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Old 7th February 2017, 07:18 PM   #1011
barrows is offline barrows
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Sabrosa, i am interested i progress on an NTD-1 variant for the 9038 PRO, but i would need output voltage >2 V. Would prefer around 2.5-3.0 V out.
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Old 10th February 2017, 01:09 AM   #1012
Sabrosa is offline Sabrosa  United States
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I'll keep you updated. To increase the output voltage you can either increase gain through the BAL-BAL, or up the NTD1's drain and source resistors, which will increase gain and reduce current. From simulations it seems best to get your gain from the BAL-BAL's op-amp. In the NTD1 gain is inversely related to current and transconductance.

My next step will be to order and test some of the FETs I've been simulating to measure their actual transconductance under these new operating points.

I have a semi-decent grasp on the testing circuit now, but the one aspect I'm not clear on is if there's a specific reason for choosing 3VRMS for the 1kHz signal generator output:

Click the image to open in full size.

Is the idea that you just need some voltage variation across R1 to vary the current and increase the accuracy of the Gm test and calculation and the exact voltage value is arbitrary? Or are you selecting the generator voltage so that the voltage at the FET's gate alternates above and below the threshold voltage and thus need a large enough VRMS?

If the FET is already biased to the operating Id and Vds by R1 and VR1, I don't see how 3VRMS from the signal generator translates into anything specific to the actual circuit operating conditions, but I definitely could be missing something.

If anyone has any clues on how to select the signal generator voltage for transconductance measurements, I'd appreciate it!

Last edited by Sabrosa; 10th February 2017 at 01:12 AM.
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Old 11th February 2017, 09:22 PM   #1013
Malefoda is offline Malefoda  France
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Question NTD1 v3 caps and...caps

Hi there,

sadly Owen seems to have stopped with this hobby (sent PM, some recently and other month ago, and no more answer) and we are like orphans here. I'll explain my problems as much as I can in order to get help, from you fellow builders. BTW, hope Owen is fine and thanks to him for what he've done!


*************************

DC with the v3:

Quote:
Originally Posted by barrows View Post
... The 330F 25V polymer caps are pretty leaky though? I see ~18 VDC at their input and over 1VDC leakage on each output. ... I cannot have over 1VDC at the inputs of my usual (direct coupled) amplifier.
Is this amount of leakage normal for these parts? I did allow for some charging/forming time, and still have more than 1 VDC at the outputs, any ideas? ... I really like the conceptive using the polymer caps here, and was excited to not have to resort to enormous film caps, but the dc levels are not acceptable for my amplifier.
Quote:
Originally Posted by vanwykca View Post
... the DC was high enough to trigger my nCore400's DC protection. I used 33uF/250v Clarity Cap ESA and it not only works but sounds great. It seems that for a DC coupled preamp/amp, the polymer caps is too leaky. The only low leakage polymer caps available doesn't have a high enough voltage rating, unfortunately.
Quote:
Originally Posted by opc View Post
... you are indeed correct, they seem to be quite leaky initially and then they settle down to much lower leakage after several hours of on-time. ... after a few hundred hours, I'm seeing between 40mV and 80mV common mode DC, and about 2-3mV differential mode DC. This would never be enough to cause problems with a downstream amplifier, even if it is DC coupled.
I tossed in a brand new pair of caps and measured an initial value of 2.3VDC common mode at the output Luckily diff mode was still below 5mV so most proper differential inputs should cope with this just fine.
... it's probably best to use standard (non-polymer) SMD electrolytics and avoid this whole problem. I will update the BOM accordingly.
I aslo was happy to see these tiny SVPF caps, no more insane cap fights, it's tiny and just works... until the last sainty check of DC prior to the UCD400 wiring... OMG! 800mV on one channel and 250mV on the other (common un to 2.5V...)! I let them burn in for dozen of hours, still get 80mV at best. And my UCD400 is DC coupled, the DAC providing digital domain volume. That means full gain on the DC! No way.

Now the questions, holding as true that these cap won't block DC not now not in ten years:

- Owen planned to give a new SMD cap in the BOM to avoid that but as far as I can see never did, someone with a suitable cap without any impact on sound quality? (wich also hold as true that these polymer caps were as good as PP caps, don't they?). I understand what we want is low ESR and low leakage curent, BOM caps are 0.014Ω and 1650A, the hybrid ones I've found are 0.02Ω and ... 3A!

- if no suitable SMD caps, next move is film caps (here we go in hell again...) :
- - solder tiny MKT so it fits the PCB and the 100kΩ load resistors can stay? But MKT vs MKP...
- - relocate the 100kΩ (is quality of the resistors critical?) and fit as you can huge cola cans, if yes:
- - - how to calculate value, 100kΩ of the NTD1 in // with my amp Zin (100kΩ), so 50kΩ targeting 2Hz@-3dB (for ended phase shift at 20Hz) ending in a 1.8μF cap?
- - - wich cap to chose to be on par with the DAC SQ? I have some in drawers, 5mm pitch 4.7μF Epcos MKT, 4.7μF Icel MKP PHC, 1.5μF Wima MKP10... or buy boutique caps la Jantzen Superior Z-cap? I can't afford crazy expensive caps but I will not put something unsatisfying that I'll buy something else later, you know that capacitor madness with bypass, change, retry and such... the right yet not too expensive ones at the first shoot. If they are known by someone...


*************************

output noise filtering if really needed:
Quote:
Originally Posted by opc View Post
Quote:
Originally Posted by barrows View Post
With the off board caps I will put 100K load resistors at the XLR jacks, hence I have removed the onboard 100K resistors. ... Could I place some caps at the position the onboard load resistors were, to provide an analog low pass filter? I would assume these would operate with the output impedance (200R) to make the corner frequency, am I correct here? I do get some noise with my amp, a course noise floor if you will, which in my experience with adjusting the analog filter on other DACs is due to HF noise from the ESS 9018.
All the above is exactly correct, and I do cover what value should be used at some point in the original NTD1 thread. I ran several simulations to get the correct values, and then I measured them in-circuit. It does exactly what you would expect, in that it attenuates above ~20kHz but there is also a tiny rolloff and associated phase shift in the pass band.
This can easily be done by soldering 1206 C0G caps across the SMD resistor terminals. The details are shown in the original NTD1 V1 schematic that Greg refers to. ...
Noise at the output is very odd, and indicates something might be adrift with the amp itself. Is it prone to oscillating? I've tried the NTD1 with dozens of amplifiers at this point, and have never heard anything at all at the output.
- Is this an issue for everyone? Barrows, did you manage to solve it, with the said 200Ω for RC calculation? (200kHz maybe, avoiding phase sifht again... )


*************************
well that's my two questions folks, DC coupling caps and if a real issue the HF noise.

If that DAC is as terrific as it's said to be then my amp may be the weak link, oh no, now my speakers may be even worst! Will I ever hear the super-terrific boutique caps then... hell on earth is capacitor!

Thanks for helping!
Matthieu
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Old 12th February 2017, 04:59 PM   #1014
opc is offline opc  Canada
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Quote:
Originally Posted by Malefoda View Post
- Owen planned to give a new SMD cap in the BOM to avoid that but as far as I can see never did, someone with a suitable cap without any impact on sound quality? (wich also hold as true that these polymer caps were as good as PP caps, don't they?). I understand what we want is low ESR and low leakage curent, BOM caps are 0.014Ω and 1650A, the hybrid ones I've found are 0.02Ω and ... 3A!
The caps you have listed will work perfectly, and are what I would suggest going with.

What I find a bit odd is that you have a large diff-mode voltage. That would imply something has gone out of adjustment with the circuit. A properly adjusted NTD1 may have common mode offset, but should not have any diff mode offset.

Some amps are fine with common mode offset, others will not be. I'm not sure about the UcD amps.

Regards,
Owen
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Old 12th February 2017, 05:09 PM   #1015
opc is offline opc  Canada
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Quote:
Originally Posted by Sabrosa View Post
Is the idea that you just need some voltage variation across R1 to vary the current and increase the accuracy of the Gm test and calculation and the exact voltage value is arbitrary? Or are you selecting the generator voltage so that the voltage at the FET's gate alternates above and below the threshold voltage and thus need a large enough VRMS?

If the FET is already biased to the operating Id and Vds by R1 and VR1, I don't see how 3VRMS from the signal generator translates into anything specific to the actual circuit operating conditions, but I definitely could be missing something.

If anyone has any clues on how to select the signal generator voltage for transconductance measurements, I'd appreciate it!
Hi Sabrosa,

I love the work you're doing with the simulations on the NTD1! I just finally (after 4 months of harassment and waiting) got my hands on the datasheets for the new ESS dacs. A complete system very similar to the one you've simulated is in the works. Preliminary measured results with the old DAC provide staggeringly good performance... exceeding datasheet specs for the old ESS DAC. I'll send you a PM to discuss further.

For the GM testing I think you may have misunderstood the setup. The voltage from the signal generator is applied to the location where "Vs" is on the schematic, and the resulting output voltage is measured across R1.

The 3V output value was chosen to give a reasonable adjustment range on the input side. If only 1V is used then your input adjustments become quite sensitive, and results will be less accurate. Larger voltages could also be used, but then you're starting to stray further from actual operating conditions. 3V was a decent compromise, but it's not set in stone. Once you have the circuit up and running, it's easy to experiment and see what works best for you.

Regards,
Owen
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Old 13th February 2017, 09:47 AM   #1016
Malefoda is offline Malefoda  France
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Quote:
Originally Posted by opc View Post
The caps you have listed will work perfectly, and are what I would suggest going with.

What I find a bit odd is that you have a large diff-mode voltage. That would imply something has gone out of adjustment with the circuit. A properly adjusted NTD1 may have common mode offset, but should not have any diff mode offset.

Some amps are fine with common mode offset, others will not be. I'm not sure about the UcD amps.

Regards,
Owen
Hi Owen, nice you're here and fine

I'll try the linked caps, Panasonic ZC. At a glance:
● Endurance: 4000 h at 125 C (High temperature / Long life)
● Low ESR and high ripple current (85 % over, Lower ESR than current V-TP)
● High-withstand voltage (25 V.DC to 63 V.DC), Low LC (0.01 CV or 3 μA) <----
● Equivalent to conductive polymer type aluminum electrolytic capacitor

My board was sent fully built and with *Adj. OK* on it, I only fine-adjusted the 1.75V for 1/2 AVCC and thats it. I don't believe it's faulty, I think its really my beach of caps that are leaky, will report after swap.

Thanks,
Matthieu
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Old 13th February 2017, 11:33 AM   #1017
Malefoda is offline Malefoda  France
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Other coupling cap possible, very seducing on paper (from a serious company):
Product Information: Features and applications of polymer thin film multi-layer capacitor "PMLCAP"/Capacitor, Power Supply Units RUBYCON CORPORATION
35ST106MD35750 Rubycon | Capacitors | DigiKey
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Old 19th February 2017, 01:55 AM   #1018
stachel is offline stachel  Germany
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First of all; sorry for my bad english.
I have a very strange issue with The Wire PSU.

Transformer primary 220V~ secondary 15V~ 15V~
If I connect 15V PSU it works correctly @ +15V= -15V=
If I connect 9V PSU it works correctly @ +9V= -9V=
If I connect both PSU in parallel, 15V works fine, but 9V is -9V and +15V output

I have spent many hours on it but not the faintest idea what's going wrong ...
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Old 19th February 2017, 03:19 AM   #1019
opc is offline opc  Canada
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Hi Stachel,

Configuration 3 in your picture is not viable. Each power supply will require its own dual secondary transformer.

Regards,
Owen
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Old 19th February 2017, 08:26 AM   #1020
stachel is offline stachel  Germany
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Hi Owen,

thanks for your reply.
Could you briefly explain why this is not viable?

Would it be vialbe if both PSUs were @ 15V?
And is it a specific characteristic of "The Wire" PSU;
would this configuration be possible with bridge rectifier + LM317/337 PSU?

Would you say it's "not best practice" or is it generally incorrect to build it that way; or even dangerous?

Thanks & Regards
Martin

Last edited by stachel; 19th February 2017 at 08:38 AM.
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