[Karlosak]

Hi,
I've finished my first DIY project: a CMOY for my HD-600. And it is better than I expected. It can really show up the power!

But I still have some minor problems:

1) At 9V voltage it had quite problems with higher dinamic passages - I got distortion (maybe oscilation?). But when changed to 2x9V it performs the hardest music passages easily and the sound also cleared up. Is it normal? Or due to oscilation problem? (After all, It doesn´t matter much - I can stick to the higher voltage and enjoy)

2) I´m using the ALPS 10K logaritmic pot (STRK09707 - the cheaper and smaller brother of the Blue Velvet) and have difficulty setting the volume - first it goes rapidly up then still the same level (cca. 60% of the range) and at the end it goes dramatically up. What´s the problem? I've wired it the same way as the Blue Velvet in META board. Is it possible that I´ve changed the logaritmic dependence vice versa. But if I change the ground with the out (on the pot) then I will have to turn it anti-clockwise (and I don´t want to). I´ve measured it and it looks like correct: turned left it has O Ohm (no voltage on the input) and turned right it has 9.8 Ohm (full voltage on the input). So the only problem is the volume curve.

Please give me any hint. Sorry for stupid questions but I´m new to the DIY and can´t sort it out myself.

Thanks

 

[MisterX]

What is the gain set to?
I was under the impression that if you set the gain to 11 the pot would not operate over its entire range.
Visit Tangents tweaks page for more information.

 

[guzzler]

it's perfectly normal that the 2x9V batteries is better, as the HD600's need a lot of voltage due to their high impedance...

g

 

[tangent]

Quote:

At 9V voltage it had quite problems with higher dinamic passages - I got distortion (maybe oscilation?). But when changed to 2x9V it performs the hardest music passages easily and the sound also cleared up. Is it normal?

That's clipping, caused partly by the high voltages you need to drive those headphones, and also by the rail imbalances you can get when using a bare resistor divider for the virtual ground. There's an article on my audio site that goes into more detail on this, particularly the further effects of the voltage limits through the op-amp.

There are three things you can do to fix clipping in this amp: 1) add more supply voltage; 2) use a more voltage-efficient op-amp; and 3) stabilize the virtual ground. As you've discovered, the first is cheap and effective, especially for high-impedance headphones.

Quote:

I've wired it the same way as the Blue Velvet in META board.

You may not have it hooked up correctly. If that pot is set up normally, the pins along the centerline are the wiper pins, and should only go to C1 on the amp. The effect you're describing sounds like what you get when you swap the wiper and the input wires, to me. Tell me, does the sound do strange things when you turn it all the way down?

 

[Karlosak]

Thanks guys for advice.
I´ve sticked to 18V and the sound is now rather good (with OPA2132PA). And the pot was connected in the wrong way Tangent - I reconnected it and it works, but I cannot use the whole range - not surprising, I´m using gain 11 (as I was told on Tangent´s great website).

 

[Sol_Zhen]

Please post some pics. We love to see finished projects.

 

[Karlosak]

I would love to, but I haven´t got any digital camera ( A friend of mine has got one, so maybe I´ll do in few days...