#151 Re: 6C33C SE-OTL Project
Posted: Wed Aug 03, 2022 12:16 pm
This amplifier has been 'off-line' for a while (I've been using my SissySIT amplifier) but I've been thinking about re-purposing it...
I will eventully put together my Pass SLOB speaker build and have the option of some 8ohm Aurel Bryan drive units that are about 95dB efficient and I've been putting together a bandwidth limited power buffer to drive them sans crossover - it rolls-off, 2nd order, below about 150Hz.
Ialso have the option, influenced by Nick's positive results with his acrylic Quasars, of using Lowther speakers for the full-range drivers in the SLOBs. These are more efficient than the Aurels and are also 15ohm so a reasonable match for the 6C33C amplifier to drive well enough in my domestic environment. Anyway, I've been wondering about modifying this amp to also be bandwidth limited like the power buffer. Here's the schematic of the amplifier:
I would like the check my understanding of the modifications to achieve a 2nd order roll-off below 150Hz so comments/feedback are welcome. Apologies but the parts aren't numbered in the schematic.
THe 1uF cap and the grid resistor form one pole of the filter so I susbstitute a cap of about 21nF in lieu of the 1uF, retaining the 50K grid resistor,
The second pole is formed from the ouput cap and the speaker load (15ohms) so an output cap of around 70uF will be required.
Does that stack up?
A derived benefit of changing the output cap is that a plastic film cap is then possible, possibly sounding better than the elextrolytic currently used but also with enabling a DC voltage rating of 250V or more, which is higher than the DC that could result from a 6C33C failure.
Cheers.
I will eventully put together my Pass SLOB speaker build and have the option of some 8ohm Aurel Bryan drive units that are about 95dB efficient and I've been putting together a bandwidth limited power buffer to drive them sans crossover - it rolls-off, 2nd order, below about 150Hz.
Ialso have the option, influenced by Nick's positive results with his acrylic Quasars, of using Lowther speakers for the full-range drivers in the SLOBs. These are more efficient than the Aurels and are also 15ohm so a reasonable match for the 6C33C amplifier to drive well enough in my domestic environment. Anyway, I've been wondering about modifying this amp to also be bandwidth limited like the power buffer. Here's the schematic of the amplifier:
I would like the check my understanding of the modifications to achieve a 2nd order roll-off below 150Hz so comments/feedback are welcome. Apologies but the parts aren't numbered in the schematic.
THe 1uF cap and the grid resistor form one pole of the filter so I susbstitute a cap of about 21nF in lieu of the 1uF, retaining the 50K grid resistor,
The second pole is formed from the ouput cap and the speaker load (15ohms) so an output cap of around 70uF will be required.
Does that stack up?
A derived benefit of changing the output cap is that a plastic film cap is then possible, possibly sounding better than the elextrolytic currently used but also with enabling a DC voltage rating of 250V or more, which is higher than the DC that could result from a 6C33C failure.
Cheers.