AKG Perception 420 Mod

[jp8]

Aside from the insulation properties, I'm afraid this liquid tape does not qualify as a conformal coating as it is too viscous. This will leave gaps and voids around and under parts. These voids will practically nullify the protective properties, at least in an environment of long time high RH and especially if the board hasn't been properly cleaned and dried. I'm talking here from own experience...

@micolas : I don't know what resistances you want to measure, but if it's related to insulation resistances between tracks, then this DMM cannot be used. Between tracks, resistances should measure in the tens or hundreds of GOhms. If it's 2GOhm or less, your board definitely needs to be cleaned.

Jan

 

[AUDIO FREQ]

Aside from the insulation properties, I'm afraid this liquid tape does not qualify as a conformal coating as it is too viscous. This will leave gaps and voids around and under parts. These voids will practically nullify the protective properties, at least in an environment of long time high RH and especially if the board hasn't been properly cleaned and dried. I'm talking here from own experience...

@micolas : I don't know what resistances you want to measure, but if it's related to insulation resistances between tracks, then this DMM cannot be used. Between tracks, resistances should measure in the tens or hundreds of GOhms. If it's 2GOhm or less, your board definitely needs to be cleaned.

Jan

Oh, I wasn't planning on using it as conformal coating for anything on a pcb or anything, I just wanted to cover up the solder joints and bare metal on anything my hands are going to touch for safety. It was either this, or shrink tubes, and I was all out of the thin gauge so I used this. I dries and shrinks on to the wire very well.

 

[micolas]

Jan: I don't know what resistances you want to measure, but if it's related to insulation resistances between tracks, then this DMM cannot be used.

Jan, I'm only interested in measuring resistors up to 1Gohm, for selection, for consistency. (...if the multimeter Victor 88c can, I don't really trust it...e.g. for the polarization of the capsules, I only measure the voltage at the output of the dc/dc converter and adjust it to my taste)

 

[micolas]

Audio Freq, do not cover the measuring jig with anything protective, use sterile gloves, without talcum powder or gel on them.

 

[AUDIO FREQ]

Audio Freq, do not cover the measuring jig with anything protective, use sterile gloves, without talcum powder or gel on them.

I only covered the solder points of spliced wires, don't want to short anything because the cable is flimsy. The dip socket, and the leads that go to the multimeter are not covered, they are cleaned well with alcohol.

 

[micolas]

I see liquid tape between the socket pins, this is the most sensitive area. Make another clean test jig.

 

[AUDIO FREQ]

I see liquid tape between the socket pins, this is the most sensitive area. Make another clean test jig.

Will do, but can I ask why? According to the datasheet, it's pretty good for insulating electronics.

 

[micolas]

It's for electrical isolation not electronic isolation.
Not good for high impedances
Anyway, I found a solution for you: use only the first 4 pins from a longer IC socket.
That way you will have an inactive part and you will no longer touch the pins

 

[kingkorg]

What high impedances? Gate is connected to source for this measurement, or am i missing something? You guys are making this way too complicated.

 

[micolas]

What high impedances? Gate is connected to source for this measurement, or am i missing something? You guys are making this way too complicated.

Kingkorg,
Here the impedance is towards zero. We teach him to be careful in case he mounts a socket in other types of test circuits or in a real microphone circuit, for sorting the different jFETs (for minimum noise for example), to follow some elementary rules, for working with high impedance
I didn't want to be encouraged to use that liquid protection tape on microphones pcb

 

[AUDIO FREQ]

What high impedances? Gate is connected to source for this measurement, or am i missing something? You guys are making this way too complicated.

Lol, sorry man, I know reading this must be frustrating for some of you. I like to ask alot of questions, curious by nature, and I like to try things out that weren't suggested...which helps me learn.

 

[kingkorg]

Lol, sorry man, I know reading this must be frustrating for some of you. I like to ask alot of questions, curious by nature, and I like to try things out that weren't suggested...which helps me learn.

Please, no need to apologize. Sure, experiment! I just didn't get what the fuss was about regarding high impedance in the test jig. You can't be too careful when assembling a mic, but i can't see you did anything wrong using that liquid tape thing if the only purpose was to test ldss. But again, maybe i missed something obvious.

 

[kingkorg]

Also, forgive if i haven't followed the topic closely enough, Perception mics have two resistors from source to ground. Biasing works differently than u87. FET, the whole nfb, gain, works differently, so idss requirements of the FET are slightly different.

 

[schsz]

I'm wondering what the decoupling capacitor value is (the ceramic capacitor that's replaced with a polystyrene one in the Microphone Parts Perception mod kit). The photo on the Micparts site shows a photo of a P220 and later photo of a ceramic marked 212 (so 2100pF). Is that the same value found in the 420 and what's the capacitance used for a polystyrene?

Also- there's another post about modding the Perception 220 to be like a U87 where a 220pF SMD capacitor's replaced to 680pF (found on the underside of the switch PCB) that's responsible for the circuit's de-emphasis EQ. Would that imply I'd need anything from an open to 470pF for a CK12 type capsule and (for a K47 type) open to 220pF?

I was also wondering about the value of the decoupling capacitor. Did you find the answer?