[Leo V]

I just did a Class A bias on the stock 4558 opamp (since I don't have the caps for the AD8620 yet...) I got 3.9K ohm, 1/2 watt resistors w/ 5% tolerance from Radio Shack, and put it together exactly like Matthew Anker of SACDmods.com, here's my pic:

Maybe I'm high, but I think the sound got smoother... I'm going to listen more before making any conclusive statements, however.

 

[Budgie]

Keep us posted, about this mod. (I think I might give it a try as I don't have any work today. )

ps- excellent photos!

 

[Leo V]

I have just re-listened to quite a few songs, and indeed the clarity seems improved. Unfortunately, I cannot A/B compare it, but I believe I can hear minute details I couldn't hear before, the transparency is really great. This seems to improve soundstaging and even continuity/smoothness for some instruments and especially voices.

This convinces me to try the JFET biasing method on the AD8620... I'm going back to those ppl threads to find what parts I need...

Budgie, I suggest you try this mod since it's fairly cheap and reversible.

As for enabling the inputs on the NC650V, I will try accomplishing what you said (+5V supply) using a flip switch from Radio Shack if I can find one. I'll install the switch on the back of the unit, and it'll feed the 5V supply when on.

 

[Budgie]

Cool. I actually have the parts for the cascode current source in with some stuff I bought.

You could test the relay switching with a chunk of wire just to make sure all will work.

I have enjoyed this tinkering so much, I just went down to the local used Hi-Fi shop and bought a cheap used old sony piece-o-crap special (CDP 190) player to take apart and hack like the mod thread suggest- take it out of the chassis and screw it to a board etc. Should be fun, and for $45 it beats watching tv. I will try to take pics. Pretty amazing upon opening it up. This thing is so cheap- It is mostly empty space.

 

[Leo V]

The sound is really amazing now... especially the voices, they are really coming alive. In good recordings I can practically feel the singer's breath. I'm sold on Class A, now I need to figure out what parts I'll need for the cascaded JFET (for the AD8620)...

So here is ppl's thread with an attached diagram. However, ppl is feeding a buffer while I'm directly driving the cables. Any advice on which parts (JFETs) to get?

Off to bed, I'll test the relay switch tomorrow morning... pictures of your sacrificial CD player would be great

--Leo

 

[Budgie]

Yow, that made a big difference in my Denon! I used a 10k resistor (my power supply voltage is +/- 15vdc). Sounds like it might beat my Onkyo. I will have to get set up to do a direct comparison.
Now, on to trying it with the cascode,( though I don't think I will hear a big difference compared to the one I just heard).
I think I will add this to the cheapo cd player, but with a toggle switch to turn it on and off.

The parts in the drawing I have for the cascode goes like this:
opamp output-100 ohms-2n5486-2n5484-minus voltage

I am taking some pictures and will get them up when I get some level of done-ness. I won't be around till tomorrow evening.

 

[Leo V]

By golly you are right! +5V does switch to the Line-in inputs! (I shorted the 2 pins on RY201.) Now all I need is to install a flip-switch that shorts these pins when enabled. I'm just thinking where I'd install it...

 

[Leo V]

My caps are here!

Successfully upgraded opamp to AD8620, output resistors to Holcos 45ohm. On my way to pick up the caps & to Radio Shack for a rocker switch.

 

[Leo V]

All done!

1) Replaced PSU caps with Black Gate 1000uF 25V caps:

2) Replaced 4558 opamp with AD8620
3) Replaced ceramic .01uF decoupling caps with 1uF Black Gates
4) Using 45-ohm Holco resistors on the output
5) Class-A bias for the AD8620, using slightly more conservative 5.6Kohm resistors (should be near 2mA)

I'm doing the testing now. Right offhand, the detail/instrumental definition seems better. I am hoping the smoothness will improve as the AD8620 burns in... it's about neck-and-neck with biased 4558 right now. More audition results to follow! (update: ) Aerosmith's SACD definitely an improvement in fidelity... check out that soundstaging!
Leo

 

[Budgie]

Very cool

Looks like the black gates were tight fit. Would a ty -wrap around the caps give more support? Probably not needed, but I like things snug. Of course it would have to be in a complementry color to avoid interefering with the harmonic colors of the music spectrum

Were did you buy yer caps at?
I would think the opamp will get better as it burns in. After all, alot of people seem to like it around here. (Tho shall not slaughter sacred sheep

) You will of course be expected to offer comments after burn in!

Seems like I remeber ppl saying some of the Analog Devices chips have a class A output and you may not get any difference with the resistor biasing it. I will see if I can find out.

I have not fiddled with the Denon anymore since the class A mod. I still need to get in and take out those mute transistors. Other wise I am very happy with the way it sounds now. Sweet!

The bare naked cheapo player mod is taking up time and so far the total cost is up to $50! It has taken some weird turns due to the ultra cheap build of the guts. The d/a converter is an 8 pin dip chip! Looks just like a opamp. The outputs from the d/a went directly to the line outs, then to a 4556 opamp, configured as a buffer, for the headphone output. Very minimilist design. (Who would have thought a cheapo player would subscribe to the minimilist Hi-Fi creado)

 

[Leo V]

Budgie, if you can find out from ppl that would be great... or I can try contacting ppl myself. The AD8620 datasheet says nothing about Class A. I'd like to know before I start constructing cascaded JFETs if it's actually gonna help

So far my listening tests have passed well... clean, open sound. The clarity and soundstaging are the best winners so far. I'll give my newly configured player a few days of break-in before judging the final result, however

Tie-wrapping is a great idea, one of the caps is about 1/4" away from the carousel tray! I'll probably tape them together in the upwards-slanted position... the tape is transparent, hence no philharmonic interference with the audiopsychedelic spectrum

I also bought a rocker switch at Radio Shack to select between the outputs. I'll probably install it on the left side of the player, next to the front panel. Do you think 30-guage thin silver wire can handle the +5V signal needed by the switch?
Leo

PS: Apparently CDP-190 is a discontinued Sony player? Would be interesting to see your pictures. I'm even more amazed that your Denon went from underdog to such high performance

 

[Budgie]

Maybe ppl would know about that output stage. I tried to PM him yesterday and got a "box full" response, so it may be hard to get ahold of him. Maybe an e-mail to Tangent or one of the other builders of amps would be worth a shot. You could try unsoldering the resistors and see if it makes a difference.

Silver wire for the switch?? Thats got to make it sound better

(it should work fine, as the current is very small )

I was making progress on the (yes- discontinued) Sony, but I just broke my last 6/32 tap, so it's back to the hardware store. (gotta think up a cute name for the project. Ynos, maybe?)

 

[Leo V]

The silver wire is simply the only one I have! Now that I think about it, perhaps it'll make the switch toggle sound a bit smoother...

Bedtime, I'll try Tangent and the Asylum in the morning.

The only other name I can think up is exSony (pronounced EXony).

 

[Leo V]

Ahh.. found the ppl post I was looking for right here.

The author compares using AD843 and AD8620. In his response, ppl practically implores the author to bias the opamps (using the JFET method):

Quote:

USE A CURRENT SOURCE ON THE OPAMP Biasing the opamp into class A with a current source is manditory. now some folks can't tell the Difference but I can without evean trying.

..now take that in context of the subject of the post (AD8620 vs. ppl's beloved AD843) and he seems very much in favor of biasing Analog Devices amps. Of course I'm probably missing a finer detail, like the difference between resistor and JFET biasing. But I was intending to replace the resistor hack with JFETs anyway, so it's only a question of what configuration I should use...

 

[Budgie]

You simply have to save some silver wire for the jfet mod, then.

( the problem with using a resistor is, the current (for the bias) is voltage dependent, so when you apply an audio signal to the circuit, it appears at the "output" end of the resistor, and the current for bias gets modulated by the audio signal, as the voltage across the resistor varies with the signal.)( that make any sense?)( the jfet cascode creates a constant current source that ignores the audio voltage, and stabilizes the bias. How, you ask? Well, It's FM!)( FM= Fu____g Magic!)