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Old 1st March 2013, 09:36 AM   #1
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Default Trimmer on Micromega Solo H

HI, it lacking schematic, before I make mistakes and intending to change opamp, I'm trying to find out which is the function of the four trimmer in the main board of the MICROMEGA SOLO H. Two regulate the output offset (but which: those closer to the output connectors or those closer to the LF356N?). And the other two?
Can anyone help me? Many thank's
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Old 1st March 2013, 06:26 PM   #2
Mooly is offline Mooly  United Kingdom
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You would have to see what they connect to. Are there four opamps or do the other trimmers go elsewhere ?

I've a Stage 2 (now retired from service) and I did an opamp swap on that. I found when measuring the offset that you can get an inaccurate result due to low level HF hash on the output. I used a simple R/C filter soldered to a phone plug. Somthing like 22K and a 1uf.
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Old 1st March 2013, 09:23 PM   #3
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Default MicromegaSoloH trimmer

Hi, thanks for your answer. I apologize for my bad english. I read your post on Stage 2 and links to TVC (Micromega BS). There is always refers to the offset trimmer adjustment. I sent him a photo of the main board Micromega Solo (on the main board is written Micromega Duo but it is a H bitstream). I think the trimmer A and B (those close to LF 356N) serve to offset, but I don't know about C and D close to the output stage, full of transistor (it is probably a stage coupled in DC).
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Old 2nd March 2013, 06:38 AM   #4
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I would guess that trimmers A and B are adjusted first to reduce the offset of the LM356 output pin to zero. Having done that the other two will be adjusted to set the final offset at the sockets to zero. It would have to be done in that oder because they would interact.

That would be my best guess without seeing the circuit You would have to use the correct ground for the LM356 to get the most accurate reading and I would still recommend a filter for the adjustment (or use a scope and do it by eye)
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Old 2nd March 2013, 09:33 AM   #5
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Default Micromega Solo trimmer

I hoped in your experience with micrormega stage 2. Let's see if I am understanding. So the first stage closer to LF356N in Micromega Solo is similar to the final stage of the Micromega Stage 2. Trimmer on pin 1 and 5 with wiper on + voltage across the resistor r29 in Micromega Stage 2, while on the Micromega Solo trimmer on pin 1 and 5 on LF356N and wiper on + voltage (pin7). To measure the offset I have to put the edge strength of the HF filter on pin 6. But what's the ground point recommended to insert the edge of the HF filter capacitor? For trimmer closer to output sockets I will use the filter mounted directly on the output socket, as you recommended. The OPA606 is valid as a substitute for LF356N?
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Old 2nd March 2013, 11:11 AM   #6
Mooly is offline Mooly  United Kingdom
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To measure the offset on the LF356, try and see if any resistor connected to the opamp goes to ground and if so then use that as ground for the adjustment.

The OPA606 looks like it should be OK as a replacement but I always advise checking with a scope to be sure.

Swapping Op-Amps... you have checked to see it's stable haven't you ?
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Old 2nd March 2013, 11:48 AM   #7
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Default Micromega Solo H

Excellent answers and it was kind of you to dedicate your time for my problem. Thank's, Mooly
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Old 2nd March 2013, 11:50 AM   #8
Mooly is offline Mooly  United Kingdom
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Your very welcome. Hope all the mods work out OK
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