I am even less skilled at analyzing SS circuits than tubes so maybe you all can help me translate this basic idea to tubes.
The schematic fragment below is from the ADC Sound shaper II owner's manual that I got with my unit years ago. I would like to understand how to implement such a thing in tubes.
So let's see if I am interpreting this right. It looks to me like the input comes into TR102 for amplification. TR104 and TR106 appear to be some sort of LTP with output taken from the collector of TR104. The shaping network is connected across the inverting and non-inverting inputs of the LTP. I presume that this is set up as a FB network.
Am I close? Would this be duplicated by seting up a tube LTP like is done for PP amps with FB brought back to the LTP PI and connecting the network across the input and FB point?
The schematic fragment below is from the ADC Sound shaper II owner's manual that I got with my unit years ago. I would like to understand how to implement such a thing in tubes.
So let's see if I am interpreting this right. It looks to me like the input comes into TR102 for amplification. TR104 and TR106 appear to be some sort of LTP with output taken from the collector of TR104. The shaping network is connected across the inverting and non-inverting inputs of the LTP. I presume that this is set up as a FB network.
Am I close? Would this be duplicated by seting up a tube LTP like is done for PP amps with FB brought back to the LTP PI and connecting the network across the input and FB point?
Attachments
> The original, with schematic.
Not the same topology as the ADC. Yes, a super-classic in tube arcania. The ADC is a better EQ. It would be heroic to copy the ADC in tubes.
First: tubes have Volts but not Amps. Generally you want to raise all impedances like 10X. At the same power level this makes voltage 3X and current 1/3rd X, better fit to tube impedance.
But that makes L102 go from 3.8H (already a huge lump of iron) to 38H (a fine output transformer). C223 goes from 0.0082u to 820pFd, small enough for stray capacitance to foul things up.
It is really so bad that it makes sense to re-design to 500 Ohm impedance passive and transformer-couple to amplifiers. I had a fine EQ like that but cut-only.
This is why God (of your choice) inspired Bell Labs to give us transistors.
Not the same topology as the ADC. Yes, a super-classic in tube arcania. The ADC is a better EQ. It would be heroic to copy the ADC in tubes.
First: tubes have Volts but not Amps. Generally you want to raise all impedances like 10X. At the same power level this makes voltage 3X and current 1/3rd X, better fit to tube impedance.
But that makes L102 go from 3.8H (already a huge lump of iron) to 38H (a fine output transformer). C223 goes from 0.0082u to 820pFd, small enough for stray capacitance to foul things up.
It is really so bad that it makes sense to re-design to 500 Ohm impedance passive and transformer-couple to amplifiers. I had a fine EQ like that but cut-only.
This is why God (of your choice) inspired Bell Labs to give us transistors.
The ADC, like most modern (opamp) band EQs, is what Steve Dove called "swinging inputs".
Dove also mentions swinging outputs. Dyna used this more than once? Here is a classic Ampeg 1-band EQ done swinging output. I have not thought to think if this can be extended to multiple bands, or how much performance would degrade (thus limiting how many band per tube and how many tubes per system).
Dove also mentions swinging outputs. Dyna used this more than once? Here is a classic Ampeg 1-band EQ done swinging output. I have not thought to think if this can be extended to multiple bands, or how much performance would degrade (thus limiting how many band per tube and how many tubes per system).
