[Bandeira]

Hello guys and girls..

Just bought a portable pimeta from a fellow headfier and and I wondered if I could suit it better to my use.
I have some but not much DIY(and electronics) knowledge so I wonder if you could help me...
With my MS1s, it goes very very well, but with my DT150 (which are 250ohm cans) it gets pretty harsh in mid-highs and highs department... and sounds kind of thin...
I am not AT ALL concerned about battery life... as I use it as a transportable...(willl be using a 2000 or 4000mah battery in the future)

It came with the following opamps and buffers:

OPAG - AD8610
BUFG - BUF634U
BUFL - BUF634U
BUFR - BUF634U
OPALR - AD8620

Will try to take a picture of the resistors, but it seems to have a gain of 1?
they have written on them:
R3--> 1001
R4--> 0512 (R4R is 0512 ,while R4L is 0428, which seems very very odd, but this gives about the same overall gain)
R5--> 0224
R6--> 0511

Also, must comment that R11s were left open.


Cheers

And thanks for the help!

Patrick

 

[Bandeira]

text update

 

[cobaltmute]

To my understanding, you higher impedance cans need more voltage swing. What are you powering you amp with now? What is the rail voltage?

 

[Bandeira]

It is 9v battery powered... I could easily make it 18v or even higher
but how about the odd stuff found in my unit? (different resistors, no R11L or R11R and gain of 1)

thanks for the help

 

[jcx]

if you keep the AD8610/20 you shouldn't make Vsupply >24V
but I'd at least go to 18V with 250 Ohm cans

I think R6 should be left open

R5, R1 can be shorted - the distortion cancellation theory that prompted adding these R doesn't apply at any Volume pot setting other than full on or full off and R5 hurts stability

R11 boosts buffer current/bandwidth - choose the rate you drain your batteries - I'd be surprised if buffer current setting differences were audible if the circuit is otherwise stable at both settings

 

[Bandeira]

But how abou the gain setting? I`ve read people setting gain at 5ish...
Is it easy to put sockets for the resistors?
I am planning on going 18v and double stacked buffers, so I`d have to put a 200R resistor in R11, right? WHat would be the impact of running no resistors in R11?

JCX-- You are recommending me to set my gain only with r3 and r4, right?

Thanks,

Patrick

 

[tangent]

Quote:

Originally Posted by Bandeira /img/forum/go_quote.gif it gets pretty harsh in mid-highs and highs department... and sounds kind of thin...

Have you read my Notes on Audio Op-Amps ?

Quote:

Will try to take a picture of the resistors

Please do, because the values with leading zeroes that you report don't make sense. Leading zeroes work against a scientific notation system like that used in electronic part value labeling.

Alternately, you can use a meter to measure their values. Do so with the power to the amp off.

Once you have the right values, you can get an exact gain from my gain calculator.

Quote:

it seems to have a gain of 1?...

Probably not. My best guess is 3, based on what I've seen so far, but again, I don't believe I'm working from the right values.

Quote:

R11s were left open.

So close them.

The PIMETA v1 docs explain how to select R11 when power draw isn't a concern.

Quote:

I`ve read people setting gain at 5ish...

Personally, I'm a fan of 2. It doesn't work in all situations, but it works everywhere I use a headphone amp.

Quote:

Is it easy to put sockets for the resistors?

It's scarcely more difficult than changing the resistors out. If you're only going to do it once, I wouldn't bother. Put sockets in for R4 only if you're going to do this several times more.

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I`d have to put a 200R resistor in R11, right?

100R. Again, see the docs.

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You are recommending me to set my gain only with r3 and r4, right?

Yes, he is, and yes, it's "legal".

 

[NelsonVandal]

IMO it has nothing to do with impedance. "pretty harsh in mid-highs and highs department... and sounds kind of thin..." is just the way AD8610/20 sounds, expensive or not. Maybe you should try other opamps. Maybe not the best, but "bestish", is LME49720. It's easy to find, cheap and sounds good. I'm not very happy with LME49710 as center amp, and I think LM6171 is cheap and good in this postition.

 

[Bandeira]

Hello,

First of all, thanks a lot you guys for the help...

Just got a meter and measured the resistors...
What came out:
The pot seems to be the ALPS RK097 10K

R1s 4.3K
R2s 4.3K
R3G open
R3r 1k
R4r 4.3k
R5r 3.4k
R6r 205k when trying to measure it measures about 5k, then keeps increasing, after about 2 minutes(!!!) with the probes touching the resistor, it measured 205K
R10 1K
R11 open

R8r 26r - the meter beeps as if it was shorted.
RLED 2.2k

which gives me the gain of about almost 5, according to the gain calculator.

What I am planning to do is:
--Set gain only with R3 and R4, as recommended... but which gain would work best with my headphones (I prefer mostly the DT150) and with the AD8620? (my knowledge on gain is very very limited)

--Is there any other changes I should make in order to change rail voltage to 18v, or even 20v (a friend of mine assembles battery packs, I might be able to grab a 19.6v/2000mAh nimh one)

--Possibily double stacking the buffers with the correct R11s - For me to use new buffers without ruining my current ones, the adaptor I should get is the regular 970601(the one without pinout change), right?

--Jumper instead of R8 - I don't use the most sensitive cans around, so I reckon hiss should not be a problem.

Anything wrong I am planning to do? Any more stuff I could be doing to improve SQ?

Cheers and thanks again!

Patrick

 

[Earwax]

Quote:

Originally Posted by Bandeira /img/forum/go_quote.gif --Possibily double stacking the buffers with the correct R11s - For me to use new buffers without ruining my current ones, the adaptor I should get is the regular 970601(the one without pinout change), right? Anything wrong I am planning to do? Any more stuff I could be doing to improve SQ? Cheers and thanks again! Patrick

Yes, don't bother stacking the buffers. Just replace them with LMH6321. I never liked my Pimeta too much with any configuration of Buf634s. LMH6321 made all the difference, it's a fine amp now.

 

[tangent]

Quote:

Originally Posted by Bandeira /img/forum/go_quote.gif R6r 205k when trying to measure it measures about 5k, then keeps increasing, after about 2 minutes(!!!) with the probes touching the resistor, it measured 205K

You can't measure all resistors in-circuit, because the meter itself changes things, like charging caps. To get the correct value in this case, you'd have to lift one end of the resistor, or perhaps remove the op-amp.

Not that it's a big issue. I wouldn't bother.

Quote:

which gain would work best with my headphones

Where do you find yourself putting your volume knob, as a percentage of the total rotation?

Quote:

Is there any other changes I should make in order to change rail voltage to 18v, or even 20v

You might have to use C2/C3 caps with higher voltage tolerance. Pics?

Quote:

For me to use new buffers without ruining my current ones, the adaptor I should get is the regular 970601(the one without pinout change), right?

You shouldn't be adapting the buffers. If you're going to stack buffers, use the DIP-8 ones. If you can only get SO-8 ones and the ones on your amp are already SO-8, I'd switch to LMH6321 rather than bother with adapters or try to stack SO-8s.

Or, as Earwax says, forget stacking and go straight to the LMH6321. I changed to it in v2 on purpose.

 

[Bandeira]

--tangent and Earwax:
on the LMH6321: ok then.. any other changes I should make to accomplish that change? UPDATE: ALREADY SAW ON THE WEBSITE, THANKS TO TACITAPPROVAL

--tangent:
1.I did remove the opamps to measure the resistors, but not the caps...

2.with my ms1s, 35% works excellent...
with the T20v2 i have to go up to 50~60% and things start to get a bit harsh
with the DT150, I can go up to 100% and not get enough volume, everything above 70% sounds harsh and seems that increasing the volume above that point does not make a lot of difference.

3. My C2s and C3s are 16v rated... to I`d fry them off line probably... 25v probably would suit me, based on your website.

4. yeah the buffers are SO-8s...

on the caps and the LMH6321, I find it quite hard to get good caps and specific stuff in Brazil. Any of you guys know a reasonable priced shop that would post them all the way down to Brazil?

cheers and thanks a lot guys, that's what makes head-fi special!

 

[cobaltmute]

You may also want to consider the Monofied Sijosae discrete buffers. I prefer the sound of them to the LMH6321.

 

[tacitapproval]

The LMH6321 needs to be modified slightly to work with v1 of the pimeta. See Tangent's site for details.

 

[Bandeira]

thanks tacitapproval... already saw it on the website.. sorry for not having seen earlier... but I can't really socket it? not very fond of soldering it directly to the board.