Analogman king of tone build help

[Lost_soul]

I build this one for a friend and it worked first time and i couldn't believe it since it's a big build.

There are a couple issues i noticed though. The first one is when i turn the drive knob on both sides all the way to max, it makes a very high whiney high piched sound.

For the second issue, in the pedal it has 4 switches that switch from a clean boost to distortion. 2 switches on each side.
So when i gradually turn the switches on one by one, the sound level decreases! Idk why this is happening. It happens with both sides and not only one side so whatever the problem is it's not in one side.

Here is the layout i followed:



I made 2 of the same board exactly so i can achieve what the V4 is.

Some changes i made: i used 1N4148 for all the diodes that are connected to the switches. I used an RC4558 Instead of the jrc4580.

Here are some pics:











And here is a sound Sample for the decrease in sound level i am talking about.
The sample goes gradually from clean boost to overdrive to distortion. Each new sound im turning on a switch and you can notice when reaching the end it becomes really low level.

[PRR]

All those wires. Each one acts like a radio antenna, either sending or receiving. They are not so very long, but they are not far apart at all. If the circuit between can be adjusted to high gain, it is pretty sure to catch its own output, feed-back, howl like a Shure PA system on 10. Instead of acoustic howl, it is electromagnetic howl. So strong that the amplifier can't work properly.

[Lost_soul]

Are you talking about issue with the drive pot or the level decrease issue?
But the wires are how the pedal is. How can i solve it?

[Mark Hammer]

"Clipping" imposes a ceiling on how wide/high the signal can swing.  The KoT provides for two forms/types of clipping.  One is inserted in the feedback loop of an op-amp, using a 2+2 diode complement that sets a higher clipping threshold.  A second type is imposed by the pair of diodes to ground on the output of that op-amp.  Because the 2+2 diodes lower the clipping threshold but not as much as the 2nd set of diodes will, engaging the feedback diodes will lower output below having NO diodes engaged.  Adding the diodes to ground on top of that will drop that signal ceiling even further, lowering the final output.  Now, if there were only TWO diodes in the feedback loop, rather than 4, the drop in volume when the diodes to ground are added would not be nearly as apparent, if at all.

Make sense?

As an aside, I like to use an LM1458 on one of the two channels, and the recommended LM4580 for the other.  The 1458 lacks the bandwidth at higher gain that the 4580 has.  This can make for a slightly "warmer" tone in that channel at highest gains.  Not a requisite, just an idea.  I also recommend an order-flipper switch, especially if one has introduced differences in the two channels.

[Lost_soul]

"Clipping" imposes a ceiling on how wide/high the signal can swing.  The KoT provides for two forms/types of clipping.  One is inserted in the feedback loop of an op-amp, using a 2+2 diode complement that sets a higher clipping threshold.  A second type is imposed by the pair of diodes to ground on the output of that op-amp.  Because the 2+2 diodes lower the clipping threshold but not as much as the 2nd set of diodes will, engaging the feedback diodes will lower output below having NO diodes engaged.  Adding the diodes to ground on top of that will drop that signal ceiling even further, lowering the final output.  Now, if there were only TWO diodes in the feedback loop, rather than 4, the drop in volume when the diodes to ground are added would not be nearly as apparent, if at all.

Make sense?

Yes i understand how that works now.
But even the switch that is not going in the feedback loop that has 2 diodes, it decreases the volume (not as much as the one with the 4 diodes in the loop but it still decreases it)

Isn't there a way to overcome this without removing 2 diodes from the feedback loop switch?
I searched everywhere and nobody was complaining of this level decrease issue from the original KOT. How does mike do it?

I read on his website that there is a "slight decrease" but i found nobody complaining of that.

In my build even when the volume and drive are maxed with the distortion switch on it's still low in volume.

I would love to know what you think.

Also i will try to use the LM1458 and see how it go.
Thank you.

[Mark Hammer]

1)  Let me repeat just how much I hate using stripboard.  Just thought I'd throw that in there.

2) Eliminating the clipping diodes should permit maximum volume, with none of those switches reducing volume when they deselect diodes.

HOWEVER...
 
Like the Bluesbreaker it is derived from, the 4 diodes in the feedback loop are also in series with a 6K8 resistor.  That "softens" their clipping action.  The 6K8 and diodes are in parallel with a 220k feedback resistor.  As long as the output of that op-amp does not exceed around +/-1200mv or so, the gain and amplification is dictated solely by that 220K resistor.  When the op-amp output reaches that amplitude, though, the diodes begin to conduct, and so does the 6k8 resistor, lowering the effective gain.

IF it was the case that the way in which you wired up the switch, or made cuts to the board, resulted in the diodes being bypassed, but the 6K8 remaining in the feedback loop, connected between output and inverting pin, the 6K8 would be in parallel with the 220k, making a feedback resistance of 6k6, and MUCH lower gain than you would be expecting.

Possible?