We did use the other circuit prior to the one shown in post 1 Martin. I remember Paul building it and couldn't get it to work, because of what you said, ie the gain is inverting. He rejigged it and that first controller is still working well in my system. It's been fantastic really, never missed a beat.
I've emailed Paul and I'm waiting for a reply regarding the boards.
Hi all
I have been away for a while and have just recieved a mail from Si (chopsaw) and a PM from Martin regarding these PCB's, I had them made by a local company that we ( our company ) use for all our 4 layer and above PCB's. I have a quote for 10x and 100+ and they are very competative IMHO, but if these boards need modifying then there will be an additional tooling charge which culd be costly, the price for the 10 up is £8 + VAT + postage and the 100 up will be approx £2.50 + VAT + postage. My original veroboard prototype was made using the very early design that Martin C kindly supplied to me, this as chopsaw has suggested has been working with no hiccups for some considerable time with his OL motor.
The reason for the revised circuit from Martin as I seem to recall was to try to make the resolution on the speed adjustment finer, however when I build the first one it didn't work so chopsaw reverted back to the originakl design, and yes there was a minor error with the reference voltage needing to be reversed polarity.
So I guess the bottom line is this, does this PCB need to be modified? and if so will the cost of the tooling for a new PCB be worth the hassle, as Martin has suggested "it is a motor controller and NOT a phono head amp" yes I believe that the basic design could be improved with the voltage reference device swapped out for something quieter (LM329) among other minor improvements, but like most things in life are the deminishing returns worth the time and cost implications, personally I don't think so, but that is just my opinion.
As it stands there is a huge voltage range that should cater for the majority of small DC motors out there, and with the adjustment of the sense resistor as Martin has suggested then the current PCB will suit virtually all aplications, I am perfectly happy to order these boards but would need an aproximate GB before going ahead, or if the die hards want to refine the board then simply mail me the new circuit and I will get a quote for the new revision PCB's...........................simpulzzzzzz
Paul