Input needed: Can someone review my schematic and layout?

duncan

duncan

Active member
Hey gang,

First off, full disclosure: I'm posting this around a few forums to maximize how many eyes can see it and to cultivate the most amount of expertise as I can.

So after finishing my first amp build (an Express circuit), I've definitely caught the amp building bug.

Instead of building an amp based off of a pre-made layout or design, I figured I would marry a preamp I love the sound of with a power section I love the sound of, while making a couple tweaks.

So I found schematics of the preamp, a cathode follower and EQ driver, and power amp, plunked them into photoshop, and put them all together in one package (hence the font differences).

Also, the schematic has component numbers assigned, but because of how the whole thing came together, I left them off the layout (but included the values). I left the heater wiring off for cleanliness.

The lead dress in the layout isn't what the end product would look like (I learned quite a bit about what to do and not to do on that front).

I took an initial run at converting the schematic to a DIYLC layout, but definitely made some errors. I posted over on EL34world and had a few guys offer some initial thoughts. I've also floated the schematic past a killer amp builder who makes a wide range of amps.

Would you guys be willing to have a look at the schematic and the layout, and let me know if you see any issues?

Thanks guys!
 

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Just a quick glance:

The schematic looks strange because it goes V1a, v1b, v2a, v2b, v3a, v3b, v3a again?

Also, in the schematic v3a (the first one) must have a grid reference to ground. You only have a series resistance. Triode gain stages the way we run them pretty much always must have a ground reference for the grid.

The 100k plate resistor for a gain stage in a gain stage/cathode follower pair is typically mounted right on the socket.

Also, those caps on the PI socket don’t need to be there.
 
T Wilcox said:
Looks similar to a 2204
I would run the buss ground to a ground tab by the input jack and leave the filter caps at the star ground like the following layout
https://ceriatone.com/ceriatone/wp-content/uploads/2016/09/JCM800_2204Ceriatone.jpg
Not sure what the odd resistor values like "2.61K" are for rather than the standard 2K7?
Click to expand...
The odd resistor values are what the preamp I'm trying to build around uses. It's essentially the brown channel from a Bogner Fish. And regarding the grounding, yeah, I haven't decided how it'll end up looking. Mostly just marking what goes to ground.

SpiderWars said:
Just a quick glance:

The schematic looks strange because it goes V1a, v1b, v2a, v2b, v3a, v3b, v3a again?

Also, in the schematic v3a (the first one) must have a grid reference to ground. You only have a series resistance. Triode gain stages the way we run them pretty much always must have a ground reference for the grid.

The 100k plate resistor for a gain stage in a gain stage/cathode follower pair is typically mounted right on the socket.
Click to expand...
Yeah, that's from me piecing things together in photoshop. The one I've attached here has them corrected:
 

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duncan said:
The odd resistor values are what the preamp I'm trying to build around uses. It's essentially the brown channel from a Bogner Fish.


Yeah, that's from me piecing things together in photoshop. The one I've attached here has them corrected:
Click to expand...
So look at v1b. Ground reference for grid? Nope.
 
I think its supposed to be in series between input and grid (not grounded) for HF rejection
Sending all signal to ground the way its wired there though, good catch
edit, added the fish schem I had for reference (not sure if its 100%correct schem)
 

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  • BOGNER The Fish corrected.pdf
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T Wilcox said:
I think its supposed to be in series between input and grid (not grounded) for HF rejection
Sending all signal to ground the way its wired there though, good catch
edit, added the fish schem I had for reference (not sure if its 100%correct schem)
Click to expand...

Yeah that was an error on my part. Here's an updated schematic, based on feedback from other sources as well.
 

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Remove the large cap on the grid of the very first stage. You’re asking for instability later down the amplification stages with it present and it serves no real purpose with the large value. Just tie the 68k directly to the grid and I mean directly to it and use shielded cable from the input to the 68k. Only ground one side of the shielded coax.
 
Update:

Board has been populated, top of the chassis has been drilled, and top-mounted components have been dry fitted. I have a local laser engraver shop doing the front and rear plates, and once those are done, I'll drill out the front and back for pots, jacks, fuses, and switches.

NK4mXNB.jpg


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