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Old 3rd July 2019, 07:51 PM   #4611
ClaudeG is offline ClaudeG
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Join Date: Jan 2015
Hi Mark

Many thanks for this very detailled and complete answer!

I understand the learning curve and that will make it somewhere more entertaining: don't we want DIY and trials... and learn from it :-)

All you say sounds very promising, this is possibly the way to go either with this evaluation board, or if too expensive with a chinese one. But in either case no doubt AKM will have many followers and a big community to complement your seaches and works, something I am interested to contribute to aswell.

Again many thanks for all this

Claude
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Old 4th July 2019, 01:42 AM   #4612
Terry Demol is offline Terry Demol  Australia
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Quote:
Originally Posted by tcqanh View Post
Mark,
Do you think these board can play DSD?
I dont like balance signal and I am a fan of Single end tube sound.
Here my product.
Nice amp tcq.

Is this a 'spud' amplifier, ie a single stage amp?

I've heard some pretty darn good SET amps and was involved with design of
one that used a 45 OP tube. Stunning sound with the right speakers.

T
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Old 4th July 2019, 01:57 AM   #4613
tcqanh is offline tcqanh
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Quote:
Originally Posted by Terry Demol View Post
Nice amp tcq.

Is this a 'spud' amplifier, ie a single stage amp?

I've heard some pretty darn good SET amps and was involved with design of
one that used a 45 OP tube. Stunning sound with the right speakers.

T
Hi Terry,

01A, 26 and 45 are the best sounding triode tubes that USA have manufactured. And my system uses all 3 of them

That photo you see is buffer tube after DAC chip. They include 01A/26 tube (switchable) along with Tango ISO NP-126 OPT. DAC board get inside it.

Tube 45 SET amp is unbeatable if we have enough high sensitive speaker.

Last edited by tcqanh; 4th July 2019 at 02:09 AM.
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Old 4th July 2019, 02:49 AM   #4614
Terry Demol is offline Terry Demol  Australia
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Quote:
Originally Posted by tcqanh View Post
Hi Terry,

01A, 26 and 45 are the best sounding triode tubes that USA have manufactured. And my system uses all 3 of them

That photo you see is buffer tube after DAC chip. They include 01A/26 tube (switchable) along with Tango ISO NP-126 OPT. DAC board get inside it.

Tube 45 SET amp is unbeatable if we have enough high sensitive speaker.
Hi Tran,

I don't own a SET amp lthough have been tempted many times, however,
helped a good friend with his development of a world class 45 amp.

His speakers are Goodmans Axiom 80 (with OB subs) and for what they do
right, ie; ndrange, they are incredible speakers. I know a few people now
playing with the Ruilitt

Do you have the Sabre DAC board inside the tube buffer base ?

Your DAC setup sounds interesting, are you driving DAC into passive I-V
-> tube -> Tango transformer.


T
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Old 4th July 2019, 03:40 AM   #4615
Terry Demol is offline Terry Demol  Australia
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Quote:
Originally Posted by Markw4 View Post
Hi Claude,

That's okay though. I hope that things will start to move faster here before too long. Also, I hope to have more sound say about sound quality of the basic eval board before long too. My initial listening tests using the balanced outputs (that are offset at +2.5v) have been to try some transformers and the balanced input on my headphone amp. I have yet to construct one of the datasheet example differential summing stages, which I expect to have some effect on sound quality.
Well it's nice to see you have changed your mind on transformers.
Has Jam has been schooling you up a bit?

Quote:

I also have not tried other reference voltage supplies (think AVCC). For one thing they did a funny ground isolation thing on the eval board for the AVCC supplies. As a result it takes some big electrolytic bypass caps on the AVCC supply to the high side of the ground isolation resistors to minimize bass distortion.
The whole VREF (AVCC) setup is strange. With 0 ohms for R14_x, the LF
distortion is lowest for a given electro cap size but there is also the distortion
hump at 5k, which the 10 ohm decoupling R appears to fix.

AD817 based regs for VREF are a simple Jung SuperReg knock off, for the
most part, wher the Reg OP bootstraps the opamp power supplies. But
AD817 has significant OP noise. They were obviously focusing on speed and
transient response with these supplies.

Also the whole 'gull wing' VREF grounding arrangement is questionable.
I think as previously mentioned (1audio), looks like there will be
considerable optimization possibilities and most likely AKM don't even know
the real performance potential of this DAC. Case in point their AK5394 ADC,
people have attained performance *far exceeding data sheet specs.

So it's fair to say this is all a good thing - we have a DAC here with unknown
potential, but it will take some work to unearth that potential.

I haven't even delved into OP voltage swing configurations and how this DAC
tolerates it. J Westlake was alluding on another thread, that the resulting
distortion is due to internal resistor non linear voltage coefficient on Sabre.
Has AKM improved this? An ability to tolerat *some voltage swing on OP
will open up many possibilities.

Quote:

The eval board doesn't come with the very largest possible caps. Why? I don't know exactly, but power is supposed to be sequenced on and sequenced off. If big caps take longer to discharge, how to I account for that if the power plug gets pulled? A crowbar circuit? Zener clamps? Don't know.
Crowbar (brute force) can work but you can also get around ramp up time
on very low noise RC attenuation networks with a schottky diode bypass on
the R before the C. The schottky forces the C high to within 0.2 volts of desired voltage, ie; enough to get things running, then the remainder 0.2 or
so volts 'floats' up to desired spec with full RC noise attenuation and the diode is out of the circuit.

None of this should be required with proper grounding design. It's not
rockets science to keep ground current loops separate.

Quote:

The dac chips can also produce pops at known times such as when some internal settings are switched, for example. It is up to the designer to make a mute circuit for that if they feel it is needed for their application.

In summary, the chip is complex, it is very different than Sabre, and while it sounds good and very promising, there is a whole lot of work to be done before we know as much as we would like. At least there is no NDA keeping designers from collaborating in places like diyaudio. As soon as eval boards hit the high volume distributors we will probably be seeing a lot people working away on finding out useful things, and or there will be a few blown chips too. Bottom line though, I think AK4499 is probably the best dac chip I have heard so far, and I think people will probably like new, non-Sabre sound better overall.
Onward and upward so to speak

Do you know the projected price of this DAC chip?

T
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Old 4th July 2019, 09:08 AM   #4616
timH is offline timH  United Kingdom
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Quote:
Originally Posted by MrSlim View Post
I've revised the AVCC schematic to show C8-9 as either Electrolytic or Film, and the board layout will include footprint's for both.

I've also added optional balanced outputs to the IV stage. R50-53 are jumpers that can be left out if the balanced outputs are not required. These jumpers reduce the amount of non-powered wiring on the board that could become antennae for external noise pickup.

Both Sheets of the BOM have been updated, as well as the Combined sheet.
I’m new to this party so was wondering if anyone could post a picture of this output stage to help me with layout please. Also I’m assuming I can use opa1602 or 1612 instead of the lme49720

Tim

Last edited by timH; 4th July 2019 at 09:10 AM.
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Old 4th July 2019, 10:04 AM   #4617
timH is offline timH  United Kingdom
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So I’ve just realised opa1612 are recommended. Just need help with layout if poss
Tim
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Old 4th July 2019, 01:45 PM   #4618
Markw4 is offline Markw4  United States
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Hi Tim,

I was asked to provide output stage layout instructions using through-hole components. My preference would probably have been to use SMD, which I think might have actually been easier to construct. In any case, the package I put together can be found at: Dropbox - Output Stage Instructions.zip

Please keep in mind that other modifications are very important too. In particular, the AVCC circuit is critical as the dac chip has zero PSRR at the AVCC terminals, and any defects in AVCC regulation are quite audible. If you would like more info on that aspect of construction, please let me know and I will try to see what I can find for you.
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Old 4th July 2019, 01:52 PM   #4619
Markw4 is offline Markw4  United States
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Location: California
Quote:
Originally Posted by Terry Demol View Post
Well it's nice to see you have changed your mind on transformers.
Has Jam has been schooling you up a bit?
Yes. He even gave me some little transformers to try that were used on a commercial product. Unfortunately, they were not as clean as the differential receiver in my headphone amp, which I am not sure is as clean as it can get. So far, I still see transformers as a sometimes necessary evil.

Quote:
...J Westlake was alluding on another thread, that the resulting
distortion is due to internal resistor non linear voltage coefficient on Sabre.
Link?

Quote:
Do you know the projected price of this DAC chip?
Sorry, don't know yet.

Agree with much of your commentary.

cheers
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Old 4th July 2019, 03:50 PM   #4620
zenonn67 is offline zenonn67
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Quote:
Originally Posted by timH View Post
I’m new to this party so was wondering if anyone could post a picture of this output stage to help me with layout please. Also I’m assuming I can use opa1602 or 1612 instead of the lme49720

Tim
Output I/V stage (from Topping D10 - ES9018K2M), one channel.
Attached Images
File Type: jpg ADA4898.JPG (145.3 KB, 316 views)
Attached Files
File Type: zip ADA4898.TSC.zip (8.8 KB, 22 views)

Last edited by zenonn67; 4th July 2019 at 03:54 PM.
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