Cirrus
Roadie
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- 312
This is hardly breaking new ground, it's a pretty well trodden DIY route, but I'm building a couple of mics.
It might be this isn't the best place for a thread about a project like this, it might be that I forget to update it, and it might be that not many people really care. But... I'm making two condenser mics.
So far, I've got almost all the bits including "donor" cheap mics in the form of two ADK 51s, which together cost £130 and will provide the bodies, metal frame, xlr sockets, headbasket and capsule mounts. I do appreciate that it's totally nonsense to build two condenser mics by buying two working (for now)cheaper condenser mics.
A bottle of Acetone and a lot of scrubbing later, the gold decals have been removed and the mic bodies are a mysterious black, like an SR-71 Blackbird.
And everything is now sat in a box, waiting for an evening of inspiration and motivation to get started. I've already began selecting certain components, using the absolutely shamefully jury-rigged testing device I was able to build out of random bits from my bag of cast-off electrical parts from previous projects:
- There are two resistors that have to be matched to, according to the 1980 Neumann schematic, 0.4%. That's beyond the power of my multimeter, so I made a "Wheatstone Bridge", which lets you cycle through a bunch of different resistors, measuring the difference between them and gradually closing in on the closest-matched pair. Out of a batch of 20 resistors, I eventually got two matched pairs, one for each mic, that were 0.05% matched
- Testing the FETs. I'm not going to pretend I understand FETS. But apparently in the U87 circuit, it's good to test your FETs for a characteristic called IDSS, and you do that by putting voltage across them and seeing what current they draw when you short two of the legs together. Lower is better, and a close match will be good to try to get a matched pair of mics, though it's not the most critical thing there - that's on the capsule.
It might be this isn't the best place for a thread about a project like this, it might be that I forget to update it, and it might be that not many people really care. But... I'm making two condenser mics.
So far, I've got almost all the bits including "donor" cheap mics in the form of two ADK 51s, which together cost £130 and will provide the bodies, metal frame, xlr sockets, headbasket and capsule mounts. I do appreciate that it's totally nonsense to build two condenser mics by buying two working (for now)cheaper condenser mics.
A bottle of Acetone and a lot of scrubbing later, the gold decals have been removed and the mic bodies are a mysterious black, like an SR-71 Blackbird.
And everything is now sat in a box, waiting for an evening of inspiration and motivation to get started. I've already began selecting certain components, using the absolutely shamefully jury-rigged testing device I was able to build out of random bits from my bag of cast-off electrical parts from previous projects:
- There are two resistors that have to be matched to, according to the 1980 Neumann schematic, 0.4%. That's beyond the power of my multimeter, so I made a "Wheatstone Bridge", which lets you cycle through a bunch of different resistors, measuring the difference between them and gradually closing in on the closest-matched pair. Out of a batch of 20 resistors, I eventually got two matched pairs, one for each mic, that were 0.05% matched
- Testing the FETs. I'm not going to pretend I understand FETS. But apparently in the U87 circuit, it's good to test your FETs for a characteristic called IDSS, and you do that by putting voltage across them and seeing what current they draw when you short two of the legs together. Lower is better, and a close match will be good to try to get a matched pair of mics, though it's not the most critical thing there - that's on the capsule.
