Over the past several months I have been working on improving my Eden WT-500 bass amplifier. The original design was quite noisy and had rather truncated frequency response, cutting the highs at around 12kHz. The modifications have been in effort to reduce noise and improve the performance of the amplifier. Among the changes which I have made were replacing the TL072 op amps, electrolytic coupling capacitors, and altering the gain staging to improve the signal to noise ratio. I employed a pair of AD825s, several LM4562s, and an OPA2132, and used film capacitors instead of electrolytics where possible. If anyone is interested, I would be happy to give more detail on the modifications. The amp sounds much better now!
At the moment, I'm trying to understand what is going in in the input section (pictured below). It appears that the input signal goes directly into a 2.2K resistor which is tied to ground with a 1M resistor, then into a 1µF coupling capacitor which is also tied to ground with a 1M resistor.
I'm hoping someone might be able to explain the function of the 2.2K resistor before the coupling capacitor. Is it perhaps serving as protection for the input of the tube? The SWR amplifier schematics that I've seen send the input straight to the tube. It seems a bit odd to put a 2.2K resistor in line with the input. At the moment, I've removed the first 1M resistor and shorted the 2.2K resistor at the input. According to another schematic that I've seen later revisions saw the removal of the 1M resistor at the input, so I'm guessing that it isn't necessary. This change has not proven problematic from what I can hear.
As they seem somewhat superfluous to me, I'm wondering if there would be any harm in removing the first 1M and series 2.2K resistors from the circuit? Understanding their role might shed some light on possible down sides to removing them from the circuit.
At the moment, I'm trying to understand what is going in in the input section (pictured below). It appears that the input signal goes directly into a 2.2K resistor which is tied to ground with a 1M resistor, then into a 1µF coupling capacitor which is also tied to ground with a 1M resistor.
I'm hoping someone might be able to explain the function of the 2.2K resistor before the coupling capacitor. Is it perhaps serving as protection for the input of the tube? The SWR amplifier schematics that I've seen send the input straight to the tube. It seems a bit odd to put a 2.2K resistor in line with the input. At the moment, I've removed the first 1M resistor and shorted the 2.2K resistor at the input. According to another schematic that I've seen later revisions saw the removal of the 1M resistor at the input, so I'm guessing that it isn't necessary. This change has not proven problematic from what I can hear.
As they seem somewhat superfluous to me, I'm wondering if there would be any harm in removing the first 1M and series 2.2K resistors from the circuit? Understanding their role might shed some light on possible down sides to removing them from the circuit.