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[BUILD] FET/500 Official Support Thread
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Facemeltingsolos
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- May 23, 2020
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Hey there!
Doing the calibration on my Rev D and everything was going well (except for realizing it was in smash mode half way through and needing to restart), until I hit that GR off switch. The LEDs went nuts and if I unmuted the tone would come in quickly and seemingly randomly. When I switch it back in the output LEDs slowly settle but on the GR side the slam LED stays lit. As I wait for my next day off, is there any area that I should be looking to? An IC issue, perhaps?
Here's a little video of the issue: FET 500 Rev D Help
And some pictures too.
Doing the calibration on my Rev D and everything was going well (except for realizing it was in smash mode half way through and needing to restart), until I hit that GR off switch. The LEDs went nuts and if I unmuted the tone would come in quickly and seemingly randomly. When I switch it back in the output LEDs slowly settle but on the GR side the slam LED stays lit. As I wait for my next day off, is there any area that I should be looking to? An IC issue, perhaps?
Here's a little video of the issue: FET 500 Rev D Help
And some pictures too.
Facemeltingsolos
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- May 23, 2020
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Oof! There was a resistor that was only half soldered!
I reflowed everything, and am waiting for an extender in the mail. Hopefully this time if it messes up I'll be able to diagnose the issue.
Facemeltingsolos
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- May 23, 2020
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Just going to add: this gain reduction issue is so weird. The input know acts as an oscillator for the intermittent signal. Low input=slow, high input=fast. I'll try to look some more but I think I might be sending it in.
hellgateLabs
New member
Quick question re: resistor tolerances. I am building a Revision A FET/500. While sorting resistors, I found that my 10M Ohm carbon resistor (R45) was coming in at just above 11M ohm. From my understanding, the gold band indicates a tolerance of +- 5%. So this is measuring around a 10% tolerance range. I know my meter could be the culprit, but I am able to measure the 15M ohm resistors without any issues.
Is this result indicating a bad resistor? Or is this falling within an acceptable range for this circuit? Additionally, if I need to replace it, will any standard 1/4 watt carbon film 10M ohm resistor fit the bill? Or are there specific brands/specs that are the best fit for this use case?
Thanks in advance for the help, appreciate all the hard work put into these kits!
Is this result indicating a bad resistor? Or is this falling within an acceptable range for this circuit? Additionally, if I need to replace it, will any standard 1/4 watt carbon film 10M ohm resistor fit the bill? Or are there specific brands/specs that are the best fit for this use case?
Thanks in advance for the help, appreciate all the hard work put into these kits!
I've hit a snag durring calibration. Everything is smooth until I get to the gain reduction calibration. With the gain reduction off (light on) and input at 9 dBu (2.18 vac) it should drop to 0 dBu (.775 vac) when the gain reduction is on (light off). Mine just stays at 2.18vac. Any idea which components to look at first?
Last edited:
hellgateLabs
New member
Thanks @mrmike186! I actually contacted them through the website right around the same time I made that post. For folks who run into a similar issue, the basic gist is that:
- The original unit used 10% tolerance resistors.
- That 10MΩ resistor is only there to prevent audible "pops" when switching between ratios. It's an arbitrary value. It really can be any resistor between 1-20MΩ. The original Rev A doesn't have that resistor at all, so if you want to be 100% authentic, you can leave it out. But you'll be more likely to get pops.
Sorry I can't offer any advice re: your calibration issue!
I have a frustrating issue on my REV A unit. I get a nasty, high frequency distortion (nothing pleasing, an almost digital clipping sound), on peaks occasionally. The bad part is, when I pull the unit out of the rack and use a 500 extender cable, the problem goes away. I think the problem occurs when pressure is put on the front panel. I can go for weeks without problems, and then the problem reappears. If I repeatedly re-seat the module in the chassis, the problem eventually will go away when I get things just right.
Again, I can't make the problem appear when out of the rack. I've tried re-flowing some of the solder joints, but haven't had any luck.
Any tips on how to troubleshoot this issue?
Again, I can't make the problem appear when out of the rack. I've tried re-flowing some of the solder joints, but haven't had any luck.
Any tips on how to troubleshoot this issue?
hellgateLabs
New member
Is it possible that the issue is with the card connector on the actual rack? Since it doesn't occur when using the extender cable, I could see a situation where the 500 module causes the rack's PCB to flex a bit under the weight, which may cause a bad contact to go in or out. Since the extender plug is super light, it may not impact the rack's connector at all. Apologies if you already investigated this possibility. Good luck!
Thanks for your response. I've tried it in multiple 500 series racks, and have gotten the same results.
hellgateLabs
New member
Bummer, sorry to hear that. Wish I could offer more help!
Hil
New member
Maybe there is something written somewhere that I am not seeing, but I am curious about the resistor spot labeled "r-opt" not shown on the BOM.
I'm working on the Rev D like pictured at the top of the page. Though it's blocked mostly, you can see the place I'm talking about on the top left of the pcb.
I'm assuming it's an optional resistor and the leftover 3.9M resistor I have goes there, but what does it do?
I'm working on the Rev D like pictured at the top of the page. Though it's blocked mostly, you can see the place I'm talking about on the top left of the pcb.
I'm assuming it's an optional resistor and the leftover 3.9M resistor I have goes there, but what does it do?
To answer your question:
https://help.hairballaudio.com/hc/en-us/articles/360046557413-FET-RACK-and-FET-500-Input-Mod
"FET/RACK and FET/500 Input Mod
If you've ever used an original URIE FET compressor, you might notice that the input pot on our version is a little hotter. The reason is that the original Allen Bradley pots had a very unique logarithmic curve that is hard to replicate with modern components. Modern parts that can, are VERY expensive and we find they end up scratchy in less than one year. In the past, we used a grey 3-deck pot that was hotter than we would like but did the trick. Recently, we've moved back to our blue Bourns 3-deck pot that is less hot and closer to the original curve. We're very happy with the performance.
However, the revision A's input is hotter by design, a full 6 dB. Some users find they have a hard time getting light compression. Here is a very simple mod you can do to the 3-deck potentiometer that will result in a 6dBish "slug" on the input. You can do this mod on any revision of FET/RACK or FET/500 and it's simple.
Newer FET/RACK PCBs have a R-OPT next to the t-pad for this resistor. If you have a FET/500 or older FET/RACK you can easily still add the mod. Looking from the bottom (rev A Rack pictured) locate the side middle lug that attaches to pin 1 of the input transformer. Solder a 100Ω resistor (anything above 1/8W is fine) from that terminal to the front middle terminal. The front is where the shaft is located."
Hil
New member
Ah, thank you. I knew it was something interesting. I am curious about comparing Revision A in the future.
Before I start the calibration — I'm having a little bit of a hard time getting the small Bourns trimming potentiometers on the front panel to read anything but a little bit below 2k. I find it odd because I managed to get the pots placed elsewhere to read right in the middle.
Anyway, I broke the leads attached to my budget multimeter so it's going to sit on my desk for a couple while a wait for a better DMM and new leads to come in the mail. In the meantime, if someone could tell me if the thing with the trim pots is a huge deal it would be appreciated.
Has anyone tried a 100k or 250k pot for a slower attack time instead of the standard 25k attack pot in an HB FET/500 ? Curious if it works by just replacing or if it's more involved---- I'm sure it increases the likelihood of more thd creeping in with hot signals and it might not be wise in a rev A , but im thinking of trying it in a rev D or F. Guessing 100k would get me close to 4ms and 250k almost 10ms. I know people have talked about slow attack mods for the rack units, but i haven't seen any reports back if it works, or if there are any issues with doing it. - thanks
So i ended up putting a 100k linear pot for attack in a Fet 500 rev d and.... it works great...Honestly, i think a 50k (2ms) would have been enough as anything past 2ms (12 oclock) lets so much transient info through that i find myself speeding the attack back up to around 12 oclock , but i do love the sound of having that extra 1ms or so.....This is coming from a guy who usually prefers 15 to 30mill attack times on other hardware and software---I guess it's the nature of the fet / feedback design/sound? At the 100ks slowest setting of about 4ms, it sounds close to or even slower than 30ms on my ssl clone ......ANYWAY, i have another question:
When i opened up the fet 500 rev d's i bought used (I've learned how to calibrate both of them from Mike at Harball's excellent instructions and video) I found a jumper on the circuit board that I think is between a lug of Q2 & R8 ( i could be wrong, i was doing this visually). I know about the T-pad mod, but this looks to be something different and i couldn't find any info on what it might be. Does anybody know what this jumper is doing and if it's a good idea to leave it there? ----
When i opened up the fet 500 rev d's i bought used (I've learned how to calibrate both of them from Mike at Harball's excellent instructions and video) I found a jumper on the circuit board that I think is between a lug of Q2 & R8 ( i could be wrong, i was doing this visually). I know about the T-pad mod, but this looks to be something different and i couldn't find any info on what it might be. Does anybody know what this jumper is doing and if it's a good idea to leave it there? ----
Yukon Cornelius
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- Nov 3, 2017
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- 1
Hey!
Just got done building a REV A 500 series and seem to be having an issue.
During step one of the calibration I was adjust able to adjust the QBias until all LEDs on the meter were lit up; however, I was unable to get anything above around 4 dBu on the output.
I have been going through this thread and the troubleshooting guide looking for answers before asking a question, but just noticed that I am getting 0 to +2.5V DC on the output of my QBias, rather than the stated -2.5V. This is not my first electron rodeo. I do not have my leads mixed up (black lead on anode of D4, red lead on the wiper of the QBias R59). I do NOT have the meter PCB uninstalled for now. Power is being supplied via a CAPI VPR 511 that I built, through a CAPI extension jig.
Any tips on where to look next? I saw a lot of other posts mentioning that the gate of Q1 should track with the voltage of the QBias control. My Q1 is getting readings of 0 VDC drain, 0 VDC Source and 0.524 VDC on the Gate at all settings for the QBias.
Just got done building a REV A 500 series and seem to be having an issue.
During step one of the calibration I was adjust able to adjust the QBias until all LEDs on the meter were lit up; however, I was unable to get anything above around 4 dBu on the output.
I have been going through this thread and the troubleshooting guide looking for answers before asking a question, but just noticed that I am getting 0 to +2.5V DC on the output of my QBias, rather than the stated -2.5V. This is not my first electron rodeo. I do not have my leads mixed up (black lead on anode of D4, red lead on the wiper of the QBias R59). I do NOT have the meter PCB uninstalled for now. Power is being supplied via a CAPI VPR 511 that I built, through a CAPI extension jig.
Any tips on where to look next? I saw a lot of other posts mentioning that the gate of Q1 should track with the voltage of the QBias control. My Q1 is getting readings of 0 VDC drain, 0 VDC Source and 0.524 VDC on the Gate at all settings for the QBias.
