Redd.47 Output Level Сontrol

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I'll just reiterate that the $30 part I linked above works great wired between the Sowter OT and the output XLR connector

I installed it on all ten of ours because in practice, like the OP we realized that even at the lowest gain setting the REDD is high enough output to clip the converters on all but the quietest sources.
 
Reduced gain on E-MU as low as possible.
Yes, I assembled it myself, as close as possible to the circuit, transformers 9970, 9980.
All voltages at the control points (according to the diagram) are close.
Yes, there is an input pad and a rumble filter as well.

Output transformer 9980 7:1+1.
In Chandler, he is connected exactly like that.
That is, the secondary windings are connected in series.
With this inclusion, the "exhaust" is stronger than 7:1.
Sovter generally advises them to be included in parallel.
For variability, I made 3 possible switching options for windings.
If you turn on the transformer windings according to the Chandler circuit, then already at 34dB, then the E-MU is very close to the clip ..

If the circuit is done correctly (in Chandler it certainly is), then everything should work fine without an output attenuator?

Then why did Chandler make an adjustable output attenuator in his REDD.47?
 
I'll just reiterate that the $30 part I linked above works great wired between the Sowter OT and the output XLR connector

I installed it on all ten of ours because in practice, like the OP we realized that even at the lowest gain setting the REDD is high enough output to clip the converters on all but the quietest sources.
I would love to buy it, but now I can not order it unfortunately.
They won't send it to me..
That's why I'm trying to do it myself.
If you could find his circuit, but there is probably also a non-linear potentiometer?

But I repeat, somehow Chandler was able to do this without a complex scheme (judging by the photo) ..
 
Very interesting, I did not know that such problems occur with this preamp..
If such a problem happens often, then perhaps this is due to the implementation of the output attenuator?
I hope there is no such problem in the version of REDD.47 from Chandler?
Originals don’t have an attenuator, there is no problem related to an output control.

There would be some clue in the reference to 0dBm and +dBm as referenced in the manual, regarding a percentage of distortion. With +14 described as “audible distortion”, it has to be a lot of distortion at that point, and turning the output down won’t fix it, turning the input down with a pad will.
 
I'll just reiterate that the $30 part I linked above works great wired between the Sowter OT and the output XLR connector

I installed it on all ten of ours because in practice, like the OP we realized that even at the lowest gain setting the REDD is high enough output to clip the converters on all but the quietest sources.
Is it not then in distortion? With a 200 or 600 ohm load resistor after the T attenuator? This is the question, is the quoted distortion point innaccurate? It shouldn’t be able to clip a converter if it’s at all accurate and it’s loaded properly.
 
https://www.soundonsound.com/reviews/chandler-limited-redd47
Distortion plot there is confusing because it references generator level, not output level. A later plot seems to suggest output limiting around +5dBu, but then:

0.15 percent THD with a -34dBu input delivering +20dBu at the output
(max Chandler 54dB gain setting)


So it can indeed clip a converter without much distortion. It also could be a 6 dB output pad switch might be enough of a fixed shift. Elsewhere it suggests, as is common, that you might overload the unit more noticeably at the lowest gain settings, since it's a harder clip.

Many other headroom specs found there, some contradictory or missing obvious context. I'd like to see a max gain distortion plot for varying input levels up to 10% distortion.
 
Yeah, my units are across the country at the moment so I can’t grab one for a test, but our struggle was always getting the output manageable. 20dB switchable pad on the input plus an output fader makes it workable.
 
Originals don’t have an attenuator, there is no problem related to an output control.

There would be some clue in the reference to 0dBm and +dBm as referenced in the manual, regarding a percentage of distortion. With +14 described as “audible distortion”, it has to be a lot of distortion at that point, and turning the output down won’t fix it, turning the input down with a pad will.
I didn’t quite understand you, in which original (Chandler is also EMI certified) there is no attenuator?

What happens to me when the output level is reduced in scheme 1 (message 33) is not a lot of (audible) distortion - it's an unpleasant sharp cutoff.
The greater the reduction, the higher the cutoff threshold.
While the preamp's input gain level can stay the same or even lower..
As you wrote in post 46, that this can be provided that the attenuator is more than -6dB (if I understood you correctly).
But in Chandler it's -10dB.
It turns out that in this position, Chandler can also have a hard cutoff?


However, if I make an attenuator as in my image according to scheme 2 and 3, then everything works fine.
In circuit 3, I can turn the preamp output level down a lot, and everything works great, with no harsh clipping or distortion.
 
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I looked at all the available photos that I could find on the net.
I "got" this...
 

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There's certainly plenty of modern mics that could use a 30dB pad.....in which case one must question the need for a preamp at all.....
 
There's certainly plenty of modern mics that could use a 30dB pad.....in which case one must question the need for a preamp at all.....
Question the need for a REDD.47 preamplifier or a preamplifier in general as a device?
 
Question the need for any preamplifier. Sometimes you only need the 48V supply.

Question the need for a preamplifier like REDD.47, with high step-up gain in the input transformer, all of which must be thrown away with various pads. They are great with low output mics, sources that aren't loud, etc.
 
I didn’t quite understand you, in which original (Chandler is also EMI certified) there is no attenuator?
I think he means the original EMI REDD 47 did not have an output attenuator. They were plug in amplifiers used in a mixing desk.

Cheers

Ian
 
Question the need for any preamplifier. Sometimes you only need the 48V supply.

Question the need for a preamplifier like REDD.47, with high step-up gain in the input transformer, all of which must be thrown away with various pads. They are great with low output mics, sources that aren't loud, etc.
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
 
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
Well, yes, you explain logically, it's hard to disagree with you!

I already have an input pad, but for more versatility, I still want to add a small adjustable attenuator (10dB) to the output, like in Chandler.

Can you please tell me if the scheme (message 49) that I tried to "peep" from the photographs can be suitable for this purpose?
True, I did not succeed in "peeping" the value resistors and the capacitor ..
 
I would love to buy it, but now I can not order it unfortunately.
They won't send it to me..
That's why I'm trying to do it myself.
If you could find his circuit, but there is probably also a non-linear potentiometer?

But I repeat, somehow Chandler was able to do this without a complex scheme (judging by the photo) ..
Where are you located ? check this... 16€ for a pair + shipping :

600 ohm T pad attenuators in stock. Europe

This is what I decided to implement into my dual REDD47, I'm about to finish my build and make some tests.
 
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,.
 
Problems with high levels from microphones is probably the reason we are not seeing more fixed gain, or limited gain range preamps like Redd47. There are many other sounding as good or better, i believe people like EMI because it is related to The Beatles, designed in UK, marketing is very important too.
The "problem" with input pad is people wanting to drive circuits as much as they can without it, then attenuate at the output. This sounds different from attenuating input by the same amount.
I believe this type of preamps have their place today, of it takes someone with enough knowledge to add proper attenuators or tell how they should be used.
 
It's not about money...
You can use fixed pad with off position, this would be the easiest thing working fine. Balanced and all. Or balanced switched pad with more positions, it only takes switch and resistors.
 
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