Electronics > Beginners
Op amp based preamp supply. Charge pump, single vs symmetrical & ripple
dazz:
--- Quote from: spec on November 27, 2018, 04:40:08 am ---You can mount the PSU modules on the board, just like a component, or am I missing something?
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Yeah, sure. In fact I have an extra pad in the pcb design to connect the boosted voltage from an external converter to give that option to the user in case s/he doesn't want to use the charge pump. Yes, I'm so stupid that I couldn't wait to make the pcb until I had a closed design :-DD. Now I'll need to modify it to use dual rails and whatever I put there to implement them
--- Quote from: spec on November 27, 2018, 04:40:08 am ---Yamaha FG350W (1981), Washburn WLD20S, and Crafter ST120 strat copy- can't play any of em :palm:
Just snagged a Fender Deluxe 112+ combo for a song on ebay. The voice coil connecting wire has pulled of the cone and snapped under the dust cover- must get around to fixing it. :)
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Ouch! I wouldn't know how to fix that. Congrats on the bargain!
dazz:
--- Quote from: spec on November 27, 2018, 04:51:08 am ---That module is just the first one in Google. It is just an example. But all the same, the minimum current draw is no big deal and is a requirement for many PSUs. (even the LM317, LM337 three-terminal regulators).
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So if my preamp draws say 5mA, I need to add a dummy load to increase the current, right?
--- Quote from: spec on November 27, 2018, 04:51:08 am ---Minor differences in the PSU rail voltage should make little difference- you will see more variation in sound between different samples of the opamps, especially different ages and suppliers.
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Ok, I was concerned that an imbalance in the rails might induce asymmetrical clipping and change the tone.
Apparently people are using LT1054 based charge pumps for the dual rails with good results
I might just put that in my pcb and then the V+/V- pads to feed +15/-15V from an external board
spec:
--- Quote from: dazz on November 27, 2018, 04:56:08 am ---Ouch! I wouldn't know how to fix that. Congrats on the bargain!
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Thanks- it was a bargain. Apart from some work by a gorilla inside, the amp is in good condition- I was expecting some beat-up wreck.
Fixing the speaker is fairly simple:
* Heat the dust cover to melt the glue and pull it off.
* Remove broken tail wire.
* Solder new tail wire to protruding voice coil wire.
* Araldite voice coil wire, solder joint, and tail wire to cone
* Re-glue dust cover.Of course, that is in theory- I changed the car battery yesterday- took four hours. |O
But I have done steps 1, and 2 already, mainly to establish the fault.
spec:
--- Quote from: dazz on November 27, 2018, 05:07:32 am ---
So if my preamp draws say 5mA, I need to add a dummy load to increase the current, right?
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Yes, spot on. But if you were using batteries it would be benificial to get a PSU that had no minimum drain requirement.
By the way, having a constant resistive load is good design practice- it helps all PSUs.
--- Quote from: dazz on November 27, 2018, 05:07:32 am ---Ok, I was concerned that an imbalance in the rails might induce asymmetrical clipping and change the tone.
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With non RRO opamps, like the TL072, you get non-symetrical clipping even if the supply rails are exactly equal in magnitude.
--- Quote from: dazz on November 27, 2018, 05:07:32 am ---Apparently people are using LT1054 based charge pumps for the dual rails with good results
I might just put that in my pcb and then the V+/V- pads to feed +15/-15V from an external board
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Sounds good to me. :)
schmitt trigger:
--- Quote from: dazz on November 27, 2018, 04:23:38 am ---
1 Due to the diode partial pressure, the voltage of -Vo is lower than +Vo
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Chinglish translations at its best.
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