Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 30, 2008 12:57:07 GMT
O.K. I see what you mean. I doubt that they could get away with that with today's high speed, opamps. You would need awfully short leads from an attenuator connected to it. IMHO, not a good idea. Alex
|
|
|
Post by dotnet on May 30, 2008 13:43:25 GMT
The pot in my A120 does sit right next to the op amp, with a long rod extending its shaft to the front plate... The op amp is a TL084, but the OPA4132 is supposed to be a good upgrade. I actually might give that one a try if I don't decide to rip out the pre-amp altogether. A stepped attenuator that never goes high-ohm shouldn't be any worse than the Alps, I reckon. I'm sure they're not using aluminium contacts Cheers Steffen. EDIT: Sorry Leo for taking your thread thoroughly off track. Maybe a moderator can merge the A120 pot/attenuator posts into my Musical Fidelity amp thread?
|
|
leo
Been here a while!
Team wtf is it?
Posts: 3,638
|
Post by leo on May 30, 2008 15:54:17 GMT
Don't worry about it Steffen, its no problem
|
|
leo
Been here a while!
Team wtf is it?
Posts: 3,638
|
Post by leo on May 30, 2008 16:01:03 GMT
Hi leo, Once more thanks for words of caution. I am using a 10K stepped ladder-type pot, but advice headed as I’d prefer to avoid scratches/pops when adjusting. BTW, I might be easily pleased, but once warmed up I am really enjoying the additional detail, texture and focus that the LM833 seems to provide over the JRC5532. If a $2 opamp can sound this nice in this DAC, I’m really looking forward what gains can be wrought by use of an LM4562 or burson audio module, which I contacted them about a few weeks back. You’re several steps ahead of me though. I received word yesterday that they’ve just received new stock. At $75AUS for a single ‘dual’, and you having tried one, are they worth the expense over a good opamp IYO. Jeff The Bursons are very good if used in the right place, they also require very good clean regulation to sound their best, dropping them in the standard Elcheapo didn't give great results tbh but using them in the modified one was a lot better. The modified dac board has had the output stage gain adjusted to much lower output, its also had one side of the differential output of the dac chip loaded down a bit. DC offset on the output of the modified version is a couple of mV's so no coupling caps are needed I still can't get that resistor mod on the standard dac to work , it gives -1.5v DC
|
|
leo
Been here a while!
Team wtf is it?
Posts: 3,638
|
Post by leo on May 30, 2008 16:06:34 GMT
Can the burson module be used in an X-Can V2 or V3? I'll see if I can find the V2 schematic, I don't think the V3 uses op-amps?
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 31, 2008 1:05:36 GMT
Mikguel Do you know if the V2 and V3's transistors run off + and - supplies ? I think the Bursons normally use + and -15V ? Alex
|
|
|
Post by jeffc on Jun 1, 2008 4:32:40 GMT
Hi Leo,
Replaced the primary power supply cap on the board from 270 uF OSCON to 470uF SILMIC ARS yesterday. Before the SQ was hyper detailed, after richer and fleshed out with instruments and vocals much more natural. So nice I was worried to play around more but decided to ditch the output caps this morning. Wow .....what can I say, another huge improvement in resolution.
Downside is a small pop when changing between steps on the pot, as predicted. Can you suggest a resistor value to stick across each RCA to stop this? Measured DC from the opamp is -0.75 V.
Cheers, Jeff
PS. I might leave trying the resistor mod until the LM4562s arrive or you find value in it?
|
|
leo
Been here a while!
Team wtf is it?
Posts: 3,638
|
Post by leo on Jun 1, 2008 11:37:48 GMT
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jun 1, 2008 12:05:18 GMT
Steffen Without that 1K series resistor at the output, and the capacitors shorted out, you would have 23mA DC through 32 ohm headphones. Definitely not recommended ! I will butt out now, and leave the rest to Leo. Alex
|
|
leo
Been here a while!
Team wtf is it?
Posts: 3,638
|
Post by leo on Jun 1, 2008 14:25:21 GMT
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jun 1, 2008 21:17:39 GMT
OOPS! I forgot the in between section. Still not good for the next stage if going directly into a pot. (I am miles away due to a Real Estate agent's 6 monthly inspection tomorrow !)
|
|
leo
Been here a while!
Team wtf is it?
Posts: 3,638
|
Post by leo on Jun 1, 2008 21:32:40 GMT
OOPS! I forgot the in between section. Still not good for the next stage if going directly into a pot. (I am miles away due to a Real Estate agent's 6 monthly inspection tomorrow !) We all get it at times mate Good luck tomorrow BTW!
|
|
|
Post by puffin on Jun 7, 2008 15:55:26 GMT
I got my Dac up and running today. I have to say that to my ears it don't sound too terrible "straight out of the box".
I want to do the mods I have seen in this thread.
Leo at post 75 gave details of the basic mods to make the thing better (before swapping caps in and out). What I want to know is how much better those mods make it. I have also seen the details of the different caps used in the "Lampucera" thread. I have some Oscons I could use. what have others used and to what effect ?
It was also recommended that a suitable coupling cap be used on the analogue out. What value would be used here. Would it be in line with each signakl out ?
|
|
|
Post by puffin on Jun 8, 2008 8:46:34 GMT
I would also add that I find the bass to be really good. What I don't want to do is remove the basic sonic signature with the mods.
|
|
leo
Been here a while!
Team wtf is it?
Posts: 3,638
|
Post by leo on Jun 8, 2008 10:20:14 GMT
I would also add that I find the bass to be really good. What I don't want to do is remove the basic sonic signature with the mods. A lot of that your hearing at the moment is coloration , theres a lot of crud stuffed in the circuit after the dac chip. If you bypass the pairs of SMD electrolytics on the dacs differential output and link out that chip on the bottom of the board it removes a lot of the coloration, you then can replace the final signal line out electrolytic coupling caps to say a pair of films, this removes more of that coloration. Then theres the op-amp, I don't often recommend any particular type of part to use as this is a personal taste thing, as long as its stable any can be tried I cannot guarantee you'd like the dac better after the simple mods, I just post my own findings incase anybody fancies a play obviously theres much more to be done to get the best out of this thing but not everybody wants to be spending the time and expense on it These things are cheap so I now have two, one for heavy modding and the other with just the few simple tweaks, it then gives me a reference
|
|
|
Post by puffin on Jun 8, 2008 10:39:46 GMT
leo. Thanks for that. Any views on the difference between the lightly modded and the heavily modded versions?
I wonder if you could let me know the cap and resistor values you say should be added to the ananlogue outs. I assume the caps would be in series and the resistors to ground ?
|
|
leo
Been here a while!
Team wtf is it?
Posts: 3,638
|
Post by leo on Jun 8, 2008 12:06:00 GMT
IMO the heavily modded one is a fair bit better but it comes at a price, the work involved is far greater, all those SMD resistors and ceramic caps have to be changed in values and an extra resistor added on one of the differential outs to better load the dac, also due to the type of regulated PSU's I use (I don't use the standard supplied PSU) most of the onboard supply decoupling caps values are lowered to better suit the type of regulation I use
For the simple mods the coupling cap on the output does not need to be too big, I used 10uf films mainly because I had a pair spare, something like 4.7uf upwards should be ok The resistor I fitted just goes to the output socket (not ground), the value depends on the op-amp used, I used 22R with the AD826, it was a value I had knocking about so fitted those, some op-amps may be better with a higher value
|
|
|
Post by puffin on Jun 8, 2008 13:12:46 GMT
Thanks leo. The info is very helpful. I have now started the basic mods !
|
|
leo
Been here a while!
Team wtf is it?
Posts: 3,638
|
Post by leo on Jun 8, 2008 14:11:27 GMT
Let us know how you get on and just shout if you run into problems Beauty is you can easily put the thing back to stock if you don't like the results, try not to over heat the SMD lytics just incase you want to refit them
|
|
|
Post by puffin on Jun 8, 2008 18:03:29 GMT
leo. I carried out the basic mods and by passed the stock phono connections. I changed the op-amp for an AD712 I had knocking about and as I only had a couple of Wima's I have so far only by-passed C9 & C10. Not sounding too bad. Smoother, so I suspect the grain you mentioned has gone.
Next stage to install some Os-cons.
SMD's Mmmm, pain in th a... I had my fill of those when modding Sonic Impact and other Class Damps.
|
|
|
Post by jeffc on Jun 10, 2008 6:01:19 GMT
puffin,
I went all Oscon in the digital section and it made a nice improvement. However, I did all caps at once so I don't know which were most worthwhile. As mentioned previously, replacing an Oscon I had before the regulator for a larger value Silmic ARS I had at hand also made a nice improvement, warmer and more welcoming sound. Tried ultra-low ESR electrolytics supplying the opamp but thought they lost something compared to the SMD ones. I noted Leo using tantalums there so tried 47uf 16V ones and they seem to work well, as I expected. Thanks Leo for the picture. Also replaced the LM833 I was enjoying with a LM4562. After a few days breaking in it has settled to produce exquisite detail and dynamics, yet warm and natural as well.
Leo, Haven't got to trying the resistor mod yet but will when I get a chance, busy building the HA kit and enjoying just listening to the DAC, at one vol setting. Now that canjunkie is in business making the JLH PSRR PCBs, would you consider it worthwhile using one to supply the LM4562? Currently I'm using the simple PSU board that came with the DAC, as is.
cheers... Jeff
|
|
|
Post by puffin on Jun 11, 2008 18:54:51 GMT
I have fitted a smattering of Oscons at the moment and will see how that goes.
leo can you send me a photo or a diagram of how you have connected the output caps and resistors.
Thanks.
|
|
leo
Been here a while!
Team wtf is it?
Posts: 3,638
|
Post by leo on Jun 12, 2008 16:32:35 GMT
For the lightly modded dac I use this circuit, I mainly fitted tants for the decoupling supply pins mainly for stability for the AD826. Resistors value on the output isn't that critical depending on the op-amp used Certainly give the JLH a go, it works well with the Elcheapo's output stage supply
|
|
leo
Been here a while!
Team wtf is it?
Posts: 3,638
|
Post by leo on Jun 12, 2008 16:33:43 GMT
This is whats currently being used with the other tweaked one, also fed from a JLH
|
|
jonclancy
Been here a while!
Mr. Ripple Eater
Amateur EAGLEist
Posts: 1,131
|
Post by jonclancy on Jun 14, 2008 17:37:48 GMT
Hi Leo,
I was just looking at the 4397 Datasheet and saw that the VA draw was nominally only 20mA. Assuming VD is the same, then a pair of Fleas (one with the dual diode mod for 3V3) could do the job. The 8416 only requires under 5mA for its 3V3 supplies.
What do you reckon???
Cheers
Jon
|
|