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Post by deepdark on Sept 14, 2015 14:20:31 GMT -6
I don't plane redisigning and rebiasing the output stage to make it run cooler haha. To quote something i've just read
"another underestimation in the REDD.47 design was that they put off an ungodly amount of heat - which meant having to regulary changing valves"
Don't know how exact this statement is, but it looks to resume what we've just discussed over the thread lol. Weird funk'ng pre, as you said.
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Post by jazznoise on Sept 14, 2015 14:42:16 GMT -6
It's a very low impedance to drive. P = I^2/R. Heat is the name of the game!
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Post by deepdark on Sept 14, 2015 14:58:44 GMT -6
even at 600, it will probably be significant
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Post by EmRR on Sept 14, 2015 16:39:00 GMT -6
Ratio is commentary on WHY the design is as it is. It makes no difference what you hook it up to now 200-600, that part changes nothing other than level. 10k is a lower than average load for a tube preamp. 15k is more standard. RCA and WE is typically 30k-50k, and an RCA preamp with a single tube drawing 4mA regularly drives a 250 or 500 ohm output over +14dBm. They do it by plate feeding the tube, and by using transformers with higher inductance than you can generally even get today. Part of the trick with the REDD47 is likely that they are driving the output transformer with a much lower Z than 10K to trick the transformer into having wider low frequency response than it would if you matched the Z with a single tube stage. As well the REDD47 output may be a less expensive transformer that can't handle DC current, AND they may be using LC resonance of a cap coupled output to boost the low end versus using a transformer naturally good enough (expensive) to pass wide flat response with a matched or 2x source Z and direct feed to achieve maximum headroom. Take the feedback out of a circuit like this and the response frequently goes in the toilet, along with the noise spec, as opposed to earlier times when the circuit had to be designed for maximum cleanliness without feedback, and the iron had to handle 2x or even matched source Z with full response.
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Post by formatcyes on Sept 30, 2015 14:20:44 GMT -6
deepdark What do you think of the redd47?
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Post by deepdark on Sept 30, 2015 14:29:50 GMT -6
Not that impressed to be honnest. Not my go to pre for sure. It's nice to record some upfront, rock vocals, guitars etc. But it's not my choice for some acoustic stuff. I think, if one would make a nice dual tube pre, the schematic on Jensen transformer website would be a nice starting point. I'm planning building it soon.
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