merlin
Well-known member
- Joined
- Aug 17, 2011
- Messages
- 378
A question came up on another forum about building a cut-down 1073 in a guitar stomp box, or something inspired by the 1073 front end. Anyway, there was confusion about reading the original 1073 schematic, which is kinda complicated. As we all know, the 1073 has a pesky 22-way multi-gang gain switch. So I thought I would draw a clear diagram of what is actually going on in the front end, for reference.
Mostly the gain switch works as three stepped attenuators, for line, mic (less gain), and mic (more gain). If we re-draw those attenuators as three simple pots, things look much clearer.
Line goes through one pot and one BA284 section. Super simple.
Mic (less gain) goes through one pot and one BA284*
Mic (more gain) goes through both sections with an attenuator in between.
The complicating factor is the gain-boost resistor, which is also switched to different values at various mic settings, to distrubute the gain in a way that optimises the SNR.
*OK, purists will know there is a minor discrepency for the MIC 40 & 45dB setting. Stop being pedantic.
This got me thinking you could build a poor man's 1073 front end using pots and a 3P3T switch, if you're not fussy about reproducing the exact original gain range (guitarists aren't). Maybe this will be useful to someone, some day?
Mostly the gain switch works as three stepped attenuators, for line, mic (less gain), and mic (more gain). If we re-draw those attenuators as three simple pots, things look much clearer.
Line goes through one pot and one BA284 section. Super simple.
Mic (less gain) goes through one pot and one BA284*
Mic (more gain) goes through both sections with an attenuator in between.
The complicating factor is the gain-boost resistor, which is also switched to different values at various mic settings, to distrubute the gain in a way that optimises the SNR.
*OK, purists will know there is a minor discrepency for the MIC 40 & 45dB setting. Stop being pedantic.
This got me thinking you could build a poor man's 1073 front end using pots and a 3P3T switch, if you're not fussy about reproducing the exact original gain range (guitarists aren't). Maybe this will be useful to someone, some day?
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