• Please note that Audiokarma will be offline briefly for updates early on Monday morning, September 28th.

12AU7 Hybrid Headphone Amp

Hum is gone (very very low) and this amp as is has no problem driving 8ohm speakers loudly while keeping cool!

I wound some signal wire today and I'm going to swap that in and see what happens.


Philip.
 
Well, ****. I'm going to have to listen to all my music all over again. This is my introduction to tubes, and so far I'm loving it.

Neil Young and Massey Hall were re-created effortlessly in my basement. Neil was performing live from my workbench to a packed house while my peers and myself sat back, with me front and centre, to this great show. I could heat his voice drift up and down, floating in front of me.

And these are little BPC Aiwa sacrificial speakers that I use on my bench. They never (read: never ever ever never) sounded so good.


I really need to get this circuit in a box. I'll go snap a few photos and post 'em up here this morning or tomorrow.


Hats off to Roggom and all his help!
 
As promised;

On the desk;


Overview of the circuitboard, power switch and indicator, and the source.
​

I twisted that brown speaker wire up with a piece of wood, three screws, and a drill-- four pieces of 24awg CAT5e. Grounds are twisted together at the signal input (RCA plug) and then bonded to the power gnd with a jumper.

I can get this amp louder than casual listenning and the MOSFETs still don't break a sweat. I thought I might've had to double them up for speaker useage, but I guess for low volumes they're fine! I still can't get over how well this setup images. there are still jumpers everywhere, so I hope that the noise floor still has room to drop and I can't wait to hear it when it's done. This has got to be the most gratifying audio-based scratch build I've done to date!


Last post of the night; good night!



Philip.
 
I moved this amp from my bench in the basement to my bedroom on the second floor. During the quietest parts of songs and / or where there's nothing playing, I can hear CBC Radio One (FM 99.1).

Does this mean that I need to shield my entire circuit, or just the tube?


Weird...
 
dnewma04 said:
CBC radio is good, just go with it.
Click to expand...

AAHHAHAHAA! It really is, Dave!

:scratch2:


So then I guess my question should be how can I get it tuned in clearer and louder?

As it is right now the volume level of the radio doesn't change with the knob, so I'm thinking it's being introduced somewhere before the MOSFET stage.

:smoke:
 
I found these at a surplus shop!

IMG_5800_sm.jpg

I still have the oak to cut for the box-- it's coming together now that I've got time :)


:banana:
 
Last edited:
Alright, I've got the box almost done and I found some acrylic that I had laying around that I'll use for a top rather than a piece of metal. I plan on putting a 45° chamfer on the acrylic and painting it with a few coats of hammertone. It should be good :)

Here's where I am so far with the box. It's made of Red Oak;

​

And I'm starting to lay out the acrylic;

​
 
Last edited:
Hey Roggom :) I can mount both MOSFETs to the same heatsink, right?


Alright, another update. I was up until 3.30a because I wanted to get it done and laid out. The two black circles represent the volume knob and the headphones/speaker switch.

Ta da!

​
 
What if I just bought 50 LM317s and now want to use them to regulate the 12.6V heater supply as well, I'd put the switch between the regulator and the 4ohm resistor, with another resistor?

I may want to run the rest of the amp at higher than 12V...

attachment.php
 
That circuit is to run 12.6 heaters (12au7, 5965) or 6.3 (Ecc88, 6cg7). remember to isolate the mosfets from the heatsink with non conductive material and get some heat sink paste. The tabs are at drain potential (12v in this case) not much but you can smoke you amp.

I have run this amp with 12~13volts. I also built on that runs on 100+ for the b+ and 26 at the follower stage. You can use the LM317 to regulate the 12v for the heaters just change the value of the resistor. They do get hot if you work them, but they work great for a nice slow warmup.

Lookin good on the build.
 
roggom said:
That circuit is to run 12.6 heaters (12au7, 5965) or 6.3 (Ecc88, 6cg7)...
Click to expand...

Thanks, but I know that much, just seeing only a 4ohm resistor there makes me curious because every reference I can find that uses the LM317 to regulate voltage shows it with at least two resistors.

lm317t-voltage-regulation-circuit.gif

If I put 6.3V out and R1=4ohms into a simulator it says that my R2 should be 16ohms... :scratch2:

Are we using the resistance of the heater as the second resistive element to get our target voltage?


Or are we using it as a current regulator...

LM317-Current-Regulator.png
 
You must log in or register to reply here.
Back
Top Bottom