New Amp build using Valve Wizard PCB boards

[Louie51]

Greetings all,

I am currently using a Basebreaker 007 which I enjoy. There are, however, a couple of features that I would like to have and I have not found anything commercially that meets my criteria listed below.

First off a FX loop so that i can move any time and modulation effects after the pre-amp. I looked into modifying the 007 but I cannot find schematics anywhere and the one repair technician i contactd who has been inside one of these amps said that he felt it wasn't feasible.

Secondly, I want to try a different tone stack. I presume that the 007 uses a pretty basic FMV stack and I find the controls be disappointing. So probably a James stack of maybe even something with a mid shift.

So my design criteria are as follows:

1. Low to medium gain preamp design. Mostly jazzy, bluesy to some mild rock.
2. Low power output staying in the 5 watt range.
3. Integrated FX loop after the tone stack
4. More responsive/functional tone stack (James?)

I am in the process of specifying a project amp build based on a set of circuit boards purchase from The Valve Wizard. The nice thing about these boards is that they provide a solid infrastructure for the implementation, especially the power. While at the same time a lot of flexibility signal flow and implementation. It is the latter where I am having most of my questions.

I have acquired the following board set.

1. Triode input PCB -
   • Used as a cascaded gain stage
2. Cathode Follower / EQ / Cathodyne PCB
   • Used for additional gain stage
   • Cathode follower
   • James tone stack
3. Effects Loop PCB
4. Octal Output PCB
   • 6V6 power tube in class A
5. Power Supply PCB

I am planning to follow the Medium-Gain Preamp Design as described in Chapter 14.5 of the Designing Valve Preamps for Guitar book by Merlin Blencowe, (BTW he recommended this forum as a good resource.)

Now some initial questions.

1. What are the differences and/or advantages between driving the tone stack directly out of the last gain stage? I am inclined to use the cathode follower method but would be interested in feedback on this choice.
2. If using the cathode follower for the tone stack is there anything that I need to be concerned with by inserting another cathode follower to drive the effects loop?
3. Are there any problems or concerns that I might encounter implmenting this amp?

Thanks for your consideration of my project.

-louie

[Jazz P Bass]

Schematic: https://music-electronics-forum.com/...8&d=1614010107

[Louie51]

Jazz P Bass thanks for the link to the 007 schematic. It will be a useful benchmark and design guide.

[Mick Bailey]

My favourite home-brew amp drives an FMV tone stack off a cathode follower and then uses another cathode follower to drive the FX loop. The amp ended up this way because I originally built it without a loop and then regretted the decision. I have two additional controls I mounted on the back panel - a wet/dry mix and level. It works really well and I like the ability to use the loop on its own as an extra gain stage. I've not found any downside to this arrangement.

The best method of seeing for yourself how the tonestack behaves either driven directly from the last gain stage or by using a CF is by using TSC (Tone Stack Calculator) and alter the input impedance parameters and component selection in your chosen tone stack.

[Louie51]

Mick Bailey Thanks for the comments. I am going to continue with the topology as described.

Unfortunately I do not have access to the TSC as I only have a mac book and no VM available to load Windows. Be that as it may I am planning on going with the James tone stack as described in Merlin's book. I'll just have to see how it sounds. Also since I will have a FX loop I can insert any number of tone pedals to get even more options.

[Mick Bailey]

TCS is available online if you have Javascript enabled. I just tried it on my Linux laptop and it looks to be working fine;

https://www.guitarscience.net/tsc/info.htm

[pdf64]

It’s a shame that the tonestack kit app is no longer available.