Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #20 on: December 18, 2017, 02:50:06 PM »
All righty....


It seems that one needs more resistance between the wiper of R76 and the leg feeding Q27 to get the FET Law calibration to work. I had to wire in a 100k pot to make sure I had enough resistance and it seems that right around 40k is where one can properly calibrate this last step. So I guess I'll have order some 50k guys and stick them in there and be finished. It's the only thing I can think of and hopefully it won't cause any issues as there is nothing connected to the other leg of the trimmer that would need the correct impedance for something. I'll post this question on the ez760 page and see if anyone answers.

In the meantime, I have the other board to figure out why I can't do the expanding part of the calibration. Then I should be all set. Maybe.

Thanks!

Paul
« Last Edit: December 21, 2017, 08:36:24 PM by Potato Cakes »


Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #21 on: December 18, 2017, 03:11:02 PM »
Also, for the LC Network that is shown in the colo(u)rbook for CL1 and CL2 and not listed in the BOM, here is a part number:

https://www.mouser.com/ProductDetail/Bourns/EMI101T-RC/?qs=%2fha2pyFaduiDbeIvXMFHbA4Jqa4pQl60iVMLBFv8s0M%3d


Thanks!

Paul

Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #22 on: December 21, 2017, 08:49:23 PM »
Received the LC network parts and the 50k trimmers to use for the FET Law adjustment rather than the 20k. I was also got through the expanding part of the calibration as instructed. The only thing that is not exact per the instructions is that the green LED lights up around 3dB of reduction rather than right at the initial start of metering. The fact that I'm using substitutes for the transistors may have something to do with this. I may try to change out R86 as that is what seems to be feeding Q30 (which is now a BC550C) which feeds the Expansion Lamp Out. I'll try this after dinner. More importantly I would like to complete the stereo matching of expansion sections per the Q2 instructions. Once that is done we are done!

An important note about the FET Law trimmer is that it need to have some resistance between the wiper and bottom leg or else the meter will bounce intermittently and cause one to believe there is something less wrong and start troubleshooting in the wrong area.

Thanks!

Paul
« Last Edit: February 25, 2019, 12:39:17 PM by Potato Cakes »

Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #23 on: January 01, 2018, 03:37:15 AM »
In the process of sorting out the power supply, I managed to blow up something on one of the boards to where it is putting out 20V on one side of the meter connector. I narrowed it down to the Limiter card and started pulling transistors till I got to Q14 then the meter seemed to be fine. So after replacing that one and Q9-13 it all powers up and now I'm waiting the 30mins so I can start the calibration process one more time to make sure everything is working before I mount both boards and close this thing up once and for all.

Thanks!

Paul
« Last Edit: January 13, 2018, 12:31:52 AM by Potato Cakes »

Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #24 on: January 01, 2018, 05:47:49 AM »
I seem to now have trouble getting through the calibration process, more specifically the Expansion part. The LED stays lit no matter what where before it would only come on at approximately -3dB of reduction. And I can't seem to get the meter to -20dB per the instructions nor the -8dB for the FET, which were not a problem previously. I believe I may have blown up more transistors. I'll replace them on one of the cards and see what happens. That will have to wait as it is super late.

Pretty annoyed that I still am replacing parts and troubleshooting after both were previously working....

Thanks!

Paul

Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #25 on: January 03, 2018, 01:23:17 AM »
I changed out the transistors for the expansion card on one of the boards and I am now able to calibrate the expansion part properly. The green LED still doesn't come on until there is about -3dB of reduction as before, which is fine for me, though I wonder since I am using more modern equivalents of the transistors in the build guide that there are some resistors that need to be changed as well to make it behave as per the calibration instructions.

I'll get to replacing transistors in the other one tomorrow and then maybe we can finally for real seriously close this thing up! Seriously!

Thanks!

Paul

Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #26 on: January 06, 2018, 01:21:54 PM »
Transistors in the second expansion board have been replaced and on initial testing this one seems to be fixed as well. I also replaced the ones in the limiter card as well as I did notice that before I was not getting the same gain reduction as the other board so some one on those might have been damaged as well.

Waiting for it to finish the warm up period then we calibrate again. Then hopefully the expander stereo linking will go smoothly. Then, that's it.

Thanks!

Paul

Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #27 on: January 09, 2018, 01:34:22 AM »
And now, it is finally finished! Mostly! I managed to misplace the two nuts for mounting one of the meters! Hilarious!

I also managed to screw up the compression calibration when testing the stereo linking and was getting a huge amount of THD on one of the channels when using the 5:1 ratio. The latter was due to another solder pad that needed jumping because it was no longer connected to its trace. I had also found one on one of the limiter cards as it was not actually limiting the output even though the meter was saying it was. I wound up having to replace another transistor (Q41) as after I messed up one of the channels the gain reduction meter would only track half of what the compressor what actually doing. I also trimmed the voltages back to 23.70VDC for both cards as I'm now paranoid about transistors blowing up. This adjustment may not be of any actual help, but I feel like it does.

This guy really isn't as impossible as it may seem since there is hardly any off board wiring. And also, especially with this guy, do not misplace any parts (especially resistors) unless you are just itching to test any newly acquired troubleshooting skills. The trick is knowing where to have your trimmers at starting points, which you kind of really understand that after going through the calibration process one time too many.  Then your OCD kicks in and you think that you should go through it one more time. But experience is a must and fewer mistakes you make the better. I pulled parts from this several times and in places where I was less than careful I ruined the solder pad, but didn't know it until I started actually trying to pass audio. Eventually, I just ordered another board set so I could look at where the traces where going to more easily do continuity checks.

The stereo linking works very well, and I didn't find matching the expansion sections that difficult (per the Q2 audio manual). The limiting light indicators still operate independently, but ultimately the gain reduction is linked via the compression card. The only thing to be aware of is the output sections do not link and one has to match them with tone for stereo material.

Changing out the FET Law trimmer to 50k was possibly not necessary as I found out that you need to have it set a certain way before you start, other wise you don't quite get to the -8dB part of the calibration. I think.

It is a very thick sounding compressor that can get really aggressive. I have been testing it with a rock song I worked on a while back and have noticed how much richer and intense the low mid frequencies sound when consistently hitting around -8dB of reduction. I think it could be nice in a parallel mix situation for mastering. Also, this guy is really, really quiet.

The expansion part works very nicely as well. I'd like to more experimenting with it on individual drum tracks to make better use of this feature.

I had Frank put an extra hole for a stereo switch which fits snuggly between the two control PCBs. Works way better than some sort of patching thing on the back.

At some point I'll do a post of my findings over on the ez760 build thread and encourage some more people to build one of these. It sounds really fantastic and I can't wait to put it to proper use. Thanks to Colin for the design and Gustav for supplying the boards.

Thanks!

Paul


PS If anyone in the states has two of the nuts for mounting the Sifam presenter or the Hairball Audio 1mA meters and has pity for what this process wound up being, maybe you could put them in an envelope and then them this way. Maybe you could send doughnuts....
« Last Edit: February 25, 2019, 12:43:10 PM by Potato Cakes »

Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #28 on: January 09, 2018, 01:37:47 AM »
One more pic.

Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #29 on: February 25, 2019, 12:47:37 PM »
Regarding the last photo, I went back through and removed all of the ground connections at the board for input, output, and link connections per Ian Thompson's Grounding 101. The chassis and audio ground points on the main board were both left connected to the star ground as both of those planes are electrically separated.

Thanks!

Paul


Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #30 on: February 25, 2019, 12:54:56 PM »
For convenience, here is a complied list of notes from myself and others regarding the build of the ez760:

First, it's not an insanely difficult build since there is minimal off board wiring, but it is not something for a beginner as there are heaps of parts with varying values and keeping track of them and their orientation can become overwhelming. Plus, chasing down traces and comparing them to the schematic will make your eyes cross as the connections are highly condensed on the individual daughter boards and is very easy to loose track of what is going where.

Also, don't forget that with these boards, the trimmers are to be turned opposite of the calibration instructions per Gustav.

With all of that aside, here we go, in no particular order:

- 1/4W resistors are fine to use in place of the 0.6W as listed on the BOM
- Unless you have a verified source of NOS transistors, use only modern equivalents. I had a bad batch of BC182B's that didn't know were faulty. Here are the ones I used - BC184C=MPSA18(backwards orientation), you can also use BC550C, BC182B=BC550C, BC212B=BC560C, BC212L=PN4355 - B and C legs have to be crossed, the PN4355 should be angled downward (towards the main board when the daughter card is connected) to ensure the crossed legs are not touching - just double check this, BC184L=2N3417
- The LC Network (CL1,2) are not on the BOM. I used this part:
https://www.mouser.com/ProductDetail/Bourns/EMI101T-RC/?qs=%2fha2pyFaduiDbeIvXMFHbA4Jqa4pQl60iVMLBFv8s0M%3d
- Stereo matching the expander section:
www.musictoolz.pl/pliki/instrukcja-obslugi-344.pdf
- Use this link to calculate between RMS and dBu:
http://www.sengpielaudio.com/calculator-db-volt.htm - It's helpful to calculate all of the dBu values to VAC(RMS) and write them down so that following along with the calibration process is easier.
- For the compressor input threshold, there is no mention of it in the calibration process. I ended up on having 8k5 ohms resistance between the wiper and the bottom leg as viewed when installed. I don't know if that is correct but I started there and everything seems to work out.
- When you get to Step 11 of the calibration, make sure that FET Bias and Inverter Set are turned all the to where you have most level you can get from those trimmers. If both trimmers are about halfway when you start, and you turn the FET one way, the output level will change. Same with the Inverter Set. My notes say full CCW for FET Bias and full CW for Inverter Set. I think that is correct, but I am not willing to double check it as my build is all buttoned up and finished after what seems to be more than a dozen calibration attempts. You're output signal should be closer to 0.69VAC when both trimmers are all the way in their correct starting positions. I think that makes sense.
- My Target Value A was 1.07VAC
- Start with the Compression Ratio full CW
- I changed the FET Law trimmer (R78) to 50k as I found that I needed more resistance to do the procedure. However, I also found that I needed to start with the trimmer set so where the wiper and the bottom leg that connects to the Control VPositve needs to be around 1k, because any lower the meter bounces around and looks like something else is wrong when you start the expander calibration. After this discovery, I thought that maybe 20k would be fine, but I had already installed the 50k trimmers so I just left them. If you want to be safe, you can use 50k. This may have something to do with using the modern equivalent transistors.
- The LED for the expansion indicator did not come on for me until about -3dB of reduction and not as the calibration instructions say. Again this may have something to do with using the modern transistors. I tried to adjust the values of R86 and R85, but nothing changed as far as the LED indication was concerned, so I left it as is.
- If you can find sockets to connect the daughter cards to the main PCB that will greatly aid you in the event you need to troubleshoot. If you can't find the correct size sockets (as in my case) then I would install the Input and Output cards first and check to make sure you are getting audio to pass with the front panel PCB connected. You should be able have a functioning Input and Output controls when the System is set to In. Then one at a time, install the Compressor card, Limiter card, and then the Expander card in that order, checking signal and the relevant calibration steps each time you install a card. Once you see that everything is working, then you can start the full calibration.
- Put a marker of some sort on a printed copy of the Initial Setup Procedure as you go through each calibration step. There are sections that are repeating a series of steps and if you have been working on this for a long period of time or if you are calibrating for the 10th time, it becomes easy to lose your place and/or skip over a step that will adversely affect the final outcome and you will have to start over. Again.
- Don't put the wrong part in the wrong place. After desoldering many connection points, my growing impatience caused me to break some to of the solder pads and then I had to trace where the connection was supposed to be going and solder jumper in place. So just stuff the boards correctly the first time. And then solder them correctly. Just like we all try to do when we start building any project. Seems easy enough...
- The large majority of these solder pads are very tiny and some of them are very close together. Make sure you have quality, thin gauge solder and fine solder tip. The iron temp should be set to at least 700F and the solder should effortlessly melt and flow into place. If your soldering skills do not land in the scale of really good to exceptional, then you will probably be in for a rough ride sorting out cold solder joints and bridges. Also, I would definitely clean the solder pads before starting this guy just to be certain.

These are all things I landed on after a massive number of attempts ending in failure and frustration. These are by no means the absolute true methods of doing this project, but if you follow the Colourbook and use these tips in conjunction with it, you will have a working unit.

On a side note, I was able get what seemed to be proper metering responses using a VU, 1mA, and a cheap DC type. My build wound up using a 1mA.

Thanks!

Paul

shabtek

Re: ez760 transistors and troubleshooting diary
« Reply #31 on: February 26, 2019, 10:08:12 AM »
Thanks Paul. Congrats, definitely need to clean pads , pencil eraser works ok but there is probably something better
"really fine players do not use stomp boxes or master volume, they match the amp to the room and turn it up to 11.  Stevie Ray, BB King, Albert King, Duane Allman, Dicky Betts, Louis Armstrong"
   -CJ

Potato Cakes

Re: ez760 transistors and troubleshooting diary
« Reply #32 on: February 28, 2019, 01:29:07 PM »
I did the eraser trick and it seemed to work well. I followed it up with isopropyl alcohol.

It's a shame these weren't popular enough for Gustav to keep the boards in stock, but I think a fair number of people who do DIY don't want to also have to source this many parts, myself being one of them half of the time. But I guess that could be said for a number of other fantastic projects on this site that have gone by the wayside.

Thanks!

Paul