denon cdp with pcm61, any potensial?

[Makofoed-6sn7]

Hello,

My much beloved cdp died the other day. I fixed a broken one at work and it sounds okay. It is a Denon dn-600f. It has pcm61 dac, does it have any potensial to make it preform better? i really want to make an eksternal dac to it, but the cs8412 and its smd euq. Cost about 60-70$, not in my budget. So, what can I do with its internal dac?

All surgestions welcome.

Best regards,

Magnus

[wa2ise]

I modified a Denon cdp that uses PCM61P DAC chips with vacuum tube analog outputs, see my web page http://pw2.netcom.com/~wa2ise/radios/tubedac.htm for details.

[Makofoed-6sn7]

Hello wa2ise,

I must admit that I have already done it. When I didn't get any answers I decided to try one of yours circuits(I have had your mod s in my head a long time), I used a 1k resistor with a 4n7 cap to load and filter the dac, then a 2µ2 NP cap out to the outputs jack. That worked great, but a little bit low on gain. Yesterday I built my own version of a 5678 tube stage. 2M2 grid leak, 30k anode resistor and a 12µf NP output cap. I used the large cap for one reason, I had to many from a crossover project... The tube were triode conected. I sounds great! Only one thing is that the tubes are very microphonic. The filament gets power from a LM317 with it's regulator pin conected to ground. HT is a simple crc filter. I didn't ad another coupling cap on the g1 on the 5678 becouse of the 2µ2 cap in the cdp. I don't know with you, but what suprised me a lot is that when I conected a signal generator with full output swing and conected a scope, I couldn't see any clip! That was about 40v P-P. I don't understand that at all. I know there must be some distortion, but it didn't clip... Any way, I used the sub min tubes becouse I love 'em.

Best regards,

Magnus

[Makofoed-6sn7]

Hello,

Just wanted to ad that I have know compared the modded Denon to my Pioneer cld-d515 Laserdisc player. The laserdisc player has a really good sound, and is not modded in any way. I tried many album, but for some reason Rush - 2112 was the one with biggest difference. The denon has a much more open and clear sound. It did suprise me that the diffrence was that obivous.

Well, now you guys know.

Best regards,

Magnus

[wa2ise]

I used a 1k resistor with a 4n7 cap to load and filter the dac, then a 2µ2 NP cap out to the outputs jack. That worked great, but a little bit low on gain. Yesterday I built my own version of a 5678 tube stage. 2M2 grid leak, 30k anode resistor and a 12µf NP output cap. The tube were triode conected. It sounds great! Only one thing is that the tubes are very microphonic. The filament gets power from a LM317 with it's regulator pin conected to ground. HT is a simple crc filter. I didn't ad another coupling cap on the g1 on the 5678 becouse of the 2µ2 cap in the cdp. I don't know with you, but what suprised me a lot is that when I conected a signal generator with full output swing and conected a scope, I couldn't see any clip! That was about 40v P-P.

To reduce that much gain, change the anode resistor to something like 3K. Or change the I/V resistor to 100 ohms, though the microphonics will become much louder. Reducing the anode resistor should avoid that. Or you could do a voltage divider with the anode resistor, say 27K from the plate and screen to the tap and cap to the output jack, and then 3K from the tap to B+. That would reduce the output gain but preserve the tube biasing/internal feedback you get with triode type circuits.

I've avoided grid leak circuits myself, not sure how hard the peaks get hit when the grid "leaks". Anyway, I've biased the filament up about a half a volt with a resistor between the filament and ground to raise the filament's negative end up about a volt. Making the grid, which I have directly connected to the DAC look to be that much biased more negative.

Glad what you built sounded so good.