martijn86
Active Member
…only use this device if you have to and performance is not critical.
It's a weird day when someone holds you at gunpoint and forces you to use a sh#tty DAC but if that day ever comes, I'll remember your advice.
…only use this device if you have to and performance is not critical.
kopczas, did you see Audio Precision trafo-feedback patent? They still use that as an output for their analog generator.
Not all transformers are created equal and good transformers cost real money. This is a US$50 item.
Consider all balanced gear from the distant past used 600 ohm transformers. I have CD players and DACs with transformers for the balanced outputs and the performance is very close to the RCA line outs.
Similarly, if you have all your gear thrown in the back of your station wagon, driving to the gig in order to set up your Peavey Audio Performer Pack (on sale now for $500!) , you might wish that you could bring your better equipped home studio with you, but this will do the job.
Yeah, FWIW: the analogue input of my K&H O300D uses an audio transformer. Can't blame bad sound yet. No hum and hiss.Hardly, sunshine. Transformers in this reviewed product are there for one very valid reason, just as the lack of similar devices in the Carver implementation were implemented for another, perfectly valid, but equally misguided reason.
Just because silicon derived line drivers have become reasonably silent and offer great on-paper specs, doesn't mean that in certain situations, an isolated, transformer driven solution, cannot provide a better overall performance.
As they say, there are many ways to skin a cat.
One thing that could have improved this design would have been a buffer between the transformer and DAC. The DAC can only source quite low current. Adding a driver with a good low impedance output can significantly improve the low frequency performance of a transformer, and might pull 10dB of distortion out of it. I really expected to see some such driver. Disappointed it isn't there. I guess the feeble output swing was a clue.
The 2705 is a vernerable part. Treated nicely it was a competent DAC. Nothing compared to modern devices, but TI were rightfully proud of it when it first came out. However that was nearly 2 decades ago. It is now listed as not recommended for new designs. One suspects this Peavey DAC has been around for a while. Which might not be a surprise.
BOM is going to be roughly $5 for the DAC and $5 each for the transformers in quantity. Add a nice case, connectors and PCB. Really this is a fair price. Upgrading it significantly would well over double the price. More like quadruple. The next step up in transformers gets you to $20 parts, better DAC, proper power management, driver stage. Think well north of $200. Good transformers start at $100 each.
Galvanic isolation, affordable, audio quality: pick any two.
More teardowns, quick and dirty!!This is a teardown of the recently reviewed Peavey USB-P transformer coupled DAC. The internals are simple enough:
View attachment 96713
Data and power are provided via the USB bus. The core of the system is a on-chip USB DAC, the TI/BurBrown PCM2705. This is a low performance DAC designed for quick implementations. Here are the TI measurements for it:
View attachment 96714
I have converted the THD+N percentages to SINAD (in red). As you see, there are two implementations: one with USB power with worse results (left) and the other with stand-alone power supply (right). Neither is much to write home about. Ours is the one on the left which best case has a SINAD of 78 dB. In the review I got around 74 dB. The reduction is due to use of transformers on the output to provide isolated/balanced output (the main reason for this device's existence).
Transformers can generate a lot of distortions especially in lower frequencies. Let's go ahead and measure that using USB-P:
View attachment 96715
At 20 Hz and full digital level input, distortion shoots up to nearly 2% for a SINAD of around 35 dB! Most of our measurements are at 1 kHz which gives these a ton of benefit of doubt.
Lowering the output signal level improves transformer distortion but then signal to noise ratio worsens so there is not a lot of gain to be had as you see in the green and blue lines above.
I suspect this level of distortion is very much audible. So only use this device if you have to and performance is not critical.
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As always, questions, comments, recommendations, etc. are welcome.
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There is no provisions in this DAC to make it shockproof more than any other DAC. Yes, if you have a display and volume control on a DAC, you have more exposure but there are balanced DACs without it. An example is Grace Design Balanced DAC: https://www.audiosciencereview.com/...asurements-of-grace-design-balanced-dac.8201/Dump this one and the top dozen SINAD leaders into a gig bag without any packing, throw the bag into your trunk, drive 30 miles and then measure the SINAD of each.
There is no provisions in this DAC to make it shockproof more than any other DAC. Yes, if you have a display and volume control on a DAC, you have more exposure but there are balanced DACs without it. An example is Grace Design Balanced DAC: https://www.audiosciencereview.com/...asurements-of-grace-design-balanced-dac.8201/
Price wasn't your point. As to the second part, you just don't know. This is not a high-reliability product. You are just assuming so based on its simplicity but that is not data. It is assumption. Here are some negative reviews from Amazon:At 3 times the price (and not through a retail chain with those margins added). That front knob is not going to survive gig bag excursions.
This is a PCB in a "bog standard" hobbyist case. There is absolutely nothing special about its build to make it more reliable than it would be otherwise. You don't know if that DAC chip is designed to last longer and tolerate heat build-up and shock more than any other. It is not like it has rubber shock absorbers and such like a meter would:One thing Peavey knows a lot better than building low-noise electronics (which they have not had to do in their application domain) is ruggedness to survive "field use". That is their business not high SINAD.
As to the second part, you just don't know. This is not a high-reliability product.
A Fluke meter has much rougher life than this device will ever have but keeps ticking because it is designed to be rugged. The Peavey is not so.
You are saying things I didn't claim. Ruggedness and reliability aren't the same thing. Without ruggedness, this would be useless for its intended purpose. Reliability would be commensurate with the price. Not sure why you are conflating the two.
I am going by experience with Peavey products.
Look at any electronics device reviews on Amazon especially at this price level and you will see positive and negative reviews, so I am not sure what point you are trying to prove by cherry-picking.
If I can cherry-pick also
View attachment 96795
Silliness is trying to be a salesman for Peavey. I don't understand your motivation to do any and all things to promote this product. The device was properly evaluated and its features and advantages stated clearly. Going above and beyond puts you on a plank going into the drink on a boat. Don't do that.This is getting silly. How much does the Fluke meter cost?
Silliness is trying to be a salesman for Peavey. I don't understand your motivation to do any and all things to promote this product.
Does that sound like a salesman for Peavey?I am not sure this should even be reviewed here.
For those not familiar with Peavey, they are a low-mid end music instrument, amps and stage pro-audio equipment much below Marshall and Fender and I don't think they have ever built a low distortion product.
A lot of tweener budding guitarists start with a Peavey amp especially if into metal thrashing. They are cheap, loud and provide the needed distortion.
Does that sound like what a Peavey salesman would say?Low distortion products are not what anybody designs to build in that business. Peavey is at low-mid end of that business.
I get it, you have an issue with Peavey for some reason, but you've really added no "context" as you like to put it. More like a bias and expectations not comensurate with price, utility, and the device actually in question.
I started my music playing many decades ago with Peavey which is all I could afford at the time and have fond memories. But I am not going to romanticize what it is not. It has its place and utility.
Transformer are apparently An Equal Opportunity Destroyer when it comes to DAC performance, whether it's this relatively cheap Peavey or an absurdly overpriced "high-end" unit from PS Audio.