Finished Pimeta, Need Advise
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DobsOnly

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Hello everyone,
Just finished building a Pimeta but I am not sure about the sound.

AD8620/8610 opamps
Gain ~6
Dual buffers on each channel
Precision resistors throughout with most everything socketed.
9volt battery supply - for testing
offset voltage .001v on each rail

Source for testing mainly Rio Karma line out

Cans used - Ety ER6 and Senn HD600
Comparing with Cmoy, Gain ~11, I finished a few months ago.

Pimeta - very quiet compared to the Cmoy, which has a slight hiss at higher volumes. The quiet background seems to promote the feeling of a slightly larger sound stage than the Cmoy.

Pimeta - Very natural sounding vocals, softer than Cmoy this is good as the Cmoy can get a little bright sometimes.

Pimeta - Bass extension seems a little better than Cmoy

Pimeta - A drumstick striking the Snare drum or Rim of the drum is much more veiled in the Pimeta than the Cmoy. You get the same feeling when a cymbal is struck. It's there and you can here it but it’s very subdued.

Pimeta - Very little if any extension in the Treble area. No sparkle

This upper region is lacking even when compared to karma -> Headset with no amp.

I run the Karma normally with EQ Off. I can set the EQ to TRANCE setting (no jokes please) and the Pimeta seems to come alive in these upper regions. I have not been able to find what the TRANCE EQ settings actually are so I don't know exactly what’s missing.

From what I have read on these forums the Pimeta should be very accurate in these Mid and High frequency areas so I'm guessing I've got something wrong.

Can you suggest some tweaks to the amp that might change or alter the sound signature? Is there anything I need to check in particular for mistakes?

I'll try this again tomorrow after some sleep... 3 hr's sleep in the last 2 days "ain't gettin it"


I might find that my ears just aren't cut out for anything better than a Cmoy. (would not be as fun but would save me a ton of money).

Thanks for any comments or suggestions.
 
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BrokenEnglish

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so mainly you're hearing a roll-off in the highs, am i right?
1st hint: if you used input caps, try to get rid of them (if your source allows to do so; basically i'd rather expect rolled off bass with input caps, but it should depend on their value)
what did you use as rail caps and bypass-caps? if handy, add a second 9v-battery to increase the voltage to 18v for proper testing.
 
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__redruM

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Quote:

Originally Posted by BrokenEnglish
add a second 9v-battery to increase the voltage to 18v for proper testing.


I second that. Also which "optional" parts did you use? What did you use for the bandwidth resistor. Is it "class a".
 
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JackH

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You might just want to give it some time.

I didn't believe this until I heard it for myself, but electronic components can and do sound different after they've been used for a while. I had read about this various places, and always figured it was BS until I built a pimeta, and had an experience similar to what you're describing. Mine had a weak high end, that actually got a little worse -- then a lot better, after a few days of use. I noticed the same thing when swapping op-amp chips.
 
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DobsOnly

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Quote:

Originally Posted by BrokenEnglish
so mainly you're hearing a roll-off in the highs, am i right?
1st hint: if you used input caps, try to get rid of them (if your source allows to do so; basically i'd rather expect rolled off bass with input caps, but it should depend on their value)
what did you use as rail caps and bypass-caps? if handy, add a second 9v-battery to increase the voltage to 18v for proper testing.



Your right about the input caps. I removed them from my Cmoy and did not use them in the Pimeta.

I'll try with 2 batteries see if that helps out.

Quote:

Originally Posted by _redruM
I second that. Also which "optional" parts did you use? What did you use for the bandwidth resistor. Is it "class a".


No input caps used
not bias into class A
I was short 3.32K resistors for R5. I used 2, 3.57K resistors I had on hand??
WIMA 6.8uf Caps in C4 and 4 Panasonic FC Series 1000uf for Rail Caps.
Large Alps RK27 Volume Control
R11 = 100ohm with dual buffers
I believe everything else is per Tangents schematic.

Quote:

Originally Posted by JackH
I didn't believe this until I heard it for myself, but electronic components can and do sound different after they've been used for a while. I had read about this various places, and always figured it was BS until I built a pimeta, and had an experience similar to what you're describing. Mine had a weak high end, that actually got a little worse -- then a lot better


Maybe so. It doesn't sound bad, just not what I was expecting and with nothing to compare it to. Well all I can do is ask.

Thanks to all for your help and suggestions!
 
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__redruM

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Quote:

Originally Posted by DobsOnly
No input caps used
not bias into class A
I was short 3.32K resistors for R5. I used 2, 3.57K resistors I had on hand??
WIMA 6.8uf Caps in C4 and 4 Panasonic FC Series 1000uf for Rail Caps.
Large Alps RK27 Volume Control
R11 = 100ohm with dual buffers
I believe everything else is per Tangents schematic.



Did you jumper R8? Also, if the increased voltage doesn't help, go ahead and bias it to class A, to see if that helps. Lastly, did you use sockets for you resistors? If so, start trying different values, for R4 and R11, maybe even R8.

Keep in mind, amps don't usually make Night and Day differences, besides volume.
 
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DobsOnly

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Well I believe the simple addition of the 2nd 9v battery has made a very nice improvement. Thanks to everyone for there suggestions.

_redruM
Yes, I did remember to jumper R8 and R3 through R8 are Socketed so I might try changing some things around later. With this improvement I think I'll just enjoy it for a while like it is.

Now I have to case it up...

Thanks Again
 
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