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thomsva 12th October 2004 01:19 PM

Denon DVD2900 tweaks
 
2 Attachment(s)
Last week I made the first steps to modify my Denon DVD2900. I have started at the output stage. The first thing I did was carefully removing the mute transistors from the front channels. The improvement was very clear. A transistor between the signal path and ground seems to cover the smallest details on the recordings. The player now makes a few small pops when turning on the power or changing records. But it’s not very annoying really.

The second thing I did was replacing the coupling caps with polypropylenes. There capacitance is now only 6,6uF compared to the original >220uF. If the cap is too small it will affect bass levels but I have calculated that with a 10k load the –3db point is 2Hz with the new caps, so I think I can live with that. Also this time the improvement was clear. The high frequencies sound cleaner.

Next I will continue working on the output stage. Have a look at TR231 in the pic below. Depending on the state of the transistor the IC215 amplification will be roughly 1 or 2. The wire that changes the state is marked “PCM/DSD”. My guess is that the stage amplification is changed depending on weather the record being played is a CD or SACD/DVDA. As the TR231 could have a similar effect on the sound as the mute transistors I would like to remove it. My logic says that removing TR231 will make the sound level change depending on what format is being played. I can live with that if the sound is improved. Has anyone made similar mods? Any thoughts?

The DVD2900 has two pairs of front channel outputs. I will connect one pair of outputs past the coupling caps directly trough a resistor to the op-amp. This should work as long as the preamp has coupling caps on the inputs. Anyone tried this?

Also more ideas about easy improvements are appreciated!

-thomas

q1 31st October 2004 10:59 PM

Hi Tomas,

Thx for the information.
I also replaced the output capacitors by 10 uf mkp audyn capacitors. Sounds better indeed!

muting transistors is a good suggestion. did not see them yet. I have no scheme...:-( how they look like?

Got the idea on this dutch site:
http://www.soundevolution.nl/article...D_2900_SE.html

Also a new clock is placed inside and better op-amps.

A new clock which can be obtained here:
http://www.tentlabs.com/Products/DAC...ACUpgrade.html

I did not do the clock my self yet. But I expect a huge difference. Because i have the same clock in my CEC transport. And the was WOW!!

Hope to hear from you.

Rene

ergo 1st November 2004 08:04 PM

2 Attachment(s)
I'm in the process of upgrading one DVD-A11...

I replaced all the opamps in analog stage with OPA2134.

Also all the caps around DAC chips got bypassed as did some other critical caps in analog stage.. look at attached photo.

Next up in list is a Tent XO2 in a few weeks.

Ergo

A 8 2nd November 2004 03:09 PM

Clock upgrade....
 
I am not sure it will be worth the effort changing the clock in these players. The clock that controls the timing is derived from 27MHz (for video) crystal and then uses Clock IC to create the master clocks for audio.
The clock then passes several IC's and many centimeters before it reaches the actual da chips.

Putting a nice clock in and let it pass all that crap seems a waste to me. In my world a good clock needs to be clean close to where it matters.

Perhaps a better approach would be to start by making sure that the existing clock circuit gets the best possible working conditions, then take it from there depending on the results.

I've just dismantled my 2900 for the next level of mods and will start to change decoupling caps for Oscon SVP's on the main board. There are also several existing options to filter ps noise on the pcb that's not being used.

/Michael

thomsva 4th November 2004 01:34 PM

Hello again,

I did remove the transistors I referred to in my first message. I also removed the muting transistors for all the other channels as well. So totally I have now removed 26 (!) transistors from the player.

The denon has two pairs of outputs for the front channels. I have the coupling caps bypassed for one of the output pairs. This is possible because the preamp has coupling caps on the input.

q1: The mute transistors are surface-mounted and very small. It took a while to desolder them carefully, but I'm really happy about the result.

So far removing the muting transistors had the biggest impact on the sound quality. Also upgrading the coupling caps was a clear improvement. Bypassing the improved coupling caps didn't change much, only a slight increase in the bass level. That effect could certainly be imaginary.

So what's next? Tampering with the clock is too challenging for me, so I'm thinking about a new psu for the audio circuits.

-thomas

DIAR 4th November 2004 01:58 PM

As you know, I achieved the biggest change for better by changing the op amplifiers from output.

I can easily send OPA627+adapter to you for testing (I can send also AD8065 if you like but then I have to listen to old NJM4580 while you're testing :bawling: ;) ) . All you need to do is desolder the old opa and change it to dip8 socket. This enables you to change opa rapidly without any risk of harming the PCB. If you like (I'm sure you won't!) you can install the old opa by just sticking it to the socket. In my opinion, AD8065 is more technical sounding opa and OPA627 is more musical (or should I say emotional). Concidering your equipment, I think you would prefer the latter. I have 5 (!) DIP8 single-to-dual OPA adapters because of the Browndog incidence so I can sell you one of them for a niominal price. You can get OPA626 from RS. I also have 5 AMD single-to-dual which are suitable for AD8065 (however I recommend buying an assembled module from LCAudio).

Any thoughts about this? :D

btw. The easiest way to desolder SMD components is using two soldering irons and heating all pins at the same time. I used that tecnique the second time I removed muting transistors and it was about 100 times easier and safer than using only one soldering iron.

thomsva 5th November 2004 01:50 PM

Diar,
Many thanks for the suggestions. I will consider them but I'm moving slowly at the moment. I like my player a lot already.

-thomas

DIAR 5th November 2004 08:29 PM

No problem :D It would be interesting to hear your thoughts about the OPA's so if you change your mind and wan't to test before purchasing, send me an email.

Have you considered Jung superregulator to power supply. In some applications Jung superregulator should be the best there is but I've also heard that it isn't a fool proof regulator. You can buy PCB's for low price from here:
http://www.aoselectronics.com/jungsrpcb.html

I'd like to get one of those but I don't know how to adjust the voltage and where to use it :D :rolleyes:

hatchiruko 15th November 2004 06:55 AM

[QUOTE]Originally posted by thomsva
[B]Hello again,

I did remove the transistors I referred to in my first message. I also removed the muting transistors for all the other channels as well. So totally I have now removed 26 (!) transistors from the player.

I have a Yamaha CDP and has a digital and analog output (RCA). I removed the mute transistors on the analog side but not exactly sure if the digital side will make any differences. Does anybody have done this?

Lucas_G 20th November 2004 04:04 PM

Re: Denon DVD2900 tweaks
 
Quote:

Originally posted by thomsva
Last week I made the first steps to modify my Denon DVD2900. I have started at the output stage. The first thing I did was carefully removing the mute transistors from the front channels. The improvement was very clear. A transistor between the signal path and ground seems to cover the smallest details on the recordings. The player now makes a few small pops when turning on the power or changing records. But it’s not very annoying really.

The second thing I did was replacing the coupling caps with polypropylenes. There capacitance is now only 6,6uF compared to the original >220uF. If the cap is too small it will affect bass levels but I have calculated that with a 10k load the –3db point is 2Hz with the new caps, so I think I can live with that. Also this time the improvement was clear. The high frequencies sound cleaner.

Next I will continue working on the output stage. Have a look at TR231 in the pic below. Depending on the state of the transistor the IC215 amplification will be roughly 1 or 2. The wire that changes the state is marked “PCM/DSD”. My guess is that the stage amplification is changed depending on weather the record being played is a CD or SACD/DVDA. As the TR231 could have a similar effect on the sound as the mute transistors I would like to remove it. My logic says that removing TR231 will make the sound level change depending on what format is being played. I can live with that if the sound is improved. Has anyone made similar mods? Any thoughts?

The DVD2900 has two pairs of front channel outputs. I will connect one pair of outputs past the coupling caps directly trough a resistor to the op-amp. This should work as long as the preamp has coupling caps on the inputs. Anyone tried this?

Also more ideas about easy improvements are appreciated!

-thomas


Hi Thomas,

I think removing TR231 seems a good idea.
How about removing everything that follows the OPA275?

DOES ANYONE KNOW whether the output of the OPA275 needs any of the resistors in series or parallel that follow in this scheme? (See picture in first post of this thread)

The 100k resisors on ground together with the 470 pF caps are probably there to prevent oscillation, but are they really necessary? CAN ANYONE COMMENT?

You do need of course one output cap in series to prevent DC ruining you amps (unless you are sure your preamp filters thsi out). 6.8 uF is surely large enough, and in case of using large prolypropyleen (speaker) caps it is wise to try smaller ones. However if you would use Blackgates you could also try 47 to 220 uF. The larger blackgate the more dark and bass-pronounced the sound gets with some lack of fine detail in the treble.

Regards,

Lucas


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