Need koch twintone II schematic

[Tonegeek]

Anybody got one? Got a switching issue and I think it is a bad driver transistor for the relay. Since it has a double sided board, of course the entire amp has to be disassembled to fix it. The amps are made in the Netherlands. I have emailed the main co. and the Canadian distributor. I need to get this fixed ASAP.
thanks

[husky]

Anybody got one? Got a switching issue and I think it is a bad driver transistor for the relay. Since it has a double sided board, of course the entire amp has to be disassembled to fix it. The amps are made in the Netherlands. I have emailed the main co. and the Canadian distributor. I need to get this fixed ASAP.
thanks

I saw one somewhere maybe at SLO Clone, I'll look
I wouldn't think it is a transistor though, more likely a stuck relay.
A double sided board usually means you do not need to remove it to fix it. Single sided no plate thru holes would be the worst.

[Tonegeek]

Got a schemo from Audionova. The relay circuit is not quite matching what is in the amp though. Also did not get a schematic for the actual footswitch, which you would think anyone could figure out, but this one has some logic ICs on the switch itself. My main issue to repair is one of the footswitch buttons does not work. I wonder if I could locate a footswitch just to try and see if that solves the problem. I removed the circuit board and tested all the transistors in circuit and they all seem good. Something is probably leaking somewhere under load or there is a voltage drop in the cable. This system grounds out the transistor base through the footswitch to engage the relay. Hit the footswitch again and the indicator LED comes on, and the relay goes off. The LED is in series with the transistor base and ground and the footswitch just bridges the LED. However, there are 3 radio buttons that also interact with the push on, push off button, so it gets complicated, quick. These buttons connect to the IC on the footswitch itself.

I will report that this amp is about like working on a Mesa Mark 4. It has a double sided board, and is crammed in a tight space. I will say I did not have to desolder anything to get the board out (lots of spade connectors). I had to take every single pot and jack loose though and I could not get the board out without slightly bending one pot on the rear of the board. It takes 45 minutes to remove the main board.

I have since put the amp back together thinking I would toss in the towel on this one, but maybe I will see if I can get some tech support from the manufacturer. Short of replacing nine transistors and the entire footswitch assembly, I am at a loss. I am way over on billable hours with this one.

Attached is the shematic if anyone is interested. The switch that does not work is the rhythm/solo switch.

[Tberg]

Hey buddy, if it's the fs5 schem you need, I've got it.
I do warrantyrepairs on Koch-amps in Denmark, I might be able to help you. I'll have to get clearence if I can post schematics from Koch, have never signed a nondisclaimer from them although I got all schems from them.

cheers

[Tonegeek]

Hey buddy, if it's the fs5 schem you need, I've got it.
I do warrantyrepairs on Koch-amps in Denmark, I might be able to help you. I'll have to get clearence if I can post schematics from Koch, have never signed a nondisclaimer from them although I got all schems from them.

cheers

thanks for the offer but I am ok for now. I finally fixed this amp, but it could have gone a lot faster. I like the switching design but the complexity of it requires the correct version schematic.

[andrew]

Gents, what type of phase inverter is this? Thanks

[xtian]

Standard long-tail phase inverter (LTPI). Just drawn differently that you're used to?

[Roe]

No its different. And it is loud and punchy. Look at the power supply. Negative voltage is applied at the cathode

[martin manning]

It's a DC coupled LTP, but the DC on the input is 0V. Negative voltage on the tail eliminates the loss of B+ and sets proper bias in conjunction with the tail resistor. The 1k and 100u cap is just a filter for the negative voltage.

[Roe]

Yes, that makes sense. Thanks.