A tube tracking console using ITB’s MkIII concepts

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rjuly

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@ruffrecords,

If I wanted to build a couple of channels to have higher gain, perhaps 70dB, say, for use with a ribbon mic...

- What would be required? Would it take another full gain block - ie three more triodes?
- Would it be possible to get lower signal to noise ratio by using two gain blocks with each adding less gain, to sum to 70dB?
- Would a different approach overall be the way to do this?

Many thanks,

- Richard
 
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ruffrecords

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If you use the twin line amp, each of the the two amplifiers can provide up to 40dB of gain. add to this the 20dB you get from the transformer and there is a total of 100dB gain available.

In a complete channel you need to subtract from this the 6dB loss in the output transformer plus any loss in the EQ which could be up to 20dB depending on the type. Taking these teo factors into account means you can still have 74dB of total gain should you require it.

I commonly set up channels for a total of 70dB gain. You get 60dB of it in the first half of the TLA (20dB transformer plus 40dB amplifier). I then allow for 10dB loss in the fader, 6dB loss in the output transformer and with the REDDEQ an insertion loss of about 16dB which means the second half of the TLA gets set for 32dB gain. This gives your channel a nominal gain of up to 60dB with the fader at zero and 10dB in hand on the fader for a total of 70dB.

Signal to noise is defined almost entirely by the very first stage. The 20dB in the transformer helps a lot because it has a very low noise figure and provides a 10 times bigger signal to the first TLA which is the dominant source of noise at high gains.

Cheers

Ian.
 

rjuly

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If it were possible I would like 75dB of gain for this pair of channels, assuming the noise floor is low enough. I’m planning to record fairly low level acoustic room sound with a ribbon mic.
My current design has no fader to attenuate the signal in between amplification blocks, but only post direct output, to control mix levels to the 2-bus. Given that I won’t have eq in the circuit, I guess I will need to attenuate at some point in the circuit to bring the level down to 75dB. Should I use a fader or perhaps a fixed resistor?

Alternatively, might there be a lower gain combination of tubes for either or both of the gain blocks that would give me the desired gain structure with lower noise?

Many thanks for taking the time to indulge my ignorance.

- Richard
 

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