Everything discussed so far is too expensive or too hard for my tastes 
Can it be simplified to the point where just a single LM1875 is set up as a Wein bridge oscillator driving a transformer? Is there a pitfall? I guess one question I have is the tracking error of a typical stereo pot (to vary the "R" and thus frequency) would result in oscillation.
Can it be simplified to the point where just a single LM1875 is set up as a Wein bridge oscillator driving a transformer? Is there a pitfall? I guess one question I have is the tracking error of a typical stereo pot (to vary the "R" and thus frequency) would result in oscillation.
Tracking error of the tuning pot is no problem concerning stability. It only changes the loop gain somewhat but that is accounted for by the lamp stabilisation.
In my design the bridge was dimensioned by fixed resistors and the pot was just to trim de speed plus and minus approx 5 %. I have no drawn schematic of it, it was just build straight away. If it helps I can draw a schematic, but that will not exactly reflect the thing of 10 years ago. So some fine tuning/experimenting yourself is needed to get it working properly.
Cheers
In my design the bridge was dimensioned by fixed resistors and the pot was just to trim de speed plus and minus approx 5 %. I have no drawn schematic of it, it was just build straight away. If it helps I can draw a schematic, but that will not exactly reflect the thing of 10 years ago. So some fine tuning/experimenting yourself is needed to get it working properly.
Cheers
Thanks. I actually forgot about your post. I saw this in a web search and I though it might be even better than using a lamp to stabilize the oscillator:
www.calvin.edu/~pribeiro/courses/engr332/Handouts/Wein Bridge Oscillators Presentation-Darren.ppt
www.calvin.edu/~pribeiro/courses/engr332/Handouts/Wein Bridge Oscillators Presentation-Darren.ppt
Hello Mark Kelly, I am trying to contact you regarding the power supply of my PT turntable. I am unable to sent you a PM on this board as I have not made previous posts. I believe you are a busy person but if you could contact me I would greatly appreciate it. I live not that far from Geelong in Lorne.
Apologies to people in this thread for this post but I couldn't think of another way of contacting Mark who I think looks at this board fairly regularly. Cheers Michael Anderson
Apologies to people in this thread for this post but I couldn't think of another way of contacting Mark who I think looks at this board fairly regularly. Cheers Michael Anderson
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