4558 based clean boost

[Ryanhardy]

I had a jrc2904 that I pulled out of some old hifi. I need a clean boost to get my plexi crunching. Ive tried building a circuit but just get what sounds like a normal sounding dist pedal but with bad sustaiin (gating effect). If someone can post a link / pic that uses only a 4558 (no other transistors)
that would be great.

The one i tried today was something like this :


How close do the resistor values have to be?  Could you sub 400k for 350k say?

[Cozybuilder]

The IC needs an AC ground reference for the signal, thus the 100K resistor should be connected to Vcc/2 (4.5V), not ground.

[ElectricDruid]

The IC needs an AC ground reference for the signal, thus the 100K resistor should be connected to Vcc/2 (4.5V), not ground.

Well, not as drawn, it doesn't. If you look, it's drawn with bipolar +/-9V power, in which case that "Ground" is the centre-voltage bias level we're all used to calling 4.5V.

Making changes to the 465K will alter the gain, that's all. It's a standard non-inverting op-amp arrangement so there's plenty of online calculators to work out exactly what the gain will be.

HTH,
Tom

[Cozybuilder]

Tom- you're right, don't know how I missed that. Carry on.

[Ryanhardy]

My 9 volt supply actually puts out about 14 volts so what kind of changes would b needed to account for that? Maybe that's a source of my problems?

[ElectricDruid]

If you're using a single 9V supply, that's the problem, and it doesn't matter what voltage it is.

That circuit as drawn is for a bipolar supply. If you're running it from a single supply, then you need to build a "virtual ground" like Cozy was talking about first up.

You'll have seen the typical circuit on a ton of schematics. 10K+10K between 9V and ground to provide a 4.5V level in the centre. Decent value electrolytic capacitor (10u? 47u?) from that 4.5V point to ground.

Then you can use the 4.5V level as "virtual ground" and connect all the ground points in the circuit to it.

HTH,
Tom

[bluebunny]

You're cross-posting, Ryan.  We won't all necessarily see all your questions, nor all the answers that get posted.  You may miss them too.  It just gets confusing all round.  Stick to posting once in the main "Building your own stompbox" forum.  Unless it's about beer and/or sausage, in which case the "Lounge" is the place to hang out.   

[Ryanhardy]

Yes my two posts have merged into the power supply issue.  Feel free to delete one if your a mod.  Anyway, i solved the power supply problem.  A glass zener diode on each lead.  It was a fluke though.  I dont know what their values are as they are so small to read.  Im also abit confused as to their function.  My understanding was that they only allow current in one direction, but apparently zeners allow ti in both.  Would the normal black and grey rectifier diodes work as well?

[NoellEagan]

Hi...i am a new user here. As per my observation it's drawn with bipolar +/-9V power, in which case that "Ground" is the centre-voltage bias level we're all used to calling 4.5V.Making changes to the 465K will alter the gain, that's all. It's a standard non-inverting op-amp arrangement so there's plenty of online calculators to work out exactly what the gain will be.