DIY CT7601PH multichannel USB bridge, crazy or doable?

[MCH]

I wonder if someone ever looked into DIY a multichannel USB bridge using the Com True CT7601PH.

I am asking because all the parts seem to be available yet i cannot find one single diy project online:
ComTrue website has available:
- Drivers
- Instructions and detailed schematic of the evaluation board:
The evaluation board seems complex, however, if you start taking out the parts that you don't need (DACs, ADC, SRC chips... ) you end up with a relatively simple board with the USB bridge, a flash memory chip and a external micro-controller, that i believe might be there only to control the SRC chips, so might be unnecessary too (the CT7601 has an internal microcontroller). The only EEPROM in the schematic is also for the SRC chips, and is not even populated in the pictures of the evaluation board i have seen.

The chip is available in one aliexpress shop at 25 euros. The shop is a small one but looks legit.

I understand that the tools to get the hex firmware files are not available to the general public (probably @IVX knows), but I understand that the ct7601_setup.exe available from ComTrue website would provide the firmware to a new build... (?)

Has anyone looked into this? am i missing something?

 

[MCH]

Well, so far i have not been able to get any firmware to operate the CT7601PH as multichannel bridge....

But i do have everything needed, included firmware, to operate one of the stereo only versions as both input and output bridge, with both i2s and SPDIF. And while the multichannel CT7601PH is still my objective, i was thinking on building a stereo input/output interface in the meantime. I don't really need one, but i thought it would be a good project to learn a bit and use some leftover parts from other projects.

I was thinking as well that i would like to have a comprehensive clock structure for the interface, I like how i can select the clock source in my motu ultralite mk5 and thought i could try and do something similar, but I could do with some help as this all is a bit too complex for me.

This is how i was thinking it could work:

The firmware i have requires the DAC in slave mode (it is the only possibilitz with CT7601) and the ADC in master mode, and even though CT7601 allows both master and slave for the ADC, i cannot change the setting of the firmware i have. There will be an external MCU that will control DAC, ADC and SPDIF transceiver and will receive the information of what sample rate is expected from the ADC from the USB bridge and program the ADC accordingly.

And now comes the tricky part for me, the clocks:
I was thinking i could reference both ADC and DAC to the same oscillator/s (there will be 2 to chose from depending on the sample rate), but i am not sure how to make that happen. Additionally, i could take the input SPDIF signal, and with the help of a WM8804, generate a i2s signal and use its clock signals as reference if desired, like the Motu can do.
Now, my question is, what piece of hardware do i need to provide synchronized clock signals to DAC and ADC?
Sorry if all this doesn't make sense at all, this is my first project with more than one audio in/out and i am a bit lost.

 

[MCH]

I wonder if someone ever looked into DIY a multichannel USB bridge using the Com True CT7601PH.

I am asking because all the parts seem to be available yet i cannot find one single diy project online:
ComTrue website has available:
- Drivers
- Instructions and detailed schematic of the evaluation board:
The evaluation board seems complex, however, if you start taking out the parts that you don't need (DACs, ADC, SRC chips... ) you end up with a relatively simple board with the USB bridge, a flash memory chip and a external micro-controller, that i believe might be there only to control the SRC chips, so might be unnecessary too (the CT7601 has an internal microcontroller). The only EEPROM in the schematic is also for the SRC chips, and is not even populated in the pictures of the evaluation board i have seen.

The chip is available in one aliexpress shop at 25 euros. The shop is a small one but looks legit.

I understand that the tools to get the hex firmware files are not available to the general public (probably @IVX knows), but I understand that the ct7601_setup.exe available from ComTrue website would provide the firmware to a new build... (?)

Has anyone looked into this? am i missing something?

Unexpectedly, my problems with the multichannel bridge have reversed. Now I managed to get the firmware for multichannel and multiple spdif simultaneous input and output, but the AliExpress seller of the chip.... Has ran out of stock.... grrrr I have even found his source in taobao, at half the price, but MOQ is 160 units... well, anyone knows where to get ct7601ph in low quantities?
(In the meantime I progress the stereo version)

 

[AnalogSteph]

And now comes the tricky part for me, the clocks:
I was thinking i could reference both ADC and DAC to the same oscillator/s (there will be 2 to chose from depending on the sample rate), but i am not sure how to make that happen. Additionally, i could take the input SPDIF signal, and with the help of a WM8804, generate a i2s signal and use its clock signals as reference if desired, like the Motu can do.

Your approach as shown assumes that the CT7601 will sync to its SPDIF input - what if it doesn't?

Also, there is a good reason why the ADC interface is normally run in slave mode - ADC clock jitter is super-duper critical and using the clock regenerated from any old SPDIF receiver with a wideband VCO is likely to substantially degrade dynamic range and anti-alias filter ultimate rejection. Your best bet is likely to be a part that can use an external crystal, like the AK4118. The topic of clock regeneration is no joke. I think the big guns are running DPLLs in their FPGAs.

 

[MCH]

Thanks for your input, I am not sure I follow (all this goes way over my head).

Your approach as shown assumes that the CT7601 will sync to its SPDIF input - what if it doesn't?

As far as I understand, the ct7601 generates the audio clocks from the external 12MHz crystal. There are also ref pin to input an external clock (CLK_SRC_REF) and output a reference clock (other comtrue chips have the same), but i don't know if it is going to be active in the firmware i have, so i prefer not to relay too much on it, but if it is active, i could indeed use it.
From the datasheet:

Also, there is a good reason why the ADC interface is normally run in slave mode - ADC clock jitter is super-duper critical and using the clock regenerated from any old SPDIF receiver with a wideband VCO is likely to substantially degrade dynamic range and anti-alias filter ultimate rejection.

I envision the spdif receiver as master as an option, not for general use. I have found it useful in some cases with my main interface.

Your best bet is likely to be a part that can use an external crystal, like the AK4118. The topic of clock regeneration is no joke. I think the big guns are running DPLLs in their FPGAs.

ES9826Q also uses an external oscillator, or are you saying an ADC that uses a passive crystal is better for this? (not doubting it, it is a question)

 

[phofman]

IIUC AK4118 uses its crystal for two purposes - to freewheel when no SPDIF signal is present (hence no PLL'd clock), and to determine incoming samplerate by comparing with the known crystal frequency. IMO the crystal plays no role in recovering the SPDIF clock via internal PLL.

 

[phofman]

@MCH: Do you have the firmware in source code, or only compiled bin which you cannot modify? Do you actually have programming docs for the interface?

 

[MCH]

@MCH: Do you have the firmware in source code, or only compiled bin which you cannot modify? Do you actually have programming docs for the interface?

No, I only have the complied .hex to burn to the flash, and I can't complain, it wasn't easy to get. From all the examples I've found in the internet except one, all use custom firmware prepared and complied by ComTrue. I have only found one person that claims to write his own firmware, and is a member here, but I don't want to bother him as it might be part of his day job (it is not ivx). I don't think ComTrue shares the programming docs easily.

In any case, the firmware I have should allow me to use all three I2S interfaces (8channel input, 8 channel output and 2 channel output, and all spdif inputs and outputs. And even a few HID buttons for volume play/pause next/prev. Which I find a cool detail that simplifies eventually adding those to a remote control.
What I will not know until I try it is if I can use the differential spdif input and the reference clock input.
Btw, as mentioned the PH versión was out of stock in low quantities but I managed to secure a CH version, same functionality just doesn't go to the highest sample rates.

 

[phofman]

Thanks for the details. IIUC the PH version is around 15USD at single quantities?

The fixed firmware along with no programming documentation is not my cup of tea but it looks acceptable if complete control over the device is not required.

 

[MCH]

85 yuan moq 160 units for the PH and 70 yuan no moq the CH. These are taobao prices, no taxes no shipping included.
Yes I will be more than happy if I manage to make it work, there aren't really many simple options for usb multichannel available to DIY, at least not I am aware of.

 

[ShadowFiend]

Unless you want to test your ability to develop or make a business with it, I don't think it is worth creating multichannel USB interface when something like MCHStreamer Kit from minidsp exist. For just 105$, you get upto 24 channel TDM8, 8-ch i2s PCM, 8-ch DSD (64,128,256) with very good software support (windows, linux, iOS)

 

[MCH]

Unless you want to test your ability to develop or make a business with it, I don't think it is worth creating multichannel USB interface when something like MCHStreamer Kit from minidsp exist. For just 105$, you get upto 24 channel TDM8, 8-ch i2s PCM, 8-ch DSD (64,128,256) with very good software support (windows, linux, iOS)

Sure, this is a hobby for me, I already have a 22x out 18x in commercial USB interface. I enjoy building this sort of stuff. In this particular case, will use it to accommodate other multichannel DAC and hdmi stuff I am already familiar with on the same board.
What I am not into is to combine a millard of boards with jumpers, even though sometimes I have no other option.

 

[MCH]

First step done, easier than expected actually, great resource Taobao. Now i can start routing tracks