The step up transformer is necessary to obtain a decent noise figure. The overall gain of 34dB does not usually need to be thrown away in pads. In the early days before high output condensor mics weere common, the best quality mics were ribbon types. These had a very low output and needed a lot of gain. Once condenser mics appeared 30 to 40dB of gain was plenty. Add to this the fact that most sources were not close miced and it all makes sense. Trying to use a REDD 47 as a stand alone mic pre with a condenser mic close micing a vocal or guitar cab is not what they were intended for.
If you have a relatively hot source and you want to benefit from the tonal properties of the REDD 47 then you should put a pad at the input.
Cheers
Ian
A Fender Deluxe at moderate volume with a U67 two feet in front of it into your average 40-45dB tube preamp can require 30+dB of pad, so it's a legitimate question to wonder what you're doing when you toss all the gain the preamp is providing, so you can use the preamp. I stopped trying to put that through a preamp like this, it goes straight to the converter from the U67 PSU output usually. People like to use LA-2A's as preamps in similar cases, since there's gain control right after the input transformer, before the amplifier itself. You start to see the logic of Jensen/Hardy preamp having a 150:600 input transformer feeding the 990 op amp, optimized for 600 ohm source. I digress.....
I do a lot of rock band recording with 40dB tube pre's and dynamics and ribbons, there's almost always a 20 dB pad in front to avoid input overload, so then it's a 20dB amplifier in practice. Go to a condenser, you need even less. Practical reality post-1970.
I was excited to discover the single tube preamp used in the RCA 76 consoles, I thought "less gain, won't need an input pad"....they still need an input pad.....30dB preamp needing a 20dB pad most times.
When the microphone output might be expected to be so high consistently, one might do better with an input transformer without much step-up gain at all, thereby removing the need for an input pad. Sheer input voltage will swamp any perceived noise penalty. Yes, the tube preamp types will no longer be 'universal', but maybe more suitable for modern sources. I don't recall which amplifier right now, but I believe the Jensen JT-13K7 (1:5, 13.6dB) was used in a more modern tube preamp for precisely this reason.
None of this is to suggest anything is wrong with the REDD.47, or that it should be redesigned, but instead to try and illustrate the problems encountered with old designs and modern approaches.
The REDD at 34dB will have a harder distortion than it will at 46dB, the Chandler version an even more forgiving distortion at 54dB, or whatever it is. This is the nature of negative feedback shaping a distortion 'knee'.
I would still like to know the maximum clean dBu this preamp is capable of, since it informs the solution to any recorder/converter overload. A 'T' attenuator with a 600R resistive load after it is great if you can get it. A 1K pot works fine. A dual 500R or 1K pot works fine for a more 'balanced to ground' approach. All should work fine. Unless a particular preamp circuit proves itself to have particular loading conditions that significantly affect the response, all of these approaches should work fine. Many old types don't need any particular loading, and don't show much difference comparing a 600R load versus a 10K load, outside of a slight shift in max gain. Others absolutely require a particular loading to avoid response variations,.
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