Potato Cakes

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #220 on: February 08, 2018, 06:53:29 AM »
All righty then,

I went ahead and built out the extra board I had laying around, put it in and it closely matched the other one right out the gate, like I knew it should since all the parts were the same. This wound up being easier than trying to replace parts on the other one. The boards are obviously fine, I just either have a bad part or I missed finding a misplaced one and I felt a fresh start, at least for my time and sanity would be best. Maybe some day I'll feel the need to replacing all of the diodes and transistors on the board I messed up to get it working. But not today.

So now that I have both working close to each other, I have a bit more precise way to match the distortion for both channels. For measuring I used the Blue Cat free analyzer that shows distortion. After you do the Fine Tuning I step and install the properly calculated values for R7 and R8, put trimmers on R56 and R22 for both channels as per the instructions starting with the stock BOM values. Make sure match the values between the corresponding resistor numbers. Set the release for both channels to full CW and with the auto release engaged (if installed) as I found that the amount of distortion and which harmonics are emphasized changes with the position of the Release. In this position, I found it easier to match both with having a descending level of odd harmonics, which is what I preferred in this circuit. I put the Attack full CCW for both just to be sure, but this doesn't actually seem to change distortion levels. Both input and output controls are set to 12 o'clock. Because I said so.

Now we fire up the tone generator and route signal through the Blue Cat analyzer while also keeping an eye on the output level. For me, the distortion for both were already pretty close, with one channel about 2dB lower in volume. This is where your skills of finesse and patience will be needed. As per the build manual, R22 will change the distortion and the peak to peak output, and R56 will change output while having a different effect on distortion. Pretty sweet, right? The idea is to get the distortion waveforms to match and to have the same output, and this will require you to make slow adjustments and making a mental note of what is affecting what. Patience and finesse. So as in the build manual, you start by determining which one is least distorted or the you like the best. You might know this from simply looking at the waveform. Or you may have to turn off your generator and play some program through it (don't change the settings on the panel!) and listen to which one sounds "better". Then you go back and match the waveform and level of the "bad" channel to the good one. What you might run into, as I did, is that the channel having R22 and R56 being adjusted to match the other may not be able to get enough level so both outputs are even. For me this meant 0.5dB, which is fine when listening back but not when you are OCD about matching meters and numbers. If this is the case, you would lower R56 just enough on the higher output channel so that both have equal output and then double check your waveform.

Playing back program material in THD mode retained the stereo image much better than before without any noticeable shift to instruments that are meant to be centered. And if you want to change the harmonic content of the distortion, you can change this after the fact by adjusting the Release control and engaging the Auto Release if that is installed, so you are not stuck with the attributes of the distortion after you close the lid.

This circuit reminds me to a fair degree of sameness to a Chandler Zener Limiter that I rented years ago. Not particularly suited for mastering/program material (which is what I rented the Zener to do but was able to smoothly do), but definitely for some aggressive drum bus and guitar/bass tracks. I haven't messed with vocal tracks through this yet.

It should be noted that I went overboard matching D1/D3 and D2/D4 and kept them within 0.001VDC of each other for both 1k and 10k measurements and not too far from that between the pairs themselves.

Last couple of things for me to work out: I still get pops with switching the relays as before. It spikes the meter, but the actual sound is more like a clock switching noise and not a tremendous explosion as the display would suggest. Still needs to be sorted. The additional 100k from the middle pin Bypass 2 header to ground didn't seem to do anything for me in this regard. I also have the radio station thing to sort out. One channel has slightly more interference and after swapping positions inside the case, it was clear it has to do with what is mounted on the board and not the switches or cabling. One thought is that when I did my distortion calibration I was at too high of a level that is raising the noise floor. I get about +7dB from unity with the THD engaged and both input and output knobs set to 12 o'clock. I am using stepped controls with 11 positions. I could readjust R56 to be at unity and lower the S/N ratio in theory, but that wouldn't solve the mystery of the radio interference. However, in its current state the static interference is pretty faint and can only be heard when there is no signal being generated and the volume of the speakers are turned up. In use, I don't even hear it when it's processing audio and even if I don't figure this out it will still be for processing tracks. So for now, I've put the lid on it and I'll get back to tinkering with it after I finish the last build I have on my bench.

If anyone has any suggestions for trying to sort out the faint radio static I would appreciate it. I know it's somewhere between the bypass connections, as it is perfectly clean when the circuit is disengaged.

Really great project and I'm glad I finally got my mine up and running.

Thanks!

Paul
« Last Edit: February 08, 2018, 07:20:49 AM by Potato Cakes »


Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #221 on: February 12, 2018, 06:57:14 PM »
Just starting my build. Excited to get going on this one!

Have a few questions before I start.

1. Can I get away with 5:1 for the input transformers? I've read that 4:1 input transformers are ok to use with a few resistors to change. 

2.  Hold control, worth adding? Was going to add it via on off on toggle and two set resistors instead of a pot. Struggling to see how useful it would be or exactly what it's doing. Some people refer to it as a kind of threshold control.

3. Side chain hpf caps.  How to calculate the cap values for the hpf, I would like to add more frequencies.

4. Good source of the 1n4153? I have only found one source and have to buy 100 at a high price.

fripholm

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #222 on: February 15, 2018, 03:08:39 PM »
Member ToBSn has made a small helper board for the sidechain filter which he offers in the Black Market. I think he also mentioned values for different frequencies. Do a search in this thread, as well as for the hold control.

There's nothing special about the 1N4153 in this circuit. It's just a general purpose diode after all. Mouser lists the 1N483B as a more modern substitute which is also end of life, but they still have plenty of them in stock. I'm pretty sure you could also use an ordinary 1N4148 or 1N914.

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #223 on: February 16, 2018, 06:18:05 AM »
Member ToBSn has made a small helper board for the sidechain filter which he offers in the Black Market. I think he also mentioned values for different frequencies. Do a search in this thread, as well as for the hold control.

There's nothing special about the 1N4153 in this circuit. It's just a general purpose diode after all. Mouser lists the 1N483B as a more modern substitute which is also end of life, but they still have plenty of them in stock. I'm pretty sure you could also use an ordinary 1N4148 or 1N914.

Thanks for the info Fripholm!

I ended up ordering the 1n4153 anyway so could be good to have aorund for synths or something.

Thanks for the info on HPF, thats all i needed.

Potato Cakes

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #224 on: February 17, 2018, 04:35:09 PM »
I readjusted R56 to lower the output and more closely match unity gain when both the input and output are at 12 o'clock, hoping that decreasing the level would also lower the level of the static interference. That was not the case. I did notice that increasing the input gain decreases the noise about 5 dB. Also, to triple check that it was radio noise and not oscillation, I pulled the connector for BYP2 and I could hear a sweeping noise and see that sweep occur on the scope as it changed frequencies, so what I am experiencing is definitely not oscillation. The noise on one channel is 7-10 dB louder than the other, and this seems to move with the board and I have confirmed it is not the transformers or the switch wiring. And as before, the radio signal has something do with the wiring connected to the BYP2 switch, as when I touch is the radio station signal comes in loud and clear. I've used normal twisted pair and individual shielded cables, so maybe there is some other combination that I need to try. I am using a shielded cable to go from the transformer to the switch for BYP1. Touching this cable does not affect the radio station signal like it does with BYP2. I have a couple of ideas to try for testing to see if I can mitigate this noise.

Thanks!

Paul

Potato Cakes

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #225 on: February 17, 2018, 10:59:43 PM »
I think I am out of ideas. I've done more testing, but I can't seem to sort out this radio interference. I did find that even when the circuit is bypassed, I can still get radio when I touch the cable going to BYP2. I also found that when the circuit is in, if touch the side of R59 that connects to T15 I can make the radio station come in clearly, but not when touching the other side that connecting to ground. I even made a jumper to connect BYP2 to itself with a shielded cable without the need for a switch and still the same results. I tried to insert WIMA film caps of various values in places I thought that would help filter RF but to no avail. I would like to see if anyone who has a working unit that has is quiet when the circuit is engaged if they can cause a radio station to transmit through the output by squeezing the cable or cables that connect to BYP2. Or if they have any ideas on how to filter the RF or anyone is using all shielded cables to make their connections.

Another fun thing that I found which I didn't notice before is that the release control changes the output level when doing THD, or at least when running tone. I mentioned before that it affects the distortion characteristics but didn't also realize it was changing the level. Very bizarre.

I'm going to give it some more thought and also see if anyone has any fresh ideas I can try before I commit to giving up. It works as is and the noise floor is low enough that it won't matter when this unit is applied to louder instrument tracks. I just want to understand what is going on for the sake of increasing my own knowledge, but if it's not to be then so be it.

Thanks!

Paul


Ilya

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #226 on: February 18, 2018, 03:37:41 AM »
This doesn't seem right. The circuit shouldn't rectify AM/FM if built correctly. There's a mistake somewhere. And release shouldn't affect the output level at all. You need to start looking from there and try to find the error. Don't give up!
PCBs, enclosures and build guides at www.rackneve.com

fripholm

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #227 on: February 18, 2018, 04:47:30 AM »
I would like to see if anyone who has a working unit that has is quiet when the circuit is engaged if they can cause a radio station to transmit through the output by squeezing the cable or cables that connect to BYP2. Or if they have any ideas on how to filter the RF or anyone is using all shielded cables to make their connections.

Tried this but I still can only get the noise that I posted as a sample a few weeks ago. That only happens when the output gain pot/switch is removed from the connector. With everything connected I'm not able to reproduce this.

Maybe you have a radio station nearby which transmits on that particular frequency?

Quote
if touch the side of R59 that connects to T15 I can make the radio station come in clearly, but not when touching the other side that connecting to ground.

T15 is in the output stage, R59 in the sidechain and they don't connect. Which ones do you really mean? ;)


Quote
Another fun thing that I found which I didn't notice before is that the release control changes the output level when doing THD, or at least when running tone. I mentioned before that it affects the distortion characteristics but didn't also realize it was changing the level. Very bizarre.

That's odd, I didn't notice this before but you are right. The release control affects the distortion AND level. On mine, it's a level change of about 1 dB over the pot's travel.


Quote
I'm going to give it some more thought and also see if anyone has any fresh ideas I can try before I commit to giving up. It works as is and the noise floor is low enough that it won't matter when this unit is applied to louder instrument tracks. I just want to understand what is going on for the sake of increasing my own knowledge, but if it's not to be then so be it.

I think I've already mentioned it, C34 (next to BYP2) does not work the way I intended it to work. It usually is shorted when the circuit is engaged - but have you tried removing it completely?

C6 and C7 control the HF response of the compressor circuit. Maybe try increasing the value of one of them or both - up to 270p shouldn't affect the audio band. C6 should have the most impact. You could also temporarily short out R1 which (in combination with C3) slightly lifts high frequencies before it hits the input.

Potato Cakes

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #228 on: February 18, 2018, 09:34:18 AM »
Radio station only happens in other builds when I have an unbalanced cable when I should have a balanaced or on mic builds when the cover is removed. This current issue is new. I had just finished another compressor build with some different mods and during the troubleshooting/testing phase it did not have a radio station pick up, even with extreme output gain settings. So I'm a bit baffled to the say the least.

I meant T13 and not T15. Sorry.

Earlier I noted the change in distortion, but did not mention any gain difference as it was only about 1dB like you mentioned. Now when I'm testing it drops significantly when turning the release control, so I'm like "what is going on now?!" I've been constantly connecting an disconnecting the headers, so I don't know if something is starting to fail. This is happening on both channels.

I haven't tried removing C34 yet. I'll mess around with C6 and 7 and see what's going on.

I know all of these problems are my doing and lately I've been discovering all kinds of fun issues with recent builds, so I place the blame on myself. I'm just frustrated because after solving all kinds of different problems, this one in particular doesn't make any sense.

I'll make the changes and report back.

Thanks!

Paul
« Last Edit: February 18, 2018, 09:48:07 AM by Potato Cakes »

Potato Cakes

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #229 on: February 18, 2018, 11:16:06 AM »
A discovery about the Release affecting output gain. I had previously adjusted R56 to get the gain back down to unity when in THD mode. When I did this, that's when I started having a 40dB of gain drop with turning the release control down. I put it back to where it was and now I just have the 1dB drop as before. When I adjust R56 to a lower value, it eventually lowers the the level down to where I want it to be but it kills the distortion, however the release doesn't drop the output level. You can see in the attached image what you get when R56 is adjusted too low. So I will have to set everything back to where I have 8-10 of gain increase in THD mode with both input and output set to 12 o'clock and just figure out where the controls need to be set in order to get unity gain.

You'll note all the noise I am getting that I'm currently fighting. When I pull the output control I get this plus a spike that moves back and forth that looks like a shark fin which corresponds to the sweeping frequency due to oscillation.

I also removed C34 and changed both C6 and C7 to 220pF but that made no change in the RF interference.

My next move is to make sure all the connections that are going to ground are indeed doing that. I might also have to replace the input and output gain pot connections to shielded cable. I did already try this with the output pot, but not both.

I am going to figure this out!! Maybe!!

Thanks!

Paul
« Last Edit: February 18, 2018, 11:20:49 AM by Potato Cakes »


Potato Cakes

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #230 on: February 18, 2018, 12:52:52 PM »
I've rigged up a step to pick off audio from different points in the circuit with tone being injected to see where noise it being amplified. A couple of observations:

- Noise at D5 is approximately 90dB lower than the signal peak. Before it was about 60dB. The noise level changes with the input gain setting

-Noise at R25/27 is about 100dB lower than signal peak when gain is set to 12 o'clock. The noise level at this point does not change with the input gain setting.

-BYP2 gives me only noise at the middle and engaged (side next to T13) pins and the level of that noise jumps intermittently.

Somehow the noise is being boosted by the time it gets to the output pot. If I could just maintain the 90dB difference like I get at D5 then I would be fine.

Time to go back to poking around.

Thanks!

Paul

Potato Cakes

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #231 on: February 18, 2018, 06:49:07 PM »
Tried some more things. Unless I my brain can come up with any more ideas, I think I'm done poking around for now. Here's where I ended up:

-Changed output/input pot and BYP2 connections with single, balanced, shielded cable. I the radio station no longer comes in clear when I touch the cable to BYP2, though the noise as before is the same.

-With a normal DPDT switch for the bypass, I had to use 8.2k resistor connected between the pole of BYP2 and ground and I was able to stop it from popping when engaging/disengaging. However, with the relay this would stop the popping when engaging but not disengaging. I also noticed at this point that I was no longer getting pops on both channels as before. I thought that it was something with how the relay was getting power and how much, so I lowered the voltage going to the relay down to 16V, but it did not fix the disengage problem. I did lead me to discover that doing this I no longer needed the resistor on the pole of BYP2 to ground to stop the pops while engaging. For the pops disengaging, I found that the level of the popping was inversely proportional to the output gain setting. Also, pops themselves contain higher frequencies, and can be lowered using a 48dB slope/octave LPF at around 16kHz. I still can't figure out how to get it to not generate an audio spike while disengaging with a relay. It happens to fast for me to get a voltage reading.

-The noise is being picked up somewhere after the input controls and before the BYP2 connection. It is present when I only have power, the output pot, and BYP2 connected with the circuit engaged. To reiterate, it's level is not affected by anything other than the output pot. This is with both stepped and variable controls. The places where I can pick off an audio signal after the output pot does show that I am getting noise but at a lower level. I just haven't been able to see exactly where in the signal flow of the schematic it gets introduced in the circuit. When I first started I thought I was D1-D4, but I'm pretty sure it's not those considering they been changed twice within the same manufacturer and a third time with a different one.

I think what I may do next is remove the connection between R30 and the output and start at the top and work my way from the input and see if I can find where the noise originates, although I don't know exactly what to do in the event I find the culprit.

Thanks!

Paul

Ilya

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #232 on: February 18, 2018, 07:00:29 PM »
What kind of a noise it is? I had several noisy zener batches both from the same and different manufacturers. Are you using 751 zener? I had Fairchild 751 that were fine and another ones from Fairchild that were noisy. Try another zeners and see if the noise changes. You don't even have to match zeners for this check.
PCBs, enclosures and build guides at www.rackneve.com

Potato Cakes

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #233 on: February 18, 2018, 10:11:52 PM »
What kind of a noise it is? I had several noisy zener batches both from the same and different manufacturers. Are you using 751 zener? I had Fairchild 751 that were fine and another ones from Fairchild that were noisy. Try another zeners and see if the noise changes. You don't even have to match zeners for this check.

I sounds to be radio interference. I have used zeners from MulitComp and Central Semiconductor. As I have stated earlier that I have swapped these out three times now, so I have a pretty good feeling that it is something else. I will, however, try it one more time because you brought it up.

Thanks!

Paul

Ilya

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #234 on: February 19, 2018, 01:57:08 AM »
Radio interference is not relevant to zeners. If you get high level of white or pink noise than you can swap zeners to see if they are the culprit.
PCBs, enclosures and build guides at www.rackneve.com

Potato Cakes

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #235 on: February 19, 2018, 12:31:55 PM »
I have replaced the zeners several times but will try one more time. If you had seen previously, when I touched certain cables I would get a radio station playing through very loud and clear, and just sitting idle the noise has the characteristic of being an RF signal that is very weak and not as consistent as white noise.

I'll try try pulling them later tonight and see what happens. If it is the zeners I might have to see about purchasing some tested matched pairs as I've already tried several different sets across different manufacturers.

Thanks!

Paul

Rob Flinn

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #236 on: February 19, 2018, 12:46:19 PM »
I have replaced the zeners several times but will try one more time. If you had seen previously, when I touched certain cables I would get a radio station playing through very loud and clear, and just sitting idle the noise has the characteristic of being an RF signal that is very weak and not as consistent as white noise.

I'll try try pulling them later tonight and see what happens. If it is the zeners I might have to see about purchasing some tested matched pairs as I've already tried several different sets across different manufacturers.

Thanks!

Paul

Simple question:

Are you using screened cable everywhere with the screen connected to Earth on every cable ?    I found this made quite a lot of difference with stray noises.   It's not sufficient to use just twisted pairs for this box.
regards Rob

Potato Cakes

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #237 on: February 20, 2018, 12:31:39 AM »
I am not currently doing so but I was thinking that might be another thing I could do. After doing all the header wiring, I've only changing the wiring slowly as I'm lazy and didn't want to redo all those connections. But I may not have a choice.

Thanks!

Paul

fripholm

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #238 on: February 20, 2018, 03:43:10 AM »
To what Rob said I might add, that it's even more effective to connect the cable's shield on only one side to ground.

Potato Cakes

Re: [BUILD] fripholm's TG1 Zener Limiter boards - support thread
« Reply #239 on: February 20, 2018, 11:15:14 PM »
I pulled the zeners again and did 120k resistor bypass trick again and the noise was lowered by about 20dB, but then I found out the overall output was down by the same amount so there wasn't any actual improvement. I did notice at this point the radio station issue returned when touching the BYP2 cable when the zeners are bypassed. I put the zeners back in and made sure the input cable was connected to ground on one end all the way to the bypass header. I also pulled C11 and C12 as well as shorting SC1 and 2 to bypass the sidechain part of the circuit with no change. Signal is still clean when bypassed. So I know that it's not in the sidechain, in the output section past the output pot, or before C1. It seems that a gain stage before the output pot is boosting this noise and sending it downstream. Guess I'll have to go back to trying to pick off signal in the circuit and see if can find a change in noise level. I think for now I'm going to say it's not wiring that is inducing this unwanted signal.

At this point all I am looking to achieve is lowering the noise a bit more. It's still low enough to be quite usable for the large majority of types of instruments that I would use this to process. Its just that I have not had this type of issue on any of the dozens of other builds, even with in circuits designed significantly impart it's own characteristics to the audio signal. My problem is that while chasing this down I have maxed out my understanding of audio circuitry. I'll focus on just trying to find where the noise starts and see if anyone has anyone can provide some insight to this situation.

Thanks!

Paul


 

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