[rickcr42]

You DO realise you just added to the "looks good,I bet it sounds good" gene pool right ?

 

[Icehawk]

Could you fit a plastic bushing or even a greased o-ring in the hole to improve the rods action?

Cool project!

 

[Jazper]

this might be a little odd to suggest, but would it be out of line to ponder the thought of hacking the circuit to add a dc servo so you didn't need the output caps - might make it sound better too...

 

[PinkFloyd]

Quote:

Originally Posted by alanb 1. Install Alps 50kohm Blue Velvet volume control - needed 'cos the original crackled like sweet wrappers. I'd put a 100kohm pot in but reverted to a 50kohm to make the amp as close to the original design as possible. Sounds fine but seems to require substantially more rotation for a given volume.

Just a thought but try replacing the 220K resistor (the one from pot wiper to ground) with a 50K or 100K type.

Quote:

Originally Posted by alanb 2. Replace the 6 1,000 microfarad capacitors with Panasonics. This was a major improvement - gonewas the bloated and overblown bass and in its place a much more evenly balanced and detailed sound. Not only that, but the caps themselves are shorter and don't foul the extension shaft for the volume control.

Yes. Your original caps would have been as dry as a stick considering they're over 20 years old, the fresh caps should have made a pretty marked improvement overall. Parallel a couple of 3300uF caps on (per channel) and you'll notice an even bigger improvement.

Quote:

Originally Posted by alanb 3. Replace the original TL082 op amp with a socketed OPA2134. This is another major improvement and has given the amp a much "quicker" and more controlled sound.

As you've socketed the amp try the el cheapo NE5532 as well, you may like it

Quote:

Originally Posted by alanb Overall a massive improvement. I'm now happy to use this as my main headphone amp.

Excellent! Now replace those noisy resistors and you'll be in heaven. Pics would be awesome!!

 

[hal55]

Just chanced across this old thread. By coincidence I pulled my Headcase out a few days ago, plugged in the Audio Tehnica AD700s and was, after it warmed up a bit after being unused for many years, rewarded with some of the best headphone sounds I've ever heard. This unit is fantastic - modified or unmodified. One of the best things I ever bought off the Accessories Club. Someone should copy the circuit and put it back into production, it's a gem even nearly 30 years later.
 
Hal55

 

[kramer5150]

LOL... Hey if it sounds good then it IS GOOD!!
 
I remember Mike (PinkFloyd)  He helped me out a lot on some DIY projects in my earlier days.

 

[Gbullimore]

Sorry for the thread resurrection..
Just got hold of a headcase and planning to restore it, nothing major just new psu caps, and maybe some low ppm resistors as there aren't many and it can't hurt!
I traced the schematic if it helps anyone else?
It's an interesting design, and has some subtleties like off setting the supply voltages for the driver stage to enable DC coupling.
Thinking of trying another opamp, but as the TL082 is very low power, maybe a more power hungry opamp will need adjustment in the PSU resistors to keep the voltage drops consistent?

 

[Gbullimore]

 

[Gbullimore]

oops.. one type, the output resistor should be R25, 120ohm, (copy/paste error!)

 

[Ufanco]

Amazing what the op did with this amp. Just for fun here’s a amp that almost as ugly.