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Old 29th July 2015, 02:25 PM   #1
JensH is offline JensH  Denmark
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Default DIY Audio Analyzer with AK5397 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 have chosen the newer AKM converters AK5397 for the ADC and AK4490 for the DAC.
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 AK5397 32-bit Premium Stereo ADC, 768 kHz sampling, 127 dB SNR
2. AKM AK4490 32-bit Premium Stereo DAC, 768 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 316 mV (-10 dBV) to 100 Vrms (+40 dBV) in 10 dB steps.
8. Overvoltage protection on the inputs.
9. Full scale outputs up to 20 Vrms differentially (10 Vrms single ended). Can be attenuated to 2 Vrms and 200 mVrms full scale differential output.
10. Single ended output impedance of 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 MiniDSP USBStreamer with an added isolator unit.
16. Expansion connector for future digital I/O
17. 20x20 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.

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 isolation between the Audio Analyzer and PC is done with a Master Clock and Isolator, see:
Master clock and isolator for the MiniDSP USBStreamer

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.
Attached Images
File Type: jpg JH Audio Analyzer block diagram 150729_01.jpg (539.0 KB, 657 views)
File Type: jpg Audio Analyzer PCB V1.jpg (200.6 KB, 637 views)
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Old 29th July 2015, 02:45 PM   #2
soekris is offline soekris  Denmark
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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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Last edited by soekris; 29th July 2015 at 02:48 PM.
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Old 29th July 2015, 02:58 PM   #3
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Location: West Australia, near to the beach, natural ambient sounds only.
Cool, sounds like a beter alternative to QA400.
We are all interested to see your test results.

Regards, Dan.
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Old 29th July 2015, 04:01 PM   #4
JensH is offline JensH  Denmark
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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?

Jens
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Old 29th July 2015, 04:45 PM   #5
jojip is offline jojip  United States
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Looks like some excellent work. Congrats.
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Old 29th July 2015, 05:08 PM   #6
soekris is offline soekris  Denmark
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Quote:
Originally Posted by JensH View Post
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?

Jens
Human handling of 750 parts, small shorts.... Trust me, it's not worth saving a little money....
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Old 29th July 2015, 05:11 PM   #7
rayma is offline rayma  United States
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Location: Upper midwest
Quote:
Originally Posted by soekris View Post
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.
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.
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Old 29th July 2015, 06:03 PM   #8
soekris is offline soekris  Denmark
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Quote:
Originally Posted by rayma View Post
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....
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Old 29th July 2015, 06:06 PM   #9
rayma is offline rayma  United States
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Location: Upper midwest
Quote:
Originally Posted by soekris View Post
I usually have 5 prototypes done and have given up hand mounting long time ago....
In the USA, we have little choice but to assemble the protos ourselves,
too expensive otherwise.
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Old 29th July 2015, 06:11 PM   #10
RNMarsh is offline RNMarsh  United States
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Location: 2457 Cascade Trail; Cool, CA. 95614
Quote:
Originally Posted by Max Headroom View Post
Cool, sounds like a better alternative to QA400.
We are all interested to see your test results.

Regards, Dan.
The test results are key for me also. And, then how it will eventually be sold.... total DIY as it is now, I cant go there. but a preassembled pcb would help.

THx-RNMarsh
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