CJ said:
The Head without pins on the capsule side (KK87) is older than the other one (KK87s) and it's also a different version. The one with the Pins it's the one with low end Loss, in the photos it's always the one on the left.
thanks
Neumann U67 Repair - Low End Loss - Help needed
- Thread starter Whoops
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Help Support GroupDIY Audio Forum:
The Head without pins on the capsule side (KK87) is older than the other one (KK87s) and it's also a different version. The one with the Pins it's the one with low end Loss, in the photos it's always the one on the left.
thanks
Gene Pink said:
Hi Gene Pink,
thank you .
Could you please elaborate on this?
what are the vent holes in the outer housing rings?
thanks
ln76d said:
Moby said:
That's Correct.
I don't know if these microphones were acquired with the KK87 heads installed already or if the heads were replaced at some point. And also no one at the studio knows that nowadays.
Summary of the Situation
Today I took the microphones to their respective studio for a listening test with the Owner/Engineer,
he was really happy with the sound and after some recording and tests the low end difference that I noticed at my shop although acknowledged he considered it marginal and neglectable.
Above all, he was happy that both microphones were sounding really good and said that in the past the mics never sounded as close to each other as at the present time.
I insisted in making more tests to the capsules but he was not interested and wants the mics as they are.
I have to say the Low End difference between the capsules is more noticeable while listening on Headphones. At the shop I always test equipment with my reference Headphones, at the studio we tested both ways through the studio reference monitors and with my headphones.
Listening with the studio speakers, after some small gain adjustment both mics sounded really close, while with headphones you can noticethat one has a little bit more bass, although the other one doesn't sound Thin at all. The owner listened both ways, acknowledge the difference and decided it was not enough for him to care, he was happy that the first microphone was fixed and that both PSU's were revised also.
I will leave it for now but will still insist in the next days for some capsule capacitance measure, cleaning the parts and connections inside the head, and checking the switches and Hi Pass circuit.
If he refuses I will consider it fixed.
just to let know what was done for future reference:
1) U67 Mic 1 had no bass and sound was thin
2) U67 Mic 1 PSU Revised, cleaned, All Filter Caps changed for 105degrees Panasonic, changed for 240V input. Output Voltages adjusted to correct values. B+ 210V +-2%
3) EF86 tube checked, measured and listening tests, also compared in circuit to another EF86 good tube. No diferences. Installed tube was good
4) U67 Mic 1 components checked, no mods were done to the circuitry in the past. Found an Open Resistor, R12 2,2M was open, resistor replaced. Everything else was fine. C9 electrolytic has no DC leak
5) Voltages at the microphone seem correct now.
6) Listening tests, mic sounds good but need another one to compare
7) U67 Mic2 that was said to be the one sounding good and with more low end in the studio came to the shop to compare
8) Listening tests Mic1 has more low end now than Mic2 that seems to have a small low end loss. It seems replacing R12 or the PSU restoration fixed Mic1 Low end Loss
9)Mic2 PSU Revised , cleaned, All Filter Caps changed for 105degrees Panasonic, changed for 240V input. Output Voltages adjusted to correct values. B+ 210V +-2%.
10) Voltages at both mics measured, all seems good and values consistent between the 2 mics
11) Capsule Heads changed between the Mics. Small low end reduction, only noticeable on headphones follows the capsule (KK87s)
12)Owner considered it a Match
Thank you all so much for all your help,
I learned a lot while troubleshooting and servicing these Mics
Today I took the microphones to their respective studio for a listening test with the Owner/Engineer,
he was really happy with the sound and after some recording and tests the low end difference that I noticed at my shop although acknowledged he considered it marginal and neglectable.
Above all, he was happy that both microphones were sounding really good and said that in the past the mics never sounded as close to each other as at the present time.
I insisted in making more tests to the capsules but he was not interested and wants the mics as they are.
I have to say the Low End difference between the capsules is more noticeable while listening on Headphones. At the shop I always test equipment with my reference Headphones, at the studio we tested both ways through the studio reference monitors and with my headphones.
Listening with the studio speakers, after some small gain adjustment both mics sounded really close, while with headphones you can noticethat one has a little bit more bass, although the other one doesn't sound Thin at all. The owner listened both ways, acknowledge the difference and decided it was not enough for him to care, he was happy that the first microphone was fixed and that both PSU's were revised also.
I will leave it for now but will still insist in the next days for some capsule capacitance measure, cleaning the parts and connections inside the head, and checking the switches and Hi Pass circuit.
If he refuses I will consider it fixed.
just to let know what was done for future reference:
1) U67 Mic 1 had no bass and sound was thin
2) U67 Mic 1 PSU Revised, cleaned, All Filter Caps changed for 105degrees Panasonic, changed for 240V input. Output Voltages adjusted to correct values. B+ 210V +-2%
3) EF86 tube checked, measured and listening tests, also compared in circuit to another EF86 good tube. No diferences. Installed tube was good
4) U67 Mic 1 components checked, no mods were done to the circuitry in the past. Found an Open Resistor, R12 2,2M was open, resistor replaced. Everything else was fine. C9 electrolytic has no DC leak
5) Voltages at the microphone seem correct now.
6) Listening tests, mic sounds good but need another one to compare
7) U67 Mic2 that was said to be the one sounding good and with more low end in the studio came to the shop to compare
8) Listening tests Mic1 has more low end now than Mic2 that seems to have a small low end loss. It seems replacing R12 or the PSU restoration fixed Mic1 Low end Loss
9)Mic2 PSU Revised , cleaned, All Filter Caps changed for 105degrees Panasonic, changed for 240V input. Output Voltages adjusted to correct values. B+ 210V +-2%.
10) Voltages at both mics measured, all seems good and values consistent between the 2 mics
11) Capsule Heads changed between the Mics. Small low end reduction, only noticeable on headphones follows the capsule (KK87s)
12)Owner considered it a Match
Thank you all so much for all your help,
I learned a lot while troubleshooting and servicing these Mics
Last edited:
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