For most of us, it's not every day that we find ourselves with a real U47 on the bench. Working on this one has highlighted my summer, so I just wanted to share...
So, my friend Téo (who runs the Infernale Machine Studio http://www.infernalemachine.fr ) found himself a quite beat up short body U47 for a reasonable price. Blurry pics, half of the shockmount was missing, dented grille, bad looking M7, said to be 'noisy' but working, and sold 'as is'... A bit of a gamble but the deal was concluded...
Click on the thumbnails to see full res pictures.
All the components of the mic seems to be original and measure well. The serial number plate is too damaged to read the serial number but date code on the Bosch capacitors says March 59. This seems consistent with the head basket N° 5201, and the NG N°4825. Late production.
Not sure the capacitor's date code can be trusted tho. As you can see on the pic, the Bosch cap bears the mention 'Importé d'Allemagne' in French! Which leads to think that the cap may have been changed at some point, thus invalidating the dating. Need to investigate this further...
The VF14 is not a 'M' type. Maybe it has been changed at some point, or maybe Neumann did fit non 'M' stamped tubes in 1959? (Telefunken stopped the steel tube production in 1954.)
There was a cold solder joint on the tube socket, but after fixing it, we got some signal. Given the poor state of the original M7, and the dirtiness of the head basket, we fitted the Flea head basket with a Thiersch ST7 PVC from a clone, and despite some hum, and intermittent noises, the sound was promising enough to pursue the restoration.
The PSU had obviously been serviced before. I could be wrong but I don't think Neumann used to source Ducati lytics in Italy, nor Soral French bridge rectifiers... The front panel indicator was shot, and a resistor had been added in front of the rectifier to lower the voltage.
I fitted new caps, fast diodes (UF4007), and changed one of the 1KOhms for an adjustable power resistor in order to be able to adjust the B+ to 105V.
Original NG were designed to produce 105V with an input voltage of 220V or 110V which were standard AC power for the time. Nowadays, with the AC power being higher, one need some kind of adjustment to avoid feeding precious VF14 with 110V B+ or more!
I changed the AC cord, cleaned the Tuchels, replaced one of them, changed the indicator, replaced some rusty screws, and tuned the output to 105V. Hum was gone!
The original cable was damaged and the Tuchel connectors were dirty and oxidized. Téo had a few connectors in better shape so I took the best parts to make a good set. I shortened the cable which doesn't look original to me (7 conductors, only one layer of shield, extremely stiff). So, despite it was working, I made a new one with Accusound CX7. That's a new tube mic cable with a quad helix shield like the old EMT.
http://www.accusoundcablecompany.com/store/product_info.php?products_id=126
I also made a Tuchel/XLR adapter for the audio output.
Next I worked on the head basket. Dirt and oxide doesn't match well with high impedance circuits and I hopped to get as much as possible out of the original M7.
I dismantled everything and off to the ultrasonic bath. (No, not the M7!). You can see the color of the bath after the grille went in...
Then, I polished all the parts, and rinsed them with isopropyl alcohol to get rid of the polish residues. Looks, and sounds, much better!
I cleaned the capsule as much as I dared. While doing so, I had a feeling that the membrane was not as much tensioned than the ST7 I'm used to wok with. We tried both sides as one is better looking than the other. Curiously, it's the one that's missing gold that sounded the best, but still, even after 72 hours of burn'in, the output level was way too low, and it had a propensity to collapse very easily (which I guess is related to the lower membrane tension).
With the ST7 we had a very good mic, but with the original M7, it was not usable at all. So we sent the M7 to Siegfried Thiersch for re-skinning....
I have done little work on the mic body itself cause it was working well. Cleaned the body tube and the bottom bell, cleaned the components, changed two wires that were damaged, and mainly concentrated on the contacts. The Tuchel was easy (once you dismantled everything to get it out that is), but the tube socket was a bit trickier. I de-soldered each pin, sucked the solder off, carefully bent the pins and got them out. The pins are copper, without any plating, so they become shiny easily when one polish them, but I was concerned that they would get oxidized fast after that, so I silver plated them. Done the the same with the Tuchel and the ground terminal while I was at it. I bent each pin a little before fitting them back in order to have a firm grip on the tube.
Silver plating the pins may seems a bit 'overkill', but I'm quite happy with the result. The mic is now dead silent. Not the tiniest little noise! First time I got that close to perfection.
Before:
After
http://
Conversely to the socket pins that were black from oxide, the VF14 pins were perfectly clean and shiny when I got the tube out, which means that someone must have attempted to service this mic recently...
The rubber band that holds the tube socket was a bit saggy, as you'd expect from 52yo rubber... I hadn't any replacement rubber at hand so I shortened it in order to re-gain some tension back, but I will change it next time I'll open the mic.
The M7 came back from re skinning so I fitted it back in its holder. I discovered another use for the handy little plastic box that Thiersch ships his work in: they make a perfect shield against dust and solder fumes during assembly!
I bent what was left of the elastic shock-mount back into shape and scavenged the missing parts on a broken Chinese copy (From the Rimshot groupbuy).
Our goal was 'working as well as possible' rather than 'looking as good as possible', so the 'cosmetic' part of the restoration was limited to cleaning everything, and blackening the background of the Neumann logo. Sending the body parts to Gleyer Galvanik would be possible for instance, but it wouldn't add anything to the sound...
Miscellaneous stuff about that particular short body U47.
The body tube is made of aluminum.
The brass screw that holds the tube to the bottom bell is M4 instead of M3. Dunno if it's original or if the bell has been re-tapped to M4 because the M3 thread was worn out?
The B+ pin on the Tuchel is shorter than the other ones, which allows ground to be connected before B+. I don't know if this was standard Neumann, or if someone cut that pin at some point... Has anybody seen a shortened B+ pin on a U47?
And now, “how does she sounds?” do you ask...
Well...(insert your favorite uber superlative here ) !!!
There's no way I could describe with words such an experience, it would be like trying to tell you how tasted a certain bottle of Chateauneuf du Pape 1966 that I drank once... You'd be still missing 98% of the event!
Suffice to say that this one is definitely the best mic I ever heard. Period.
(And that statement include several U47)
Axel
Edited for bad link.
So, my friend Téo (who runs the Infernale Machine Studio http://www.infernalemachine.fr ) found himself a quite beat up short body U47 for a reasonable price. Blurry pics, half of the shockmount was missing, dented grille, bad looking M7, said to be 'noisy' but working, and sold 'as is'... A bit of a gamble but the deal was concluded...
Click on the thumbnails to see full res pictures.
All the components of the mic seems to be original and measure well. The serial number plate is too damaged to read the serial number but date code on the Bosch capacitors says March 59. This seems consistent with the head basket N° 5201, and the NG N°4825. Late production.
Not sure the capacitor's date code can be trusted tho. As you can see on the pic, the Bosch cap bears the mention 'Importé d'Allemagne' in French! Which leads to think that the cap may have been changed at some point, thus invalidating the dating. Need to investigate this further...
The VF14 is not a 'M' type. Maybe it has been changed at some point, or maybe Neumann did fit non 'M' stamped tubes in 1959? (Telefunken stopped the steel tube production in 1954.)
There was a cold solder joint on the tube socket, but after fixing it, we got some signal. Given the poor state of the original M7, and the dirtiness of the head basket, we fitted the Flea head basket with a Thiersch ST7 PVC from a clone, and despite some hum, and intermittent noises, the sound was promising enough to pursue the restoration.
The PSU had obviously been serviced before. I could be wrong but I don't think Neumann used to source Ducati lytics in Italy, nor Soral French bridge rectifiers... The front panel indicator was shot, and a resistor had been added in front of the rectifier to lower the voltage.
I fitted new caps, fast diodes (UF4007), and changed one of the 1KOhms for an adjustable power resistor in order to be able to adjust the B+ to 105V.
Original NG were designed to produce 105V with an input voltage of 220V or 110V which were standard AC power for the time. Nowadays, with the AC power being higher, one need some kind of adjustment to avoid feeding precious VF14 with 110V B+ or more!
I changed the AC cord, cleaned the Tuchels, replaced one of them, changed the indicator, replaced some rusty screws, and tuned the output to 105V. Hum was gone!
The original cable was damaged and the Tuchel connectors were dirty and oxidized. Téo had a few connectors in better shape so I took the best parts to make a good set. I shortened the cable which doesn't look original to me (7 conductors, only one layer of shield, extremely stiff). So, despite it was working, I made a new one with Accusound CX7. That's a new tube mic cable with a quad helix shield like the old EMT.
http://www.accusoundcablecompany.com/store/product_info.php?products_id=126
I also made a Tuchel/XLR adapter for the audio output.
Next I worked on the head basket. Dirt and oxide doesn't match well with high impedance circuits and I hopped to get as much as possible out of the original M7.
I dismantled everything and off to the ultrasonic bath. (No, not the M7!). You can see the color of the bath after the grille went in...
Then, I polished all the parts, and rinsed them with isopropyl alcohol to get rid of the polish residues. Looks, and sounds, much better!
I cleaned the capsule as much as I dared. While doing so, I had a feeling that the membrane was not as much tensioned than the ST7 I'm used to wok with. We tried both sides as one is better looking than the other. Curiously, it's the one that's missing gold that sounded the best, but still, even after 72 hours of burn'in, the output level was way too low, and it had a propensity to collapse very easily (which I guess is related to the lower membrane tension).
With the ST7 we had a very good mic, but with the original M7, it was not usable at all. So we sent the M7 to Siegfried Thiersch for re-skinning....
I have done little work on the mic body itself cause it was working well. Cleaned the body tube and the bottom bell, cleaned the components, changed two wires that were damaged, and mainly concentrated on the contacts. The Tuchel was easy (once you dismantled everything to get it out that is), but the tube socket was a bit trickier. I de-soldered each pin, sucked the solder off, carefully bent the pins and got them out. The pins are copper, without any plating, so they become shiny easily when one polish them, but I was concerned that they would get oxidized fast after that, so I silver plated them. Done the the same with the Tuchel and the ground terminal while I was at it. I bent each pin a little before fitting them back in order to have a firm grip on the tube.
Silver plating the pins may seems a bit 'overkill', but I'm quite happy with the result. The mic is now dead silent. Not the tiniest little noise! First time I got that close to perfection.
Before:
After
http://Conversely to the socket pins that were black from oxide, the VF14 pins were perfectly clean and shiny when I got the tube out, which means that someone must have attempted to service this mic recently...
The rubber band that holds the tube socket was a bit saggy, as you'd expect from 52yo rubber... I hadn't any replacement rubber at hand so I shortened it in order to re-gain some tension back, but I will change it next time I'll open the mic.
The M7 came back from re skinning so I fitted it back in its holder. I discovered another use for the handy little plastic box that Thiersch ships his work in: they make a perfect shield against dust and solder fumes during assembly!
I bent what was left of the elastic shock-mount back into shape and scavenged the missing parts on a broken Chinese copy (From the Rimshot groupbuy).
Our goal was 'working as well as possible' rather than 'looking as good as possible', so the 'cosmetic' part of the restoration was limited to cleaning everything, and blackening the background of the Neumann logo. Sending the body parts to Gleyer Galvanik would be possible for instance, but it wouldn't add anything to the sound...
Miscellaneous stuff about that particular short body U47.
The body tube is made of aluminum.
The brass screw that holds the tube to the bottom bell is M4 instead of M3. Dunno if it's original or if the bell has been re-tapped to M4 because the M3 thread was worn out?
The B+ pin on the Tuchel is shorter than the other ones, which allows ground to be connected before B+. I don't know if this was standard Neumann, or if someone cut that pin at some point... Has anybody seen a shortened B+ pin on a U47?
And now, “how does she sounds?” do you ask...
Well...(insert your favorite uber superlative here ) !!!
There's no way I could describe with words such an experience, it would be like trying to tell you how tasted a certain bottle of Chateauneuf du Pape 1966 that I drank once... You'd be still missing 98% of the event!
Suffice to say that this one is definitely the best mic I ever heard. Period.
(And that statement include several U47)
Axel
Edited for bad link.
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