[FT] xDevs.com KX LTZ1000A fairy-tale, or the story of little jumper.

[syau]

After taking some effort to clear the USA Custom  , received the parcel today.

[Keith956]

Well all the parts arrived and last night I built the board. Checked it out and hooked up to a 12V power supply and measured the Vref with a calibrated HP3458A. So far it's looking good with the output 7.008220 and noise down in the 1-2uV, time to leave it on to burn in.

Some comments about the board for anyone else building one. The PCB (rev B03):
- It would be nice to have capacitors labelled on the silkscreen. True there isn't much room but at least C4 and C8 could also be marked.
- Add holes for mounting the board on standoffs. This would mean a bigger board but then more component info could be added too.
- The low tempco resistors were mounted vertically, fortunately they just fit.
- The BOM on the xdevs site misses R9 (0 ohm), R12 (2.2K) and VD1 (LED).
- The pin numbers of Q1, 3904 are incorrect on the schematic.
- The silkscreen could show the tab on the LTZ1000. OK so you can figure it out.
- The silkscreen should show the polarity for J1 and J2. Again this may need the board being slightly larger.
- I'd have liked to see some protection from reversed power supply connection.

These are not criticisms of the good design just suggestions.
Keith

[nedrysoft]

Hi,

I’m just about to build one of these, I’m waiting on the PCB to arrive from OSHPARK, I managed to snag the ltz1000ach from mouser.

The only parts I’m missing is a couple of the Vishay resistors.

I have seen talk of alternative parts, so I’m asking the following questions with the fact that this thread is over a year since the last result, given the great conponent famine I’m hoping people will be able to make suggestions.

So does anybody have a source for these Vishay parts, I have the 120R and the 1K foils but the remaining ones seem harder to find, I should also probably mention that I’m based in the U.K as that may impact on availability of either Vishay or alternatives.

I saw mention of Rhi point in the U.K. and I’ve contacted them and waiting for a response, although 13K isn’t a standard econister on their site so I had to select custom, so I’m not sure whether they are able to supply such low quantities.

Obviously I am at the mercy of what’s available and what companies will deal with individuals.

Furthermore I have seen the offer of calibration services being offered by members, are people still willing to offer this service should I manage to source the remaining missing resistors.

Many thanks

Adrian

[Kleinstein]

IT looks like Mouser still has 1 piece of 13 K BMF (S102K) in stock, at least from Germany. The 13 K are used as a divider with the 1 K so should ideally be the same type.

The 70 K resistors are supposed to be a bit less critical and the values does not have to be exact 70 K. Smaller slightly increases the TC before regulation, larger slightly increases the noise.
Good thin film types may be good enough.

[nedrysoft]

Thanks, sadly by the time I was able to look somebody else had bought it.

I’m waiting on a response from rhopoint to see if I can get the required values of resistors from them, I’m happy to wait for the right parts to become available, I have the bulk of the components including the ltz1000ach which was up until yesterday, the problem part, but I checked at 2 or 3am this morning on the off chance that some were in stock.

[Dr. Frank]

Please have a look into the big 'Ultra Precision Reference LTZ1000' thread, for different values of the resistors.
I have published a table for all my references, which resistors I have used (econistors from G.R., or BMF from AE, supplied by Rhopoint) and which oven temperatures I have measured.

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg3263778/#msg3263778

13k/1k (divider ratio of 14) gives an oven temperature of around 70°C,  which I do not recommend at all for long-term stability.
12.5k/1k gives about 60°C, and 12k/1k gives 50..55°C, which I have used for all of my references, A-type as well non-A.
Depending on your application, you could also run the A version on that lower temperature, if your lab temperature is never higher than ~35°C.

12k is available at Rhopoint as standard value for an econistor, I don't remember if this value was also available for the BMF series
BMF resistors with 10k / 800 will give the 13.5 ratio for 60°C, and 10k / 900 gives 13.11 ratio, as a replacement for 12k/1k.

Frank

PS: 12k is not available for BMF. As can be seen in the link above, I have used BMF resistors 120 Ohm, 1k, 2x 70k, and a 12k econistor, the green one.

[nedrysoft]

Many thanks for the reply, I appreciate it.

I’ve had contact with rhopoint so I will be getting them from them, just going through the invoice back and forward.

My mouser parts have shipped as well.