Attenuators with transformer preamps, a good idea ??

pcrecord

Quality recording seeker !
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I have to say this video and conversation has me leaning a bit more towards the RND 511 pre vs the ISA for my next pre
The 511 seems a very good choice for someone already having a lunchbox. I don't think Focusrite offers the ISA in that format, but if you could find a used Red per.. this could be interesting too !
Very different beasts, the texture and silk option of the 511 seems to be appealling. I know you often aim for some mojo sounding gear.
I remember you telling me about the LA-610 and how you would push everything to maximum to see how it sounds.. eh eh eh ! ;)
I'm changing the tubes on one of them in a few weeks, I'll probably do a video on it too.. Stay tuned for that !

But this experience with the attenuator re-confirmed to me that the ISA is all about Clean sound, no noise, no distortion.. but still offers this nice transformer sound.
 

kmetal

Kyle P. Gushue
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My tastes have evolved some over the years.

I'm changing the tubes on one of them in a few weeks, I'll probably do a video on it too.. Stay tuned for that !
Oh yeeeeeaaaaaa

But this experience with the attenuator re-confirmed to me that the ISA is all about Clean sound, no noise, no distortion.. but still offers this nice transformer sound.

Totally. From what i understand they chose the lundhal xformer, specifically because it's one of the cleanest xformers available. Plus if you consider the isa was made for a console, with eq and compressor, it makes sense that its cleaner with tons of headroom. The ISA is one of those pres that just sounds right imho.

I would be curious to hear the attenuator in series, just to hear how the isa saturates.
 

Boswell

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I would be curious to hear the attenuator in series, just to hear how the isa saturates.
Sufficient attenuation between the output of a pre-amp and a following ADC allows the ADC to capture either the effect of transformer saturation or the onset of clipping, whichever is appropriate for the pre-amp's output architecture.

I've done a bit more digging in the Focusrite literature, and, from what I can tell, the ISA One, Two, 428 and 828 are based on a common design that has input transformers only and no output transformers. The information is well hidden, but with these models, it looks as though the output will clip.
 

Boswell

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UK
This is for the U-pad in your balanced attenuator, right? Well, 40dB is easy, as it's 100x in voltage and hence ratios. To 1%, you can use a shunt of 2R and series of 100R. Series resistors of 10K Ohms and a shunt of 200 Ohms are readily available values, and would work OK in this configuration (where OK is not a short circuit). Use two 100 Ohms in series if you can't get 200 Ohms, but if you are considering that, then 4.7K series and 2x 47 Ohm shunt would work marginally better over the range of other likely circuit impedances.
 

pcrecord

Quality recording seeker !
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Feb 21, 2013
Location
Quebec, Canada
This is for the U-pad in your balanced attenuator, right? Well, 40dB is easy, as it's 100x in voltage and hence ratios. To 1%, you can use a shunt of 2R and series of 100R. Series resistors of 10K Ohms and a shunt of 200 Ohms are readily available values, and would work OK in this configuration (where OK is not a short circuit). Use two 100 Ohms in series if you can't get 200 Ohms, but if you are considering that, then 4.7K series and 2x 47 Ohm shunt would work marginally better over the range of other likely circuit impedances.
Thanks a lot, I'll relay that answer..
 
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