Yes take loads of class to advertise a product under conditions that represent a 0% use case.
And your strategy of spreading fear, uncertainty, and doubt has its merits as well.
You can read the data sheets for the LME49724, LME49720/LM4562 as easily as I can. I fully expect that my measurements will confirm those in the LME49724 data sheet. I've included the data sheet figures below. Note that the figures show the THD+N and not the raw THD. The THD will be lower (no +N).
A 47-50 kΩ input impedance is very, very common in the audio world. Some go higher (upwards of 100 kΩ is not unheard of). Take the Focusrite Scarlett 18i20, for example. It has a 60 kΩ input impedance on its line inputs.
As you pointed to earlier the difference between 47 kΩ and 100 kΩ is academic, so clearly my data for 100 kΩ input impedance are in fact quite representative of Real World applications.
That's not to say that 100 kΩ is representative of all applications. For example, your Purifi amps have 2.2 kΩ input impedance. Given your rather aggressive posturing here (and elsewhere), I wonder if you have a competing product to sell and are, thus, trying to discredit my work due to its mention as a possible buffer candidate for the Purifi amps. Just wondering...
Tom
Attachments
Last edited:
One input, SE.
The volume control is a transformer attenuator (Sowter 9335).
One UB would be used (possibly in 6 dB gain configuration) before it.
Does it make to use sense a second UB post VC, considering the low-impedance output characteristic of the transformer and the current-gain? A genuine question...
The volume control is a transformer attenuator (Sowter 9335).
One UB would be used (possibly in 6 dB gain configuration) before it.
Does it make to use sense a second UB post VC, considering the low-impedance output characteristic of the transformer and the current-gain? A genuine question...
Requesting industry standard data for this board is considered trolling? Anyone who has a use case that requires driving 2v into a 100k load already has this ability from their source gear. Making this board redundant. And sorry I have no interest in making such a board, or buying one either. I only discovered it from the Purifi thread. Where people were discussing using it for an input buffer. And when I read the test conditions, it was clear they don’t accurately represent the performance they will achieve in this application. This is why standup, salt of the earth manufacturers provide 600R load data by default.
Seems like someone has a guilty conscience. It’s pretty bad when you’re a troll for politely requesting industry standard test data.
Seems like someone has a guilty conscience. It’s pretty bad when you’re a troll for politely requesting industry standard test data.
Thank you for your question.
As far as I can figure from the data from Sowter, the Sowter 9335 presents a 10 kΩ input impedance. So you could just drive the volume control directly from your source. I suggest adding the Universal Buffer to the output of the volume control. This will give you a low-impedance output and prevent the load (power amp) from affecting the frequency response of the transformer.
If you are concerned that your source may not be able to drive the transformer directly, I suggest this arrangement: Source -> Universal Buffer -> Sowter -> Universal Buffer.
Thanks,
Tom
"Industry Standard"??? 10V (rms?) into 600 Ohms _might_ be used in the professional world. Even there, 600 Ohm matched-impedance balanced lines are a vestige of the old analog telephone world. 10V (rms?) will drive most any power amplifier well beyond clipping. I'm not sure how that can be considered a useful spec. Also, 10Vrms is 14.14V pk (28.28V pk-pk) which pushes to or beyond the maximum swing for op-amp driven from +/-15V rails
Perhaps this spec is your own particular hobby-horse. If so, then ask once, politely. Unless you're willing to pay Tom money to provide your customized measurements, it's his business how he wants to respond to multiple requests for data, products, services, etc. Don't impugn his good name just because he doesn't drop all other activities to provide answers to your arbitrary request.
Perhaps this spec is your own particular hobby-horse. If so, then ask once, politely. Unless you're willing to pay Tom money to provide your customized measurements, it's his business how he wants to respond to multiple requests for data, products, services, etc. Don't impugn his good name just because he doesn't drop all other activities to provide answers to your arbitrary request.
It’s industry standard that this data is provided with such a product. Maybe not the impedance most will drive with it. But it’s a good indicator of performance under load. Which is why it’s standard in most opamp datasheets.
As a DIY enthusiast, I have no pony in this show, but your request was the opposite of polite. I’d say more like abrasive. Also, I’m not really concerned with vanishingly low distortion numbers, I think this universal buffer has a few very useful features that can help many situations for the Diy’er.
See Post #125.
600 Ω is not standard in "most opamp datasheets". 10 kΩ is standard. 2 kΩ and 600 Ω were added within the last decade or so as opamp designs were improved to provide low THD under heavy load. Many opamps are still specified only for 10 kΩ load.
Tom
600 Ω is not standard in "most opamp datasheets". 10 kΩ is standard. 2 kΩ and 600 Ω were added within the last decade or so as opamp designs were improved to provide low THD under heavy load. Many opamps are still specified only for 10 kΩ load.
Tom
Yes after I was accused of being a troll and competitor after politely requesting industry standard data my tone may have shifted slightly.
Thank you. I think it's a pretty useful circuit as well. I'll be using a few of them in my various test setups and quite possibly in a preamp as well.
Tom
I find post # 114 to be bang on the money. So have many others I’ve shared this thread with.
Here’s the thing Tom. You have been a very vocal crusader for IC opamps over the years. And you love to crap all over discrete designs. Yet when it comes time to show data that highlights the weak areas of IC’s, the data is always absent. Sure IC’s are getting better. But for many applications discrete opamps will run rings around them.
Oh he loves data that highlights the strong points of his designs. But when it comes to data that shows the weak points, it’s completely missing. But his target audience doesn’t know any better. So it works for him. Rarely does the data he shares represent real world use cases. It’s mostly just hype. The more zeros in the THD= automatically superior. Test conditions are irrelevant.