[cello]

So, after listening through my Meta42 for a while now, I'm realizing that, although it improves the bass and soundstage, it seems to have a strange effect on the upper mids, making them somewhat harsh and unappealing. Since I hand-built my Meta42, I'm wondering if it's possible that a particular component could cause this problem. Could it be the op-amp? The pot? The caps? The buffers? The color of the LED??

The resistor values I'm sure are fine --previous responses to this problem have been about them, and I've already made sure they're all right.

 

[guzzler]

what opamp are you using?? if it's something very revealing like an AD8620, it is likely to be your source this harshness is coming from, although it could also be a dislike of the AD8620... if you can afford it, you could try an OPA627 (gain >5) or OPA637 (any gain)...

g

 

[cello]

Guzzler, I'm using two OPA134s in a dual-channel adaptor from tangent.

 

[KTpG]

Quote:

Originally posted by guzzler try an OPA627 (gain >5) or OPA637 (any gain)... g

You have that reversed, I think... 627 any gain, 637 gain>5. (just to clarify)

 

[Voodoochile]

What color LED are you using?

Actually, is your pot 10k or 50k? And what is the value of your R2?
Do you have R8 or R9 in place?

I could understand your remark if using the AD8620, but the 132 or 134s... I doubt it is your OPA choice, suffice to say.

edit: I do see your remark about your resistors, believe it or not.

 

[Voodoochile]

What's happening, cello?

 

[cello]

sorry...somehow i missed your previous reply... anyhow, the pot is actually 100K, R8 is jumped, R9 is 47 ohms, R2 is 1 megaohm (it's supposed to be 10x the value of the pot, i believe).

 

[Voodoochile]

No glaring problems there... hrmmm.

 

[peranders]

Quote:

Originally posted by guzzler if you can afford it, you could try an OPA627 (gain >5) or OPA637 (any gain)...

Mixup: OPA627 any gain, OPA637 more than 5

 

[cello]

yeah it's possible that the amp is totally fine, and the source perhaps is a tad bright, and the amp simply accentuates it. It's coming out of macintosh G4.

Is it possible there could be some instability issues? Some sort of oscillation that's going on in the circuit behind my back that's causing high frequencies to become harsher?

Also, note that I'm not comparing this to any other source, or any other headphone amplifier, so it could be that I just have sensitive ears...

 

[tangent]

What's the idle current draw of the amp? What chips are in it? Are the class A cascodes in place? (You may have already answered some of these previously, but it will be helpful to gather all the answers into one place.)

 

[guzzler]

apologies all, my mistake

g

 

[cello]

oh man - I actually don't have a multi-meter, plus I'm going to maine for the weekend. So the responses to those questions might have to wait a bit.

 

[ppl]

I Think your problem is the OPA-134 this series of op amps gets my vote as one of the worst sounding op amps ever made. use the AD-8620 or use a BD adaptor and use a pair of OPA-627's be sure to include the cascode current source for the Op amp Class A Bias. this i am sure would make you alot more happy with your Amp.

 

[cello]

which of those two op-amp choices would you recommend? I'm leaning towards simply getting an AD-8620 as it would require less work.

But if you think biasing the amp into class A with a pair of OPA-627s would make it sound significantly better than the AD-8620s, then I'll do that. I'm also going to get a multimeter after this Thursday (I have two problem sets due then...

) so I can respond to tangent's questions.