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In Reply to: Old DACs vs. new ones? posted by J Corner on May 4, 2005 at 03:54:56:
They have converted me from being a vinyl addict & digital luddite into a digital only fan - disposed of most of the vinyl hardware & software some months ago.But it has been a long, hard and expensive road. However the good news is it is getting better and less expensive :-)
My original foray into digital via a Rotel 865BX left me unimpressed. Theta Data III/Theta DSPIIIa was improved but still not great. The breakthrough came via the expensive Meridian 800 series and that fitted nicely into my multi channel system.
Since then I've become a fan of modification of players and this has reaped significant improvement.
I tried an Audio Note DAC and was ultimately disappointed with its performance, mainly because of a mismatch with SS gear. It is designed for tube AN gear. Late last year the Aussie dealer kindly offered me a later version to trial but it has never materialised so I've given up on email enquiries. IMO, AN is a problematic product. For sure trial one as it has an excellent reputation, but be prepared for the lack of synergy I encountered.
The Benchmark DAC1 is not perfect by any means, but is the best value around at the moment. At the moment I'm listening to some music in the office here using a DAC1 and the reproduction is clean and most musical. Some of this is also attributable to the modifications done on the Denon 3000 CDP and the Plinius 8100 amp so one should not get carried away and expect Nirvana from any one item. It is a SYSTEM which is only as good as its weakest link so it is futile spending heaps on any one component and expecting a miraculous conversion.
That said, it is worth investing in a good DAC if the rest of the system is compatable. Those CDs are not nearly as bad recording wise as I used to think. Sure there are bad examples released as happens in any format, vinyl included, but generally the CDs here are good to excellent with a few absolutely stunning.
Now, as a confirmed nutter and fan of modification of digital gear I've taken the step a stage further and have had a Benchmark DAC1 modified by Steve Nugent of Empirical Audio. It is still in the US and I will not receive it for some weeks yet, but Steve reports dramatic results among the best, if not the best, he had heard from any DAC (including the much praised Dodson which I have not had the pleasure of hearing). The only mod I've baulked at is the installation of a Superclock III but at around $USD2,500 for the basic DAC1 & mods it could be one of the most cost effective ways to go.
For now I've got to be patient waiting to trial it out here and will give you a report, but you will have to wait until July as my daughter will not be bringing it back with her until late June :-(
Follow Ups:
Are you getting the DAC1 opamps changed also by Empirical?I know Steve mentioned his modded DAC1 w/ opamp change may be his best, but Dodson 218...
If the asynchronous conversion to 110 kHz can somehow be defeated, and replaced with classic oversampling conversion (like the time-resolute Burr Brown DF1704 in "slow rolloff" mode), I think this DAC would be killer...
more to the point, how do you plan to interface the 8Fs output of the DF1704 with 4Fs input of the AD1853?
The AD1853 includes a digital filter with 8x oversampling so you wouldn't use it if you wanted to change the digital filters, but it isn't designed for a specific input rate like 4Fs. It's compatible with sample rates from 32K to 192K. The DAC1 precedes it with an upsampling digital filter set to 110 KHz which is a little below 3 Fs. But you're right in that the changes required would be too extensive and he'd be better starting with a design that was closer to his own philosophy.
Unlike some of its rivals the 8Fs filter in the AD1853 cannot be bypassed but thats a moot issue. The point is at 44K1, the output of the DF1704 is 352K8 or 8Fs. The max input sample rate of the AD1853 is 192Khz approximately 4Fs, assuming Fs is 44K1. Interfacing the two would require a decimating digital filter if done correctly or the discarding of every other sample if not.
I'm not sure why you talk about interfacing the two digital filters since if one was to use a DF1704 they would discard the AD1853 and use separate DACs. Probably go with PCM DACs instead of hybrids. Sure, Todd's not really a technical guy and probably didn't fully appreciate what would be involved when he tossed out that idea, but no one would try to interface the DF1704 to the AD1853. The data format isn't even compatible and the whole idea in the first place was to get rid of some of the digital filtering by removing the upsampler, not increase it. Of course, you could replace the AD1853 with the somewhat comparable TI PCM1792 which does have the slow rolloff feature he was after and maintains a similar topology to the 1853. Then he would just have to pull the oscillator and the ASRC. But like I said, might as well start with something closer to that goal :)
The issue was about modifying the Benchmark DAC1 not designing from scratch. At some point it ceases to be a DAC1 and I think it is pretty safe to say removing the AD1853 takes one beyond that point.
I'm sure Steve's turbomod DAC1 sounds great, having heard his turbomod P3A. But it's always tough to pull out that kind of $ for Any mods.Why don't you set up shop and offer the DF1704 mods for DAC1 for "reasonable" price? I seriously don't know what the heck Benchmark is doing with this 110kHz stuff. I'd much rather see 88.2kHz or 176.4kHz, or maybe even NO upsampling at all.. Heck, if you can offer it, I might even buy a DAC1.
All the mods as shown below have been implemented.I'm reconsidering about the Audiocm Clock III and might have it installed also.
Here is what Steve emailed me about the pros & cons of the DAC1:
As for the Superclock, this is definitely a good idea. The asynchronous upsampler reclocks the data with this clock and it is currently a $2 can-oscillator. Not good jitter specs compared to a Superclock.
The design of the DAC-1 has several good things about it and some bad ones. First the good things:
1) power supply is decent - transformer
2) Capacitor locations are reasonable
3) Current flow in the board for both power and signal is not bad due to the unbroken ground-plane
4) Chip selection for upsampler and DAC are good
5) high-quality board
Bad things:
1) layout is not optimum - some long traces
2) regulators locations are not optimum
3) too many op-amps - increases noise.
4) Input pulse transformer is grounded - can cause hum
5) uses dual op-amps - not as good as singlesAnd about the mods outlined below -
"Your unit is breaking-in nicely. I have been using it a lot since it is now my best-sounding DAC. BTW- a review from Mad Dog will be posted soon on Positive-feedback.com of my reference P-3A DAC. It will say basically that only the Dodson 218 beats it. I believe its possible that the modded Benchmark may actually beat the 218....."
WHAT HAS BEEN DONE:
Benchmark DAC-1 Turbomod
The Benchmark DAC-1 is an attractive DAC for several reasons: It has balanced outputs, two active volume controls, a headphone amp, and it sounds great right out of the box. This Turbomod improves several areas. It is AC-coupled to eliminate DC-offset, so we make it DC-coupled and tune-out the DC offset.
Most of the other changes improve power delivery and power supply. The op-amps deliver the best HF extension and clarity that we have ever heard in a DAC, so we know why the designer selected these. However, the same op-amps have difficulty achieving the "weight" of the performance. Our power delivery changes make a significant improvement in this area, but we offer an upgraded op-amp as an option. The input pulse transformer is a decent one, but it is grounded, which can cause low-level hum in some systems. We also offer an upgraded transformer, ungrounded, as an option. We recommend using the "calibrated" volume controls if possible. If you must use the volume knob on the front panel, we can mod the op-amps and capacitors associated with this for an additional charge.A Benchmark DAC-1 with Turbomod and Op-amp replacement actually outperforms our reference, the P-3A, when in balanced mode. The most clear and holographic soundstage we have ever heard from a DAC.
Turbomod details:
Two bridge rectifiers replaced with HEXFRED's
Replace regulated voltage filter caps
Improve power delivery to DAC and upsampler chips
Improve power delivery to 10 op-amps - Black Gates and HF caps
Upgrade DAC filtering
Replace all voltage regulators.
Eliminate AC-coupling and tune-out DC offset
Improve digital input coupling
Pricing:
Turbomod - $1050Option 1: Dual op-amp replacement - $300
Option 2: Pulse Transformer upgrade - $150
John
Interesting times
When John Atkinson of Stereophile tested this DAC, he registered 128 picoseconds using a toslink, which should have been a worst-case scenario. My recollection is that is one of the lowest, if not the lowest level that Atkinson has measured.So, it would be interesting if someone tested this unit with the Superclock in it and found out whether these guys' claims that the stock BM has "not good jitter specs compared to the Superclock" have any substance to them.
I can certainly accept the idea that the $1000 might make it "sound better" but, when they're talking numbers, I'd like to see the proof.
Test results are fine... but consider the following as an example:Compare the Lavry DAC also tested and measured by Stereophile, to
the Benchmark. The Lavry costs from memory almost 10 x the
Benchmark, it is used by mastering studio owners world wide and the
general concensus is that it sounds better than the Benchmark... by
a solid margin. I haven't heard one person say otherwise.Well the Benchamrk measures as good as the Lavry, in some ways
better.It is frustrating and measurements are very important but they just
don't tell the whole story.Cheers,
Terry
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Be-Bop and Mahler
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