It would appear that commercial ground isolators use audio frequency transformers that are either driven directly from the instrument or via a buffer amplifier. Either way these retail for about USD $150.
Is there any reason not to use an linear optical isolator such as the IL300 as outlined in the following link
Audio-Optical Isolation Amp | audioXpress
I'm not aware of any commercial products that use this approach.
If that isn't suitable what about a ADC running to a digital opto isolator and then back through a DAC, or a voltage to frequency to digital opto isolator then frequency to voltage converter back to analogue. Surely you should be able to build something for less than $150.
Is there any reason not to use an linear optical isolator such as the IL300 as outlined in the following link
Audio-Optical Isolation Amp | audioXpress
I'm not aware of any commercial products that use this approach.
If that isn't suitable what about a ADC running to a digital opto isolator and then back through a DAC, or a voltage to frequency to digital opto isolator then frequency to voltage converter back to analogue. Surely you should be able to build something for less than $150.
No need to pay $150 for an audio transformer - these are about $9 each : 2PCS / 10K:10K Z11 xigangpian audio isolation transformer balanced and unbalanced audio conversion isolator-in Transformers from Home Improvement on Aliexpress.com | Alibaba Group
But are they any good? The seller says they sound good, but I don't see any distortion specs or any other technical information other than the frequency response.
Humbucker pickup going into a Boss Gt-1 effects pedal powered by an isolated power supply. The GT-1 is connected to a mains powered computer via USB and the analogue output goes to a mains powered amp
USB isn't isolated so there's a ground loop. Disconnecting the USB or plugging the amp into an isolation transformer makes the hum disappear.
USB isolators (the 480 Mbit/s high speed type) are even more expensive than audio isolators.
The requirement is "not to sound terrible".
If a supplier says that their low cost transformers are just like the expensive Jensen transformers, but omits specs then you would have to be sceptical.
Line Input | Jensen Transformers
Last edited:
I referenced the IL300 which is designed as a linear opto isolator.
https://www.vishay.com/docs/83708/appn50.pdf
The $7 transformers sold for car-audio are often ample for buffered audio lines (not right from guitar). While they may cost $25 now, it IS worth owning one/several.
That *linear* opto is an old-old idea of mine. Performed poorly with 1980 devices and limited insight, though the potential was excellent. I'm glad to see it has been taken-up by a Big Dog. I doubt they can recover the development cost or keep it in production.
That *linear* opto is an old-old idea of mine. Performed poorly with 1980 devices and limited insight, though the potential was excellent. I'm glad to see it has been taken-up by a Big Dog. I doubt they can recover the development cost or keep it in production.
Tell that to the owners of Neve mixing consoles, or the millions of listeners who love the sound of songs recorded on those consoles, which are FULL of transformers.
You won't be too likely to find out whether something sounds terrible just from THD figures as sine wave test tones are quite unlike music. I'm also skeptical that they'd be just like Jensen transformers but I do know from experience that very cheap transformers (ones I've wound myself) can sound perfectly decent.
If you want to spend more then get the transformers which have a higher nickel content - it gives better measurements. I have a couple on my desk at present and have made a rudimentary measurement of the LF distortion threshold so I know they're pukka.
2PCS / 10K:10K permalloy audio isolation transformer, balanced and unbalanced conversion audio isolator-in Transformers from Home Improvement on Aliexpress.com | Alibaba Group
I use a wall wart with my mp3 player and the noise is terrible.
I had to earth the zero volt line to get it hum free.
Sorry, you seem to be getting beat up a little here. It might help to tell us what the big picture is. Are you in need of an isolated DI box to go into a mixer for a live performance? Are you just a hobbyist who likes the idea of building a DI for much cheaper than buying one? Are you trying to fight a ground loop you are experiencing right now?
I don't think that optoisolator is the way to go. It's more of a design project than just building a circuit at this point. You can fight a ground loop by just isolating individual connectors in your chain. Or another option, I think if you buffer those cheap transformers, you will be more than satisfied with performance.
I don't think that optoisolator is the way to go. It's more of a design project than just building a circuit at this point. You can fight a ground loop by just isolating individual connectors in your chain. Or another option, I think if you buffer those cheap transformers, you will be more than satisfied with performance.
Hello PRR. Most interesting to learn about your involvement in "opto" linear circuits. Thanks mjbmikeb2 for the Vishay link to its application note50.
The "unipolar" IL300 circuits by Vishay have potential applications in diy Class aP amplifiers [Passlabs Forum]; because they also operate using "unipolar" analog pulses. I'll meditate on and experiment with IL300 devices.
Best
Anton
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.