Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Effects => Topic started by: Vdelli on January 22, 2018, 01:25:40 am

Title: Copicat MkII preamp circuit
Post by: Vdelli on January 22, 2018, 01:25:40 am

Hi, yesterday I was able to try a 1960 copicat in front of an old Fender Bandmaster. That sound just blow my Mind, even without the delay enganged! It's delivers a very cool distortion I never heard before.. So after looking for one I found out that the Copicats are very expensive if you find one! After looking on the schematics I was thinking about to build that preamp by myself. Do you guys think it's possible to do that without the delay?

Schematics: http://www.vintagehofner.co.uk/britamps/watkins/schematics/copicat.jpeg

Title: Re: Copicat MkII preamp circuit
Post by: smackoj on January 23, 2018, 04:27:00 pm

Hi; do you mean that you are playing through the Echo unit but it is not powered on or perhaps powered on but the echo portion not engaged? IMO trying to duplicate this effect would be really difficult. At least to try and get the same sound. Way too many old parts in there that aren't available anymore. You might try one of the do-it-yourself pedal forums and see if someone can help you create a copy using jfets, mosfets, bjts, or opamps?

Title: Re: Copicat MkII preamp circuit
Post by: Vdelli on January 25, 2018, 06:10:20 am

Hi, yes that's exactly what I mean. If I understand the circuit right, the whole echo unit is going to ground if you turn down the "Echo Volume" and the preamp signal bypasses the  the echo unit. I gives this preamp a try and build it. It's a very simple circuit, so that should be no problem.

Title: Re: Copicat MkII preamp circuit
Post by: Vdelli on January 27, 2018, 10:20:42 am

Ich build that preamp yesterday. Works great! The only issue I have is that I get hum if I roll back the guitar volume or the guitar is not connected to the cable.

Title: Re: Copicat MkII preamp circuit
Post by: smackoj on February 01, 2018, 11:39:19 pm

Looks sharp......chasing noises is a real pain

Title: Re: Copicat MkII preamp circuit
Post by: bnwitt on February 02, 2018, 11:58:24 am

maybe you should add some 68k resistors to the input jacks and see if that stops the no input noise issue.  Reconfigure the 2 jack assembly to a typical Fender setup

Title: Re: Copicat MkII preamp circuit
Post by: Vdelli on February 09, 2018, 03:27:55 pm

Hi, it's not really a "no input noise" the noise is there when a guitar cable is plugged in without a guitar or when a guitar (doesn't matter wich guitar) is plugged in and I roll back the volume on the guitar just a bit.

Title: Re: Copicat MkII preamp circuit
Post by: Willabe on February 18, 2018, 11:47:11 am

When a guitar cord is plugged into any amp without the guitar also plugged in, it will act as an antenna and pick up any/all stray noise in the air. 

Title: Re: Copicat MkII preamp circuit
Post by: Vdelli on February 19, 2018, 07:29:19 am

Thanks for answer Willabe,

Sure, but what I can't  figure out is, why I get hum and noises if I roll back the volume on the guitar. There is only no noise if I turn the guitar volume to max. Maybe a rare impedance issue...hm...