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AS3340 stability
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2, 3  Next [all]
Author AS3340 stability
ixtern
In some earlier topic there was mentioned about poor AS3340 stability (20 minutes to get stable).
As I have such chip in TH VCO Maximus (fonitronik edition) I have checked it's behavior.
First I measured stability with original tempco adjust circuit. Here are results (measured with 6-digit frequency meter). In the first column there are minutes from turning on supply voltage, in the second - frequency in Hz.

Minute Hz
1 1065.5
2 1062.5
3 1060.8
4 1059.3
5 1058.0
6 1057.1
7 1056.5
8 1055.7
9 1055.4
10 1055.0
11 1054.5
12 1054.3
13 1054.2
14 1053.8
15 1053.8

Looks like stable frequency is get after 14-15 minutes.

Then I have modded VCO like in Rob Hordijk article (Precision tuning of the AS3340 VCO).


Here are the results:

Minute Hz
1 1046.3
2 1044.8
3 1044.0
4 1044.0
5 1043.5
6 1043.3
7 1043.2
8 1043.3
9 1043.0
10 1043.0
11 1043.1
12 1043.2
13 1043.0
14 1043.2
15 1043.2

We can see that after 5 minutes VCO is rather stable. So AS3340 VCO is not a bad chip.

One comment: Zero voltage between both 5.6k resistors is not so easy to set as the voltage is constantly drifting. 0V was set after about 15 minutes of drifting (with 5-digit multimeter) with accuracy 0.1mV.

P.S. My TH Maximus was modded before I made these measurements: -5V line, +-10V reference voltages for frequency sensitive parts. 3340 chip is supplied through TL431 +10.5V.
tobb
Yeah,you get what you pay for,no miracles..
rolfdegen
Hallo ixtern

Thanks for your test results for the AS3340. I will check it again later with your circuit variant and my two AS3340 chips.

But I think I stay with Curtis CEM3340-G. It strikes me as the better choice and quality to be.
The CEM3340 is very stable immediately after switching on the supply voltage (VCC +12V VEE -12V) and easy to adjust. See my video.

CEM3340 frequency stability


AS3340 frequency stability


Greetings Rolf
infinitemachinery
The AS3340 is a fine chip. Just like any other IC it needs supporting circuitry to work properly.
ixtern
rolfdegen wrote:
Hallo ixtern

Thanks for your test results for the AS3340. I will check it again later with your circuit variant and my two AS3340 chips.

But I think I stay with Curtis CEM3340-G. It strikes me as the better choice and quality to be.
The CEM3340 is very stable immediately after switching on the supply voltage (VCC +12V VEE -12V) and easy to adjust. See my video.

Greetings Rolf

Hi, Rolf

It is hard to evaluate whole chip line after one chip test. It may be bad design, bad adjustment procedure or simply bad chip. Although I have four AS3340 chips, until now have built only two AS3340-based VCO - one Maximus and one Timo Rozendal's VCO. Then I have stopped as there was no good enough for me 3340 VCO project on the market (I need only panel+pcb set as I prefer to choose part myself). All of them has flaws unacceptable to me. Maximus at least can be modded due to relaxed THT design, Timo's SMD is a big no no.
So I must design VCO myself. Schematic is not a very big problem but I am too lazy (or too busy) to make PCB and panel design. I have ended with two VCO so far.

I may check other AS3340 chips if I have some time in the future but I am also curious about difference between AS3340 and CEM3340 so I perhaps will order one or two from thonk to test them.

Regards.
guest
thanks for doing the tests here. one quick question: was the rest of the circuit in the same thermal state at startup in both of your two tests - either had been off for an hour, or had just been on for an hour and quickly restarted after putting the new chip in? it would be nice to disambiguate between chip drift and circuit drift.
ixtern
guest wrote:
thanks for doing the tests here. one quick question: was the rest of the circuit in the same thermal state at startup in both of your two tests - either had been off for an hour, or had just been on for an hour and quickly restarted after putting the new chip in? it would be nice to disambiguate between chip drift and circuit drift.

Whole VCO off for an fifteen minutes perhaps in both cases. I think it is enough to get the stable "off" temperature for simple home measurements. You may be right that this may be circuit drift, so more interesting are relative differences in results from two cases than absolute values from the one.
tobb
infinitemachinery wrote:
The AS3340 is a fine chip. Just like any other IC it needs supporting circuitry to work properly.


Some would call it useless,gently i call it then not compatible.

Anyhow ,its not a proper working CEM3340 clone...so definitely not compatible.

At first we where excited,now we know better.
alfa
Dear Ixtern
Thanks for Your correct engineering approach and following instructions. When You made on both 5.6k resistors voltage drop the same (difference between them zero), currents through pin1 and pin2 are the same and it means that thenpco is trimmed.
These procedure must be made for any 3340 IC. Without these first procedure - any other steps are incorrect.

If You write us an e_mail alfa@alfarzpp.lv - we'll send You several evaluation samples of new projects.
cretaceousear
tobb wrote:

Some would call it useless,gently i call it then not compatible.

Anyhow ,its not a proper working CEM3340 clone...so definitely not compatible.

At first we where excited,now we know better.

Ah, but it got CEM to re-start remanufacturing so not useless!
rolfdegen
ixtern wrote:
...
First I measured stability with original tempco adjust circuit. Here are results (measured with 6-digit frequency meter). In the first column there are minutes from turning on supply voltage, in the second - frequency in Hz.

Minute Hz
1 1065.5
2 1062.5
3 1060.8
4 1059.3
5 1058.0
6 1057.1
7 1056.5
8 1055.7
9 1055.4
10 1055.0
11 1054.5
12 1054.3
13 1054.2
14 1053.8
15 1053.8

Looks like stable frequency is get after 14-15 minutes.



I have measured other values with original tempco adjust circuit. The frequency gets higher with time!? Measure on my first AS3340 confused

My second AS3340 corresponds to your measurement and stabilizes after 15 min.

I think my first AS3340 chips are broken. I will buy another one again.

I will once again take a measurement with a cold power supply and note it here..

Greetings Rolf
alfa
Dear Rolf

Certainly, IC could be damaged or something wrong with it.
But before, You must be sure that all other things are correct.
I've attached Your schematics with two questions.
Please, check picture and write answers:
1. what is the tempco of indicated resistor?
2. voltage between indicated nodes?

[/img]
rolfdegen
Thanks for the answere.
I have to change my circuit once again according to your specifications. This can take a while.

Is it ok if I only change the Tempco Pins?
alfa
Dear Rolf
Yes. In these schematic it is simpler to trim.
alfa
Dear Rolf
Abour Your schematics:
1. Net connected to pin 14 is connected to GND?
2. Both resistors 5k6 connected to pin3 - negative supply?
rolfdegen
ok. Thanks i will test again..
ixtern
rolfdegen wrote:

Is it ok if I only change the Tempco Pins?

No, because you will go out of 1V/Oct scale using pins 1-2 for the tempco adjust only. Another pin must be used to trim 1V/Oct - pin 14 with resistor and trimpot to the ground. Resistor don't need to be 0.05% - but should have low ppm. Simply I just have such one 1k6.
rolfdegen
Ah.. ok. The frequency now stable in 5min (power of for 1min)

It is a better result than at the beginning. hyper

One chip is broken. I probably always tested with this confused
alfa
Dear Rolf

What is the voltage noted in point 2?
rolfdegen
It was 0,000V.
rolfdegen
Today i make a detailed test and ordered two new AS3340 for purpose test.
alfa
If it was 0 V, then tempco is trimmed.
rolfdegen
Yesterday ist was trimmed an the voltage at point 2 was 0.0 mV.

Today when the AS3340 starts cold we have the voltage at point 2 from 7.4 mV. The voltage gets smaller over time and frequency get higher.

When I start warm (power supply 1min off), the AS3340 needs about 8min until the frequency is stable.

Now.. i will test with VEE -5V (79L05).
rolfdegen
Vee -5V at Pin 3 is an little bit unstable. I think VEE -4.94V is not high enough.

If I set Pin 3 with resistor 560R back to -12V then its verry stable.
alfa
Using internal zener (560R, -12V) - additional heating. Better to use external -5v.
If you see that your -5v on the base of lm79l05 is unstable, check recommended input/output capacitors. They must be placed according to recommendations.
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