ctef, as shown in the picture you provided, removing the plastic makes it easier to mount the smt decoupling caps.
Well, I planed to solder the caps on bottom side of PCB. So, no need to remove pins. Are this 2mm extra (the board thickness) critical in the case?
May be, yes. Closer is better...
May be, yes. Closer is better...
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Cap decoupling
Hi Stephan, In theory, yes, closer is better. I'm not sure it will make a huge difference. EC Designs solution is elegant. That is why I did the same on my second build. I plan to go back and redo parts of my first build. I will use SMT caps under the board just as you suggest. I don't want to remove the socket at this point. The big leaded caps I have I think are an issue as far as noise and switching transients. Interesting how nice it still sounds. I am aware that I am losing some details, the really low level stuff..... 😱 Dave
Hi all,
Well, I have music, but unfortunately I also have a hiss problem while playing. The hiss is less if the CD is recorded at a louder level. If I pause or stop the transport. the hiss stops. Any ideas?
Well, I have music, but unfortunately I also have a hiss problem while playing. The hiss is less if the CD is recorded at a louder level. If I pause or stop the transport. the hiss stops. Any ideas?
AD797
Hi Dwight, I believe your AD797's are oscillating. Do you have any other Opamps to try? Make sure to use same type meaning singles or duals. I think the 797 is a single? This oscillating is a common problem with the 797. Dave
Hi Dwight, I believe your AD797's are oscillating. Do you have any other Opamps to try? Make sure to use same type meaning singles or duals. I think the 797 is a single? This oscillating is a common problem with the 797. Dave
Hiss
Wonder if the capacitor to ground on the spdif is the wrong value or open. Another thing to consider is if the receiver filter values are correct? I think that is on pin 20. Did you put the 75 Ohm resistor across the input of the spdif to terminate the coax? The spdif is a bit of a mess. The design they used is poor. I think you said no transformer on the input. Maybe a ground loop although the coupling cap on the RXin should prevent that. Another consideration is the polarity at the board. There is a + and - on the board at the spdif connection. If reversed I'm not sure what that would do. Your getting there if it makes music. That is a big win. Now it's just some debugging to do. 😎
Wonder if the capacitor to ground on the spdif is the wrong value or open. Another thing to consider is if the receiver filter values are correct? I think that is on pin 20. Did you put the 75 Ohm resistor across the input of the spdif to terminate the coax? The spdif is a bit of a mess. The design they used is poor. I think you said no transformer on the input. Maybe a ground loop although the coupling cap on the RXin should prevent that. Another consideration is the polarity at the board. There is a + and - on the board at the spdif connection. If reversed I'm not sure what that would do. Your getting there if it makes music. That is a big win. Now it's just some debugging to do. 😎
I have had identical problem. I am not sure I nailed down the cause but felt it was due to a bad solder joint on DEM circuit. I use the Grundig 9009 circuit and the caps had some bad joints. Again, not sure but that was where my thinking was.
When it is occurring you can clearly hear it during quiet or silent periods of playback, but you hit pause or the track ends and DAC goes quiet.
Hi Dave,
Some other people on the net have said the AD797 is subject to oscillation noise. I have not found a fix for the problem so far. So, I ordered a pair of OPA627BP. I'll give you my impressions after I've had a chance to listen to them.
Some other people on the net have said the AD797 is subject to oscillation noise. I have not found a fix for the problem so far. So, I ordered a pair of OPA627BP. I'll give you my impressions after I've had a chance to listen to them.
Grundig DEM mod
What is your impressions of the Grundig DEM clocking scheme? I have been considering giving it a try. I am currently using 120 pF Silver Mica and an air variable. A very clean sound and highly detailed. Although I see John Brown thinks the induced jitter spectra is to high at that frequency. What do you think is the best? I see all sorts of things out there. 😎
What is your impressions of the Grundig DEM clocking scheme? I have been considering giving it a try. I am currently using 120 pF Silver Mica and an air variable. A very clean sound and highly detailed. Although I see John Brown thinks the induced jitter spectra is to high at that frequency. What do you think is the best? I see all sorts of things out there. 😎
I/V opamp
Hi Dwight, I have the OPA627BP in my first build. Really very good. Can add a slight darkness to the sound. Really not bad. A member of my Audio club likes the SOIC version on a DIP adapter. Claims it has a different sound. It is certainly possible as the SOIC uses a different die. I plan to try the SOIC version as soon as my budget allows. Beware of fakes. I see TI suggest buying from ARROW Electronics. I'm told a gentleman on Ebay is selling real ones at a fair price. PM me for his Ebay name. I have not tried them from him. Dave
Hi Dwight, I have the OPA627BP in my first build. Really very good. Can add a slight darkness to the sound. Really not bad. A member of my Audio club likes the SOIC version on a DIP adapter. Claims it has a different sound. It is certainly possible as the SOIC uses a different die. I plan to try the SOIC version as soon as my budget allows. Beware of fakes. I see TI suggest buying from ARROW Electronics. I'm told a gentleman on Ebay is selling real ones at a fair price. PM me for his Ebay name. I have not tried them from him. Dave
Tube stage
I tried a version of the 6GM8 SRPP with a 2SK170 fet. The design used to high a value for I/V resistor. An interesting sound although I could hear the compliance range being exceeded. For 1541 dac you use 6.5 Ohm I/V resistor and that means very high gain is needed. Try a Gomes tube stage as suggested by Thorsten. If you want a higher I/V resistor value and don't mind adding a 2 mA CCS with a 2SK170 jfet, you can go up to 12 Ohm I/V resistor. The CCS is like Pedja used in the Aya dac with the AD844. It might be easier to go with a OPA627 simple (inverting) I/V, use an Edcor based passive filter following that. I'll attach the filter schematic. It is flat to 20 Khz and very inexpensive. The cost here is the OPA627. 🙂
I tried a version of the 6GM8 SRPP with a 2SK170 fet. The design used to high a value for I/V resistor. An interesting sound although I could hear the compliance range being exceeded. For 1541 dac you use 6.5 Ohm I/V resistor and that means very high gain is needed. Try a Gomes tube stage as suggested by Thorsten. If you want a higher I/V resistor value and don't mind adding a 2 mA CCS with a 2SK170 jfet, you can go up to 12 Ohm I/V resistor. The CCS is like Pedja used in the Aya dac with the AD844. It might be easier to go with a OPA627 simple (inverting) I/V, use an Edcor based passive filter following that. I'll attach the filter schematic. It is flat to 20 Khz and very inexpensive. The cost here is the OPA627. 🙂
Add a blocking capacitor if you don't use a 2 mA CCS. Transformers don't usually like a voltage offset on them. Just a helpful hint. 🙂
I am very happy with the Grundig circuit. My path started with the usual Philips speced 680pF cap across 16 17. I replaced with 200 pF silver mica. Much improved. Then did the Grundig circuit with Riken resistor and an inductor in line with the reference voltage from pin 15. At the time I felt it was a big step forward. Then used 8uf organic polymer smt caps in the Grundig c550,515 positions. I think this was an improvement. There was a lot of time between mods, so not a really scientific test. I am quite happy with the sound, so not heavily motivated to experiment further.
Attachments
Grundig DEM
I am still unclear about the capacitor values for C550 and C515. One post it looked like .1 uF another 1 uF and your at 8 uF.
Do you know what Grundig used? I appreciate any comments and thanks for sharing. 😉
I am still unclear about the capacitor values for C550 and C515. One post it looked like .1 uF another 1 uF and your at 8 uF.
Do you know what Grundig used? I appreciate any comments and thanks for sharing. 😉Hi all,
My OPA627BP's arrived yesterday along with some other op-amps I bought from mouser. The 627 is clean, no hiss etc. It sounds a little dark, and has a lot of body. I played it overnight to burn in. I experimented with the AD825. It was a little hard on the top end. One of them died during the break in. I still like the 797 most. The sound is open, and neutral. I bought them a few years back and don't remember the source.
I tried adding .1uf decoupling caps to both pins 7 and 4. But still no noticeable change in hiss.
My OPA627BP's arrived yesterday along with some other op-amps I bought from mouser. The 627 is clean, no hiss etc. It sounds a little dark, and has a lot of body. I played it overnight to burn in. I experimented with the AD825. It was a little hard on the top end. One of them died during the break in. I still like the 797 most. The sound is open, and neutral. I bought them a few years back and don't remember the source.
I tried adding .1uf decoupling caps to both pins 7 and 4. But still no noticeable change in hiss.
Making progress
Hi Dwight, Glad to hear the thing plays with the OPA627. If you want to try to get the AD797's to work.... Try putting 1800 pF polystyrene cap across inverting input to ground like in the Aya Dac. That will help with some high frequency dac ripple currents. It might be enough to settle the AD797 down a bit. If it works the hiss should be gone. You might consider trying the 627 SOIC version on a DIP adapter. My audio club friend says it is a different die and sounds better to him. Not dark. I plan to try that soon. 😉 Dave
Hi Dwight, Glad to hear the thing plays with the OPA627. If you want to try to get the AD797's to work.... Try putting 1800 pF polystyrene cap across inverting input to ground like in the Aya Dac. That will help with some high frequency dac ripple currents. It might be enough to settle the AD797 down a bit. If it works the hiss should be gone. You might consider trying the 627 SOIC version on a DIP adapter. My audio club friend says it is a different die and sounds better to him. Not dark. I plan to try that soon. 😉 Dave
😱
Something is wrong, horribly horribly wrong ... 😉
I'm guessing oscillation! Can you post your layout?
Analogmetric Dac
Dwight has the same Analogmetric dac. Same layout. Difference is I bypassed the entire analog stage. Oscillation with AD797 is pretty common. AD825 I haven't tried those.
Dwight has the same Analogmetric dac. Same layout. Difference is I bypassed the entire analog stage. Oscillation with AD797 is pretty common. AD825 I haven't tried those.