I am interested! I have a few ideas on the preamplifier. I will try to write them up but in a long while.
Cool. I was planning to build a FET based preamp shortly, and that could incorporate the codec in it, for experimenting. I will let you know when I get on it.
For some people who do not want to modify their guitars, the preamp-converter could be built as a standalone unit. There are some units commercially available($$) like that but I think it is very interesting to make DIY version.
OK. This is great.
Can you get some optocouplers too, please. I think, a good idea would be to disconnect the digital signals by optocouplers. Thus the PC power supply would not touch the ADC nor the preamplifier and cannot spread electromagnetic noise.
On the pre amplifier: the guitar humbuckers pickup coils, whatever they call them, differential or not, are just coils, right. Just a piece of copper wound up. Just a simple electromagnetic induction caused by the moving string near a coil and a magnet. This woud run current. The current can be converted into voltage by a resistor. Or by a current to voltage converter which is an inverting amplifier without R1. Wouldn't any of these work for you. Either a resistor followed by a buffer or an amplifier or a current to voltage convertor. You can also continue with currents in case you so prefer. You can still do so by amplifying the coil current with the current to voltage converter but with a resistor in series to the output before the feedback. This is a combination of the standard current to voltage convertor and the standard voltage to current convertor. I do not know how to call this. A current amplifier? A current to current convertor which ensures 0 load to the source?
The same applies to microphones with coils. ( A. k. a. dynamic). There is a point which I am not very clear with, though: some people may claim some microphones are "optimised" to work the best only with a given load and nothing else. Sounds strange.
I do not understand fully what you mean but, I believe you would like to get the signal from the humbuckers, pre amplify this signal, digitise this signal with the said ADC, encode the digital signal and send the encoded sigmnal to the PC.
Does the ADC with USB have encoder? I had a quick look and I did not see any. Do you plan to get a separate ADC, encoder and USB interface. ( The last two may be available together too. Or all of them. ) You can do encoding with PIC, too.
I am puzzled why you need encoding. I guess for error correction. Or for compression. Do you really need these? This is a guitar. What when there are errors. There may be another reason. You may need to send a specific format not to a PC but to a recorder or whatever they have there. I have heard a lot of people record with recorders as opposed to a PC for whatever reason, most likely noise. Seems to be very fashionable: recorder, then PC to work the sound out a bit ( a lot when I sing and play
), then a CD, then... What happens then? Do you perform in a pub or get gigs so you can sell your CD while performing? I wish you do and make a lot of money!
Can you get some optocouplers too, please. I think, a good idea would be to disconnect the digital signals by optocouplers. Thus the PC power supply would not touch the ADC nor the preamplifier and cannot spread electromagnetic noise.
On the pre amplifier: the guitar humbuckers pickup coils, whatever they call them, differential or not, are just coils, right. Just a piece of copper wound up. Just a simple electromagnetic induction caused by the moving string near a coil and a magnet. This woud run current. The current can be converted into voltage by a resistor. Or by a current to voltage converter which is an inverting amplifier without R1. Wouldn't any of these work for you. Either a resistor followed by a buffer or an amplifier or a current to voltage convertor. You can also continue with currents in case you so prefer. You can still do so by amplifying the coil current with the current to voltage converter but with a resistor in series to the output before the feedback. This is a combination of the standard current to voltage convertor and the standard voltage to current convertor. I do not know how to call this. A current amplifier? A current to current convertor which ensures 0 load to the source?
The same applies to microphones with coils. ( A. k. a. dynamic). There is a point which I am not very clear with, though: some people may claim some microphones are "optimised" to work the best only with a given load and nothing else. Sounds strange.
I do not understand fully what you mean but, I believe you would like to get the signal from the humbuckers, pre amplify this signal, digitise this signal with the said ADC, encode the digital signal and send the encoded sigmnal to the PC.
Does the ADC with USB have encoder? I had a quick look and I did not see any. Do you plan to get a separate ADC, encoder and USB interface. ( The last two may be available together too. Or all of them. ) You can do encoding with PIC, too.
I am puzzled why you need encoding. I guess for error correction. Or for compression. Do you really need these? This is a guitar. What when there are errors. There may be another reason. You may need to send a specific format not to a PC but to a recorder or whatever they have there. I have heard a lot of people record with recorders as opposed to a PC for whatever reason, most likely noise. Seems to be very fashionable: recorder, then PC to work the sound out a bit ( a lot when I sing and play
), then a CD, then... What happens then? Do you perform in a pub or get gigs so you can sell your CD while performing? I wish you do and make a lot of money!For purposes of adapting the outgoing signal of the pickup into the ADC, a buffer preamp is necessary. There is a thread in instrument/amp section of DIY discussing pickups and such
http://www.diyaudio.com/forums/instruments-amps/206423-impedance-matching-di-mic-pre.html
The PCM2902 series can run as a 'standalone' codec chip in USB input/output mode. You don't need to worry about ADC to USB output conversion. That is why I suggested it for a simple interface. There are some codec chips that can do some Digital Signal Processing on board as well but you need to get involved more, like you say with PIC control etc to access the functions.
If you want optical isolation then the S/PDIF with Toslink type optical interface is the standard for that method. You would need a couple of more chips to do that, but the PCM2902 is S/PDIF capable.
More info on the protocol and standards here
S/PDIF - Wikipedia, the free encyclopedia
http://www.diyaudio.com/forums/instruments-amps/206423-impedance-matching-di-mic-pre.html
The PCM2902 series can run as a 'standalone' codec chip in USB input/output mode. You don't need to worry about ADC to USB output conversion. That is why I suggested it for a simple interface. There are some codec chips that can do some Digital Signal Processing on board as well but you need to get involved more, like you say with PIC control etc to access the functions.
If you want optical isolation then the S/PDIF with Toslink type optical interface is the standard for that method. You would need a couple of more chips to do that, but the PCM2902 is S/PDIF capable.
More info on the protocol and standards here
S/PDIF - Wikipedia, the free encyclopedia
Differential Current Input Pre Amplifier
I have just read your reply. An instrumentation amplifier may do the job. Have a look at the attachment. In case a differential current input wouldn't do the job, either an impedance can be put on the front or a voltage instrumentation amplifier with two buffers upfront can be used.
I have just read your reply. An instrumentation amplifier may do the job. Have a look at the attachment. In case a differential current input wouldn't do the job, either an impedance can be put on the front or a voltage instrumentation amplifier with two buffers upfront can be used.
PCM2902
I have copied the PCM2902 ready to use schematic from their manual and connected 2 simple pre amplifiers as well as 2 simple post amplifiers.
The post amplifiers are to be used as pre amplifiers to a pair of amplified speakers / headphones. These can be buffers.
The idea is to have the microphone, the guitar and the PCM2902 with amplifiers on the side where the musician is and some digital cables going to the PC / Digital Recorder. The PC will send the information back through digital cables and play whatever is being recorded through a pair of monitors and / or headphones.
The return may be unused to reduce noise.
All digital should be disconnected from the PC through optocouplers and a separate power supply should be used for the PCM2902 and Amplifiers, not the PC.
For some applications, optocouplers need not be used, the simplified PCM2902 schematic as per the manual may be used and the PCM2902 and Amplifiers can be powered through the USB. I haven't read the power consumption diagram but I am sure this will be well within the limits of USB. This is why they have mede PCM2902.
I have copied the PCM2902 ready to use schematic from their manual and connected 2 simple pre amplifiers as well as 2 simple post amplifiers.
The post amplifiers are to be used as pre amplifiers to a pair of amplified speakers / headphones. These can be buffers.
The idea is to have the microphone, the guitar and the PCM2902 with amplifiers on the side where the musician is and some digital cables going to the PC / Digital Recorder. The PC will send the information back through digital cables and play whatever is being recorded through a pair of monitors and / or headphones.
The return may be unused to reduce noise.
All digital should be disconnected from the PC through optocouplers and a separate power supply should be used for the PCM2902 and Amplifiers, not the PC.
For some applications, optocouplers need not be used, the simplified PCM2902 schematic as per the manual may be used and the PCM2902 and Amplifiers can be powered through the USB. I haven't read the power consumption diagram but I am sure this will be well within the limits of USB. This is why they have mede PCM2902.
Attachments
VST plug ins
Yeah, it should be a pretty straightforward circuit to put together, being careful about isolation of digital and analog supplies and the component layout.
Steven, I wanted to post some suggestions for you and others who may be interested.
Once you have the guitar or mic signal digitized, and sent to the USB input (or optical) of the computer..welcome to the world of VST plug-ins.
Here is an example
I am using a different one but this is kind of freeware open architecture programs that will take the digital USB and process it with ''virtual'' effects, amp simulations and speaker simulations. Can be used for digital recording or live playback.
Yeah, it should be a pretty straightforward circuit to put together, being careful about isolation of digital and analog supplies and the component layout.
Steven, I wanted to post some suggestions for you and others who may be interested.
Once you have the guitar or mic signal digitized, and sent to the USB input (or optical) of the computer..welcome to the world of VST plug-ins.
Here is an example
I am using a different one but this is kind of freeware open architecture programs that will take the digital USB and process it with ''virtual'' effects, amp simulations and speaker simulations. Can be used for digital recording or live playback.
Because I have more than one guitar, the digital converter for me would be in a preamp unit that I plug into directly after the guitar. It would loop out the USB to the computer, and like you said the playback could loop back from the computer into an amp or mixer for live playing. That is pretty much what I have and it is very versatile. It could be built to go direct into a guitar body or microphone though.
For some people ''pure analog sound'' can only be done by using analog effects, tube amps etc. But the computer generated sounds are, to me: VERY convincing. It would be fun to post a whole bunch of audio samples, some using real amps and effects, and then some with the digital version. Don't state which one is which, and then let people guess which is analog or digital.
Check out some demos:
best amp simulator I've found so far Overloud TH2 - YouTube
Check out some demos:
best amp simulator I've found so far Overloud TH2 - YouTube
Great piece of software! I will be happy to use this.
Instead of tons of garbage, one can get a pad PC, a digitiser and a power stage and play on the beach!
Of course, the most important feature is the pitch adjustment. Thus I can sing out of tune and out of key and the software to tune the voice in accordance with whatever played on the guitar!
Instead of tons of garbage, one can get a pad PC, a digitiser and a power stage and play on the beach!
Of course, the most important feature is the pitch adjustment. Thus I can sing out of tune and out of key and the software to tune the voice in accordance with whatever played on the guitar!
Theoretically ( and practically ) there is no sound which cannot be generated by a DSP in a PC software. Once you have the digital signal, as pure as possible, the DSP can simulate any kind of sound: Can make the audio sequence sound like a tube amplifier.
I personally prefer pure sound: God's Sound: Whatever the guitar gives, do NOT do anything except displaying the sound. No tube effects. No transistorised effects. Nothing.
Of course, distortion is welcome as per the world guitar standards of the United Nations Academy of Music Guitar Faculty Electrical Guitar Department named after Lord Lessley Paul with Sir Keith Urban presiding.
I personally prefer pure sound: God's Sound: Whatever the guitar gives, do NOT do anything except displaying the sound. No tube effects. No transistorised effects. Nothing.
Of course, distortion is welcome as per the world guitar standards of the United Nations Academy of Music Guitar Faculty Electrical Guitar Department named after Lord Lessley Paul with Sir Keith Urban presiding.
BTW, finding fast optocouplers seem to be some kinda challenge. PCM2902 communicates at 12Mbits/s rate. You posted some Japanese optocouplers which I have a great respect of, but I doubt these are available through the general and professional suppliers.
I've had a quick look at the PS9121, PS9821. The only difference is the package. These can reach 15Mbits/s. Max Vce is 3.3 V which is what USB and PCM2902 use. There was another one from the same sequence which can reach 25Mbits/s. And another one rated at 15Mbits/s with max Vce = 5V.
I've had a quick look at the PS9121, PS9821. The only difference is the package. These can reach 15Mbits/s. Max Vce is 3.3 V which is what USB and PCM2902 use. There was another one from the same sequence which can reach 25Mbits/s. And another one rated at 15Mbits/s with max Vce = 5V.
Yes that is precisely the point of VST plug ins..everything (almost anything) can be done in software..if you have enough processing power.
Hey here is a cool idea: Play on the beach and just stream over wifi. You don't even need to bring your amp!! Just need to send your music stream and anybody with an ipod touch or similar already could hear you!! Rock on man
This is a great idea for the future.
For now, one may wish not to put optocouplers but to use the power from the PC. Thus, one does not need anything to use this.
USB gives 5V power supply. A converter can be used to get anything from 5V. There are switching converters which would give 3 to 18 V out of 1.8 as far as I remember as well as switching inverters to get the negative. I haven't searched but I assume there would be a single IC switching converter to give + - and ground from + and ground.
This way, as you have suggested, the PCM2902 and surroundings can be put in the microphone or the guitar and no power supply is required.
For now, one may wish not to put optocouplers but to use the power from the PC. Thus, one does not need anything to use this.
USB gives 5V power supply. A converter can be used to get anything from 5V. There are switching converters which would give 3 to 18 V out of 1.8 as far as I remember as well as switching inverters to get the negative. I haven't searched but I assume there would be a single IC switching converter to give + - and ground from + and ground.
This way, as you have suggested, the PCM2902 and surroundings can be put in the microphone or the guitar and no power supply is required.
There is no way to know this is a reply. Someone may think this is a new comment. Who cares, though.
Please do not quote the entire post just above yours. There is no need for it and it only leads to clutter. I have removed the over-quotes.
Thanks.
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