[BUILD] New FET/RACK Official Help Thread - Please read first post!
- Thread starter mnats
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Help Support GroupDIY Audio Forum:
Echo North
Well-known member
saqeef said:
There can be a slight burning odor yes. How are your DC rails now (+30 and -10)?
Echo North
Well-known member
saqeef said:
What is your AC V reading at each orange wire of the transformer VS chassis ground now?
Finished building my Rev. A. Power supply tests, before stuffing pcb, were right, 30.9vDC and - 9.80vDC at CR9.
After completing the building I have immediately noticed that powering up the Fet Rack leaves the meter all on left and not only right as it should do when on GR mode. TP18 is fixed at 0.00vDC and doesn't move when turning the qbias set. Plus CR9 now measures 0.00vDC and no more - 9.80vDC. Where could I begin troubleshooting?
After completing the building I have immediately noticed that powering up the Fet Rack leaves the meter all on left and not only right as it should do when on GR mode. TP18 is fixed at 0.00vDC and doesn't move when turning the qbias set. Plus CR9 now measures 0.00vDC and no more - 9.80vDC. Where could I begin troubleshooting?
Echo North
Well-known member
frenkonio said:
Remove Q1 and Q11 and see if that brings your rail back to life.
If not remove CR9 and diode test it w/ your meter.
Mike
Echo North
Well-known member
frenkonio said:
Components can fail early or get damaged from heat (soldering) or static electricity (handling). It’s why manufacturers do burn ins.
You can email us for a new one.
Mike
Echo North
Well-known member
frenkonio said:
Definitely. You need that CR9 working to have a bias voltage and have the meter work in GR mode.
seanweaverguitar
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Thanks to Mike and Mnats for all of their help on my previous Rev A build and the great kits. I have 3 more FET/RACK kits still in shipping boxes along with a Lola but refuse to start even the first solder joint until a few things make a little more sense from the get go (this may turn into a year long process but I'm not normal...normally closed?)
The main thing that's been confusing the @#$@ out of me the past several months of studying the schematic is trying to make sense of the switching in the GR Meter Driver & GR Control Amp/Ratio sections....
On the Hairball schematic which I've generated an 18x22 print of for the workbench, I'm confused by the NO/NC designations on the GR, +4, and +8 switches, the same way I am confused by the ratio switching in the GR Control Amp section. It's hard to even know how to phrase my questions since the whole thing is still confusing me but I'll try to express exactly what I'm struggling with in a clear and succinct pair of questions:
1. If Normally Closed is indicating a complete circuit, then I'm having a nearly impossible time seeing how the circuit is completed/closed from the NC position through the rest of the schematic. I don't see the NC side of the switch leading to any other lines on the schematic. I THINK I understand what's happening when a switch is flipped to NO, because then I can trace what I think is a circuit, but that actually confuses me more because even in my very incomplete understanding, doesn't Normally Open always mean a circuit is broken/opened/not complete? That's what every electronics book I'm reading says....So I'm thinking that I see the circuit complete with the switch in the NO position but can't draw the connection via NC, which is wrecking my mind. I don't see how that could be possible....obviously I'm missing something monumental here.
2. Does NC on the schematic correlate to the buttons pushed in (all buttons in at NC). Or is it that the schematic is drawn with the buttons in their outward (not pushed in) position? That was my best guess since it looks to my untrained mind like I can see the circuit completed through the GR amp section resistors when one of the Ratio switches is flipped to NO on the schematic. But that doesn't make sense to me if Normally Open is an open circuit after all....
Any light than can be shed on helping me begin to make sense of this section would be greatly appreciated!!!! I've been really trying for months upon months now.
Also, realistically, would some kind of oscilloscope be useful if something goes awry in any one of these next 4 builds? I'm sure there's a better section of Group DIY to gather suggestions but if a scope would help, I'm open to tracking one down....I do want gear but far more want to learn how it works. Thank you all so very kindly
The main thing that's been confusing the @#$@ out of me the past several months of studying the schematic is trying to make sense of the switching in the GR Meter Driver & GR Control Amp/Ratio sections....
On the Hairball schematic which I've generated an 18x22 print of for the workbench, I'm confused by the NO/NC designations on the GR, +4, and +8 switches, the same way I am confused by the ratio switching in the GR Control Amp section. It's hard to even know how to phrase my questions since the whole thing is still confusing me but I'll try to express exactly what I'm struggling with in a clear and succinct pair of questions:
1. If Normally Closed is indicating a complete circuit, then I'm having a nearly impossible time seeing how the circuit is completed/closed from the NC position through the rest of the schematic. I don't see the NC side of the switch leading to any other lines on the schematic. I THINK I understand what's happening when a switch is flipped to NO, because then I can trace what I think is a circuit, but that actually confuses me more because even in my very incomplete understanding, doesn't Normally Open always mean a circuit is broken/opened/not complete? That's what every electronics book I'm reading says....So I'm thinking that I see the circuit complete with the switch in the NO position but can't draw the connection via NC, which is wrecking my mind. I don't see how that could be possible....obviously I'm missing something monumental here.
2. Does NC on the schematic correlate to the buttons pushed in (all buttons in at NC). Or is it that the schematic is drawn with the buttons in their outward (not pushed in) position? That was my best guess since it looks to my untrained mind like I can see the circuit completed through the GR amp section resistors when one of the Ratio switches is flipped to NO on the schematic. But that doesn't make sense to me if Normally Open is an open circuit after all....
Any light than can be shed on helping me begin to make sense of this section would be greatly appreciated!!!! I've been really trying for months upon months now.
Also, realistically, would some kind of oscilloscope be useful if something goes awry in any one of these next 4 builds? I'm sure there's a better section of Group DIY to gather suggestions but if a scope would help, I'm open to tracking one down....I do want gear but far more want to learn how it works. Thank you all so very kindly
Ok Mike. Progress. Now I got CR9 working, was able to set bias, verified all voltages following the troubleshooting guide, all good till point 6. I'm stucked at Null Adjust and consequently at GR Meter adjust. Lowest value I can get with R75 is 0.7vDC. I have verified all resistors, caps, solder joints etc. No way. Where could I begin?
(EDIT): after an hour for searching a cause I found a bad trace from Q12 to Q11, no continuity.. I soldered a small cable and was able to do the null adjust as long as the gr meter tracking. Rock on!
(EDIT): after an hour for searching a cause I found a bad trace from Q12 to Q11, no continuity.. I soldered a small cable and was able to do the null adjust as long as the gr meter tracking. Rock on!
Echo North
Well-known member
seanweaverguitar said:
NC/NO is just telling you where the switch is in relation to the button being out, or pushed in. In this case NC is when the switch is out, not engaged, so there is no circuit to complete.
Mike
seanweaverguitar
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Hairball Audio said:
Perfect. Thanks again Mike. That's what I thought so my confusion was taking NC/NO a little too literally. Makes perfect sense now and confirms what I thought.....it'll be another month or more before I get started (I may be moving into a house and everything's in upheaval right now) but all three FET/RACKs and Lola arrived safely the week before last. As build questions come up I'll try to keep them as short as possible!! (something I'm working on, in life --- sometimes it takes me a million words to ask a 2 second question). To be continued. I appreciate all you do.
Sean
seanweaverguitar
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Next question (I'll keep this short): in looking at the 5002 data sheet (http://library.hairballaudio.com/datasheets/5002.pdf), on the secondary I'm not clear how the two 150-ohms are adding up to 600-ohm series. I searched the archives here and understand that's AC impedance.
Also, when it says "feedback" beneath the white/black wires on the diagram, is the wht/blk primary ---> grey secondary connected back to the primary on the schematic what that's referring to? Last, I think I've made some sense of the Blu/Yel, Grn/Red windings connected in series leading to OUT - and + but am still a little hazy on what the other winding is there for (Gry/Vio). Obviously I don't need to necessarily know all of this to get back to another build but will feel better at least trying. Thanks as always
Also, when it says "feedback" beneath the white/black wires on the diagram, is the wht/blk primary ---> grey secondary connected back to the primary on the schematic what that's referring to? Last, I think I've made some sense of the Blu/Yel, Grn/Red windings connected in series leading to OUT - and + but am still a little hazy on what the other winding is there for (Gry/Vio). Obviously I don't need to necessarily know all of this to get back to another build but will feel better at least trying. Thanks as always
Echo North
Well-known member
seanweaverguitar said:
Here is an email from the HB transformer guru I received about 10 years ago:
"turns ratios work exactly like you would think. 1:2 means you put 1 in on the primary and get 2 out on the secondary. but the impedance ratio is the SQUARE of the turns ratio. so 150ohms:600ohms is a 1:4 impedance ratio, but a 1:2 turns ratio. all of this means that when you're combining equal transformer windings in series, rather than adding (or multiplying by two) you have to square it. so two 150ohm windings in series makes one 600ohm winding. in parallel they don't divide. if you have a 1:1+1 transformer, with a 150ohm:150ohm+150ohm impedance ratio, if you put the two secondaries in parallel, you now have a 1:1 transformer, each side with a 150ohm impedance."
Echo North
Well-known member
The 5002 has a tertiary feedback winding that deals with any DC offset in the output amp stage.
seanweaverguitar
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Thank you for this Mike. I do appreciate the answers/time. That helps a lot!!!
Hello
I have built the REV A FET/Rack and am having trouble setting the QBias.
Working through the troubleshooting section I don't appear to have -10VDC at CR9... It in fact appears to be tied to the chassis (through continuity tester) along with the same rail as R66, R72, R76, R64...
From the DC voltage sheet, all the transistors appear to have the correct voltages apart from
Q12
E = 0.411
C = 26.7
B = 0.96
Q13
E = 0.391
C = 26.93
B = 0
This is obviously related to the discrepancy at CR9, but thought id provide as much info as possible!
Cheers
James
I have built the REV A FET/Rack and am having trouble setting the QBias.
Working through the troubleshooting section I don't appear to have -10VDC at CR9... It in fact appears to be tied to the chassis (through continuity tester) along with the same rail as R66, R72, R76, R64...
From the DC voltage sheet, all the transistors appear to have the correct voltages apart from
Q12
E = 0.411
C = 26.7
B = 0.96
Q13
E = 0.391
C = 26.93
B = 0
This is obviously related to the discrepancy at CR9, but thought id provide as much info as possible!
Cheers
James
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