late said:Anyone have used Hairball 8020 meter?
To adjust the metar, use 500R-1k 10turn pot in parallel. But how?
1). +/-20v
JP1...6, TP+20v, TP-20v
2).Unity gain
Initial gain is set by AOT1,2
3).Distortion w/o compression
minimum distortion adjustment AOT 7,9
4).Distortion at 20dB GR
distortion under hard compression adjusted by AOT8/10, usually 10R is fine
5).Com threshold
Com threshold adjustment: AOT3,4
6).Lim threshold
Lim threshold set by AOT5,6.
7).Check: reqresp, max gain, min gain, S/N, timeconstants.
imo said:My schematic has a 200r trimmer already installed with the 22r.
baadc0de said:Great to know it's not that uncommon...!
I have for now put two philips BC capacitors (1000uF) in antiseries, which gives about 500uF of capacitance but blocks DC both ways. I'll let you know if it helps any.. the output transistors are NOS Motorola ones from electrochronic as are the rest of transistors.
The reason to put in another capacitor - a fake bipolar one - is because in the previous configuration it smoked not only R77 but also a winding on the output transformer (which now reads open). So this is more intended to protect the trafo. If anyone came to a solution to this, please let me know!
warpie said:baadc0de said:One interesting problem for the crowd here, maybe someone has any ideas..
Sometimes, when excessive low frequency information is in the input (such as from a preamp when recording a kick drum or direct bass guitar) and the gain reduction is set to a slow enough attack and quite a bit of makeup, the TG1 starts smoking R77. Could the output transistor pair be somehow to blame? I don't know enough about transistors, but say if one of them faults into being a straight line for a time?
It all works out if I power it off for some time. The output transistors are not heatsinked, maybe I should do that?
Thanks!
Ha! welcome! You're not alone. I've been mentioning this problem for quite a while but unfortunately it looks like a mystery
http://www.groupdiy.com/index.php?topic=37400.msg512287#msg512287
http://www.groupdiy.com/index.php?topic=48297.msg617261#msg617261
I'm pretty sure it's not a heat problem as I'm using heatsinks on the transistors. What transistors do you use?
What wattage is the 56ohms resistor? Do you have good heatsink on the PSU regulators?
In my case a 2watt resistor with a BIG heatsink on the regulators gives me a maximum of around 40C which I suppose it's OK.
Still though, I don't know what causes it. :
Good luck and let me know. It's been my nightmare for more than two years now ;D
It'll be good if other people can report too.
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