Echo Foxtrot - yet another simple tube preamp (coming soon)

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You are not good for my wallet, my friend.
 
Finished up the prototype today, it sounds fabulous. It's basically everything Echo Foxtrot is but a little more flexible, I really like how Matchless did the tone control with the rotary on this one.

The output is hotter than I typically like pedals to be, so I plan to put a dropping resistor on the output. Also a couple parts have footprints that don't fit as well (one too small, a handful too big) as I expected them to, but that's obviously an easy fix. So a couple quick tweaks and I'll spin a v1 board and let everyone know when they're ready. In the meantime I'll be removing Echo Foxtrot from the shop tonight, it's going to be replaced by the Diplomat.

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Any particular reason for having the led behind the tube instead of in the middle of the socket?
Yup, a few reasons. First and foremost, it's easier to install and swap out if you need to change fir any reason. Second, there's only room for a 3mm LED under the socket, you would have to drill it out if you want to use a 5mm, which makes it impossible for anyone using ceramic sockets. Also on some tubes (including EF86) the inner structure of the tube blocks the light, and putting the LED behind it instead of under it helps the light shine through more visibly.

I used to put the LED under the socket, but it only took three or four fried LEDs to make me realize that it wasn't ideal from a repairability perspective.
 
Nathan -- are you using this switch for the tone control?
Yup, that's the one. Also purchasable from Mouser, StompboxParts, and PedalPCB (when he can keep them in stock, I imagine they sell out a lot due to Arachnid). The Matchless actually uses a 6-position switch, but I added a couple extra values and used an 8 position. Partially because 8-position switches are easier to find, and partially because I wanted to have some options that made it more suitable for use on bass.
 
Yup, that's the one. Also purchasable from Mouser, StompboxParts, and PedalPCB (when he can keep them in stock, I imagine they sell out a lot due to Arachnid). The Matchless actually uses a 6-position switch, but I added a couple extra values and used an 8 position. Partially because 8-position switches are easier to find, and partially because I wanted to have some options that made it more suitable for use on bass.

ooooh... think I'll mate it to that 60w power amp board then feed in to this pair of Sony 250w/10in er's I have.....

Arachinid and similar fv1 based effects.. seen a couple peeps make a variant stage phaser with it. this going to be a standard 9v box or does it have a little leeway?
 
this going to be a standard 9v box or does it have a little leeway?
The plan is for it to be a 9V box, but the main limiting factor is going to be L7806. The EF86 heater has to have a 6-ish volt supply and it will pull around 200mA. The higher the input voltage, the hotter that L7806 is going to get, and if you get too hot it will go into thermal shutdown. Max input voltage for the NE555 is 16V, so depending on how hot that L7806 gets you have wiggle room everywhere else.
 
Most of the parts are clearly marked in the PCB you tested. Can you post a list of any changes or additions to them? Trying to put together a couple of parts orders right now including one to AES for the high voltage caps.

Thanks!
 
Most of the parts are clearly marked in the PCB you tested. Can you post a list of any changes or additions to them? Trying to put together a couple of parts orders right now including one to AES for the high voltage caps.

Thanks!
The only parts change I'm planning on this one is the addition of a resistor, but I plan for it to be a common value, likely 220k or 470k. The only other thing that's going to change before release is footprints, namely the 4n7, 2n2, and 1n HV cap footprints are going to use the same size footprint as the 47n so they can scoot closer together, and the 390p footprint for some reason needs to get way bigger. I don't understand why my 390p cap is so much bigger than my 680p cap for the same voltage rating, but it is what it is.
 
Yup, a few reasons. First and foremost, it's easier to install and swap out if you need to change fir any reason. Second, there's only room for a 3mm LED under the socket, you would have to drill it out if you want to use a 5mm, which makes it impossible for anyone using ceramic sockets. Also on some tubes (including EF86) the inner structure of the tube blocks the light, and putting the LED behind it instead of under it helps the light shine through more visibly.

I used to put the LED under the socket, but it only took three or four fried LEDs to make me realize that it wasn't ideal from a repairability perspective.

The LED placement works really well, especially if you put some crinkled up aluminum tape on the back cover.


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