Take a look at the directions again. It is a little weird to do because when the 2.245V is off a bit, you must turn the trimmer in the OPPOSITE direction farther away from the target then turn GR off and reset the 2.487V.djroshi said:
[BUILD] CAPI FC526~500 Series~FET Limiter Kit~Official Support Thread
- Thread starter jsteiger
- Start date
Help Support GroupDIY Audio Forum:
Don't worry about it Doug. Now that we know what the dealio is, I should be able to replicate and try it here. I am 99% sure it will be no issue. The low voltage was the original issue anyhoo not higher but I still think we are good.emrr said:
Are you sure you are at 20:1? Check the voltages at the comparators pins that I attached in post #79 of this thread.
I would check the orientation of the top yellow LED, the one adjacent to the green one. It sounds like that one is in backwards and blocking the voltage flow below the green one.
Would that cause the green LED to not light up though? Because with GR engaged nothing is lit.
Measuring the voltage between GND on the main board and the leads of the LEDs gives some confusing results.
With GR OFF I get -14.76V on all leads except for D11-G anode which is at -12.69V and accordingly the green LED is lit.
D-11GA = -12.69V
D-11GC = -14.76V
D-10YA = -14.76V
Everything else = -14.76V
With GR ON I start getting positive voltages, whereas with GR OFF the voltages are negative.
D-11GA = +14.51V
D-11GC = +12.89V
D-10YA = +12.89V
Everything else = ~10mV
The LEDs definitely appear to be installed correctly? Pretty difficult to get a photo in which the knicks on the anode were clearly visible, but the length of the internal lead is pretty clear and the longer ones definitely have knicks in them.
Measuring the voltage between GND on the main board and the leads of the LEDs gives some confusing results.
With GR OFF I get -14.76V on all leads except for D11-G anode which is at -12.69V and accordingly the green LED is lit.
D-11GA = -12.69V
D-11GC = -14.76V
D-10YA = -14.76V
Everything else = -14.76V
With GR ON I start getting positive voltages, whereas with GR OFF the voltages are negative.
D-11GA = +14.51V
D-11GC = +12.89V
D-10YA = +12.89V
Everything else = ~10mV
The LEDs definitely appear to be installed correctly? Pretty difficult to get a photo in which the knicks on the anode were clearly visible, but the length of the internal lead is pretty clear and the longer ones definitely have knicks in them.
Attachments
With GR engaged, turn the input pot down all the way. I assume the green LED will illuminate. The GR on/off switch does nothing more than turn the audio going to the sidechain amp off. It does nothing directly with the LED's.
When the voltage at TP10 goes just below the voltage that is at the comparator pin, the respective LED will illuminate.
So, using the data that you posted, when the voltage at TP10 drops just below 2.503, the 0dB green LED will light.
When the voltage at TP10 drops just below 2.456, the -.5dB yellow LED will light.
When the voltage at TP10 drops just below 2.423, the -1dB yellow LED will light.
And so on.
Your voltages at the comparator pins look good so the only other thing left in the circuit is the LED's.
When the voltage at TP10 goes just below the voltage that is at the comparator pin, the respective LED will illuminate.
So, using the data that you posted, when the voltage at TP10 drops just below 2.503, the 0dB green LED will light.
When the voltage at TP10 drops just below 2.456, the -.5dB yellow LED will light.
When the voltage at TP10 drops just below 2.423, the -1dB yellow LED will light.
And so on.
Your voltages at the comparator pins look good so the only other thing left in the circuit is the LED's.
here is a fun one. my leds dont do anything. when i first put the kits together it seemed to work but they werent doing what they were supposed to.
now when i turn them on one of the unit blinks all of the leds and the other does not
otherwise the units seem to be working
any ideas where i should start looking?
i have verified that the polarity is correct on the leds
now when i turn them on one of the unit blinks all of the leds and the other does not
otherwise the units seem to be working
any ideas where i should start looking?
i have verified that the polarity is correct on the leds
radrobgray
Member
- Joined
- May 20, 2015
- Messages
- 9
Any further assistance? I really have no idea where to go from here. Thanks.jsteiger said:
With no GR taking place, can you measure the DCV at TP7 (top left corner of the PCB)? Also what make and model of DMM are you using?radrobgray said:
Sounds like you have different issues with both units? I think this should be handled one by one. It would be best to get one unit functioning correctly and then use that as a benchmark for the other. I have had guys install one or more of the LM339's backwards. That can be easily overlooked at first.daveriot said:
The first Rev of the Test Points Guide has been added to the first post of this thread. This is just a start for now. I will be adding more info to this doc soon.
I made part # and tolerance corrections for the 300k and 1M R's. I also changed R41 from 1k2 to 750R. I like to keep the Rev of the doc the same as the Rev of the PCB so things don't get too confusing.emrr said:
radrobgray
Member
- Joined
- May 20, 2015
- Messages
- 9
I got -.302vdc at TP7 w/ GR off. I'm using a Victor VC9805A DMM.jsteiger said:
OK this is super high, or too close to 0V. When the VVR FET is properly biased for 0.5dB of loss, this reading should match (or be close to) the bias voltage I have written on the bag with the SN that the FET came in. My pinch-off range is typically from -1.4V to -1.7V for the VVR FET.radrobgray said:
I can think of 4 possibilities why this would not match or be pretty close.
1. I use a Fluke 177 to sort and record all FET data. If the input Z of your meter is not close to mine, it will drastically skew the measurement since that part of the circuit is so high impedance. From the looks of your meter's spec sheet, the results should be similar. FYI, the Fluke has an input Z of >10M. My B&K 889B bench meter has an input Z of 1M. I cannot use it to sort FET's or confirm my Fluke readings. So, probably not that.
2. The MTR FET and VVR FET somehow got swapped during assembly. They are not at all interchangeable like with other 1176 style kits. I chart, measure and make sure that the transfer characteristics of all FET's fall into a certain range at multiple predetermined amounts of gain reduction. This means that the MTR FET will accurately reflect what the VVR FET is doing. These 2 FET's do not need to have the same pinch-off voltage. This only means that the MTR FET pinch-off must be equal to or closer to 0V than the VVR FET. If these got swapped, once the MTR FET gets biased in the incorrect VVR position, the VVR FET that ended up in the MTR spot will essentially do nothing. Now, the FET's that have a too high pinch-off voltage for VVR purposes, get sorted into the MTR position. So far, they have all been in the -1.1V to -1.399V range. This does not exactly explain your situation either but will for sure save somebody some time in the future.
3. Your VVR FET is not biased correctly for the 0.5dB loss. The more your turn the Q_Bias trimmer CCW, the lower the output will get and the lower the bias voltage reading at TP7 will be. I would recheck this adjustment and I would actually look here first.
4. There is something else messed up in the -10V part of your build that we have not uncovered yet.
Happy Sunday folks!
I have finally had some spare time to expand and elaborate on the support docs for the FC526 project. I have just posted new docs and links that can be found in the first post of this thread.
Here's a recap of what is new:
I have added a Meter Zero Adjust doc. This will mostly help folks who are buying assembled modules but I suggest that anyone who has a FC526 take a quick peek.
I have updated the Test Points Guide. It now includes some specific info on testing the audio path and the sidechain elements of the build. Also included are some things to look out for as well as meter voltage specifics.
Lastly, I have updated and improved the Calibration Guide. This includes some important pitfalls to look out for as well as a much easier and versatile way to bias the VVR FET. Not only does it make the bias adjustment easier, it also double checks your audio path at the same time.
That's it for now so please visit the first thread and update your support docs folder for this build.
I have finally had some spare time to expand and elaborate on the support docs for the FC526 project. I have just posted new docs and links that can be found in the first post of this thread.
Here's a recap of what is new:
I have added a Meter Zero Adjust doc. This will mostly help folks who are buying assembled modules but I suggest that anyone who has a FC526 take a quick peek.
I have updated the Test Points Guide. It now includes some specific info on testing the audio path and the sidechain elements of the build. Also included are some things to look out for as well as meter voltage specifics.
Lastly, I have updated and improved the Calibration Guide. This includes some important pitfalls to look out for as well as a much easier and versatile way to bias the VVR FET. Not only does it make the bias adjustment easier, it also double checks your audio path at the same time.
That's it for now so please visit the first thread and update your support docs folder for this build.
Here a little pic for motivation !
They are all not properly calibrated, but as there is no stereo option, I don't care too much, they sound superb the way they are.
I updated the color scheme on the knobs with orange, which I like a lot more then yellow.
The 2 orange ones use 1731, the yellow one uses red dots. All relatively transparent.
I ordered 2 Raindog OP Amps from Hairball. let's see, wether they give a bit more color.
In which position will they have the most coloration ? Any tips ?
at last, I'm always a bit confused with the direction of the GR switch, it's the only one which goes up to work.
fantastic workhorses,
yeehaa
They are all not properly calibrated, but as there is no stereo option, I don't care too much, they sound superb the way they are.
I updated the color scheme on the knobs with orange, which I like a lot more then yellow.
The 2 orange ones use 1731, the yellow one uses red dots. All relatively transparent.
I ordered 2 Raindog OP Amps from Hairball. let's see, wether they give a bit more color.
In which position will they have the most coloration ? Any tips ?
at last, I'm always a bit confused with the direction of the GR switch, it's the only one which goes up to work.
fantastic workhorses,
yeehaa
