DIY Audio Analyzer with AK5397/AK5394A and AK4490

JensH

Member
Paid Member
2009-07-30 9:54 pm
Audio Analyzer with AK5397/AK5394A and AK4490

For more than 3 years I have been working on and off (mostly off) designing a high-end Audio Analyzer. Parts of the design have been implemented as separate units. I have finally put the pieces together on one PCB (+ some small existing interface PCB's).

Some of the design goals were:

1. The Audio Analyzer should work as a sound card, enabling use with a wide selection of Audio Analyzer SW packages.
2. The performance should be somewhere between a good high-end sound card and an AP, R&S, SR etc.
3. The performance should approach the limits possible with the ADC and DAC used.
4. It should be possible to use it with any relatively modern PC. This is the reason for choosing a USB interface to the PC. SPDIF/Toslink was considered, but this makes it difficult to use portable PC's.
5. The PC should be electrically isolated from the Analyzer to avoid ground loops and noise.
6. No fan for cooling!

I have selected to use high-end converters from AKM. I have previously made a design based on AK5394A and AK4399. This design shows a very good performance, but it was not ideal in terms of flexibility, due to limitations in the input and output stages. The input stage was a relatively straight-forward design based on OPA1612 and OPA1632. The performance is fairly good, but there is no attenuator, so the input range is limited.
The output stage has a limited drive capability, since it is based on the OPA1632.

For this design I originally chose the newer AKM converters AK5397 for the ADC and AK4490 for the DAC. After testing the AK5397 I decided to go back to the AK5394A, since the distortion is much lower.
The input stages of the new design are based on a JFET/op-amp combo, with LSK389 and LME49990. This part of the design has been verified on a separate PCB, with attenuator and gain options.
The output stages are based on LME49990 buffered by LME49600.

Main features:
1. AKM AK5394A 24-bit Super High Performance Stereo ADC, 192 kHz sampling, 123 dB SNR (changed from AK5397)
2. AKM AK4490 32-bit Premium Stereo DAC, 192 kHz sampling, 123 dB SNR
3. Dual fully differential inputs and outputs on XLR connectors
4. Dual single ended outputs on BNC
5. AC and DC input switchable
6. 44.1, 48, 88.2, 96, 176.4 and 192 kHz sampling, selected by the Analyzer SW. Potentially 384 and 768 kHz sampling later on (TBD).
7. Full scale inputs from 100 mV (-20 dBV) to 100 Vrms (+40 dBV) in 10 dB steps.
8. Overvoltage protection on the inputs.
9. Full scale outputs up to 10 Vrms differentially (5 Vrms single ended). Can be attenuated to 1 Vrms and 100 mVrms full scale differential output.
10. Single ended output impedance of 50 ohm (changed from 25 ohm)
11. Single ended input impedance of 100 kohm
12. On-board low jitter crystal oscillators (NDK NZ2520SD).
13. Parallel control lines for relays, controlling the attenuators, gains and AC/DC settings.
14. Power supply is integrated on the board (except for the transformer).
15. USB interface is implemented using a completely isolated XMOS based design (changed from USBStreamer).
16. Expansion connector for future digital I/O
17. 20x25 cm PCB

The parallel control lines may be controlled from either manual switches, e.g. rotary switches for the level settings. Other possibilities are to control it with a microcontroller or from the PC via a USB to serial converter. Initially I plan to use manual switches. Update 161222: Settings can be controlled from the PC via the USB interface.

For the power supply a 2 x 15 V and 1 x 9 V transformer is needed. I plan to use an R-core transformer with 2x15 V and 2x9 V, 30 VA, which I have also used for the AK5394A/AK4399 design.
The transformer may be changed to a 2x15V or 2x18V ring core transformer with a slightly modified power supply design. Update 161222: A ring core transformer is used. Primary voltages selectable between 100 to 120V and 220V to 240V.

The isolation between the Audio Analyzer and PC is done with a Master Clock and Isolator, see:
Master clock and isolator for the MiniDSP USBStreamer
Update 161222: The isolation is now part of the XMOS based USB interface.

I have just received the PCB this morning. It will take some time before I will be able to start testing, since I plan to mount the PCB by hand. And I still need to get some of the parts. There are around 750 parts in the design.


I would like to thank Demian Martin (1audio) for his design inputs, reviews and encouragement.

Update April 8, 2017:
GB is now open. See:
GB for RTX6001 Audio Analyzer with AK5394A and AK4490
Update:
Group buy is closed.

Hardware modifications:
To make it easier to find the descriptions of the hardware modifications, I decided to make a list here.

Disassembly and assembly + overvoltage:
GB for RTX6001 Audio Analyzer with AK5394A and AK4490

The overvoltage modification was originally described here:
GB for RTX6001 Audio Analyzer with AK5394A and AK4490

Shield and stability:
DIY Audio Analyzer with AK5397/AK5394A and AK4490

*Moderator note: Second block diagram added at Member's request.*
 

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Hi Jens,

Nice work, I'll take a couple when available and working, have been waiting for something like that and even considering making one....

Forgot about mounting by hand, you will never get done and/or waste time hunting mounting errors.

I can recommend my local assembly house here in Korsør, KE Supply, they're small and flexible and reasonable low cost on prototypes.

I can even help with parts on reels for prototypes. And if you're not used to manufacturing, I can help you there too.

If you would like additional input or review, I'll be happy to assist. You really also should have integrated the XMOS USB interface, pretty easy...
 
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JensH

Member
Paid Member
2009-07-30 9:54 pm
Hi Søren,

I think I can manage to mount one board for initial testing. The PCB I just got is not made for automatic assembly (it is a HASL type). But later it will of course be necessary to mount it on an automated assembly line.

What do you mean by "mounting errors" by the way?:D

Jens
 
Hi Søren,

I think I can manage to mount one board for initial testing. The PCB I just got is not made for automatic assembly (it is a HASL type). But later it will of course be necessary to mount it on an automated assembly line.

What do you mean by "mounting errors" by the way?:D

Jens

Human handling of 750 parts, small shorts.... Trust me, it's not worth saving a little money....
 
If this is a low cost house, how about making up a run of stuffed boards to sell here?
I'm sure there would be plenty of interest.

They mount my dam1021 :)

But it depends on confident you are about design errors.... If the design is as simple as it looks like with few errors then it might be feasible.

But it's up to Jens. I usually have 5 prototypes done and have given up hand mounting long time ago....
 

JensH

Member
Paid Member
2009-07-30 9:54 pm
I don't think it makes sense to sell bare PCB's in this case.
Once the performance has been verified to be OK, it is time to look at the next steps. Assembled boards is definitely a possibility. Perhaps even complete units, but that is still TBD.
 
I don't think it makes sense to sell bare PCB's in this case.
Once the performance has been verified to be OK, it is time to look at the next steps. Assembled boards is definitely a possibility. Perhaps even complete units, but that is still TBD.

Don't know your capabilities or your you plans.... If you don't already have any production lined up I could take care of that, putting them into my pipeline, I'm used to procurement and production in low to medium volume and at low cost.... As I said, I was already already planning doing something very close to yours....
 
750 parts is manageable IMHO Its even worse If the cheap house mounts the wrong parts on some position.

No, then you go down to them and say: You mounted the wrong parts, please replace them with the correct ones, easy for them as they normally have the right tools....

I actually have some prototype PCB's and parts for a power amp laying here, with just 157 smd parts and none smaller than 0805. Planned to hand mount those, but after a couple of years they're still laying here....
 

JensH

Member
Paid Member
2009-07-30 9:54 pm
Schematics? Maybe later.

No, I have not tested the AK5397. This will also work as a test PCB for the AK5397. If the performance is not good enough, I can easily go back to the AK5394A. This would sacrifice some dynamic range and the possibility to use high sample rates, but if the distortion is significantly lower with the AK5384A then it could be worth doing.
 
Soekris,

I think you might have a niche market here. You would also be providing a much
needed service. As we DIYers are growing older, our eyes, patience, and coordination are also becoming challenged as parts are growing smaller and component layout on Surface Mount Boards is becoming difficult.

I would appreciate viewing some pics of your companies shop or yours
and some of the products/boards they've procuded.

With SMT manual layout one sneeze, one startle, one slip, and it can take more
than Sherlock Holmes to locate a part wedged on a wall molding or picture
frame, or between the weave of a carpet.
 

JensH

Member
Paid Member
2009-07-30 9:54 pm
I finished mounting the PCB yesterday. I have attached a picture of the assembled PCB.

Today I have started testing the performance.
The outputs look promising. I have measured the THD with a Panasonic VP-7722A. At 1kHz 0dBFS I get -104dB. The data sheet says -112 so there is still room for improvement. I get the lowest distortion at -11dBFS, where I measured a THD of -122dB. Measurements were done at 48kHz sampling.

On the input there is still some work to do. I have got signals through, but there is a high noise level on one channel and a high distortion on the other one. I need to investigate this further.
 

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