Vintage DACs

Cool, did you catch I socketed the resistor/cap pll filter and put in a teflon cap on my Adcom? =>

SBAF DAC Talk II

Spoiler

Spoiler: 24/96

SM5813 / DF1700 adapter board with DF1704

1 pieces CS8414CS SOIC28 to DIP28 replace CS8412-CP

Considering these to do a 24/96 upgrade... but only on a sacrificial GDA-600... not this one until verified it works! I'm a bit tight on time lately, might not happen for a while.

@caute If in the mood you're welcome to borrow this DAC anytime! Maybe do the 24/96 on your stock GDA ;D

 

What values are you using here? And where dinld you source the Teflon capacitor?

 

Weellll... needs a bit of work!

Plan was to start here: Teflon cap (orig 0.047uF => 0.0068uF) Resistor (orig 1K => 120ohm)

Digikey, but need to research a different cap, it's a high-voltage version and 10%?- missed those little specs on the digikey page and ordered too quickly, it looked good haha. Also have to order fresh 120ohm resistors, the antique I tried did not work.

Anyway, really wanted to get those socket-ed so I could close the thing up, didn't want to take it all apart again... then get good parts when ready to experiment.


Bit of fun comparing to the psaudio w/Crystek. ***SBAF DAC Talk II Lyr+ as pre! Yggdrasil dismantled for A2 reinstall after LIM (in since released).

 

I was at first interested in the PS Audio Digital Link III until I realized that: a) it upsamples everything to one locked frequency and b) all that wasted space in the box just to have a bigger chassis.



I do like the PCM1798. It’s just too bad not many more high end DAC’s don’t use that hybrid chip because it doesn’t spec well and it has just been around forever.

 

I was speaking about this mod :
https://www.audioasylum.com/cgi/t.mpl?f=tweaks&m=30297

I have used a 220nf mkt, 1000ohm resistor and a 3.3nf styroflex cap right on the pins and it makes for an audible improvement though probably not that big of a difference in overall scheme of things. Bigger gains can be had by optimizing the decoupling and bypass caps of opamps, dac chip, receiver chip etc.

 

Thanks. I will have to give that a try.

Although I thought Theta already did a bunch decoupling. There are blue MLC’s all over the place.

 

Sunvalley Model 2 D/A just arrived from Japan, Eitr is due to arrive today, so I'll have some listening impressions soon.
I took off the case and grabbed a couple pics. The tiny DAC chip is the BB PCM1718E(highlighted in pink rectangle), 6922/6DJ8/E88CC output tubes and a triplet of unlabeled chunky polyester looking output caps per channel. Current tubes are Sovtek 6922 and will be getting out of there soon.

 

excited for impressions! is eitr gonna be your main source?

yes, pls let us know how other 6922s fare in this DAC. had to look up PCM1718 lol, seems like a very underutilized IC.

 

Yep I'm just doing PC to Eitr for now, if it turns out to be a great DAC then I'll think about another pi2aes or other higher end streamer/DDC, I want Urd without cd player, but would probably stay in reality and go with a singxer su-6.

 

WARNING - shameless plug ahead:

Or a PI2AES-LITE since you won't need I2S or Balanced AES.

 

Just fired it up, chain was:

PC>USB>Eitr>coax>Sunvalley Model 2>Scott 222C>Altec 604E's

Initial thoughts are very positive, compared to Gungnir MB(A2 Unison) the most immediate difference is soundstage. It's bigger and more layered in every dimension to the extent that it seems larger than life. I was expecting better microdynamics because of the tube output stage, but the larger dynamic changes were what I first noticed, and a big surprise, didn't expect more dramatic volume swings/impact compared to Gungnir. Definite high frequency emphasis, but since it's a multibit chip that was on for 2-3 minutes before listening I'll reserve judgement.
I'm going to let it warm up overnight and do some more listening before posting more impressions, maybe give new toy syndrome time to abate.
I'll be unhappy if it does get better with warm up though, I don't think I'll appreciate the heat(except in the winter) or cost of leaving tubes running 24/7. I wish multibit DACs had a standby switch that kept the chip running but powered down everything else that's non-essential when you're not listening. Perhaps I can figure out a mod, or more likely, someone else can figure out a mod and I'll implement it. No schematic to be found after 30 minutes of googling however.

 

i would contact mfr and ask if it's meant to be kept on all the time... this is giving me nervous vibes--both the tube DACs i've owned were not meant to be kept on 24/7, and even if they had a standby switch, it usu doesn't turn the tube heaters off, and the DAC still isn't meant to be left on at all times.

edit: in fact, come to think of it--i don't know anyone w a tube DAC that keeps theirs powered on 24/7.

this is a *very* different DAC from your gungnir and the same rules don't apply to it, schiit uses medical/aerospace ICs that need to be powered on for sometimes a month+ to sound their best. I've heard some rumors that medical-grade multibit chips aren't even used until 3 weeks of continuous power is supplied to them, as in--in the actual medical industry.

also, to give you some context, my sfd-1 (tube output buffer only) sounded best after ab 30m-1hr, and my Abbas .11SE (almost all tubed, bb) sounds like perfection after 5-10 mins. Way different chips, way diff overall DACs, but both w vintage IC inside. These vtg R/2R chips do not need to "warm up" much at all...

 

Luckily it doesn't sound any different this morning. I won't worry about leaving it on all the time to get the best sound, and I'm happy to be able to finally turn my DAC off when I'm not using it. Thanks for the info!

 

The standby switch just switches on B+, but leaves the filament on. Not really sure if that truly helps prolong the life of the tubes though. It is there on many high powered amps just to prevent warm up noises. It does help prolong them for a bit if you turn on your amp with the amp in standby and let the tubes heat up first. Even the Freya +/N does this with timing relays.

The only way I can see things to keep the chip running is if you could turn it off, remove the tubes, then turn it back on. Then do the reverse when you want to listen. But this is one of the reasons I don't like tubes in multibit DAC's. You can't keep them on all the time with the tubes running all the time, lest you burn the tubes out.

For multibit DACs like Gungnir, one could rig a switch to the analog power transformer to be able to cut it on and off as needed while keeping the digital side up all the time. If feeding from one transformer, that gets more complicated - doable by cutting traces from the filter cap(s) to the regulators, but not something I would want fool with.

 

The datasheet for PCM1718 says delta-sigma though, not multibit.

Although if it does need warm up I can see how tubes would accelerate that process since they are a heat source themselves

 

I got confused because it said multibit delta-sigma, so I assumed that meant multibit, I don't know much about DACs

 

I was under the understanding that most of the TI chips are hybrid ones (excluding the MB ones). I could be wrong.

 

That’s a different kind of DS. The basic one is just one level like Class D and is converted to analog audio signal.

This image from Altmann sound should give you an okay idea of what it means



The basic thing is that it shouldn’t need 24 hour warmup like the Schiit DACs

 

I haven’t seen it for DACs but there’s high precision oscillators called OCXO which are encased with a temperature controlled unit

 

I've now had a couple "warmed up" listens to compare with non-warm up, there's no noticeable difference to me after about 15-30min of warm up, which could be totally unrelated to the dac chip, and just the tubes reaching steady state. A bit of HF emphasis remains, which works great with my desktop single driver speakers that lack top end extension, and can possibly be mitigated to some degree with tube/output cap rolling, but it'll be a couple weeks before I have different tubes to try. Now that I'm thinking about it, I could set up switchable output caps based on listening preference without much trouble. Worst case, the Altecs have HF attenuators on the back for adjusting to different rooms/listening positions, so I could just dial it back for digital listening and then to my usual level for vinyl. Even if nothing changes, I think I'm pleased enough with this unit to sell the Gungnir. Thanks for all the helpful replies.