414 EB P48 with strange things and strange subs
« on: February 17, 2021, 03:55:09 PM »
T3 which is supposed to be a SK30 was replaced with a SK118. The weird thing is this: Whoever installed it shorted all the legs together. Now, this microphone "works" but has two issues (I think)

1. You can pick up a radio station. I have heard this is NOT normal and I can't pick up the station on any of my other condenser mics.
2. The output seems low to me. Certainly quieter than my other condensers.

When I "unshort" the 3 legs it doesn't work, just a bunch of crackle and pop.

Thoughts? Right sub for T3 / Sk30?


Gus

Re: 414 EB P48 with strange things and strange subs
« Reply #1 on: February 17, 2021, 04:30:42 PM »
T3 is a constant current device

Look up the Id vs gate to source voltage (voltage difference the top of R9 and the "top" of R8)


Re: 414 EB P48 with strange things and strange subs
« Reply #2 on: February 17, 2021, 04:39:07 PM »
T3 is a constant current device

Look up the Id vs gate to source voltage (voltage difference the top of R9 and the "top" of R8)


Care to speculate why it works with all the legs shorted? Radio station?

Gus

Re: 414 EB P48 with strange things and strange subs
« Reply #3 on: February 18, 2021, 05:00:00 AM »
speculate? It is a simple circuit

The NPN is an emitter follower with a CC circuit in the emitter part of the circuit instead of a resistor.

With the transistor shorted together you have a very bad design emitter follower using the wrong value resistance in the emitter circuit.

A link to a thread at this forum reply 97 might help
https://groupdiy.com/index.php?topic=75491.msg964588#msg964588

« Last Edit: February 18, 2021, 05:59:15 AM by Gus »

Re: 414 EB P48 with strange things and strange subs
« Reply #4 on: February 18, 2021, 09:50:27 AM »
Great link, thank you.

My plan is this: To replace t3 with a 2N5457 and then maybe play around with R8 value until I achieve 45mA?

Re: 414 EB P48 with strange things and strange subs
« Reply #5 on: March 26, 2021, 09:37:51 PM »
It's working now, but I'm still picking up a radio station! it seems to be coming in on the cable as if I move the cable around it will lower the radio station level.

Any thoughts on why?

T3 is a constant current device

Look up the Id vs gate to source voltage (voltage difference the top of R9 and the "top" of R8)



R9 to R8 measures .755 Vdc
« Last Edit: March 26, 2021, 09:44:32 PM by mkiijam »

abbey road d enfer

Re: 414 EB P48 with strange things and strange subs
« Reply #6 on: March 27, 2021, 03:46:52 AM »
Actually, whatever the Vgs voltage, it's the voltage across R8 that matters. I believe it should be around 3V, for ca. 0.4mA quiescent current.
Regarding radio interference, it's probably not related. Check connections between body and ground, between  C17/18 and ground and continuity between basket and body.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: 414 EB P48 with strange things and strange subs
« Reply #7 on: March 27, 2021, 12:09:02 PM »
Actually, whatever the Vgs voltage, it's the voltage across R8 that matters. I believe it should be around 3V, for ca. 0.4mA quiescent current.

Thanks. Across R8 measures 3.4Vdc. I have a 2N5457 in for T3 as I couldn't find any originals.

All of the grounds check okay.

I'm going to make a separate post asking for a reference level test. I need to know if the output level is within a reasonable amount and have no other 414 to use. My tests thoughts are these:

Someone with a 414 P48 and an SM57: Please play a 1kHz test tone through any speaker. Place SM57 1-2 feet away (but measure accurately and record the distance). Aim SM57 directly at the cone as best as possible and as square as possible. Record level in audio file or just let me level. Place 414 in same position as record level same way.

When I do these tests on my end I will place an SM57 and 414 and should get the same "RATIO" as you did IF my 414 has the right output?

abbey road d enfer

Re: 414 EB P48 with strange things and strange subs
« Reply #8 on: March 27, 2021, 06:20:50 PM »
Someone with a 414 P48 and an SM57: Please play a 1kHz test tone through any speaker. Place SM57 1-2 feet away (but measure accurately and record the distance). Aim SM57 directly at the cone as best as possible and as square as possible. Record level in audio file or just let me level. Place 414 in same position as record level same way.
That wouldn't be a very valid test, since a very small difference in placement can result in significant change in level when using sinewaves in an uncontrolled acoustic environment. You need pink noise or warbled sine. Most DAW's offer the possibility of pink noise. In order to minimize the effects of different frequency response, the pink noise should be filtered around 1kHz.

Quote
When I do these tests on my end I will place an SM57 and 414 and should get the same "RATIO" as you did IF my 414 has the right output?
No need for anyone to make measurements.
The datasheets indicate a sensitivity of 1.9mV for the SM57, and 6 mV for the 414 in cardioid position.
That's a 10dB difference.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: 414 EB P48 with strange things and strange subs
« Reply #9 on: April 01, 2021, 10:04:11 AM »
The datasheets indicate a sensitivity of 1.9mV for the SM57, and 6 mV for the 414 in cardioid position.
That's a 10dB difference.

Okay. So the 414 should be 10dB louder at a given distance, blah, blah?


 

Related Topics

  Subject / Started by Replies Last post
14 Replies
6232 Views
Last post August 03, 2004, 06:42:39 AM
by clintrubber
4 Replies
445 Views
Last post September 17, 2020, 12:16:15 PM
by rockinrob86
4 Replies
265 Views
Last post February 26, 2021, 03:22:32 PM
by ruffrecords
2 Replies
150 Views
Last post April 03, 2021, 04:05:28 PM
by dbelousov