Thinking about it further, this trim pot only adjusts the offset DC voltage, not the bias current. The latter is a bit difficult to fine tune. You'd have to add a tiny trimmer to R9 or R10. The root problem - the fact that transistors in the circuit are miss-matched - is best addressed by reducing the transistor parameter spread, i.e. binning, sovling the output offset and channel balance in one definitive swoop.
I used TE Connectivity Dynamic 3000 series headers and connectors. They're reasonably priced, and can be had gold plated so you can feel fancy. They are somewhat bulky though. They also come with alignment/hold clips, but they're easily removed with some pliers. I'll try and snap some pics when I'm not lazy and finish the case up.
Richard,
I've been thinking about this idea and wondering if installing a panel mounted gain switch would be a doable useful idea. I'm currently populating the boards and have not yet installed any of components involved - r3, r3a, r4, sw1 jumper; and I'd prefer to plan ahead now rather to have to de-solder later.
I assume it would be.necessary to join the sw1 on both boards to a common switch. The current pin header and jumper might be adaptable, but there are probably more suitable components - probably some kind of plug(s) that would permit the panel switch to detach from the boards. And, I suspect there are some electronic considerations as well.
I'd appreciate your thoughts.
Warren
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The two pads "SW1" were intended to be for not just the jumper (included in the kit / BOM Mouser 517-647-01-02, 649-71363-202LF) but also for soldering wire leads to a DPST or DPDT panel switch or DIP unit.
Come to think of it I'm pretty sure there are press on connectors for the pin strip header, so you could use that to make the switch unpluggable from the board.
The gain switch is designed to have minimal impact on the circuit operation ... though it would be good practice to keep the lead wires reasonably short and twisted together.
/R
Come to think of it I'm pretty sure there are press on connectors for the pin strip header, so you could use that to make the switch unpluggable from the board.
The gain switch is designed to have minimal impact on the circuit operation ... though it would be good practice to keep the lead wires reasonably short and twisted together.
/R
Yes, I love this amp too. I have some polystyrene caps I want to try. I have just lowered the gain and I'm going to put it in a properly earthed chasis as I had some hiss. Its partly the gain was too high for my HP and the build was sprawled across my workbench. Should be fine when I'm finished. Also keen to try some of the new national opamps in this one.
I had thoughts about trying an AD825 on an adapter, but haven't looked any further into it. It means studying data sheets and that's not happening yet. I'm using 825's in an old Marantz CD player and they sound quite good. I tried a lot of op-amps before settling on the 825's. I found that it's a challenge finding one that sounds good, across the board with all genres of music, and doesn't introduce something bad with the good when there is an improvement. There was one, can't remember what, that sounded spectacular to me but my wife heard some high frequency noise that I couldn't hear at all, and she hated it. So out they came and back in went the 825's.
Building my Sapphire 3, I was tempted to solder in the OPA134's without the socket. I may do some experimenting down the road, but right now I'm too pleased with the unit as is and I'm more intrigued with the idea of a Sapphire pre-amp.
It's tempting to think that one might get better results rolling input caps. I'm very impressed with these ClarityCap MR's. I have some Mundorfs to try, but I'm thinking, it sounds so good, why bother?
It'll take some time to get bored with it, then I'll try something different!
Building my Sapphire 3, I was tempted to solder in the OPA134's without the socket. I may do some experimenting down the road, but right now I'm too pleased with the unit as is and I'm more intrigued with the idea of a Sapphire pre-amp.
It's tempting to think that one might get better results rolling input caps. I'm very impressed with these ClarityCap MR's. I have some Mundorfs to try, but I'm thinking, it sounds so good, why bother?
It'll take some time to get bored with it, then I'll try something different!
Wanders, you need to calculate the gain and order the right part that gives you the right gain for your headphones. You can also have two gain settings and switch between them depending on the cans you are using. If you have the part, then use it to get the amp going and order a replacement.