Info on TDK/Lamda DC-DC Convertor for API +/- 16V to 24V

[corgan4321]

Hello,

I'm troubleshooting a recent LAZ EQn build where both of my units are functioning properly with 24V input, but have some self oscillating low noise injected when running on +/- 16V into the DC-DC convertor. I thought this was a problem other builders that have used a similar DC-DC conversion might know about. I searched for topics here and found the original topic where people discussed the sue of the TDK/Lambda, but unfortunately the schematic wasn't linked there anymore. Does anyone have access to this?
I have read the TDK/Lambda manual extensively and see that there is a remote on/off function with the RC pin, could anyone explain to me then what the Q1 is doing in the LAZ EQn build? When I short pins "RC" and "-Vin" the noise problem goes away and the EQ seems to function properly.

below is the CC6 TDK/Lamda manual and also I included a snapshot of the LAZ EQn layout with my notes in red.

https://www.mouser.com/datasheet/2/400/c-e_e-1101879.pdf

 

[Rob Flinn]

Hello,

I'm troubleshooting a recent LAZ EQn build where both of my units are functioning properly with 24V input, but have some self oscillating low noise injected when running on +/- 16V into the DC-DC convertor. I thought this was a problem other builders that have used a similar DC-DC conversion might know about. I searched for topics here and found the original topic where people discussed the sue of the TDK/Lambda, but unfortunately the schematic wasn't linked there anymore. Does anyone have access to this?
I have read the TDK/Lambda manual extensively and see that there is a remote on/off function with the RC pin, could anyone explain to me then what the Q1 is doing in the LAZ EQn build? When I short pins "RC" and "-Vin" the noise problem goes away and the EQ seems to function properly.

below is the CC6 TDK/Lamda manual and also I included a snapshot of the LAZ EQn layout with my notes in red.

https://www.mouser.com/datasheet/2/400/c-e_e-1101879.pdf

Are you sure that these units aren't supposed to be built to run from either the the lamda or the 24v from the edge conn ? That's what I thought as the case, and the extra tab on the edge conn should be cut off if you are running from bipolar 16v.  If so you might have screwed the lamda but riving 24v into it's output.

 

[corgan4321]

Yes you're correct, however, you can simply remove the TDK/Lamda convertor and apply +24V at the jump pin which is what I did to test my EQs.

As I'm doing more thinking, I'm wondering if the Q1 at the Remote control input is some kind of soft start? If so, perhaps DC-DC convertor is not fully powering up and giving me my full +24V output. This could be confirmed by the fact that if I short the Remote control pin as it says to do in the manual, the convertor gives me my +24V and the EQ sounds great...

I'm hoping someone might have the schematic that Peter used to get the DC-DC section.

 

[Rob Flinn]

There was no diagram for the dc-dc convertor if the docs I have are anything to go by.  The only thing I have is the pic you attached to the first post.

Why don't you test the dc-dc convertor outside of the the EQN just to make sure it works ?  They are known to be a bit temperamental if you read back through the build thread.

 

[corgan4321]

thanks rob,

heres the thread where the tdk is originally discussed:

https://groupdiy.com/index.php?topic=28577.0

it seems someone posted a circuit at some point but its no longer there.

I feel confident the actual dc-dc components i have work fine because when I short out the remote control pin, the power comes on fine. Also, I got two extra ones and they exhibit the same behavior.
I think the issue is still with the "turn-on" circuit that is discussed in the thread I linked above, I just don't understand what to do to fix the issue.

 

[corgan4321]

I managed to trace out the DC-DC conversion circuit attached here.  With +/- 16V I get +/- 14V after the voltage drops over the chokes and diodes.

When I apply +/- 16V to the V+ and V- inputs of the TDK/Lamda I get good 24V output so clearly it's something going on in all the regulation area, I'm just not skilled enough to know what to change. I attempted to increase bias on the transistor by decreasing value of R1 but that didn't seem to do anything...

 

[Rob Flinn]

The zener & the transistor are the most likely parts to have an issue.

You could use the diode function on your multimeter to do basic tests on them.

 

[Rogy]

Hi,

I built 8x EQN puppies last year and had the issues you describe.

The 4 inductors specified in the BOM have too high DC resistance; this messes with the soft start circuit. Replace them with those low-DCR ones: https://www.mouser.be/ProductDetail/fastron/micc-n-221j-01/?qs=UrFqKgNWc7SjepZxKrG97Q==&countrycode=DE&currencycode=EUR and you should be good.

For reference hereby the softstart circuit that Dan Kennedy shared with Peter Lazaro. Peter made some mods to this circuit but it should get you started.

Good luck, those are fantastic EQs once you get them going.

Best Rogy

 

[corgan4321]

Amazing, thank you so much Rogy!

I've ordered those inductors and hope they do the trick.

 

[corgan4321]

I just wanted to update that I just swapped out the inductors for the 220uH ones that are spec'ed on Dan Kennedy's schematic with the lower DCR and found that one of my EQns worked perfectly! The other one maintained the same issue, but after realizing I had changed the zener diode in the working one while troubleshooting last week, I went ahead and put a new zener in the issue EQn. This solved it.

I'm not sure if I had previously mucked up the zener somehow or if the new ones I ordered are more suitable for this circuit but here are the good ones linked:

https://www.mouser.com/ProductDetail/512-1N4750A

Thank you for your help Rogy and Rob!

 

[Rogy]

Congratz, well done!

Grtz Rogy