New build - Dual Channel Dual Mode 2204

[Snicksound]

Very cool build, Snicksound.

I know you no longer have the amp, but do you have any guts photos you could share? Curious to see the final board and layout. Also, I have a couple of questions, if you don't mind:
1. The 47R resistor after the rectifier, how did you arrive at the value?
2. About the FET boost, I've heard Jason of Headfirst saying that he think it works best after the input grid stopper, but I noticed from your schematic that you placed it before, and was wondering if you had tried both ways and, if so, what difference there was, if any.

Thanks!

I'm attaching a gut shot, although there was some further tweaking and improvements after that.
Not gonna lie, it looks pretty bad on picture, but it's super quiet (bit of hiss with FET boost on that's it).
Relay is under the green perfboard.
Not my best work visually but functionally no issues.

1. I actually ended up removing the 47R as you can see in the final schematic. I just wanted a little bit of sag in the PSU, but in the end it made too little difference and only dumped more heat in the chassis.
2. Haven't heard that, although I know that's what his schem calls for. I just liked the idea of an extra grid stopper between the FET Boost and the input grid, and the PCB already has a "gate stopper". To be honest I didn't follow his schematic to the letter. I increased the 1M resistors to 2M2 (if you build it as is your input impedance drops to 333k with the boost engaged), reduced the input cap to 2.2nF, and mostly I added a 0.33uF source bypass capacitor with a 5kD pot in the way so I can dial in the amount of treble boost I want (the pot on the back next to the input). As is, the Boost only hit the amp harder but with a full range signal meaning it would just sound blocky and farty if you tried to get any kind of real gain out of it. With those mods I can still use it as a fat boost (that cuts just enough lows to work well) or turn it into a very aggressive treble booster.

[adew]

Thanks for the photo and info. Looks great!

Yes, I wondered if the 47R resistor was worth the trouble, so it's interesting to hear that you decided to remove it. Thanks for the good info re the FET boost, too. I have a build coming up that will use one, so I may try your method with the higher value grid leak resistors and the grid stopper on the valve socket. Your mod to the FET boost sounds cool. Shall definitely bookmark this in case I want to do the same.

Cheers!

[Snicksound]

Thanks for the photo and info. Looks great!

Yes, I wondered if the 47R resistor was worth the trouble, so it's interesting to hear that you decided to remove it. Thanks for the good info re the FET boost, too. I have a build coming up that will use one, so I may try your method with the higher value grid leak resistors and the grid stopper on the valve socket. Your mod to the FET boost sounds cool. Shall definitely bookmark this in case I want to do the same.

Cheers!

Thanks!

Here's a demo of the variable source bypass, which I decided to call an "Attack" control cause that's kind of what it does in a way.
Again, it's a 0.33uF cap from the FET's source, into a 5kD pot (reverse log) wired as a backward variable resistor. So when it's totally off you have 5K of resistance in the path of the cap (reminder that the source resistor is a 6k8 so it still has some impact) and way up you have no resistance at all.

I've experimented with fixed values and what I found was that no resistance at all sounded too harsh, but even just a small 100R was enough to improve it. And from there to say 2k is where you have the most difference. So that's why I went with 5kD, it has a nice sweep, and easier to set it very high while still having a bit of resistance in the path.

Note that I also upped the drain bypass capacitor from 500pF to 1000pF. The difference is a lot more subtle than I would've thought, but I like it better this way with the "attack mod" because the bypass cap really boosts the treble gain and I wanted to concentrate on the mid frequencies.

[adew]

Thanks for the additional info and the video. Amp sounds great!