A follow-up on to R18/19: You want to use them even if you do not use the input pots, assuming you are using the input protection zeners on the board. This should be covered somewhere in the article, I believe near the end. The idea is that zeners do not like to be presented with a voltage directly.
Also, be careful with the amount of heat you apply to those Old Colony boards. They don't like a lot of heat.
If you use the board single ended only, don't forget to ground the negative input using a small resistor. I think I used a 220 ohm.
I still have some left over transistors and maybe a few other parts I am not using if you want them. You can contact me through the board mailing service if you are interested.
Not sure about P5 off-hand. Sorry.
Also, be careful with the amount of heat you apply to those Old Colony boards. They don't like a lot of heat.
If you use the board single ended only, don't forget to ground the negative input using a small resistor. I think I used a 220 ohm.
I still have some left over transistors and maybe a few other parts I am not using if you want them. You can contact me through the board mailing service if you are interested.
Not sure about P5 off-hand. Sorry.
About P5:
I think you will need one pot per channel, or a dual gang pot for both channels. Seperate pots may give you more control to accurately match the gain between channels, but I don't think this should be much of a problem. It seems most constructors (myself included) use fixed resistors (R15) to control the gain.
Hope this helps.
I think you will need one pot per channel, or a dual gang pot for both channels. Seperate pots may give you more control to accurately match the gain between channels, but I don't think this should be much of a problem. It seems most constructors (myself included) use fixed resistors (R15) to control the gain.
Hope this helps.
You can use a piece of wire to connect the pads of P5. You can then adjust the amount of gain by adjusting the value of R15. If you leave R15 at 124 ohm as called for on the BOM, you should get about 20dB of gain. Hidden in the very last sentence of the instruction manual, Nelson explains that an R15 value of 430 ohm should yield about 10dB of gain. Less gain (10dB) yields better performance, provided your system can be satisfied with less voltage coming out of your pre-amp. It is easy to swap resistors for experimentation, but again, be careful how much heat you apply to the Old Colony PCBs.
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