DAC60 vs. Benchmark vs. PS Audio Link III

markC · « **Reply #180 on:** 1 Jun 2008, 05:49 pm »

Anyone that has pulled the filter components, and the inductors were .39mH, I'd be most greatfull if you would sell a pair to me. I have a new idea.

capo · « **Reply #181 on:** 1 Jun 2008, 06:25 pm »

Mark,

It looks like Mouser has some. Search on 390 uH inductors. I don't know much about applicability of wee little inductors but here is the list:

http://www.mouser.com/Search/Refine.aspx?FS=TRUE&Ntt=*390*+*uH*+*inductor*&Ne=688458+688737&N=1525871+1323043+4294626973+4294741869+4294741289+1323038&Ntx=mode%2bmatchall&Ns=P_SField&OriginalKeyword=390+uH+inductor&Ntk=Mouser_Wildcards

markC · « **Reply #182 on:** 2 Jun 2008, 12:14 am »

Thanks, Capo, I'll check it out. Seems like I can eliminate another pole in the filter and get even better FR results. Worth a try I think, while I'm in there changing the I/V resistor.

capo · « **Reply #183 on:** 2 Jun 2008, 05:14 am »

Mark,

There is also Digikey and Newark to check out if Mouser doesn't have what you are looking for.

Please keep us posted on your filter exploits!

Bill

regal · « **Reply #184 on:** 2 Jun 2008, 12:58 pm »

Quote from: capo on 1 Jun 2008, 05:04 pm

Regal,

Thanks for the schematics. They are interesting.

Regarding the B+ power supply, I think it still has some problems, even with the choke.

With the schematic I posted the CCS will improve PSRR, we could even casode and get an even better improvement. Should take the PS out of the equation.

regal · « **Reply #185 on:** 7 Jun 2008, 12:37 pm »

Any updates on the Aikido? I'm about to convert the SRPP to Broskies compound amp and am a little nervous to do all this surgery if its not worthwhile.

regal · « **Reply #186 on:** 10 Jun 2008, 07:10 am »

I scraped the compound amp idea, to much surgery.

I did replace the cathode by-pass cap+resistor with a yellow LED (Digikey 511-1229-ND) and added a 300 ohm grid stopper in front of the bottom tube. Treble is much better.

markC · « **Reply #187 on:** 11 Jun 2008, 02:37 am »

I just ordered new value inductors. I can't seem to find similar cylindrical, radial lead ones though. I'm a little concerned that the axial "resistor look" ones are not of the same quality as the originals. They look similar to the ones used as power supply filters; such as the ones before the Dac chips. I was able to find shielded ones though.
Next step is to replace the experimental parallel resistor set up with a single Vishay Dale 127 ohm r and remove one 220 uH inductor. The lost inductor will be replaced with silver wire and the remaining one will be changed to 470uH.
Looks good in simulation, but only my ears will provide the conclusion.

capo · « **Reply #188 on:** 11 Jun 2008, 04:41 am »

Regal,

Smart move not to try to cram an Aikido in the Lite chassis. The LED sounds like an interesting idea. Where do you stand on the post DAC analog filter now -- are you using the original or have you made any mods?

Regarding tube dissipation, perhaps you have seen the following Allen Wright post. I'll post links in case you haven't. He likes the 6922, etc. tubes but says they need to be run fairly hard. Broskie recommends 10mA for 6DJ8, etc. in the Aikido. He also thinks grid stoppers are important, and you've got one of those now. See:

http://db.audioasylum.com/cgi/m.mpl?forum=tubediy&n=135459&highlight=6dj8+ma&r=&session=

I just posted to my DiyAudio thread with a few pictures. I was able to get the Aikido working tonight. Currently it is running with the Twisted Pear Buffalo, not with the Lite DAC yet. I just moved it over to my listening/living room and am going to break it in for a few days.

*****

Mark,

Thanks for the filter update. I wonder where the radial filters in the Lite DAC come from?

Could you tell us what your filter looks like, in terms of which kind of passive components and values. Is it just a parallel cap and series inductor now?

regal · « **Reply #189 on:** 12 Jun 2008, 04:10 pm »

Quote from: markC on 11 Jun 2008, 02:37 am

I just ordered new value inductors. I can't seem to find similar cylindrical, radial lead ones though. I'm a little concerned that the axial "resistor look" ones are not of the same quality as the originals.

I actually found some large air-core shielded inductors at Digikey. They were expensive but have a thick shield. Haven't hooked them up yet.

markC · « **Reply #190 on:** 13 Jun 2008, 02:53 am »

Capo:
A seriers inductor 470 uH and a parallel cap .47uf. This is the simullation that looks good, but not yet implemented.
The cap is in place, but currently listening to the two 220 uH coils along with paralleled resistors to give me a 133.5 r value on the I/V. The parts arrived today.

Regal:
Care to share the part #?

regal · « **Reply #191 on:** 13 Jun 2008, 06:01 am »

Digikey 257-1109-ND, its big and needs to be offboard. Haven't tried it yet.

capo · « **Reply #192 on:** 19 Jun 2008, 09:22 pm »

I tried the DAC with the Aikido (6n23p-ev, 5687, 200v)/LCLCLC psu/tube rectification, without the post-dac analog filter.

No glare. So that experiment makes it more likely the glare is coming from the SRPP stage and/or B+ CLC->regulator power supply.

At this point I'm inclined to follow Mark and make a less aggressive filter with high quality parts. And also maybe follow Regal with a slightly modified SRPP stage.

regal · « **Reply #193 on:** 20 Jun 2008, 12:37 pm »

One thing I found about SRPP stages. The load with the lowest distortion is given by this equation:

Rload= 1/2(Rk-1/gm)u

For my amp this worked out to where I should add a 5k resistor across the +- output.

This lowered THD by 40%.

markC · « **Reply #194 on:** 21 Jun 2008, 03:14 am »

I still haven't replaced the filter circuit components, (too busy with summer, yard work etc.) I do remember, however a vast improvment of the glare going away after reducing the value of the I/V resistor, (thanks Regal). I will get to it soon and share the results. Glad to see others still at it.

markC · « **Reply #195 on:** 28 Jun 2008, 02:41 pm »

I've got about 25 hrs. on the latest filter mod now and I think I'm done messin' with this DAC. The results, to my ears, are very positive. Smooth presentation with nothing over-emphasized. Highs have a nice sparkle to them and no glare. In the near future I'll take it to my friend's place and compare it with his DAC. That will give me more perspective, but I'm quite confident that the little DAC-60 will hold it's own.

regal · « **Reply #196 on:** 24 Jul 2008, 12:38 pm »

I wanted to post my final mod that has left me not wanting to change anything else. First I tried the Grounded-Cathode / Cathode follower mod. Very clear and detailed and measured better than most any SS DAC. However it sounded too much like SS. So on a whim after putting the SRPP back I decided to hook the output cap to the plate of the bottom tube (instead of the cathode of the top tube.)

This increases the output impedance to 3.5 kOhms, high - but fine for amps with 50 kOhm or higher input impedance.

This mod makes the DAC-60 have the same configuration as the first stage of the Aikido. It is single ended not push pull (like the SRPP.) The sound is very natural and full of life. I used 200 ohms for the cathode/plate resistors.

markC · « **Reply #197 on:** 24 Jul 2008, 09:37 pm »

Did this flesh out any more life in the top end? If only I could get a bit more of the steel sound and feel of a plucked sting and more realistic brush on brass cymbol, I'd be a happy guy.

regal · « **Reply #198 on:** 24 Jul 2008, 10:00 pm »

Yes the top end has a closeness/life, better spacial separation.

Mituk · « **Reply #199 on:** 23 Nov 2008, 04:50 pm »

Hey, I have a DAC-60 which ain't working anymore so I need the electronic circuit schematic for it. Ive seen the schematic in this forum but the picture is so small that its unreadable. I'd appreciate a larger, readable picture.