maxheadroom
Well-known member
i had the same problem as you described in the first sound sample.
fet boy
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fucanay
Well-known member
Here is a picture from my DAW.
Ugly huh? Looks clipped too, right? So then I read this from the diyfactory page that MattA set up:
Is it possible the trimmer is raising that too high and causing this. I keep thinking that since I have voltages too high on the Fairchild 2N5457 by about a volt. It seems most people haven't used the On Semi ones and are probably sitting at the wrong bias voltage.
I know I can put the 22k resistor in there to lower the range of the pot and not hear the oscillation because it's out of range, but shouldn't there be a way to fix it so we don't have to limit the range?
Matt
Ugly huh? Looks clipped too, right? So then I read this from the diyfactory page that MattA set up:
Is it possible the trimmer is raising that too high and causing this. I keep thinking that since I have voltages too high on the Fairchild 2N5457 by about a volt. It seems most people haven't used the On Semi ones and are probably sitting at the wrong bias voltage.
I know I can put the 22k resistor in there to lower the range of the pot and not hear the oscillation because it's out of range, but shouldn't there be a way to fix it so we don't have to limit the range?
Matt
fucanay
Well-known member
No Love for the fetboy?
Shameless bump.
Matt
Shameless bump.Matt
maxheadroom
Well-known member
is your noise when you short the input with gnd and full gain also there?
3nity
Well-known member
hi guys i powered mine few days ago and i noticed that the electro caps got hot! did someone had the same problems?
Thanks.
Thanks.
fucanay
Well-known member
[quote author="maxheadroom"]is your noise when you short the input with gnd and full gain also there?[/quote]
Dunno what you mean really. It's just in what I would call normal operation. SM57 Mic plugged in, TRS output to my RME Fireface. Turn the pot up, crazy noise.
[quote author="3nity"]hi guys i powered mine few days ago and i noticed that the electro caps got hot! did someone had the same problems?
[/quote]
I didn't notice, but I'll try to check it later tonight. I wouldn't think they should be hot though.
I'm trying to figure out how to use my scope. I don't have any real probes, using pain in the ass alligator clips. I'll keep you guys posted.
Matt
Dunno what you mean really. It's just in what I would call normal operation. SM57 Mic plugged in, TRS output to my RME Fireface. Turn the pot up, crazy noise.
[quote author="3nity"]hi guys i powered mine few days ago and i noticed that the electro caps got hot! did someone had the same problems?
[/quote]
I didn't notice, but I'll try to check it later tonight. I wouldn't think they should be hot though.
I'm trying to figure out how to use my scope. I don't have any real probes, using pain in the ass alligator clips. I'll keep you guys posted.
Matt
Svart
Well-known member
My fetboys do the same thing as well..
BUT...
They only do it when plugged into something. If I have them sitting on a bench plugged into a sig gen and an Oscope then I have pure goodness all the way up to clipping. IF I plug them into anything I get the hiss/hum crap that you are all getting. I've tried everything I know to try and it has me quite confused.
BUT...
They only do it when plugged into something. If I have them sitting on a bench plugged into a sig gen and an Oscope then I have pure goodness all the way up to clipping. IF I plug them into anything I get the hiss/hum crap that you are all getting. I've tried everything I know to try and it has me quite confused.
fucanay
Well-known member
Right now, I'm worried about this PSU board. If I'm using my scope right, it has tons of ripple. I'm building up another one right now to see if that is contributing to the problem. Can everyone tell me what they are using for a PSU?
Matt
Matt
Svart
Well-known member
toroid, rectifier, linear reg and tons of cap.
I get no ripple at all on the supply lines.
I get no ripple at all on the supply lines.
fucanay
Well-known member
[quote author="Svart"]toroid, rectifier, linear reg and tons of cap.
I get no ripple at all on the supply lines.[/quote]
Well, I rebuilt the PSU and it does the same thing. Though, this is not the thread for learning how to use my scope anyhow, I'll say I'm doing it wrong for now.
That leaves me in the same place as you, totally stumped.
Matt
I get no ripple at all on the supply lines.[/quote]
Well, I rebuilt the PSU and it does the same thing. Though, this is not the thread for learning how to use my scope anyhow, I'll say I'm doing it wrong for now.
That leaves me in the same place as you, totally stumped.
Matt
maxheadroom
Well-known member
which frequency did you set with the signal generator?
i had the same problem with oszillating, then i tryed to reduce the
gain of the first stage. result better but still there. then i reduced the gain again. result better but still there. only with bass or guitur in very high gain mode, the oszillation was comming.
with sig-generator i saw on the oszi nothing strange, only clipping.
so then i go down with the frequency i watched one one stage the I/O and saw a stange distortion, that must be THIS noise.
try this way.
i had the same problem with oszillating, then i tryed to reduce the
gain of the first stage. result better but still there. then i reduced the gain again. result better but still there. only with bass or guitur in very high gain mode, the oszillation was comming.
with sig-generator i saw on the oszi nothing strange, only clipping.
so then i go down with the frequency i watched one one stage the I/O and saw a stange distortion, that must be THIS noise.
try this way.
fucanay
Well-known member
I was actually testing the PSU, not the actual fetboy boards, so no signal was applied. I've ruled out transformer interference as a problem because I hooked up a +24VAC wallwart supply and got the exact same thing. So it's in the fetboy boards themselves.
I'm going to order the NPNs used in the original schematic from tape op as well as the On Semi 2N5457. There has to be a weak link in there somewhere and the only thing I can think of is the transistors and the different hfe and voltages of them depending on brand. Everything else would be really hard to screw up.
Matt
I'm going to order the NPNs used in the original schematic from tape op as well as the On Semi 2N5457. There has to be a weak link in there somewhere and the only thing I can think of is the transistors and the different hfe and voltages of them depending on brand. Everything else would be really hard to screw up.
Matt
3nity
Well-known member
i tried them both brands and very difficult to match them mostly all of them come matched at 18.5V
Very difficult!
Very difficult!
matta
Well-known member
Man,
I built my own pair in a mater of hours, wrote the documentation based on my EXACT build procedure and have been trouble free from day one and use these pres daily in my studio.
Incase you want to compare PCB's here is one of the pair:
Incase anyone hasn't seen it: http://www.diyfactory.com/projects/fetboy/fetboy.htm
As you have shared it is a pretty simple design and I can only think your transistors are causing a problem. If I'm not mistaken my JFET's were the Fairchild brand if it is any consolation and I went through 60 to get 2 pairs that were even closely what was called for HFE wise? One was quite well matched, the other was easy to fix using the trimmer.
Hope that helps get to the bottom of your problem.
Matt
I built my own pair in a mater of hours, wrote the documentation based on my EXACT build procedure and have been trouble free from day one and use these pres daily in my studio.
Incase you want to compare PCB's here is one of the pair:
Incase anyone hasn't seen it: http://www.diyfactory.com/projects/fetboy/fetboy.htm
As you have shared it is a pretty simple design and I can only think your transistors are causing a problem. If I'm not mistaken my JFET's were the Fairchild brand if it is any consolation and I went through 60 to get 2 pairs that were even closely what was called for HFE wise? One was quite well matched, the other was easy to fix using the trimmer.
Hope that helps get to the bottom of your problem.
Matt
fucanay
Well-known member
That's what I'm thinking too. But I tried to match everything. Maybe I didn't do it right. I need to build a test circuit for them I guess. More research to do.
Matt
Matt
fucanay
Well-known member
Man, these boards really suck to take parts off of. I tried to put Q2/Q3 and I totally lifted a pad. Fortunately, the opposite sides pad is the one that was supposed to be connected, so it isn't totally wrecked. But I don't think I'll be trying that again.
I checked the HFE on a couple of more BD139s and got them to exactly 20000 and it still does it. I should have socketed all of those parts.
This project is really frustrating.
Matt
I checked the HFE on a couple of more BD139s and got them to exactly 20000 and it still does it. I should have socketed all of those parts.
This project is really frustrating.
Matt
matta
Well-known member
[quote author="fucanay"]Man, these boards really suck to take parts off of. I tried to put Q2/Q3 and I totally lifted a pad. Fortunately, the opposite sides pad is the one that was supposed to be connected, so it isn't totally wrecked. But I don't think I'll be trying that again.
I checked the HFE on a couple of more BD139s and got them to exactly 20000 and it still does it. I should have socketed all of those parts.
This project is really frustrating.
Matt[/quote]
Matt,
After all these posts I still don't think we have a seen a pic of your board. Maybe you are so into it you can't see the wood from the trees and a fresh set of eyes might be able to spot something. Why not post a pic?
Cheers
Matt
I checked the HFE on a couple of more BD139s and got them to exactly 20000 and it still does it. I should have socketed all of those parts.
This project is really frustrating.
Matt[/quote]
Matt,
After all these posts I still don't think we have a seen a pic of your board. Maybe you are so into it you can't see the wood from the trees and a fresh set of eyes might be able to spot something. Why not post a pic?
Cheers
Matt
fucanay
Well-known member
[quote author="matta"][quote author="fucanay"]Man, these boards really suck to take parts off of. I tried to put Q2/Q3 and I totally lifted a pad. Fortunately, the opposite sides pad is the one that was supposed to be connected, so it isn't totally wrecked. But I don't think I'll be trying that again.
I checked the HFE on a couple of more BD139s and got them to exactly 20000 and it still does it. I should have socketed all of those parts.
This project is really frustrating.
Matt[/quote]
Matt,
After all these posts I still don't think we have a seen a pic of your board. Maybe you are so into it you can't see the wood from the trees and a fresh set of eyes might be able to spot something. Why not post a pic?
Cheers
Matt[/quote]
Tomorrow morning, it shall be done. Promise.
Matt
I checked the HFE on a couple of more BD139s and got them to exactly 20000 and it still does it. I should have socketed all of those parts.
This project is really frustrating.
Matt[/quote]
Matt,
After all these posts I still don't think we have a seen a pic of your board. Maybe you are so into it you can't see the wood from the trees and a fresh set of eyes might be able to spot something. Why not post a pic?
Cheers
Matt[/quote]
Tomorrow morning, it shall be done. Promise.
Matt
Svart
Well-known member
The strange thing about mine is that with a sig-gen on the input and a scope on the output, the unit works great! I can do 1hz to 500Khz easy, no oscillation at all at any gain right up until clipping. Once I plug in an instrument and plug it into the converter, it oscillates, hisses, hums and generally just throws a tantrum. I'm in the same boat with the PCB, I've changed so much stuff on it that the pads are coming off.
fucanay
Well-known member
Ok, here they are. These pictures are pretty high resolution, so it may take a while, but the detail is there.
http://fucanay.fischerworks.com/diy/fetboy_in_progress/
Matt
http://fucanay.fischerworks.com/diy/fetboy_in_progress/
Matt
