USB line input

[GatorGnet]

I'm looking to create a 1/4 inch input to USB board. There are several commercial units out there but I wanted to make some mods once I get a working unit.

The ones out there already take a 1/4inch audio(mic, guitar, ect) and creates a line input on the pc similar to a sound card line in. I would like to keep it as simple as possible on the first one then change it around once I get the hang of it.

I was thinking a USB PIC as the controller?

 

[Vizier87]

I was thinking a USB PIC as the controller?

if I understood your question this is the site:
UBW (USB Bit Whacker) Project

Sparkfun forums host its support too.

 

[Gobbledok]

You want an audio line input, which connects to your PC via USB?

If that's what you want, you need an IC like the TI PCM2906. It is an audio D/A and A/D converter, which connects to your PC through USB. Not a simple project though.

 

[Sceadwian]

What do you intend to modify, I don't see any reason why you wouldn't use a commercial unit, for basic audio input like you're talking about the devices are quiet small, no bigger than a typical adapter.

 

[GatorGnet]

I only looked over the bit wacker for a min but how would you connect a two wire line input to that? I'll look it over a little bit more later but thought I would ask.

As far as moding it, I haven't gotten that far but I have some ideas on what I want. But without a way of creating a single input yet I am not working that far ahead.

Stupid question but could it be done with RS232?

 

[Gobbledok]

Like I said before...

Use the PCM2904/PCM2906. This chip will do it for you.

Here's a schematic:

Your desired input signal goes into C9 and C10. You can eliminate the connections to pins 15 and 16 if you aren't also using it as a line out.

There are probably other similar chips which don't have as many features which are easier to use. You'll have to read the datasheet/s.

 

[Sceadwian]

You having a good idea of what you want to do and not sharing it with us leaves us with no way to help you other than to wildly suggest things that might possible work.
You still didn't answer the question I asked, for what reason do you not want to use USB line input devices, all the work is done for you and the audio end of things on most of those are pretty standard.

 

[Nigel Goodwin]

I'm looking to create a 1/4 inch input to USB board. There are several commercial units out there but I wanted to make some mods once I get a working unit.

The ones out there already take a 1/4inch audio(mic, guitar, ect) and creates a line input on the pc similar to a sound card line in. I would like to keep it as simple as possible on the first one then change it around once I get the hang of it.

Just buy one - they are very reasonably priced and perform excellently - if there's some kind of mod you desire then mod the commercial unit, although I can't really see what you'd want to change?.

 

[GatorGnet]

I wasnt trying to hold anything back was just giving the idea of what I wanted to do. I want to learn how to build the analog input ---> A/D ---> USB converter for a guitar input device. As far as mods I really don't need to change the schematic much but I want to be able to build multiple inputs/usb outputs on the same board. What I might end up building is a rackmount case with the inputs on the front and usb connections on the back. The reason for multiple input/outputs is for different guitars going to different software processors on the pc so each output would need its own id.

The PCM2906 looks okay but seems a bit harder to find. Digikey shows it as a not in stock item. I wanted to also see if it was possible to do it with a PIC however an IC that doesn't need programmed(expect id) is an easier option.

The commercial units made for guitars usually run $40-$200 for one input so I wanted to find a way of building them. This isn't just for one unit either, I would like to keep building them. I have run into cheap ones that are basically just a cord but I have heard about latency issues with them.

 

[Sceadwian]

I want to learn how to build the analog input ---> A/D ---> USB converter for a guitar input device.

As already said.. It's not recommend.. There is no way to do a project like this 'easy' it's going to be complicated no matter how you do it. Using simple USB audio line inputs is good, they're cheap, simple and cleaner audio than you get from even most dedicated commercial boards.

 

[Nigel Goodwin]

I wasnt trying to hold anything back was just giving the idea of what I wanted to do. I want to learn how to build the analog input ---> A/D ---> USB converter for a guitar input device. As far as mods I really don't need to change the schematic much but I want to be able to build multiple inputs/usb outputs on the same board. What I might end up building is a rackmount case with the inputs on the front and usb connections on the back. The reason for multiple input/outputs is for different guitars going to different software processors on the pc so each output would need its own id.

The PCM2906 looks okay but seems a bit harder to find. Digikey shows it as a not in stock item. I wanted to also see if it was possible to do it with a PIC however an IC that doesn't need programmed(expect id) is an easier option.

The commercial units made for guitars usually run $40-$200 for one input so I wanted to find a way of building them. This isn't just for one unit either, I would like to keep building them. I have run into cheap ones that are basically just a cord but I have heard about latency issues with them.

Commercial ones run about £20 in the UK - are stereo, and have line inputs and outputs. Buy one of those and add your own guitar preamp to it - it's going to be cheaper than sourcing the chip that's inside them.

 

[Triode]

While I understand wanting to know how to do something yourself, this is very specific, which means it won't apply to a lot of other things. I'm newer to electronics but in the year or so I've been at it I've learned that if you want to get anywhere, do things the most simple and practical way first then build up the complexity. What you're talking about would involve not only clever use of specialized chips, but some custom drivers, and custom board fabrication taking sheilding and interference into account.

 

[GatorGnet]

Thank you to everyone that jumped in to help. I didn't think that this would have been such a complicated project. I guess when I asked for the simplest way I knew it wasn't going to be that easy but didn't think it would take that much.

 

[Triode]

Well, I see a lot of complication on the software side, if there are existing drivers that you could build it to work with then it might not be that hard, but then you would basically be cloning another device anyway.

 

[GatorGnet]

Like I said before...

Use the PCM2904/PCM2906. This chip will do it for you.

Here's a schematic:

Your desired input signal goes into C9 and C10. You can eliminate the connections to pins 15 and 16 if you aren't also using it as a line out.

There are probably other similar chips which don't have as many features which are easier to use. You'll have to read the datasheet/s.

This has been the best option overall. Is there a way to make the input mono instead of stereo? Could you just connect the VinL + VinR pins together as one input?

 

[Sceadwian]

Yes, you should be able to connect input L and R together to get mono. I have a little adapter that does this if need be.

 

[Nigel Goodwin]

This has been the best option overall. Is there a way to make the input mono instead of stereo? Could you just connect the VinL + VinR pins together as one input?

You mean apart from buying one ready built at less cost than the parts

As already suggested, just short the inputs together to make it mono, or just use one channel - no point in recording too copies of the same mono signal. Recording software is designed to record either one or two tracks from these devices.

 

[GatorGnet]

I agree with you Nigel but I'm the type of guy that just has to build it myself. I already have a couple commercial units and like them. One of the ones I have seems to have a gate that cuts off the input once the guitar sustain reaches a point, which I hate. I just want to work on another project, learn, and make some new things later.

Depending on how I can use the existing drivers I might just use the two channels as two different inputs. Some of the software I have you can choose which channel you want to use but others it just lets you choose the device. Thoughts?

 

[Nigel Goodwin]

I agree with you Nigel but I'm the type of guy that just has to build it myself. I already have a couple commercial units and like them. One of the ones I have seems to have a gate that cuts off the input once the guitar sustain reaches a point, which I hate. I just want to work on another project, learn, and make some new things later.

Can you even buy the specialised IC you need? - and even if you can, how much would it cost?. Buying a cheap line IN and OUT USB sound card is probably the cheapest (and certainly the easiest) way to go about it. You can then add your own specific analogue circuitry to make it a guitar input.

It's really down to what you consider a 'component' - what's the difference between a large SM IC, and the same IC ready soldered on a PCB?.

Depending on how I can use the existing drivers I might just use the two channels as two different inputs. Some of the software I have you can choose which channel you want to use but others it just lets you choose the device. Thoughts?

All the ones I've used allow you to select either channel independently, or both as 'stereo' - but stereo is a fairly meaningless term as far as it goes, it's simply two independent mono tracks - which could be entirely different. It's quite plausible, and commonly done, to use it as a multitrack recorder - recording one or two instruments/tracks at once whilst playing back the preceding tracks.

Audacity is free, easy to use, and works really well - my daughter has used it to record two gigs she was sound engineering for on her old Toshiba laptop. She recorded each indivdual act on a different pair of tracks, then afterwards you can edit them and save them as a stereo CD quality recording.

 

[GatorGnet]

Can you even buy the specialised IC you need? - and even if you can, how much would it cost?. Buying a cheap line IN and OUT USB sound card is probably the cheapest (and certainly the easiest) way to go about it. You can then add your own specific analogue circuitry to make it a guitar input.

Both Mouser and Digikey carry the 2900 but Mouser is cheaper at $8.53 US for singles.

Thank you for pointing out Audacity! We also use several effects software that replaces the pedals.