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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Yep, I'm considering making my own breakout boards at least.
It's been a nightmare doing it this way, here's an update, all wired up, ready to be powered up and tested. I'm not holding out much hope though, at least I've learned how not to do it
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
It works, folks.....I'm astounded. I did have some teething problems, turns out the input ground was soldered to a dummy terminal on the input jack socket. It's got a bit of gain, and the bottom end is breaking up, in a nice way, much the sound I'm after, but I think I need to add a volume control. I'm thinking of adding a pot to adjust the gain. Here's the circuit diagram, I increased the value of the 10uF cap.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
So I've wicked off some solder and cleaned the board up. I tried removing the input resistor, seems to work fine. I've ordered some aluminium polymer caps to try, and some different output caps. I'm looking forward to playing around with this circuit.....
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
So I've made some modifications, adden a handful of aluminium polymer caps, which seems to have improved the bottom end distortion a bit, changed the output cap too, and then I added a 5k Ohm trim pot between the feedback resistors, with the wiper connected to -IN, so I can vary the gain. I've turned the gain down and pretty much eliminated the bottom end distortion. At the right level, it should sound ok, with just a bit of bottom end breakup. I'll carry on with it tomorrow.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Well, I finally sussed out what the problem was, after literally eliminating everything else.
My first thought was that there wasn't enough capacitance across the rails, I increased it to a millifarad.
I increased the input and output resistors, increased the input cap 100 fold, narrowed the bandwidth......
As a last resort I tried it on 18 volts instead of 9 volts.....works perfectly.....Seems it was clipping the rails at 9 volts......I instictively knew it was something to do with the rails, hence increasing capacitance, I didn't realise it would need 18 volts to work though.
Here is the latest reincarnation....I can start tidying it up now
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
RS stocks the PP9's, I've removed the pot completely now.
I've been playing around with it a bit more, and it seems that if the gain is set to more than about four (13:3 ratio on feedback resistors), it starts bouncing off the rails even at 18 volts.
I'm definitely impressed with this op amp, it's way faster than the textbooks say you want, but my reasoning is that tubes (valves) are pretty fast devices too. I still want to tune it some more, though, maybe add some switches, etc.
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