after replacing all the OA90's in both the Left and Right channels with AA143's, here's what the result is. Is it absolutely perfect? There is still a bit of flatness at the bottom peak, but the distortion is gone, and the sound is pretty amazing. I'll take this as gospel truth that these diodes, when leaky, definitely affect the

Update on the BM1600: Rewired according to Martin's picture - works fine. Now I did some improving - 3 AA119 germanium detector diodes in the IF section had more leakage than I like, so I replaced them with new AA119's, selected for very-low leakage (they all have leakage to some extent). And an OA90 (very-high leakage) replaced with a very

Martin Thank you! That is the correct connection. All Preset voltages normal now! Menahem

I have a BM1600 - type 2113 - open here, with the 4 FM presets not working. I have a post and a pic in the Workbench forum. If any of you with one of these beautiful antiques could have a look inside your's and check to help me with locating the solder blob which this floating wire belongs to, I'd be most grateful! The SM is not much help here