Hi gents,
So far I`ve modified my PSX by shorting the coupling caps of the AV output and feeding it directly into an AC coupled preamp. Although I enjoy the sound of this solution there are two major drawbacks:
DC output bias causing “pops” and fairly high output impedance due to direct feed of DAC outputs to the preamp.
To overcome these, I decided to use below shown JFET source follower stage between the DAC`s outputs and the muting circuit. I have used the RCA outputs and kept the muting circuit, but removed the “strange little thing” (which is a common mode choke from MURATA) and also the SMD ferrite beads. Apart from the cap at the output of the muting circuit I have removed all other caps connected between the signal and ground in order to avoid further high frequency attenuation.
This “buffer – solution” leaves me with only one coupling cap per channel as I can use the DAC`s DC level for biasing the JFETs. The JFETs provide a high impedance seen by the DAC which is favourable. thus the DAC and the output are nicely decoupled.
You can of course use other JFETs than 2SK170, but you may need to adjust the circuit slightly.
Listening tests are ongoing so I´ll keep you informed.
So far I`ve modified my PSX by shorting the coupling caps of the AV output and feeding it directly into an AC coupled preamp. Although I enjoy the sound of this solution there are two major drawbacks:
DC output bias causing “pops” and fairly high output impedance due to direct feed of DAC outputs to the preamp.
To overcome these, I decided to use below shown JFET source follower stage between the DAC`s outputs and the muting circuit. I have used the RCA outputs and kept the muting circuit, but removed the “strange little thing” (which is a common mode choke from MURATA) and also the SMD ferrite beads. Apart from the cap at the output of the muting circuit I have removed all other caps connected between the signal and ground in order to avoid further high frequency attenuation.
This “buffer – solution” leaves me with only one coupling cap per channel as I can use the DAC`s DC level for biasing the JFETs. The JFETs provide a high impedance seen by the DAC which is favourable. thus the DAC and the output are nicely decoupled.
You can of course use other JFETs than 2SK170, but you may need to adjust the circuit slightly.
Listening tests are ongoing so I´ll keep you informed.
Attachments
Hi Mick,
it will be quite exiting for me too. I have already done this kind of modifikation on a Pioneer DVD player (DV-343) and the result is very good, indeed better than my so far playstation. Now it will be fun to see if the playstation can pass my favorite again.
By the way: I took my idea from the decware web-site where Mr. Decker is modifying a DV-343 with a tube cathode follower stage. For me the tube stuff was to much effort, so I decided to go for the JFET.
So long,
Jürgen
it will be quite exiting for me too. I have already done this kind of modifikation on a Pioneer DVD player (DV-343) and the result is very good, indeed better than my so far playstation. Now it will be fun to see if the playstation can pass my favorite again.
By the way: I took my idea from the decware web-site where Mr. Decker is modifying a DV-343 with a tube cathode follower stage. For me the tube stuff was to much effort, so I decided to go for the JFET.
So long,
Jürgen
Just a side note, which may be interesting for those of you, who suffer from the low output voltage of the PS1:
The NJM2100 opamp is used with unity gain in the stock form, but it can be used with higher gain. Replacing the feedback R from 18k to 27k will increase the output signal voltage by about 50%. E.g. at 1 kHz there is an increase from 1.1V to 1.6V. The signal is still undistorted and there is no clipping.
Cheers,
Mick
The NJM2100 opamp is used with unity gain in the stock form, but it can be used with higher gain. Replacing the feedback R from 18k to 27k will increase the output signal voltage by about 50%. E.g. at 1 kHz there is an increase from 1.1V to 1.6V. The signal is still undistorted and there is no clipping.
Cheers,
Mick
Mick_F said:
But has anyone checked the voltage on the VREFH pin , that is supposed to control the output of the DAC ? I would have, but I couldn't get the datasheet for my DAC. I have a AKM DAC and only a datasheet for AK4309, which has fewer pins. So I couldn'T figure out which pin it is.
My supposition is that the low output comes from putting this pin to a lower voltage.
I did, I think it was page 17 or something like that...
Nope! Page 11, right here :
http://www.diyaudio.com/forums/showthread.php?postid=776434#post776434
There are just 4 NC pins coming out of one of the sides of the DAC. The new unit is smaller, but pin compatible.
We made almost all the mods in the first 25 pages, no?
For me, the breakthrough came on page 38 (post #376 ), where I came up with the procedure for full replacement of the output stage.
Actually, yesterday I modified another PS1 in a similar way but using better shielded cables etc. I will post some new images soon. I tried to use good MKT caps instead of the Wimas, but I could not accommodate them in the small space availablel close to the DAC. The only way would have been by using much longer leads (then I could have placed the large MKT caps in a corner of the case where there is more space) but I am quite sure that longer leads would null the effect of better caps. So I kept the Wimas...
Mick
Hi gents,
yesterday evening I finished implementing the JFET output stage in my PSX. In contrary to my drawing I have used 3u3 output caps (MKT type) because space is very limited and I tried to keep the circuit as small as possible.
Before closing the case I did some measurements. Gate-Source voltage is 0.1V which seems a bit low for me. Maybe it would be better to use source resistors of approx. 1.5k.
Anyhow I left the resistors, screwed everything together and started listening. First impression was an increase in detail and space, I enjoyed the sound and soon forgot about testing.
So I will have to do more A/B comparison with my other PSX using the AV connector (direct DAC output).
My preamp is a Pass P clone, the poweramp an Aleph 0s clone. I am using Canton speakers (Ergo RCS) togethter with a Linkwitz dipole sub crossed over at 50Hz. My listening room has 35 squaremeters.
More listening experience and pics of the mods soon.
Jürgen
yesterday evening I finished implementing the JFET output stage in my PSX. In contrary to my drawing I have used 3u3 output caps (MKT type) because space is very limited and I tried to keep the circuit as small as possible.
Before closing the case I did some measurements. Gate-Source voltage is 0.1V which seems a bit low for me. Maybe it would be better to use source resistors of approx. 1.5k.
Anyhow I left the resistors, screwed everything together and started listening. First impression was an increase in detail and space, I enjoyed the sound and soon forgot about testing.
So I will have to do more A/B comparison with my other PSX using the AV connector (direct DAC output).
My preamp is a Pass P clone, the poweramp an Aleph 0s clone. I am using Canton speakers (Ergo RCS) togethter with a Linkwitz dipole sub crossed over at 50Hz. My listening room has 35 squaremeters.
More listening experience and pics of the mods soon.
Jürgen
kec said:
No. It's been mentioned, but that's it.
One way to do it is to flash the BIOS, perhaps using a Game Hunter card. But that's hardcore. There might be other ways. For example, when one of the surface-mount fuses goes, the PSX will go directly to CD playback mode. The problem is that the CDM stops working also. Something such.
As for remote, THIS allows you use controls on the unit and remote at the same time. It has no Pause button, though.
By the way, I don't mind where this thread is going. I check in here every now and again.