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Denon DA-500


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The Denon DA-500


I started a thread back when I bought my first Denon DA-500. Since then, Deepak has picked one up, and I've picked up a second one, and others have been looking for one. So it's generating a little more interest. Now talk has turned towards possible improvements.

The basics:

  • PCM-1702 based
  • buffered op-amp output stage?
  • 3 optical inputs
  • 2 coaxial inputs
  • 1 optical output
  • 1 coaxial output
  • 1 analong output

This isn't meant to be strictly a modding thread. But I thought it would be good to grab the posts regarding the DA-500 from some other threads and get them all together.

From my previous threads:

A lot of the sound is probably due to the PCM1702. The 1702, along with the 63 and 1704, are tremendously nice sounding converters IMO. However, you can improve the performance of your DA-500 by changing the op-amps. It seems to have M5218 and NJM4570 op-amps; change the i/v converter to THS4032, and use maybe a single-to-dual adaptor with a couple of AD825s for the buffer. Add in some bypassing/decoupling if there isn't any. Try maybe 0.1uF across the rails and 100uF to ground, although there may be more optimal configurations. I think you'll enjoy the results :)

Here's the analog section of the DA-500. Some highlights are:

M5218 op amps (IC502 and IC504) are filters

PC4570 op amps (IC501 and IC503) serve as I/V and buffer

C514 and C515 are the output capacitors


A good modding thread from the diyAudio Forums:

diyAudio Forums - A little Denon DAC mod

Some additional internal shots I took today...




Digital Section:



Analog Section:



It seems that as a PCM-1702 based DAC, it's a reasonable platform to start, especially when considering the more-than-reasonable cost of one of these units. So, for those in the know, what are some of the best places to improve? And if anyone needs P/N that can't be made out in the pics, I'm sure I can open mine back up again.

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Okay, looks like 4570 for I/V and 5218 for LPF. The bypassing arrangement pretty much stinks; I don't see bypassing from both rails, and certainly not across the rails, so substantial alteration in that respect is probably in order. Definitely so if you have any interest in using the THS4032.

So, gameplan, I guess....

Rel-Cap RTE can probably fit and sub in for whatever they're using for the filter caps at the moment. Looks like it's probably MKS (mylar) or MKP (metallised polypropylene) based on the package shape and size. Polystyrene (aka KS) is considerably better for filter applications.

For bypass, you're probably looking at, after soldering in an op-amp (or an op-amp on an adaptor), soldering caps directly from pins 4 and 8 to ground, observing polarity where applicable. Although, inductance could become a problem, so if that does happen, you can put around a 1-4 ohm resistor between the larger rail capacitor (e.g. the electrolytic) and the rail. I'd say probably start with somewhere around 100-330uF for rail cap, and have 0.1uF in parallel. Then, put 2.2uF across the rails. I'm basing this off of some recent results I've been getting using a spectrum analyser and an oscilloscope. With certain op-amps, sometimes you really will need that resistor in series with the electrolytic, so don't count it out as a possible remedy to problems, especially since the placement of the rail caps could be such that you really have to consider the effects of lead inductance. When you bypass across the rails, do it right on the pins of the op-amp on the adaptor.

For the I/V, again I'd say use THS4032, although you could also try thr AD8022 as the rails are +/- 12V. For LPF, I've recently been getting some pretty good results with the AD797. You could try the AD8599 dual which, as far as I understand, is compensated differently but it is a similar topology. At least, it behaves like it is. It's a bit slower, the distortion is higher, but it's less cranky about running in unity gain and it's a dual, making your life easier. It is SOIC, though, so it will need an adaptor, just like the THS4032.

What's left? I guess you could change the regs if they're noisy. You'll probably need a scope to really see what's going on and make sure you don't make things worse. You could also switch out the resistors, if they're carbon film, for metal film. Looking at how small those are, you'd probably have to use something like RN50/CMF50.

I noticed it uses a YM3623. This receiver seems to be fairly infamous for jitter problems...maybe try looking into improving the loop filter if anything can even be done about that, like on the CS series chips. That won't really do much about low frequency but might help with high. I've seen adaptors for it to be swapped with CS8414, but I have no idea how well those work.

Other than that? I dunno, could swap out for PCM1702-K. I got measureable and audible results out of doing that with the Transdac.

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For SOIC to DIP adapters, I saw a neat technique on diyhifi of putting the chip on the bottom of a DIP-8 socket... gets the chip 1-2mm closer to the the pins and gives you room on top for stuff like the rail to rail cap, etc.

DIYHiFi.org • View topic - KC7

Look for carlosfm's post (about the 3rd one or so), with pics. His bypassing techniques were what i was going to use for a start if I went to the THS4031/2 chips (100uf Pana FM right on the power pins to ground, etc.).

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I was suggesting soldering the adaptor directly into the board, though socketed probably would work. I have I/V and LPF both socketed on my DAC. I don't see much gain in soldering the chip directly to the dip socket like that versus using a good adaptor like the ones Aries makes (A724-ND or A744-ND from digikey). In fact, I'm not sure it would work as well, especially when we factor in the bypassing stuff that needs to be done. Input impedance at the inverting input goes up dramatically at high frequency, so milliohms in the high frequency region from the adaptor is a drop in the bucket. I don't know how much stray capacitance is going to affect it or not; some of that will depend on how good a job you do on the bypassing as well as what the rest of the circuit layout looks like (which I, obviously, can't see from these photos).

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So, I got a bit better look at the circuit...

One of the other problems lies in the I/V. I'm not sure if it's just that this phenomenon was not well understood at the time, but they have essentially nothing damping the current step at the inverting input, nor do they have anything damping the non-inverting input. Both of these things can end up causing the i/v to barf on transient response when using something like the PCM1702, depending on the op-amp. They do, at least, have a feedback capacitor which helps _a lot_. If you're feeling particularly adventurous, you may want to cut the traces to the inputs and wire in a 100 ohm resistor in series between the non-inverting input and ground, and something along the lines of 100-500 ohms, probably, in series with i-out to inv. I'm not sure what specific value is optimal.

I don't know if the THS4031 is especially suceptible to this problem since my DAC already has these measures in place. The AD797, though, performs very poorly without it, and in fact sometimes needs a capacitor to ground as well. The OPA627, interestingly enough, is less suceptible to this problem, and this fact makes me wonder if it is not the reason some people have reported favourable results with the OPA627 compared to some other op-amps for I/V, as I didn't find the performance particularly superlative compared to some other options.

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