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Post by bluegrassdan on Jul 6, 2021 20:40:29 GMT -6
Howdy, Working on my latest design and I need help deciding how to configure gain staging in a most user-friendly way. We've got two tube gain stages with a basic rotary switch attenuator between them. The first tube stage seems to work very well with up to 18dB of NFB as a gain control. Thus allowing condenser mics to be used on the input without "having" to pad it down. Of course, there is still a typical -20dB switchable pad if needed. I now have some options to consider with the engineer in mind: Option 1: Two rotary switches (similar to attached photos). "Input" adjusts the NFB to reduce the first gain stage. "Gain" or "Level" or "Atten" is the between stage. Option 2: One rotary "gain" switch, combination mid-stage attenuator and NFB adjust. For example, max gain would have no NFB for full 60dB gain. The lowest gain would have the most NFB. This could be similar to the Gyraf G9 where part of the switch covers attenuation while the other positions adjust NFB. Biggest drawbacks: Option 1. Users may overdrive the front end without realizing it. This could be helped by making the -6dB NFB actually be centered at "0" (see picture). Option 2. It takes the power to shape harmonics and saturation out of the user's hand. Curious to know what everyone thinks.   |
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Post by Tbone81 on Jul 6, 2021 20:48:49 GMT -6
Option 1
As the engineer I want the control. And if I screw up the gain staging…well, that’s on me. Knowing proper gain staging is part of the job.
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Post by superwack on Jul 6, 2021 21:21:33 GMT -6
I like option one as well.
Unsolicited advice but it may be confusing to some people to put the mid frequencies to the left of the mid frequency gain knob because you have chosen to do decimals so at a quick/distant glance they all seem like low frequencies (i.e. it looks like the dial goes from 21 - 72)
I love the sound of your other preamp and saw you were asking about transformers so I know this isn’t the old design + EQ. Looking forward to learning more about it
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Post by bluegrassdan on Jul 6, 2021 21:23:54 GMT -6
Unsolicited advice but it may be confusing to some people to put the mid frequencies to the left of the mid frequency gain knob because you have chosen to do decimals so at a quick/distant glance they all seem like low frequencies (i.e. it looks like the dial goes from 21 - 72) That is a very good idea. I was pondering this myself earlier. Consider it done! |
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Post by jcoutu1 on Jul 6, 2021 21:39:05 GMT -6
I like option one as well. Unsolicited advice but it may be confusing to some people to put the mid frequencies to the left of the mid frequency gain knob because you have chosen to do decimals so at a quick/distant glance they all seem like low frequencies (i.e. it looks like the dial goes from 21 - 72) I love the sound of your other preamp and saw you were asking about transformers so I know this isn’t the old design + EQ. Looking forward to learning more about it I literally though the same thing about the frequencies. Had to zoom in. +1 for option 1. |
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Post by javamad on Jul 7, 2021 4:39:47 GMT -6
My €0.02
Option 1 .. control is always better.
On the labelling .. a couple of points … people may or may not agree ..
1. The plus/minus symbols don’t make much sense on knobs that are setting discrete, labelled values .. so the Gain and Freq knobs could lose them and still be clear.
2. To someone looking at a glance its not clear that the Freq is for the Mid … baybe tie them together visually with a border or something?
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ericn
Temp
Balance Engineer
Posts: 14,918 
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Post by ericn on Jul 7, 2021 6:10:29 GMT -6
What ever sounds best in the circuit your using, but I do prefer the control of 2.
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gyraf
New Member
Posts: 11
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Post by gyraf on Jul 8, 2021 4:36:48 GMT -6
The thing is that you can't trust the user to optimize interaction of several gain stages - so you run the risk of having sub-standard noise and distortion performance, depending on the user's xp level..
This why there's usually one unified gain control, and often a quite complicated one (V76, PV76, PQ1546 etc.) - the G9 solution is the best I could do on a available single-deck switch
But if you are SURE on quality/xp of your users, the dual-control gives much more fine-grained control of the unit's sonics
/Jakob E
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Post by bluegrassdan on Jul 8, 2021 11:11:44 GMT -6
The thing is that you can't trust the user to optimize interaction of several gain stages - so you run the risk of having sub-standard noise and distortion performance, depending on the user's xp level.. This why there's usually one unified gain control, and often a quite complicated one (V76, PV76, PQ1546 etc.) - the G9 solution is the best I could do on a available single-deck switch But if you are SURE on quality/xp of your users, the dual-control gives much more fine-grained control of the unit's sonics /Jakob E This is what I’m thinking. I teach classes in audio and gain structure eludes even advanced students. Some of the subtle aspects of input gain staging have confounded me, even when designing and trying to get the input stage how it needed to be. |
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Post by bluegrassdan on Jul 8, 2021 11:14:00 GMT -6
And it is unknown what folks are gonna plug into it.
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Post by donr on Jul 8, 2021 11:38:31 GMT -6
Maybe put a thin bar line under the two midrange controls so the user knows they’re linked.
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Post by bluegrassdan on Jul 8, 2021 22:06:12 GMT -6
The thing is that you can't trust the user to optimize interaction of several gain stages - so you run the risk of having sub-standard noise and distortion performance, depending on the user's xp level.. This why there's usually one unified gain control, and often a quite complicated one (V76, PV76, PQ1546 etc.) - the G9 solution is the best I could do on a available single-deck switch But if you are SURE on quality/xp of your users, the dual-control gives much more fine-grained control of the unit's sonics /Jakob E What do you think about something like this, Jakob? The NFB points can always be shifted one way or the other. (NFB is applied only to the first gain stage.)  |
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