Sound Skulptor forums
Build help and troubleshooting => MP573 Microphone preamplifier => Topic started by: G.Matheson on December 30, 2024, 07:23:57 PM
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Hi,
as I'm not an electronics expert, and I can't seem to find this specific info on the product documents, I would like to ask what the output impedance for the MP573 preamp. Digging online I've only found an old post by Jean from when the product was first released, and there it says it's 600 Ohms. Looking at the archive schematics from previous versions it looks like the output circuit hasn't changed, but I would like to be certain.
Context: I'm going to build a switchable balanced attenuator post output transformer / pre AD converter (RME Fireface UC Line inputs, +4dBu _ 10 kOhm input impedance). I know it would be much easier to get PAD500 but filling lunchbox slots with those is not an option at the moment, so I can only build an external attenuator box, and I would like to get all my specs right before getting components.
Attached below is a link to a google.doc with summarised answers I've received on DIY forums. The info is based on the assumption that the output impedance of the MP573 is 600 Ohms. If it's not too much to ask, could I just get confirmation that I can use these suggestions to calculate my resistor values? It's only 3 paragraphs or so, but if not no worries, I'll figure it out :)
BALANCED ATTENUATOR INFO (https://docs.google.com/document/d/1m7gkyyGdNcCJBJDXtVyPlnZQk1zAFkNVgHbJNRXhLaU/edit?usp=sharing)
Thank you, Giulio
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The real output impedance at 1kHz (just measured) is 66 ohms.
How much attenuation do you want to do?
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Oh ok thank you!
Initially I was (somewhat arbitrarily) planning on 2 settings: -12 and -24 dB. Then based on my equipment headroom (and if I understand correctly also on the 600 Ohm assumption) it was suggested to me that an attenuation between 8 - 12 dB would be enough to drive the output transformer without clipping my AD converters. But it was also implied that other considerations might be appropriate if the output impedance is equal or minor to 100 Ohm.
Would you recommend something different?
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o --/////--o 1k
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/ 680R or 330R
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o --/////--o 1k
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Thank you so much!