Modding a Denon da-500. This noob needs some advice. - diyAudio
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Old 2nd January 2010, 10:05 PM   #1
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Default Modding a Denon da-500. This noob needs some advice.

I have been reading a lot about the Denon DA-500 dac. It is one of the few dac's with 3 or more inputs. Because i need 3 toslink inputs and the rest of my system is all vintage Denon, i really want this DAC. The sound quality should be decent, but i found a lot of info here on modding this DAC. Most threads are very old, and not all the info is complete enought for me to understand, so i tought i would start a new thread. Im a bit of a noob in this stuff, but i build other electronics before, and i get most the basics.


Killing the clock
In this thread im reading about stopping a clock has a bad infuence on the dac's sound quality. This clock is not used for the actual DA decoding. Its only there to support the DAC detecting the right signal. After that signal has been locked the clock is not needed anymore and only couses noise. The thread sugests that its possible to "kill" the clock and improving the sound quality.

There is a simple schematic in the thread that shows how to build the mod. The way i understand it, i have to use a cap, a resistor, a transistor and a diode that have to be connected to the ciruit that is already there creating this:
Click the image to open in full size.

This will somhow stop the clock i gues? But are there any effects on the way the dac works? After powering up the dac and with my PC, PS3 or DTV decoder (all connected trough TOSLink) will i still be able trough switch the inputs on the dac, and stuff like that? Or will the clock remain dead and not allow switching inputs because the dac cant lock on to the signal?


Changing OpAmps
I also read a lot about swapping the opamps for other ones. With a budget for something like max 75$ in opamps what would be the best choice for the opamps? and i gues there is more than 1 opamp, so which ones shoudl i change. Also if i change the opamps do i need to chnage other things too, or can i just swap them?

The power suply
I really think the PSU makes a huge diffrence in audio equipment and from what i am reading there is enough room for improvement in the DA-500. I found some very cheap toroidal transformers i could use to build a whole new PSU with a nice overkill in caps. I could use 2 diffrent transormers for the 12v and the 5V part. As far as i can see from the pictures there is room enough and the cost would be around 25$ so if it would help its a very simple and cheap mod to make. Or would it be better to change the PSU as they did in this thread?

When rebuilding the PSU are there any special things i can do to make it as good as possible?

Bypass caps?
This post show 2 caps installed somehere on the PCB. What do these do, and should i place them too?

Interior mods
In mods of other dacs i have seen some pictures there they placed a metal wall between the PSU and the rest of the electronics. I gues this maybe would lower any noise of the PSU. I also saw some pictures that of modded dac that had copper foil on the inside. Again for the same reason i gues. Do things like these realy help, or are they a waste of time?

Any other mods i can make?
All of these mods should help a lot, but are there any others i should take a look at? maybe replacing some other parts with better ones?

I know these are a lot of questions, but i would really appreciate some help here! Im a noob but i wanna learn!
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Old 3rd January 2010, 07:05 AM   #2
Mooly is offline Mooly  United Kingdom
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I can't answer all your questions but just some thoughts...
That mod... what the circuit does is hold pin 6 low (100uf cap turns on transistor) for an ideterminate time at switch on until cap charges via C-B junction. If pin 21 goes high or is high then the transistor is off and the osc runs.
Without knowing exactly how it all works, stopping an osc like that doesn't seem a smart move... it can cause lockups etc in logic devices. As I say though, without knowing exactly how it all works etc, it's impossible to say. The action of the transistor means the osc starts unpredictably too... not cleanly.

PSU... personally I would leave alone and perhaps look to (and measure) any rails and see how clean they all are. Adding an external PSU while OK in theory, might in practice be worse... thinking wiring, secondary leads radiating noise (caused by rectifier commutation) etc etc.
I would look to replacing caps with high quality low ESR types for the reservoir and local decoupling. Is there suppresion over the bridge/s rectifiers. Perhaps add 0.1 or 0.047uf surface mount caps on the print side between electroylitic legs if they have 5mm pitch or 2.5mm pitch etc.

Opamps... again, to be sure you need to see the circuit. Bipolar or FET. Is DC offset likely to be a problem. Are they single opamps ? do they make use of the DC null pins, as different opamps use different arrangements (and even pins, 1, 5 and 8)
Opamp decoupling... adding a small (0.1uf) cap directly accross the supply pins is beneficial. Never (as a general rule) decouple supply to ground as that introduces rail disturbance into critical signal grounds.
Those two caps look to be near 8 pin I/C's (opamps)... again look at the circuit.

For decoupling... use an oscilloscope, correctly grounded and correctly grounded to the relevant point you are looking at and measure
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Old 3rd January 2010, 01:39 PM   #3
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Thanks for your reply. That kill the clock mod seems to be a popular mod here, and people say it really makes a diffrence (more info). So im sure it works. I just want to know if there are any side effects in controling the dac. I dont have any schematics of the dac, so i cant see how everything exactly works yet.

In the same tread im writing about (and in others) i can read the the PSU really has a few faults in its design and that a few small mods really help. Im doing those small mods for sure, im just wondering if a whole new PSU with a overkill in caps, toroidal transformers and schottky rectifier.

The opamps are a double opamps as far as i know, so they dont have the offset connections. When browsing ebay i did see some converting solutions where 2 single opmamps in smd where mounted on a dip socked to work as 1 double opamp, so maybe it possible to place any omamp in this dac
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Old 3rd January 2010, 04:50 PM   #4
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I would want to see the circuit details before hacking it about that applies even for the opamps really.
Are they FET or Bipolar... if they are FET and the circuitry is high impedance with unmatched impedances then a Bipolar opamp may not work well.

If you are set on modifying it then fair enough... just be aware.
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Old 6th January 2010, 03:32 PM   #5
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I have been hearing a lot that this dac is good but isnt perfect, and i would be better of looking for another DAC. I do want this dac tho. Its one of the few dac with multiple inputs, and its pretty simple to work on. I also like the fact that is denon (like the rest of my equipment). For now i am sticking with this one. Its will be my first DAC i will mod. When i get bored with this one, i will move on to another one.


Anyway, i will be recieving the denon tomorow, i also ordere some parts for the PSU.

I finaly was able to buy service manual somewhere. You can download it here:
MEGAUPLOAD - The leading online storage and file delivery service (datasheets of the analog stage IC's are included)
The schematics are pretty easy.

So this thing uses 4 dual opamps. 2 for every chanal. 1 is used for I/V and buffer, and one is used for filtering. I have been reading some stuff about opamps, but cant really find what opamps i should use. I have been reading very good things about Burson Audio discrete opamps. They are not very cheap but according to some reviewa are very, very good. I was thinking i could replace the PC4570's with these burson's, and the opamps in the filters with something cheaper. Any opinions?
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Old 6th January 2010, 03:58 PM   #6
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I'll have a proper look later... the 5218 looks to be used as a "gyrator"
Are the opamps in your DAC 8pin DIL types or are any SIL types... they were available in both types.
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Old 6th January 2010, 05:24 PM   #7
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From the PCB layout they look to DIL so you have loads of choice. For the 4570 I would try a good FET opamp. One I have used very sucessfully is the OPA2604... it's one of the most "analogue" sounding devices I have heard used as an I/V convertor. For the 5218... well you could use a OPA2604 here too. The LM4562 is bipolar, but held in high regard by many.

Edit... No experience of Burson, and have heard good and bad reports.
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Old 6th January 2010, 06:31 PM   #8
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The OpAmps are DIP.

I kinda feel like trying the OPA2604 as a replacement for the 5218's and the Burson Discrete OpAmp for the PC4570. I like the idea of not having to many chips in the analog stage. I have been reading good things about the burson stuff, so why not try it? I do think they are a bit to expencive to also use as a replacement for the M5218. I can get the OPA2604 for as low as 6 euro. The bursons will cost me just over 50 euro per unit, so they are 10x as expencive as the OPA2604 :P Oh well, its fun to try i gues!

If i am going to replace the opamps should i also replace the resistors and the caps around them for something of simular quality? If so, what should i look for?

I also saw some stuff on ebay where 2 single opamps like the OPA627 are converted to 1 dual opamp. (The item on ebay) Is this any good, or would a OPA2604 be the same?
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Old 7th January 2010, 07:23 AM   #9
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The OPA627 is a high speed device and needs to be implemented correctly. If fitting on adapters you [may] run into stability issues. With anything like this you need to use a 'scope to check.

The OPA2604 should be fine as a drop in replacement. Ultimately how any device "sounds" depends on the exact circuit configuration and interaction with all around it... you are going to have to try them and see.


Changing resistors will have zero effect IMO here.
Caps... you could perhaps usefully change the electroylitics around the DAC for low ESR types... that fit properly and also the output coupling cap, but that's about it.
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Old 7th January 2010, 11:08 AM   #10
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Im also not to sure about those single-dual opamps conversions. I wonder what happens if you leave all those offsets disconnected. I gues strange things can happen.

I gues im going with that OPA2604 as a replacement for the 5218's and the Burson discrete's as a replacement for PC4570. I just hope that the opa2604 are not going to be the weaker link in the chain that will effect the Bursons preformance.

I am going to change those caps for sure. Just thought maybe the quality of the resistores would have a effect too.
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