thanks william2001
I've now jumpered both the input and the output caps (I started by putting a signal into the DiyFE and monitoring the output of the Mofo with a scope while monitoring bias points with a voltmeter while I crossed each cap with a resistance substitution box starting with 3 megs and meekly progressing towards a short [figuring 3 megs ain't gonna allow any destructive current]). (I'm still unclear about why the caps need to be so large because I figure the "R" in 1/2pifcr is, eg in the case of C3, the 50k input impedance of the Mofo.) (The FE is fed by the output of the low pass [apprx 480 hz] of a steve bench 6922 crossover, and the Mofos power 15" Altecs in large Karlson boxes.)
I've now jumpered both the input and the output caps (I started by putting a signal into the DiyFE and monitoring the output of the Mofo with a scope while monitoring bias points with a voltmeter while I crossed each cap with a resistance substitution box starting with 3 megs and meekly progressing towards a short [figuring 3 megs ain't gonna allow any destructive current]). (I'm still unclear about why the caps need to be so large because I figure the "R" in 1/2pifcr is, eg in the case of C3, the 50k input impedance of the Mofo.) (The FE is fed by the output of the low pass [apprx 480 hz] of a steve bench 6922 crossover, and the Mofos power 15" Altecs in large Karlson boxes.)
I like to use an online calculator to quickly see what the cutoff frequency would be with a particular R and C combination. Here's one: Cutoff Frequency Calculator
As an example, I used it to make sure the fc was very low for the feedback loop of my Stasis FE (in my signature). The values I'm using yields a cutoff of less than 1Hz. (R=24.95kΩ, C=10uF (film) The parts I'm referring to in my Stasis would be analogous to C2 and R2 in the case of the FE '22.
If we're jumpering the input cap (C1), I would advise making sure the source feeding your front end has no DC output on it. (Shame on the designer if it does...)
As an example, I used it to make sure the fc was very low for the feedback loop of my Stasis FE (in my signature). The values I'm using yields a cutoff of less than 1Hz. (R=24.95kΩ, C=10uF (film) The parts I'm referring to in my Stasis would be analogous to C2 and R2 in the case of the FE '22.
If we're jumpering the input cap (C1), I would advise making sure the source feeding your front end has no DC output on it. (Shame on the designer if it does...)
I wanted to make a correction to something I stated at #1003 (obviously too late to edit the post). I should have said R=4.99kΩ. Fc is still very low, ~3Hz in this situation. Many times you will see something in the 2Hz to 5Hz range when you do the calculation.. (Run NP's numbers on the FE '22, 3.3uF and 10kΩ, what do you get?)
I must extend a heartfelt thank you to william2001 and Ben Mah for their assistance and patience with me. Of course the driving force of Nelson Pass too! I've go so much respect for Nelson and those like him...
SO with a little help from my friends the new FE 2022 is up and running. By chance, it went into a chassis with the exact same PSU and layout as my Wayne2018 build and today I am listening to them, one after the other. They both have their magic! Once again I am impressed with how may versions of excellent there are
. The FE2022 is young so it may take on different presentation with time but for the moment it is a bit more "crisp" than Waynes2018, which itself did not reach its whole full until I rebuilt it (new board from scratch) with matched three legged fuses. Everything mattes.
Nothing mattes if it does not get built and listened to! This pursuit of fine music from your minds and my hands, it's super fine
You super smart guys make this building stuff look easy. Heck, you make it possible! It is Very satisfying to pursue HiFi in this manner generated by the generous gift of time and patience and pure genius too! Thanks Big Time!
SO with a little help from my friends the new FE 2022 is up and running. By chance, it went into a chassis with the exact same PSU and layout as my Wayne2018 build and today I am listening to them, one after the other. They both have their magic! Once again I am impressed with how may versions of excellent there are
. The FE2022 is young so it may take on different presentation with time but for the moment it is a bit more "crisp" than Waynes2018, which itself did not reach its whole full until I rebuilt it (new board from scratch) with matched three legged fuses. Everything mattes.Nothing mattes if it does not get built and listened to! This pursuit of fine music from your minds and my hands, it's super fine
You super smart guys make this building stuff look easy. Heck, you make it possible! It is Very satisfying to pursue HiFi in this manner generated by the generous gift of time and patience and pure genius too! Thanks Big Time!
Hoping to get some help with my front end kit.
I borrowed it to my friend along with a Mofo i just built and he somehow blew a mosfet in the mofo and one channel of the Front end I had built as a preamp. I easily fixed the Mofo but the FE has me stumped.
I built the FE using a 48V wall wart. Opening it up I found R9 burnt up. I replaced it and it automatically started smoking and caught fire.
I traced the schematic and found the KSA992 blown. I replaced it along with R9 again but then R6 started heating up and smoking after about 15-20 seconds. I pulled the supply in time to find the KSA992 blown again so I replaced it.
I tried a dim bulb tester but that did not control the board resistors from heating up so I stopped plugging it in and came here for help.
I confirmed all resistors are good but something is up with the KSA992. I replaced both 1000uf caps just in case.
Hoping none of the J113 are damaged and causing the issue.
I borrowed it to my friend along with a Mofo i just built and he somehow blew a mosfet in the mofo and one channel of the Front end I had built as a preamp. I easily fixed the Mofo but the FE has me stumped.
I built the FE using a 48V wall wart. Opening it up I found R9 burnt up. I replaced it and it automatically started smoking and caught fire.
I traced the schematic and found the KSA992 blown. I replaced it along with R9 again but then R6 started heating up and smoking after about 15-20 seconds. I pulled the supply in time to find the KSA992 blown again so I replaced it.
I tried a dim bulb tester but that did not control the board resistors from heating up so I stopped plugging it in and came here for help.
I confirmed all resistors are good but something is up with the KSA992. I replaced both 1000uf caps just in case.
Hoping none of the J113 are damaged and causing the issue.
Since both R6 and R9 heated up and smoked, my guess would be that the J113 CCSs were not working, probably toasted J113s. So as a minimum, Q3 and Q4 are bad.
You should probably purchase a bunch of J113s and replace them. The good thing is that they are not expensive,so purchase extra. You may need to adjust R7 and R8 to suit the new CCS J113s. I believe the Q3 CCS is around 3mA and the Q4 CCS is around 9mA.
You should probably purchase a bunch of J113s and replace them. The good thing is that they are not expensive,so purchase extra. You may need to adjust R7 and R8 to suit the new CCS J113s. I believe the Q3 CCS is around 3mA and the Q4 CCS is around 9mA.
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Yes, should be same process.
I just checked, and the Q4 CCS should be set to 9mA: DIY FE 2022 CCS currents
The other J113s perhaps may be damaged too.
I just checked, and the Q4 CCS should be set to 9mA: DIY FE 2022 CCS currents
The other J113s perhaps may be damaged too.
When operating the single ended voltage source on one of my cards, I reversed the polarity by accident and it smoked R9 (and presumably KSA 992), so the single ended voltage circuit is not agnostic to polarity of the V plus and V minus. I turned it off pretty quickly. NP sent me KSA 992 to see if that fixes the card, but I haven't tried them yet. I also had to replace R9.
