[alphaman]

Thx for the response ... I'll get to the rest of the reply later as I'm still troubleshooting ... but I wanted to address a quickie:

Quote:

You should have been testing only for DC offset, from the start. It is not a sufficient test, but you would have seen the problem without risking your expensive IEMs or your junk cans. Nothing you've reported about how the problem sounds tells us anything more than a high DC offset measurement would have.
 
Maybe you're annoyed now, thinking I'm armchair quarterbacking. But, a DC offset test is one of the standard testing steps. When you rolled that op-amp, you should have gone back through that test sequence. Plugging cans in is four paragraphs down the sequence, and it recommends starting with the cheapies.

In my orig. post, I noted the gazillion times I've cycled thru battery changes and OPA rolls and misc. tweaks. Even batt changes requires I remove the cover, creating some risk for messing something up. My routine was to use my default cans, the Senn IE-8s. Frankly, then, even with $$$ cans, I'll still take the risk since: the Pimeta2 has proven to be v. reliable/durable; the sequence method is mostly (IMO) for initial builds/testing; TIME=$$ (especially in today's economy) and, my 'problems' generates content for HF and more biz and troubleshooting-skill-building for you/readers-of-this-post [For more enlightened philosophical discussion on these issues, see my HF Profile. ]
 
This just in ...
 
I just discovered that the orig.-installed Q3R and Q2 are not 2N3904 but 2N5088. Although I trashed the Q3L I removed earlier, i now assume it was 2N5088. I got mixed up because on your schema, you label the defaults as 2N3904 but on your Parts List they are Alternatives.
To be cont ...

 

[tangent]

I think you're chasing the wrong thing by continuing to swap Q3L. The circuit is not super-specific about the type of transistor it takes here. That's one reason I'm not particular about 2N3904 vs. 2N5088 in the docs. They're both small-signal NPNs, which is all that matters here.
 
Swap that op-amp again and do the bias current test. Those are far more likely to give interesting results.

 

[alphaman]

Quote:

I think you're chasing the wrong thing by continuing to swap Q3L. The circuit is not super-specific about the type of transistor it takes here. That's one reason I'm not particular about 2N3904 vs. 2N5088 in the docs. They're both small-signal NPNs, which is all that matters here.
 
Swap that op-amp again and do the bias current test. Those are far more likely to give interesting results.

I'm away from my testbench so it'll be a few hrs before I can re-test.
 
I did change the opamp. Several X's using several diff models: 2132, AD825, and I now have 5532 plugged in. Same confusing result.
 
BUT ... (and not sure I made this clear in the orig. post) ... with the opa (or even buffer) REMOVED I continue to get that 2.6V wrt gnd (so, that's what buffer sees, and sends to the jack as a pwr-on pop). IOW, it's coming from an in situ Q3L. Any clues as to how much voltage SHOULD be present (i.e., w/o opa)?
 
Also this may not have been clear in OP above:
When I changed that Q1 with a broken leg, I also CONCURRENTLY changed Q3L because it looked bent and roughed up (not sure it was damaged but since i was in the area anyway, and had a new 2N3904 on-hand, I thought I'd play it safe). But the orig. Q3L was almost surely a 5088, so me now thinks diff model/manuf = diff bias metrics??

I don't have any 2N5088s in my bin ... just about every other small-signal NPNs, like 3904, etc.
 
EDIT:
Issue Resolved (I think...)!!
 
It was the small-signal NPN  "species" that I'd speculated was suspect, above.
 
I found a BC639 in my bin , and threw it in [CAUTION: despite the European "BC" prefix, this trans. uses Japanese pin config. Mine is a Fairchild.]. No need elaborate: L-ch is behaving normally again -- as is the whole amp AFAICT. Just to re-confirm, I did throw the 3904 and 2SC2240 back in -- in case something else, known to me or not (like cold solder joint, etc), "magically" fixed the issue. But those produced same problem as before -- returning the BC639 into position restored orig. functionality.
 
Guardian: All is as it was before. Many such journey's are possible.
Kirk: Let's get the hell out of here.
from Star Trek -- The Orig. Series, Epi "The City on the Edge of Forever" 1967.
 
Sorry, Tangent, it was the small signal trans. so nahhh ... nahhh ... na... nahh nahh
Seriously, tho ...WOW ... what an epic. I may ditch DIY for a while and give Fiio and others some of my upcoming head $$'s. As  I said above, time=$$ and I'm not sure about the DIY hassle any more. Great sound, good initial learning experience ... but as an ongoing "hobby" ... methinking paradigm shift
 
 

 

[alphaman]

Abstract: R7, and other "signal-path" R's -- using "high-quality" resistors
 
That 100-ohm R7 resistor is directly in the signal path. Has anyone experimented with upgrading this to a higher-quality R? I was thinking Vishay's newer (and $$$!!) "PTF":
 
http://www.vishay.com/docs/31019/ptf.pdf
 
 
SOME FEATURES
• Extremely low temperature coefficient of resistance
• Very low noise and voltage coefficient
• Very good high frequency characteristics 
• Can replace wirewound bobbins
 
 

 

[i_djoel2000]

you can even use this if you want, no one can stop you: http://www.partsconnexion.com/resistors_vishay_var.html

 

[alphaman]

Quote:

you can even use this if you want, no one can stop you: http://www.partsconnexion.com/resistors_vishay_var.html

Cool! Has anyone used this R? If so is there an important improvement in SQ?
IAC... actually, it's YOU --  i_djoel2000 -- who's stopping me ... by not offering to send me FREE samples
How about touring them? ... like some others on this forum do for various high-$ (= unaffordable) gear. 
 
Speaking of samples ... Vishay does have a sample program ... hmm...
 
 
 

 

[alphaman]

Okay ... I'm recanting a bit on my promise to back off a bit on DIY ... but since my soldering iron is out of basement storage from that pesky troubleshooting job (see above  ...
... on the topic of substituting better-quality parts, anyone experiment with trans. from Zetex or Toshiba, etc. for the class-A ckt? In some DIY circles, Zetex get some attn. I couldn't get the Toshiba 2SC2240 to work, but I didn't tweak the bias resistance; 2240 and its PNP "equiv." 2SA970 are popular in some circles.

 

[geofftnz]

Built the amp today... all goes, no magic smoke got out, buffers don't seem to get too warm. Bit of a hum off the pot, so I grounded to PG as suggested.
 
Where I do have a problem is the interconnection with the DAC. The DAC is powered by the amp: V+, IG and V- are passed, with IG providing the ground reference for the DAC. Unfortunately OG of the DAC sits about 0.5VDC above IG of the amp, with around 80mV of 10kHz tone on it (at a guess - will hook the scope up soon). Coupling the signal grounds with a 47uF electrolytic (left over from the DAC construction) or a spare 6.8uF Wima film cap quiets the noise, so I'll do some experimenting around that. I'm still not sure whether this is oscillation within the amp (unlikely, because it only appears with the DAC hooked up) or DAC, or something to do with the DAC ground connection to USB ground. Needless to say USB is probably not the ideal electrical environment to hook a sensitive audio circuit up to...
 
Apart from that, it sounds good and I can't wait for my case (and batteries) to arrive so I can finish the build!

 

[firefish15]

I/O jack question.
 
Hi, I'm building my first Pimeta amp. I just realized I ordered just the input jacks (Mouser 502-35RAPC4BH3), but no output jacks from the parts list.
The 502-35RAPC4BH3 is a switched jack (http://www.switchcraft.com/Drawings/35rapc__h3_cd.pdf) with 5 pins. Pins 4 & 5 are connected to the tip and are shorted when a plug ins not inserted. Similarly pins 2 & 3 are connected to the sleeve. Pin 1 is ground.
The questions I have are:
1) The left channel uses the tip, so I would connect pin 4 to IL. What would I connect pin 5 to? Pin 2 would go to IR, what is pin 3 connected to?
2) Can I use the same jack for the output?
 
Thanks,
Paul

 

[firefish15]

Quote:

I/O jack question.
 
Hi, I'm building my first Pimeta amp. I just realized I ordered just the input jacks (Mouser 502-35RAPC4BH3), but no output jacks from the parts list.
The 502-35RAPC4BH3 is a switched jack (http://www.switchcraft.com/Drawings/35rapc__h3_cd.pdf) with 5 pins. Pins 4 & 5 are connected to the tip and are shorted when a plug ins not inserted. Similarly pins 2 & 3 are connected to the sleeve. Pin 1 is ground.
The questions I have are:
1) The left channel uses the tip, so I would connect pin 4 to IL. What would I connect pin 5 to? Pin 2 would go to IR, what is pin 3 connected to?
2) Can I use the same jack for the output?
 
Thanks,
Paul

Correction for my previous post.
1) The left channel uses the tip, so I would connect pin 5 to IL. What would I connect pin 4 to? Pin 2 would go to IR, what is pin 3 connected to?
2) Can I use the same jack for the output?
 
 

 

[geofftnz]

Quote:

Correction for my previous post.
1) The left channel uses the tip, so I would connect pin 5 to IL. What would I connect pin 4 to? Pin 2 would go to IR, what is pin 3 connected to?
2) Can I use the same jack for the output?
 
 

Either leave them open, or connect them to IL/IR. If you're using it as a normal socket, then it wont matter. They're there so you can interrupt the signal path when you plug something in. I'm planning on putting one of these as a line-in between the DAC and amp in my build. When another source is plugged in, the internal switch disconnects the DAC.
 

 

[MisterX]

There is no need to connect pins 3 & 4 to anything. 
 You could just go with # 502-35RAPC2BH3 if you do not need a jack with a switching function.
 
And... Yes, you can use it as an output jack as well.
(The parts list ID is listed as IN/OUT and the quantity is listed as 2)

 

[firefish15]

Thanks Goefftnz and MisterX

 

[SoundOfKhaos]

 
Quote:

Hi,
 
In case you're interested, you can indeed build a Pimeta v2 handheld amp with the following features:
- Serpac H65 enclosure
- Li-Ion cell pack 14.8V 0.75Ah with protection circuit
- Integrated modified Linkwitz Crossfeed circuit
- Integrated Bass Boost and Volume Boost circuit
- Integrated battery level control circuit with bi-color led
 
For some of you this may be a bit over-engineered, but to me it was a good exercise.  The amp sounds brilliantly and qualitatively excellent, and the cells last for well over 10 hours.  As a proof, see the following pics.
 
 

Spoiler: Warning%3A%20Pic

 
Lots of cables for the filters and boosters, but eventually it will fit.  On the bottom see the bass/volume booster circuit as a piggi-back board to the R4 pins.
 
 
 

Spoiler: Warning%3Apic

 
The 4 circuits all connected.  The Linkwitz circuit required the big caps to be soldered horizontally, while one of the C4 Wima caps had to be moved to the scratchpad area.
 
 

Spoiler: Warning%3A%20pic

 
On the bottom of the pic see the battery control circuit, which goes as a vertical piggi-back board onto the sratchpad area.
 
 

Spoiler: Warning%3A%20Pic

 
All fits precisely into the enclosure.  The Li-Ion pack has been R&D'ed for this purpose - newest technology you can build these days.
 
 

Spoiler: Warning%3A%20Pic

 
Finally, the enclosure can be closed and the product is finished... happy listening!
 
Cheers.

 
I'm still having trouble keeping my mouth closed. I do not have the skill, or knowledge to accomplish something of this caliber yet but I find this to be very inspirational to keep learning. Amazing work. Can I ask about how long this took? For design, fabrication and troubleshooting and stuff. Just amazing.

 

[alphaman]

Anyone using (and achieving GOOD results with) LM6171? I was thinking something like this: