Redd.47 Output Level Сontrol

[vmanj]

Greetings to all.
I want to make an output level regulator.
Chandler REDD.47 uses a potentiometer for this, probably after the transformer.
Who knows, please tell me the scheme of how this can be implemented?

 

[soapfoot]

I used a bridged T attenuator bought from Hairball audio.

Works great

 

[vmanj]

I understand, thanks.

 

[soapfoot]

A potentiometer would probably be a bit less-satisfactory, as the impedance load on the transformer would change with level.

 

[iampoor1]

A potentiometer would probably be a bit less-satisfactory, as the impedance load on the transformer would change with level.

Actually the load across the transformer stays the same...it's the output resistance that varies between 0 and a couple hundred ohms

 

[vmanj]

Does this mean that the circuit in my image can work fine?

 

[alphasnk]

Does this mean that the circuit in my image can work fine?

It will work, you will lose bass as you turn the volume really down, that's the only thing..

 

[soapfoot]

Yeah, despite the fact that I misspoke above, you really do want a bridged T attenuator if you don’t want the preamp’s output Z to change as you turn the output fader.

This one will work great. At $31 it costs a little more than a pot, but will give much more satisfactory performance.

It’s PCB mount, but Hairball also sells a daughter PCB that you can use to adapt it for flying leads

https://www.hairballaudio.com/catalog/parts-store/attenuators/bourns-600-t-pad-attenuator-14-shaft

 

[ruffrecords]

It will work, you will lose bass as you turn the volume really down, that's the only thing..

Why is that?

Cheers

Ian

 

[Winetree]

I'VE USED THIS
https://capi-gear.com/catalog/product_info.php?cPath=48&products_id=256

 

[alphasnk]

Why is that?

Cheers

Ian

Isn't it due to the impedance? At the extreme end of reducing the volume, you can hear only high frequencies

 

[ruffrecords]

Isn't it due to the impedance? At the extreme end of reducing the volume, you can hear only high frequencies

Not at all. It is exactly like any other level control in a circuit. A Neve we used a 2K pot slugged with a 1K resistor from wiper to ground as monitor level controls strapped right across the secondary of the transformer. The load varies from 2K down to 660 ohms and the transformer can easily handle that.

Cheers

Ian

 

[TwentyTrees]

Thanks for the clarification Ian. Is it safe to assume this scheme would work in any situation where an output stage is driving a transformer with a 600 ohm secondary into a bridging input?

 

[alphasnk]

Not at all. It is exactly like any other level control in a circuit. A Neve we used a 2K pot slugged with a 1K resistor from wiper to ground as monitor level controls strapped right across the secondary of the transformer. The load varies from 2K down to 660 ohms and the transformer can easily handle that.

Cheers

Ian

You've explained it before, and most of us learnt that from you. I was only saying that without the resistor, it's a little more crude when you turn the volume down..

 

[vmanj]

Yes, it seems that when the output level is reduced, for example, in the Chandler Redd.47, the low frequencies also decrease.

https://www.amazona.de/test-chandler-limited-emi-redd-47/

 

[soapfoot]

There’s sometimes a significant difference between “it works” and “it works optimally.”

And in this case, if using a simple pot then consistency of performance across the control’s range might depend to some degree on the input impedance of the next piece of gear in line.

But with a constant-impedance output attenuator, it should behave the same at all levels of attenuation (which is worth an extra 15 bucks to me)

 

[ruffrecords]

You've explained it before, and most of us learnt that from you. I was only saying that without the resistor, it's a little more crude when you turn the volume down..

Indeed and of course it depends on the pot you use and the range of control you need. Neve always used slugged linear pots because a linear pot is much more consistent than a log one.

Cheers

ian

 

[ruffrecords]

There’s sometimes a significant difference between “it works” and “it works optimally.”

And in this case, if using a simple pot then consistency of performance across the control’s range might depend to some degree on the input impedance of the next piece of gear in line.

But with a constant-impedance output attenuator, it should behave the same at all levels of attenuation (which is worth an extra 15 bucks to me)

And a constant impedance atternauator will not work 'properly' unless fed from the correct impedance and loaded with the correct impedance. They worked fine in the old days when you could pretty much guarantee that Zout = Zin = 600 ohms. Add to that that most of todays three pot bridged T attanuators are nothing like constant impedance and you can see why the current paradigm of low Z out and high Z in predominates because it is much kmore predictable and much less susceptible to componenet variables.

Cheers

Ian

 

[soapfoot]

Speaking practically, I've built ten REDD.47s with Sowter 9970 input and 9980 outputs.

In all ten, I used the above-linked Bourns bridged T attenuator as an output fader after the Sowter 9980.

It works very well in that application. I have not tried a potentiometer as-configured above to compare.

 

[My3gger]

I used 1k pot with two Cinemag 30k:600 output models, 5:1 Edcor and some home made 5:1 to try them out. 1k pot works well in practice although T pad is a bit better. Especially when very good transformers are used and one wants the rest to be as good as possible. "The problem" with Redd47 is very limited gain range, not lack of gain with 46dB max, it really needs an output pad.
Did anyone notice how sound is changing when switching gain positions? At higher input levels 34dB position sound kind of falls apart a bit, i like 40dB best, 46dB has more of sometimes annoying high frequency distortion. I never tried to extend the range of gain switch for this reason, maybe it is something to try out and hear how lower than 34dB of gain sounds. IIRC, this is what Chandler did down to 16dB while retaining stability.