Fabios 1272 finished
- Thread starter [silent:arts]
- Start date
Help Support GroupDIY Audio Forum:
![[silent:arts]](https://cdn.imagearchive.com/groupdiy/data/avatars/m/0/172.jpg?1620371656){kind=avatar}
[silent:arts]
Well-known member
[quote author="Flatpicker"]Yes, inspiring! How did you mount those switch-plates to the front panel? Does the FP have studs? Can't tell from the pics.[/quote]
the Front Panel has M3 threaded cavities (is this correct ???) on the back where the switch plate is screwed to
the Front Panel has M3 threaded cavities (is this correct ???) on the back where the switch plate is screwed to
i have a question about the di.
My units di doesnt work very well.
It passes audio, but the noise is extremely high.
My unit had an accident and got subjected to about 33volts instead of the ususal 24v.
I changed parts so that the micpres work ok again, but the di doesnt.
Could the transistors be damaged? I guess all the other parts should be able to take 33v easily...?
/J
My units di doesnt work very well.
It passes audio, but the noise is extremely high.
My unit had an accident and got subjected to about 33volts instead of the ususal 24v.
I changed parts so that the micpres work ok again, but the di doesnt.
Could the transistors be damaged? I guess all the other parts should be able to take 33v easily...?
/J
AnalogPackrat
Well-known member
Well, I finally got some more bench time with my Fabio 1272 boards and thought I'd share a couple of things. First, I've got it hooked up on my ProtoPanel thing for ease of, uh, prototyping. I went kinda crazy with front panel controls just to see what was useful. I took some of rascalseven's ideas and combined them with the JLM simple mod and hotrod and ended up with four gain adjustments.
First there's a 5k log pot attenuator (from rascal and JLM simple) after the input iron. Then there's a 12 pos first stage gain control switch (standard 1272 R values), then there's the half-fader (JLM hotrod), and finally there's a 5 pos second stage gain switch. I'll post pics later.
Anyway, recall that I had top mounted my relays, which turns out to be wrong. But Fabio came up with a simple fix--reverse the protection diodes and swap relay pwr and gnd. Did that. Well, guess what? No switchy on the input selection. If the switch was set to mic when the unit was powered up it would be fine. Then I could switch to Hi-Z <click>, but it wouldn't switch back. Checking the coil voltage on that relay I see 4.08V when it should be 0. WTF? Tracing around the board I found the problem. I had installed the "auto-switch" option thinking I might use it. Well, when you swap the realy pwr and gnd, which also power this little piece, no worky. Wrong polarity on Mr. transistor--he's always on and won't let IN_CTRL go to 0V.
Since I no longer plan to use the auto thing, I just snipped the transistor out and now all is well <clickety-click>. So, if you do what I did with the top mounted relays, you will either need to leave that transistor (QSW) out, or figure out how to set it up with an NPN switch somehow.
While I was tracing around looking for solder bridges at the relay itself, I noticed that I had Vcc on several input pins. Huh. That's not right. Those are the Hi-Z feeds... There's an easy to miss link (jumper) that connects the Hi-Z Gnd to the main circuit Gnd. It's labelled SE2 and, well, it's important! Floating gnd on the Hi-Z active buffer kinda makes it hard for those active devices to work.
So there you go...a couple of troubleshooting tips for this project. Now I need to test it with some real audio. Tomorrow...
Cheers,
A P
First there's a 5k log pot attenuator (from rascal and JLM simple) after the input iron. Then there's a 12 pos first stage gain control switch (standard 1272 R values), then there's the half-fader (JLM hotrod), and finally there's a 5 pos second stage gain switch. I'll post pics later.
Anyway, recall that I had top mounted my relays, which turns out to be wrong. But Fabio came up with a simple fix--reverse the protection diodes and swap relay pwr and gnd. Did that. Well, guess what? No switchy on the input selection. If the switch was set to mic when the unit was powered up it would be fine. Then I could switch to Hi-Z <click>, but it wouldn't switch back. Checking the coil voltage on that relay I see 4.08V when it should be 0. WTF? Tracing around the board I found the problem. I had installed the "auto-switch" option thinking I might use it. Well, when you swap the realy pwr and gnd, which also power this little piece, no worky. Wrong polarity on Mr. transistor--he's always on and won't let IN_CTRL go to 0V.
Since I no longer plan to use the auto thing, I just snipped the transistor out and now all is well <clickety-click>. So, if you do what I did with the top mounted relays, you will either need to leave that transistor (QSW) out, or figure out how to set it up with an NPN switch somehow.
While I was tracing around looking for solder bridges at the relay itself, I noticed that I had Vcc on several input pins. Huh. That's not right. Those are the Hi-Z feeds... There's an easy to miss link (jumper) that connects the Hi-Z Gnd to the main circuit Gnd. It's labelled SE2 and, well, it's important! Floating gnd on the Hi-Z active buffer kinda makes it hard for those active devices to work.
So there you go...a couple of troubleshooting tips for this project. Now I need to test it with some real audio. Tomorrow...
Cheers,
A P
thanks!
I think i figured out why my Di inputs arent working properly.
When i fried the 24v psu regulator i must have gotten atleast 30v on the circuit instead of 24v.
The 2n4416 cant take that much, but everything else in the circuit can take atleast 35v.
Im just guessing, but do u think should change it?
I did remember to mount that link though!
:green:
/J
I think i figured out why my Di inputs arent working properly.
When i fried the 24v psu regulator i must have gotten atleast 30v on the circuit instead of 24v.
The 2n4416 cant take that much, but everything else in the circuit can take atleast 35v.
Im just guessing, but do u think should change it?
I did remember to mount that link though!
:green:
/J
skipwave
Well-known member
Amazing work Volker! Inspiring. :thumb:
I'm staring at my Carnhill iron from the group buy, and the parts to stuff the 283 board - which just has to find it's way through customs and I'm ready to rock.
I'm staring at my Carnhill iron from the group buy, and the parts to stuff the 283 board - which just has to find it's way through customs and I'm ready to rock.
AnalogPackrat
Well-known member
Jonkan,
You may have popped the 4416. Try swapping it out (though it's in a tight place and hard to get at).
Got a little time to test one of mine out. Here's a couple of photos:
Front of protopanel
Back of protopanel
As you can see I'm using Lynx output iron. I manually swept the pre and the -3dB points are well below 20Hz and about 50kHz. Not too shabby!
Did a quick listening test close micing my modded Champ12 with an e609S. Sounds really good! I need to do some more critical recording and listening comparisons with different mics and gain settings to decide what controls I want to keep for the final build. I'm surprised at how quiet it is even in this wide open state.
I'm having one problem, though. My DI input motorboats when I get the gain much above minimum. I can get it to start oscillating with any of the controls, so I'm thinking it's a stupid layout or grounding thing. I do have the output right beside the DI jack (Duh!) on the protopanel. Of course the actual build will have the XLRs on the back. But I used shielded wire everywhere and even ran 2+shield to the DI to separate the shield (to chassis ground) from the DI "gnd" which connects at the pcb. Since there is no conductive chassis on my protopanel thing, I ran a short piece of buss wire between the chassis lugs on the XLRs. All my shields connect there and it is grounded to the star point. Maybe my slightly sloppy grounding is getting me in trouble here. Any ideas?
:guinness:
A P
You may have popped the 4416. Try swapping it out (though it's in a tight place and hard to get at).
Got a little time to test one of mine out. Here's a couple of photos:
Front of protopanel
Back of protopanel
As you can see I'm using Lynx output iron. I manually swept the pre and the -3dB points are well below 20Hz and about 50kHz. Not too shabby!
Did a quick listening test close micing my modded Champ12 with an e609S. Sounds really good! I need to do some more critical recording and listening comparisons with different mics and gain settings to decide what controls I want to keep for the final build. I'm surprised at how quiet it is even in this wide open state.
I'm having one problem, though. My DI input motorboats when I get the gain much above minimum. I can get it to start oscillating with any of the controls, so I'm thinking it's a stupid layout or grounding thing. I do have the output right beside the DI jack (Duh!) on the protopanel. Of course the actual build will have the XLRs on the back. But I used shielded wire everywhere and even ran 2+shield to the DI to separate the shield (to chassis ground) from the DI "gnd" which connects at the pcb. Since there is no conductive chassis on my protopanel thing, I ran a short piece of buss wire between the chassis lugs on the XLRs. All my shields connect there and it is grounded to the star point. Maybe my slightly sloppy grounding is getting me in trouble here. Any ideas?
:guinness:
A P
khstudio
Well-known member
Volker,
Looks Great man!
I was wondering how much if any hum your getting from mounting the Power Tranny in the chassis & at what level of gain?
I'm currently mounting my 1272 in the case & was debating the external tranny but I'd rather just put it in the back corner of the chassis.
Yours looks VERY close to the OT... I'm assuming the OT isn't that sensitive?
Thanks,
Kevin
Looks Great man!
I was wondering how much if any hum your getting from mounting the Power Tranny in the chassis & at what level of gain?
I'm currently mounting my 1272 in the case & was debating the external tranny but I'd rather just put it in the back corner of the chassis.
Yours looks VERY close to the OT... I'm assuming the OT isn't that sensitive?
Thanks,
Kevin
[silent:arts]
Well-known member
[quote author="khstudio"]I was wondering how much if any hum your getting from mounting the Power Tranny in the chassis & at what level of gain?[/quote]
no hum from the power tranny.
I measured the boards powered up from an external PSU and with the internal with nearly no difference.
no hum from the power tranny.
I measured the boards powered up from an external PSU and with the internal with nearly no difference.
indigom
Well-known member
nice box! clean build you have there.
Fabios's 1272 was my first real DiY project. I was so lucky that it didn't smoke. I used Sowter all the way on it. It is my most quiet box, but with balls. Love it. cheers guys,
Jay
Fabios's 1272 was my first real DiY project. I was so lucky that it didn't smoke. I used Sowter all the way on it. It is my most quiet box, but with balls. Love it. cheers guys,
Jay
kellyrmartin
Member
This project looks great. I am curious. Would this project wind up being about the same price completed as you would spend on another 1272 type clone prebuilt such as a vintech or something? Also, would this project sound as good as a real neve module?
