Fender 5E1 Preamp Output

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heatwalk

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Oct 17, 2020
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32
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Chicago
Hi All,

I've been learning tube equipment through the world of repairs but have been getting more into DIY builds recently. Wanted to make a dead simple tube preamp/DI for guitar that I could slowly build off of, so just the preamp of a Fender 5E1 seems like a great start. I could add tone controls after I get the basics working. Open to output being unbalanced or balanced, for sending into a mixer channel strip / interface, or into a power amp.

Looking at a few schematics and sifting through some forums I've gathered and am confused by a few potential possibilities and what is technically sound. Tapping off of the output side of the coupling capacitor coming off the plate Ive come across different additional connections. Keeping it as simple as possible right now, avoiding a buffer stage at least for now would be ideal (unless deemed necessary).


Without a transformer, am I able to go straight to Tip of 1/4" out off of the coupling cap? Or do I need to provide an additional ground reference post-cap with a resistor from tip to ground, choosing a value based on frequency response? Instead of a resistor, I've seen send jacks use a potentiometer to act as a level control?

Using an output transformer I get the added possibility of additional distortion, a balanced output and impedance matching, seems like a win other than cost. What would an ideal ratio be for impedance purposes. 10k : 600/150? Or something higher like 30k:600?

If I wanted the option of an unbalanced out in addition to the transformer route, can they be used simultaneously, or would I need to use a switching jack to disconnect the connection going to the primary of the transformer if I wanted to go the unbalanced route?

Thanks.
 
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Bo Deadly

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Dec 22, 2015
Messages
3,214
Location
New Jersey, USA
If you want to cheat a little you might use London Power modules:


Although I don't consider this cheating at all. It's a great way to get started if you're learning. At the very least a power supply and line out could be very important to exploring custom circuits.
 

CJ

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Jun 3, 2004
Messages
14,883
Location
California
the transformer will help with hum rejection, and i remember getting more bass,

what plate voltage are you using?

80K plate R feeding a modern audio input at 10K would be 8:1 Z so sq root for turns ratio is 2.8:1,

easy to do 4:1 for even better bass so a 10K to 600 would work fine,

jensen 10K would be awesome at 100 bucks,

i did a Neve core version and it worked great, even tough the core was kind of small.

so maybe even a cheap DI xfmr like you find in a proco box might work if you don't push it too hard.

12ax7a.jpg
 

heatwalk

Active member
Joined
Oct 17, 2020
Messages
32
Location
Chicago
Looked into the kits but decided to just get on with drawing up some terminal strips so I can just swap out and learn from the experience. We'll see. Will report back the plate voltage after I get a power supply wired up. Was initially going to go for the schem listed 150V, do you suggest changing that? Thanks on XFMR info, will poke around but a jensen sounds appealing.
 

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