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Old 5th October 2011, 06:39 PM   #11
slor is offline slor  United States
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Ah so, as they say, or used to. Thanks, that's a lot to think on. Do you have recommendations for cap values in both C3 positions?
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Old 5th October 2011, 08:36 PM   #12
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Can you take a photo of the front and the circuitboard?
I worked with this little mixer many years ago.
The schematic which you furnished is for the Gates Universal Line Amplifier.
The gain structure is not the same as for your mixer.
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Old 5th October 2011, 08:59 PM   #13
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Maybe best to first check if hum is a problem before chaging values without any need - eg. DC power the first stage heater (or all heaters), using a battery - I have a 7.2Ah 6V VRLA I keep just for that purpose.

Any larger value in cap is going to be better - so likely to depend what you have lying around, and what physical size suits. If you do have a hum problem, then changing those caps may still not appease the issue, as there are still other mechanisms, such as lead dress and general grounding to consider.

Ciao, Tim
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Old 6th October 2011, 07:31 PM   #14
slor is offline slor  United States
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Here are some more views of the unit. Thanks for the tip on the correct model number too, turns out mine is a 5233....
Attached Images
File Type: jpg Gates1.jpg (185.6 KB, 53 views)
File Type: jpg Gates2.jpg (128.4 KB, 49 views)
File Type: jpg Gates3.jpg (156.3 KB, 47 views)
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Old 6th October 2011, 08:11 PM   #15
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That's a Gates Bi-mote.
Unfortunately, I'm not sure that you can reduce the noise that much.
This is just from memory but, as I recall, the two inputs go directly to the Daven Attenuators. The outputs from the attenuators go to the input transformer.
About the best that you can do is to operate the mixer with the input attenuators as high as possible and the Master as low as possible.
I've always wanted to get my hands on one of those mixers and re-design it for better performance.
Nonetheless, they were good mixers for their time.
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Old 9th October 2011, 07:34 PM   #16
slor is offline slor  United States
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Yes people who have used these units--myself included--tend to really love them. There is, however, the noise.

I wonder what would happen if you simply removed one gain stage. After all, it's no longer necessary to drive signal through miles of telephone lines....
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Old 29th October 2011, 05:18 AM   #17
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I just rebuilt one of these that had been hacked up before I got it. I removed the two-channel passive mixer section (both attenuators) and made it into what it really is; that is, a single-channel mic preamp. While mine is not dead quiet at high gain (this thing has a LOT of gain), it's certainly quiet enough to use with ribbon mics at the gain level they need. I routinely use it to mic strings from about 6-8' away and the noise floor isn't troublesome at all. I've been toying with making one of the gain sections switchable, but since it works well now I'm not that motivated to do so. I also added a switchable 20dB pad on the input so I can get the circuit gain up a bit higher for ribbon mics and pad it down for hotter mics and sources. I really like the sound of this pre, especially with ribbon mics.

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Don
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