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the Pimeta-V2 thread - Page 34

post #496 of 627


 does anybody of you try to add to the pimeta v2 a preamp out connector by adding a dual opamp in the scratchpad area? Something like suggested by Warren in the tweaks section. Maybe you are able to show some hint/idea/picture about how it was done? I'm looking into correctly wiring the dual opamp that would be needed for that and also to be able to correctly fit it in that scratchpad area.


Thanks in advance,


Edited by tent - 1/31/13 at 2:49pm
post #497 of 627

up? ;)


I'd also like to add another newbie question: do I need to put single opamp at the OPAG socket or if I have just double opamps is it ok to use a double also in this one?


thanks in advance,


post #498 of 627
Originally Posted by tent View Post

do I need to put single opamp at the OPAG socket


Yes. A dual op-amp's pinout is not a superset of a single's.


5 minutes' study of the datasheets would have answered this for you, faster, and you'd probably have learned at least one other thing along the way accidentally.

post #499 of 627

yes, I dit that indeed in meantime.. I was lazy and threw in the question while up-ping.. ;)

anyway, since I'm still without any single opamp I'll need to search about one (I have only dual opamps ghosh!), now I started firstly in testing the PSU by checking V+ and V- compared to IG with my meter (I'm using a 9V NiMH battery as power source) on OPALR, but I read 4.5V on V+ and -3.4V on V-.. that looks to be quite off, right? The same measurement I can read if measuring the correct pins on OPAG.. so Is there something wrong? in the woltage splitter most probably (could it be defective)? or is there some further checking step that I should do, still without opamps?


thanks in advance,


post #500 of 627

It's normal to get bogus results for that test without OPAG installed. It's kind of like complaining about low gas mileage on your car with the transmission in neutral.

post #501 of 627

uhm.. I see.. so I'll need to figure out how to get a single opamp like opa132 since I have some opa2132s and put it in opag and recheck again. Thanks!




PS: btw. I just noticed that on texas' site the OPA132P is considered obsolete, only U version is available.. so what would be the replacement of OPA132 when all of them will be obsoleted? I mean having same quality and sound?

Edited by tent - 2/4/13 at 12:11am
post #502 of 627

There are many op-amps that will work here. I've reviewed a few of them. OPA134 and OPA227 are still being made in PDIP, for just two examples.

post #503 of 627

Thank you Warren. I think I'll use OPA134 then to match it with my OPA2132s...

but one question still for my understanding: if instead I would like to use OPALR with LM4562NA, what would you suggest better in OPAG? OPA227 or OPA134? I understood that LM4562 has no single version companion...



post #504 of 627

If I had given you four examples, would you now be asking me to rate all four configurations?


There is no objective answer, and I don't have a subjective one, since I haven't listened to all combinations of op-amps. I don't even have a review of the LM4562 up, so I clearly haven't even heard them individually.


You're just going to have to try it.

post #505 of 627
I understood that LM4562 has no single version companion...





http://www.ti.com/product/lme49710 wink_face.gif

post #506 of 627

Wow thanx Misterx! ;)

Why do they use such confusing and cumbersome numering system to name their chips??



post #507 of 627

Hello, news and updates: I've managed to get around a single opamp for OPAG and still the difference between IG and V+ is 3.00V and IG and V- is -4.71V with my 7.2VNiMH 9V battery.. still do you think it's ok, Warren?


I've also tested further: There is no DC offset between OL or OR and OG, no DC between OG and IG, no other strange DC is seen in other sides.. I've also tested music using some old crappy headphones and music seems to come out even if volume seems to me quite low.. even at full pot turned up (I use my SANSA as source, if I use my iPod with Fiio Line OUT of course I get a lot more power.. but to me PIMETA was a method to get more volume from SANSA).


I've used basically only the values of original schematic for all my resistors...


Another thing I checked and found kind of "wrong" is the ClassA BIAS circuit: the LED2 is not powering on, the LED1 is bright when I turn on BIAS and is very dimmed when I turn off the BIAS. Additionally trying to adjust the bias to 1mA (so looking for 1V across RBLIM, I'm only able to get close to 0.653V, but I can't go further because the trimpot seems to be at one turning end (5k trimpot as per schematic as well).


How do you see it? Is allright? Is something probably going on with the split ground regulator?



EDIT FYI: actually I noticed that now that RBLIM is 0.653V I actually cannot see even LED1 powering on (unless of course I turn off BIAS)

Edited by tent - 2/6/13 at 3:08pm
post #508 of 627

I've now listened to it anyway with this setup (no BIAS, one OPA2132 in OPALR and one LM6171 in OPAG) with the ipod and the Fiio Line out and I have to say it really sounds amazing there! The bass boost circuit is a bit too much even if impressive itself as well, no particulare difference noticed at the moment when turning on or off this BIAS but probably something is fault.. could it be the LED2 is failed? For the V+/V- IG voltage difference instead it seams at the moment not to be a problem.. chips are not hot after use.. but wondering still if it is normal or if I should attempt to change the virtual ground trans.. and also the gain seems to me to feew like suggested in the schamatics..



post #509 of 627
Originally Posted by tent View Post

still the difference between IG and V+ is 3.00V and IG and V- is -4.71V with my 7.2VNiMH 9V battery.. still do you think it's ok, Warren?


Nope. You shouldn't measure more than about a tenth of a volt off of ideal.



volume seems to me quite low.. even at full pot turned up


Also a good problem indicator. The stock PIMETA v2 gain, while lower than that of the CMoy, is still fairly high as headphone amps go.


(Why? So that uncompensated op-amps like the OPA637 will work. If not using uncompensated op-amps, you probably want something lower.)



LED1 is bright when I turn on BIAS and is very dimmed when I turn off the BIAS.


The brightness of LED1 should only change as a function of supply voltage changes.


This suggests that your problem may be a dead short across the battery, causing its voltage to drop.


So, one test is to be measuring voltage across the battery terminals while you flip the switch. It shouldn't change much, if at all. If it does, your amp is drawing more than the battery is intended to supply, but with NiMH you can pull 1C continuously without problems. That's on the order of 4-5x the expected supply current of a PIMETA v2. One 7.2V NiMH "9V" datasheet I just looked at fully characterizes the battery up to 3C. (900 mA!)


You can try measuring current directly instead, but be sure to use your DMM's high current range first. It's quite possible to get multiple amps out of a NiMH battery for short periods, which will blow the fuse (or the meter, if there is no fuse) on low current ranges.


Another test is to measure resistance from the top of LED1 to V- while the amp's power is switched off, or the battery is removed. I get 56 kΩ here on one of my PIMETA v2s. If you get something much lower, especially near zero, you have a short or you've got something connected across the rails that you shouldn't have.



RBLIM is 0.653V I actually cannot see even LED1 powering on (unless of course I turn off BIAS)


I can't be sure that's wrong without knowing the Vf of your LEDs.


With a 7.2 V battery, you shouldn't be using 3.7 V LEDs as shown in the schematic. To a first approximation, you can add the two Vf values and get the minimum supply voltage. The transistor behaviors change that a bit. At these low voltages, they may well change it more than 10%, which is why I say it's only a first approximation.


I use two 3.7 V white LEDs in one of my PIMETA v2s (the red one in the docs) but it has never been tried with less than an 8-cell (9.6V) NiMH battery.

Edited by tangent - 2/7/13 at 2:14am
post #510 of 627

Uhm.. ok then let me check carefully what it could be...


First of all the battery: I just discovered it is a 8.4V 200mAh NiMH and not 7.2V like I belived... not easy to understand which is the matching datasheet tough..

basically it is this one: http://ecx.images-amazon.com/images/I/61m1PaFM3aL._AA1500_.jpg


But now I have the battery empty since I was letting the board running overnight with the idea of letting it roll out......gh..... question is: should/could I dare to plug in the wall wart to charge it or is it risky at this point since some short is suspected? Maybe if not turning on the pimeta but just recharge the battery?


Anyway what I could do is measure the resistance between LED1 and V- and I read 11.61k and 9.8k (I measured both LED1 pins) so it seems to be compatible with your suspects.. so maybe some not so evident short or contact??


Also the led V value is unknown to me (I was having them lying in my parts bin, were actually new ones, but no idea about voltage etc.. just blue led with 2.5mm diameter I'd say.): is there a method to know V of those with the meter? otherwise I could just attempt to change them with others.. led2 on the other hand does not even light on with both BIAS settings..




Edited by tent - 2/7/13 at 1:21pm
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