Author Topic: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x  (Read 237917 times)

serg200010 and 2 Guests are viewing this topic.

Offline Edwin G. Pettis

  • Frequent Contributor
  • **
  • Posts: 451
  • Country: us
  • The plural of anecdote is not data.
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #350 on: January 11, 2017, 05:39:55 pm »
Julian1, if you check the data sheet of the 1240W trimmer, you will find that in addition to the end-to-end TCR of ±10 PPM/°C, there is an additional term of ±25 PPM/°C through the wiper, this term will cause a larger TCR to be seen from the wiper.  An additional problem for these trimmers is a requirement for a minimum amount of current through the wiper to maintain a good 'connection' between the wiper and resistive element, too little current can cause instability in the wiper's output.
 

Offline julian1

  • Frequent Contributor
  • **
  • Posts: 721
  • Country: au
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #351 on: January 11, 2017, 06:18:12 pm »
Julian1, if you check the data sheet of the 1240W trimmer, you will find that in addition to the end-to-end TCR of ±10 PPM/°C, there is an additional term of ±25 PPM/°C through the wiper, this term will cause a larger TCR to be seen from the wiper.  An additional problem for these trimmers is a requirement for a minimum amount of current through the wiper to maintain a good 'connection' between the wiper and resistive element, too little current can cause instability in the wiper's output.

Thanks Edwin. I confirmed that it's problematic, by shielding nearby components with Kapton tape then pointing a heatgun at the trimmer for 10C rise, and then logging the result. It is is as you say.

The other issue is the precision fixed 120 ohm in series with the zener. This is fine in the ltz-1000 type circuits when the zener is running at a few mA. But at 120 ohm it is dropping 2.9V with the current of 24mA through the dw232! Calculating out its tempco contribution, gives 6uV/C.

After discovering this, I've changed the circuit to use a 10ohm series resistor + 10ohm current adjust trimmer both on the high side of the zener.

This reduces the voltage-drop 10x on the resistor and by the same amount its contribution to tempco. The divider for the other op-amp input which was the vishay trimpot can then be exchanged for a fixed resistor divider with values chosen to center the needed 24mA current.

The details are here, http://blog.julian1.io/2017/01/11/dw232-circuit-4.html 

« Last Edit: January 11, 2017, 06:57:48 pm by julian1 »
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14076
  • Country: de
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #352 on: January 11, 2017, 06:59:26 pm »
From the parts used I would guess something like scale up by a factor set with the trimmer and than use the 120 Ohms to set the current. What is the circuit used ?

AFAIK about the only advantage of a smaller resistor is less self heating. 25 mA and 3 V is already 75 mW - so a low TC and high power rating could be important. Lowering the voltage and resistor on the down side increases sensitivity to the OPs offset.  So there is a limit on how low the voltage drop should go. Also wire resistance gets more important with resistors in the 10 Ohms range. A 10 Ohm trimmer is also rather low and could have more trouble with the wiper contact. So I would prefer something like 20 Ohms and 100 Ohms +100 Ohms trimmer in series in parallel.

The high current shows it's downside.
 

Offline julian1

  • Frequent Contributor
  • **
  • Posts: 721
  • Country: au
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #353 on: January 11, 2017, 07:09:26 pm »
Quote
It might not be so much more effort to stabilize much of the circuit compared to only the chip itself.

This is a really interesting point. At first I was a bit disappointed by how slow the stabilization loop was compared with using an on-die heater such as in the ltz-1000 circuits. But the the tradeoff is that a lot more can be done for the divider resistors.
« Last Edit: January 11, 2017, 07:11:25 pm by julian1 »
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14076
  • Country: de
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #354 on: January 11, 2017, 08:00:30 pm »
The loop with sensor on the chip and an external heater can be quite slow. But this should be still fast compared to the time it needs for the rest of the circuit to stabilize. Many instruments need something like 15 minutes minimum and maybe 1 hour to get really stable.

The main disadvantage is that the capacitors for the analog temperature circuit might get quite large. Warmup time should be still rather fast. For final stability the limiting part is more like humidity in the board and this needs quite long, even if the thermal system is fast.

For stabilizing more of the circuit, a few more resistors are not a problem, as long as the thermal power is constant and low. I would expect the power for the stabilization to be about proportional to the power of the part that is stabilized - something like 1-3 times the power. Variable and higher power parts like OPs might be better outside. A constant temperature box was quite common in old the days instruments.

Using a resistor as a heater could be a problem, as the heat follows a square law. So it might be better to to use a transistor and control it's current at a more or less constant voltage. This way also no power is lost to an extra control element. As a first step one could still have the resistor (or maybe a diode) at the reference and use the heat from the controlling transistor to heat a metal case around the critical part of the circuit.
 

Offline julian1

  • Frequent Contributor
  • **
  • Posts: 721
  • Country: au
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #355 on: January 15, 2017, 05:09:48 am »
Quote
What is the circuit used ?

Basic circuit (ignoring stabilizing caps, emitter-follower current buffer, decoupling etc), has been this one,



After playing with the 10ohm fixed + 10ohm trimmer in-series on the high-side of the zener, I had issues getting repeatable runs with the regulation. So I've followed your advice - and the circuit is now a 120 fixed resistor + 100 trimmer (set at ~= 10ohm) in series with the zener and a fixed-resistor divider.

The fixed-divider pair are what I had available - super-cheap 1/4 watt resistors from Ebay.




Despite this, the results look a lot better,

The stabilization locks in quicker, with no excursions,


 
And there is no weird secondary spiral around the tempco apex!



After getting to operating temperature, a 10 minute run has only one observation point not within a 10uV range using 6.5 digit daq.



Some more plots are here, http://blog.julian1.io/2017/01/15/dw232-circuit-5.html
« Last Edit: January 15, 2017, 05:19:14 am by julian1 »
 

Offline julian1

  • Frequent Contributor
  • **
  • Posts: 721
  • Country: au
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #356 on: January 15, 2017, 07:06:41 am »
There is a emitter-follower 2n3904 immediately on the output of op27 to provide the necessary 24mA current drive for the zener.

I am wondering how bad this is in terms of PSRR?. According to the op27 datasheet schemtic, the op27 output stage is simply a class AB amplifier powered directly by the rails - so is hanging another npn emitter-follower after it really a problem?

The alternative would be to swap the op27 over to the opa277 (better op-amp anyway at lower bandwidth) which has a max current output of 35mA which is enough to drive the zener directly. Although that seems like a lot of current for a soic package, and perhaps any gains made for noise, and PSRR/isolation would be cancelled by thermal effects in the op-amp.
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14076
  • Country: de
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #357 on: January 15, 2017, 09:56:00 am »
The output stage of the OP is not a problem for the PSRR and drift. Having an extra external emitter follower is more or less needed at this current level to keep the heat dissipation low for the OP and this way prevent thermal effects. If at all the input stage can be slightly influenced by the supply voltage. However with modern OPs and the usual 78xx regulators for the supply PSRR is usually not a big problem.

The fixed divider is relatively high impedance for the OP27.  For this reason the OP277 or similar would be a better choice. If the OP is just there to provide the current to the zener reference even the cheaper OP07 could be good enough. With the 120+x Ohms to set the current, variations at the OPs output voltage should be reduced by the a factor of about 20 - 100, as the zener resistance is much lower than 120 Ohms.

I am not sure the 100 Ohms port in series to the 120 Ohms is such a good idea. I just don't trust the wiper contact so much - but this a pure feeling. I would prefer adjustments to the 51 K resistor (e.g. a 330-470 K resistor in series with a 50-100 K pot that comes in parallel to that resistor).

I think the next step for better stability would be a case, to get air current out and make the temperature more uniform - this is especially important as the heater is not directly at the chip and there is quite a heat source.
 

Offline bertik

  • Contributor
  • Posts: 30
  • Country: ch
    • W's Laser Web Site
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #358 on: January 15, 2017, 11:07:18 am »
Hello,

here a status report, I was investigating about a dozen diodes.

In brief, there is quite some tension to obtain a reasonably low TC0 point and low noise at the same time.

There are two sets of diodes which differ a lot, but are fairly consistent within each set:

Set 1: 2DW232 from Group Buy
Set 2: 2DW233 from technix
Set 3: fake 2DW232 with internal DO-style diodes


Here a list of typical values I measured.

"nominal" means fixed standard I and T values for comparison,
"TC0" means current for a desired TC0 point around 30+/-10C

Tempco mV/C was measured between 22 and 28C, and current for mV/mA between 9 and 11mA,
both were extremely linear in this range.

                                    mA      T     Vz      Noise uV_pp     tempco mV/C     mV/mA       

Single diode Set1
nominal current and T     10      25    5.4        0.5                  +1                    +7
TC0 point                       2.5     35    5.2        4


Series diodes Set1 
nominal current and T     10      25    6.2        0.5                 -0.5                 +9.5
TC0 point                       26      25    6.2        0.3


Single diode Set2
nominal current and T     10      25    5.3        0.7               +1.5                   +2
TC0 point                       0.5     40    5.2        15


Series diodes Set2
nominal current and T     10      25    6.1        4                 +0.04                  +5
TC0 point                       7.5     40    6.2        5


Single diode Set3
nominal current and T     10      25    5.6        1         
TC0 point                       none found


Series diodes Set3
nominal current and T     10      25    6.4        5           
TC0 point                       none found


Comments:

1) Surprising is the high noise for series configuration of Set 2. Also the low noise for the single diode configuration of the fake diodes.

2) The only combination with low noise and TC0 near room temp is series configuration of Set 1, however at around 30mA. Which is a bit high for practical purposes.

3) This means that for a more reasonable current of 10mA and low noise, temperature stabilization appears necessary.

4) The tempco of the forward diode with -1.5mV/C was lower than what is usually assumed

5) I was trying to see whether one can cancel the tempco at 10mA/25C by an extra LM234 current regulator, along the lines of page 8/fig 15 in http://www.ti.com/lit/ds/symlink/lm334.pdf   by using the forward diode of the 2DW23x.

However it turns out that given the measured values of tempco mV/C and mV/mA, this is physically not possible (it would require negative resistances of R1 or R2).

6) It would be interesting to compare more diodes from different batches.


Edit:
7) BTW for the fake diodes the polarity was reversed, that may explain the discrepancy of data sheets.
« Last Edit: January 15, 2017, 11:16:13 am by bertik »
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14076
  • Country: de
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #359 on: January 15, 2017, 12:15:31 pm »
A way to get a zero TC at a lower current (e.g. for set 1) would be using only half (or more 2/3) the forward diode. This could be a resistive divider over the diode. So kind of averaging between single diode and series connection. I think this is easier than a modified current source.
A slight shift to lower currents could be possible if only the voltage of the zener is used to derive the current. But this would be only something like a + 0.02%/K for the current instead of something like a +0.5%/K to shift it all the way to 10 mA.
The other way around (using the voltage over the forward diode to set the current would shift the compensation point for the single diode slight up (and thus towards lower noise), to maybe 3 mA for set 1.

The lower than normal -1.5 mV/K for the forward diode fits the relatively high voltage of the diode.

For the diodes from set 2 it is strange so see so much higher noise in the series configuration. Is this real ? Normally there is not that much noise for a forward diode.
The lower differential resistance for set 2 would also be an advantage.
 

Offline Gyro

  • Super Contributor
  • ***
  • Posts: 9410
  • Country: gb
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #360 on: January 15, 2017, 12:32:45 pm »
Quote
A way to get a zero TC at a lower current (e.g. for set 1) would be using only half (or more 2/3) the forward diode. This could be a resistive divider over the diode. So kind of averaging between single diode and series connection. I think this is easier than a modified current source.
A slight shift to lower currents could be possible if only the voltage of the zener is used to derive the current. But this would be only something like a + 0.02%/K for the current instead of something like a +0.5%/K to shift it all the way to 10 mA.

Just a reminder that I tried that approach on set 1 with reasonable results at lower currents...

https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/301/
Best Regards, Chris
 

Offline bertik

  • Contributor
  • Posts: 30
  • Country: ch
    • W's Laser Web Site
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #361 on: January 15, 2017, 01:41:59 pm »
For the diodes from set 2 it is strange so see so much higher noise in the series configuration. Is this real ? Normally there is not that much noise for a forward diode.


Yes it is, I tested a couple (4 and 6) of each of Set1 and Set2 and within each set variations are minor.
Strangely also Set3 shows this behaviour but I tested only 2 of those.
 

Offline bertik

  • Contributor
  • Posts: 30
  • Country: ch
    • W's Laser Web Site
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #362 on: January 15, 2017, 01:46:59 pm »
Just a reminder that I tried that approach on set 1 with reasonable results at lower currents...

https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/301/

Oh indeed yes, thanks for reminding - the earlier parts of the thread went out of my brain buffer.... I will try that!
Perhaps even one resistor works by stealing some current from the forward diode, depending on the sign of the needed correction. A quick calculation will show whether this would be feasible.

Incidentally I really aim for like 10mA since below the noise increases substantially, at least for the diodes I got.

Thanks for your answers!
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14076
  • Country: de
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #363 on: January 16, 2017, 05:53:04 pm »
The idea of splitting the diode to adjust the TC for currents in a rather large current range has one weakness: it needs 2 extra stable resistors, especially if you are in the middle range. In principle it should work.

For the idea of modifying the current source to shift the TC a little, I found a relatively simple circuit for use with just the zener reference. As far as this is possible for the different part is resembles how the LTZ1000 works: the voltage over the forward diode is used to set the current for the zener part.
The positive features are that one only needs one really stable resistor with already low sensitivity of about 1/100. The other two resistors are less critical by a about a factor of 10-20. The current for zero TC will be slightly higher than for a constant current, but not by much (could be 10% as a rough estimate). With the 2DW232 output voltage would be near 5.4 V and thus relatively well suited to divide down to a stable 5 V, e.g. with divider directly at the reference.

The capacitor included helps startup - one might need some small additions here too. By pure luck the shown circuit with standard parts shows zero TC in the temperature range.

 

Offline julian1

  • Frequent Contributor
  • **
  • Posts: 721
  • Country: au
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #364 on: January 16, 2017, 08:16:26 pm »
Quote
I am not sure the 100 Ohms port in series to the 120 Ohms is such a good idea. I just don't trust the wiper contact so much - but this a pure feeling. I would prefer adjustments to the 51 K resistor (e.g. a 330-470 K resistor in series with a 50-100 K pot that comes in parallel to that resistor).

Is the circuit more tempco sensitive to the 100ohm trimmer wiper, than a pot+fixed across the 51k? Perhaps because of the low resistance of the zener. I will definitely swap it around if that's the case.

I put the 100 trimmer in series with the 120, because that's how the ltz1000 circuit did it for the tunable tempco circuit in the ltz1000 datasheet (there it is a 120 + 200 trimmer). But maybe that's not a good example, because they use the on-die transistor collectors for the inverting op-amp inputs and didn't have the choice.

I am looking at buying 10ppm/C thin-film SMT 1206 resistors, in which case it might be possible to position all the tempco sensitive stuff on a carrier with the dw232 embedded in some thermal epoxy  .
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14076
  • Country: de
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #365 on: January 16, 2017, 09:48:07 pm »
I would be somewhat careful with precision SMT resistors. Especially the larger SMT form factors tend to be sensitive to board bending and expansion of the board. Still you need the large Form factor to get rid of the heat. I would prefer the old style THT form factor for precision parts.

For a constant temperature, I would prefer a metal enclosure around the critical part (e.g. part of PCB): reference and the 3 critical resistors. The OPs might already be better outside. Only an extra divider to get scaling (e.g. to get 10 V) and maybe some resistors to set the temperature are possibly also better inside.
Potting with epoxy could cause more trouble than good - it can swell with humidity and have delayed relaxations.

With the wiper of the pot, I would expect some uncertainty in the contact resistance. Even if this is only in the 10 mOhms range, this would be 0.1% of a 100 Ohms resistor. I would really prefer trimming with the 51 K resistor (we have the choice here), with something like fixed + trimmer in parallel. Or with the pot + coupling resistor version.
One might use a trimmer to do the adjustment and than replace it with fixed resistors for the final version.
AFAIK the TC is not changing that fast with the current. So the current setting does not need to be so super exact at zero TC. From the curves Bertik showed something like 5 % might be good enough if the temperature is stable. Though a better tuned TC could reduce the sensitivity to changes in the set temperature and may allow for just regulating an outer shell for the whole circuit (except power regulation).

For the circuit, the 3 resistors have a sensitivity of about 1 ppm change of output voltage for an 100 ppm change in resistance. The reason the low ohms resistor is more important is, because it gets quite some current and thus has more self heating.
 
The following users thanked this post: julian1

Offline CalMachine

  • Frequent Contributor
  • **
  • Posts: 477
  • Country: us
  • Metrology Nut
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #366 on: January 18, 2017, 01:22:26 am »
Got some goodies today!  :-+   I'm excited to start testing and prototyping
All your volts are belong to me
 

Offline julian1

  • Frequent Contributor
  • **
  • Posts: 721
  • Country: au
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #367 on: January 18, 2017, 02:51:01 am »

For the circuit, the 3 resistors have a sensitivity of about 1 ppm change of output voltage for an 100 ppm change in resistance. 

I had a play with removing the current adjustment trimmer completely - in favor of using fixed resistors. The result has been quite positive.

It is possible to use a fixed resistor divider anywhere in the range of 4.7/10k to 5.1/10k on the inverting op-amp input. This gives a change of up to 9mV on the reference output and corresponding change in zener current.

The important part - is that within this range - it is possible to adjust the set-point temperature to align with whatever the new TC0 is as it changes with the zener current.

This reduces the circuit to needing just a single trimmer (for set-point temperature). It is also more practical - and there is no complicated binary search for TC0.  Instead we can do a single datalogging cold-start to get a plot of the TC0 point, and then dial in the regulation set-point in one step according to the value read.

On this basis, I think I'll abandon the carrier idea - and instead get some precision low tempco Vishay resistors for the divider.

The only unknown - is that all tests used the same dw232 component, so I don't have much sense of how sample variation in the dw232 may change things.

More details and plots,
http://blog.julian1.io/2017/01/18/dw232-circuit-6.html
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14076
  • Country: de
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #368 on: January 18, 2017, 03:47:43 pm »
It is possible to do the fine adjustment with the temperature instead of the current. Form the older data, a 10% change in the current gives something like a 15 K shift in the temperature for zero TC. So the temperature might be used to do the last 5-10% adjustment (if needed). The data from the other users here suggest that there is a spread of more than 10% in the optimum current. So one will likely still need an individually matched resistor or something like a parallel (or series) combination of 2 or 3 resistors to get close enough. The resistors for finer steps do not need to be so accurate.

Even with larger THT parts it is still possible to have the resistors in the temperature regulated part too. Even with the heater directly at the chip, this heater can also partially stabilize the rest of the circuit. It depends on where the thermal insulation is. Even with 3 critical resistors this is no that large. One can combine a heater at the reference with one at a metal enclosure (e.g. use a diode (e.g. 2,x V zener) to heat the reference directly and the transistor to heat the case.

A final circuit / board needed to judge about long time stability would need good resistors - temperature regulation can compensate for a high TC, but not for aging of the resistors.
 

Offline bertik

  • Contributor
  • Posts: 30
  • Country: ch
    • W's Laser Web Site
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #369 on: January 18, 2017, 08:02:21 pm »
The idea of splitting the diode to adjust the TC for currents in a rather large current range has one weakness: it needs 2 extra stable resistors, especially if you are in the middle range. In principle it should work.

For the idea of modifying the current source to shift the TC a little, I found a relatively simple circuit for use with just the zener reference. As far as this is possible for the different part is resembles how the LTZ1000 works: the voltage over the forward diode is used to set the current for the zener part.
...

Now I was looking into both proposals: splitting the voltage 1:2 over the forward diode, as described above, does indeed work moderately well: it moves the TC0 current to 10mA while the temperature is about 26C degrees. And the noise stayed below a uV_pp, so this looks OK. However for one thing: the stability is reduced, it yields about 3ppm/C which is in between the curves shown previously (see yellow curve in attachemt).  This was for two SMD mini melf 25ppm resistors 910 and 1800 Ohms soldered across the pins, perhaps this can be improved.

But I also found this more recent proposal interesting, and analysed the circuit numerically. As far as I can see, barring a mistake, for the measured (linearized) tempo values of the two diodes, it turns out that this circuit implies a Zener current of about 70mA!  (Assuming current through forward diode is 10mA at 25C). There does not seem to be enough degrees of freedom for the resistors to get around it (R2 and R6 come out as proportional).

Incidentally my diodes are far different as compared to the first noise measurements in the thread: no way sub-uV noise for 1-2mA!  It is more than 10 or 15uV there. I get low noise only in the order of 10mA and above.



 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14076
  • Country: de
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #370 on: January 19, 2017, 05:16:49 pm »
The proposed circuit with a different current through the forward diode and zener is not for a current much different from the TC=0 point of just the zener diode. Getting the current from the diode voltage shifts the zero TC point only a little higher (maybe 10%). The main advantage of that circuit would be that only R1 needs to be really stable, the other resistors are less critical by about a factor of 10. Accordingly these resistors only allow a minute adjustment for the zener current.
With a ref chip from set 1 (high current ones) the operating point would be more like 2,x mA (thus R1 should be about 300-400 Ohms) and 5,3 V from only the zener diode. The current for the forward diode should be keep smaller so the other resistors stay less critical. So this might not be good for super low noise, more like a simple, hopefully stable reference, that might be good for dividing down to 5 V.

In principle this circuit might work with a reference from the 2 nd set and there shift the zero TC current for the series reference from 7.5 mA towards maybe 10 mA / 2 mA.
However the lower current through the forward diode is not that good, and the stability advantage is essentially gone.

With temperature stabilization of the whole circuit, it might be possible to use 2 ref chips as 2 zeners and one forward diode in series. This should give an intermediate operation current maybe in the 5 mA range and thus low noise.
 

Offline rsjsouza

  • Super Contributor
  • ***
  • Posts: 5980
  • Country: us
  • Eternally curious
    • Vbe - vídeo blog eletrônico
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #371 on: January 23, 2017, 07:13:10 pm »
Thanks to technix I got my bag of 20 units yesterday. In the search of suitable documents I couldn't download the SJ document linked in the first thread (it asked for a login). I then found this page which links to three versions (1974, 1992, 2002). 
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline gamalot

  • Super Contributor
  • ***
  • Posts: 1300
  • Country: au
  • Correct my English
    • Youtube
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #372 on: February 10, 2017, 04:34:55 am »
Hello VoltNuts,
                      I am interested in sourcing 2DW232/2DW233 from 17th Radio factory in Shanghai ...

Can anyone pint me to their website and/or provide contacts details ?

Thank you very much !
Best regards

Flinstone

I don't think they have any website or other contacts details except a phone number, do you speak chinese?  :-//

Offline chickenHeadKnob

  • Super Contributor
  • ***
  • Posts: 1054
  • Country: ca
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #373 on: February 10, 2017, 07:13:37 am »
Zlymex has been offline since Jan 4 on this forum. It is the new year holiday period for China but I am starting to worry.. hope it is going good with you.
 

Offline Gyro

  • Super Contributor
  • ***
  • Posts: 9410
  • Country: gb
Re: Ultra Low Noise Reference 2DW232, 2DW233, 2DW23x
« Reply #374 on: February 10, 2017, 06:44:19 pm »
technix is Chinese, he's the one who's been talking to them in person, he lives near the factory.
Best Regards, Chris
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf