I'm building a Tangentsoft Pimeta headphone amp. I will probably use an AD843 opamp, as it is supposedly on par with the much more expensive OPA627 and sounds good with Grados--or so I've read.
My question is about the buffers. The design suggests BUF634Ps. I know there is a range of quality for opamps--the opa627 is a definite step up from the cheaper opa132, for example. Is this the case for high speed buffers as well?
I'm just wondering what my options are with this part. I'm willing to spend a few more $ to get better sound out of the buffers and the Pimeta. I just can't seem to find a good resource discussing the advantages/disadvantages of different buffers. Any info appreciated...thx
My question is about the buffers. The design suggests BUF634Ps. I know there is a range of quality for opamps--the opa627 is a definite step up from the cheaper opa132, for example. Is this the case for high speed buffers as well?
I'm just wondering what my options are with this part. I'm willing to spend a few more $ to get better sound out of the buffers and the Pimeta. I just can't seem to find a good resource discussing the advantages/disadvantages of different buffers. Any info appreciated...thx
I think there should be plenty of threads on head-fi about this and tangent's pages are usually quite helpful as well. Anyway, for the Pimeta the BUF634P is probably your only real alternative. There are other IC options (Intersil HA-3-5002 for one) but the pinout is different. You can find several discrete class A buffer designs as well, but I don't remember seeing one that was small enough to fit on board and the current requirements rule out batteries as a power source which was what the Pimeta was originally designed for. Bottom line: Stick with the BUFs or find a more sophisticated design (e.g. PPA or M3) 
/U.
/U.
This remains a pretty contentious issue but I think Nisbeth is more or less right, unless you are willing to do some re-wiring the BUFs are the way to go. If you are willing to re-wire things then the options are almost mind-numbing and I don't think there is a real consensus on which buffer is best.
The only other option is to grab one of those diamond buffer boards that were built for the Millet Hybrid a while back... I seem to recall that a few people used them in the PIMETA with very positive results. IIRC they were pin compatible with the BUFs.
The only other option is to grab one of those diamond buffer boards that were built for the Millet Hybrid a while back... I seem to recall that a few people used them in the PIMETA with very positive results. IIRC they were pin compatible with the BUFs.
slowpogo said:
This is DIY at it's finest. Not a matter of spending a few more $, rather a matter of spending a lot more time to pick the buffer you want and redesign (Or design from scratch) to implement it onto a Pimeta. It can easily be cheaper to build a discrete buffer than to go stacking BUF634 and the opamp driver and global feedback make it more forgiving (I mean tolerant) than some other amps.
It is not necessarily a matter of more power being a problem from a battery powered / portable amp, necessarily, the BUF634 in it's good sounding implementation is in wide bandwidth mode, and that in conjunction with AD843 is not a power miserly setup at all. A discrete buffer could consume no more power if it isn't biased entirely to class A operation but that's something you have to decide. It could even consume less power.
What's involved here? Picking the buffer topology you feel will fit in the space allotted, perhaps first using a circuit layout program to define the circuit board max area you can get away with using - and that may depend on how tall your case is going to be, you could even bridge that buffer board across the L/R channel opamp (or maybe a bit extreme but possibly even across (overtop) a pair of AD843 on a browndog in a Pimeta, but that far from the power rails you might want some supply decoupling caps on the board and pre-amped it might be wise to build into a metal enclosure for more noise immunity though a Pimeta isn't very well ground planed to begin with so maybe that's overkill. But overkill is what it's all about?
Anyway, it's do-able, but on the other hand if you want to build one of Tangent's amp designs and want an upgraded buffer, the PPA2 is what you're looking for, but if it's more elaborate then you wanted you don't "have" to build it up that much, it could be populated more like a Pimeta and whatever extent you want it PPA2-like as the addt'l bonus. It's really up to you.
Funnily enough, I spent an hour or two listening to the AD843 and OPA637 side by side yesterday.
I've got to say, I think I actually prefer the AD843 from what I've heard so far. The Tangentsoft site mentions the OPA637 having a slightly veiled quality. It's very tricky to describe. The OPA has lots of detail, but it seems to keep it at the back of the overall sound, things don't jump out so much.
I was also listening to the AD8610, which probably came lowest out of the three.
The AD843 is snappier, clearer and more upfront.
Presently, I think there are two main kinds of audiophiles. There are guys who listen to a lot of classical and jazz who tend to prefer smoother more relaxed sounds, like you'd get from a valve amp. But if you listen to anything with a quick pace and lots of dynamics you'll probably prefer something faster.
I'm listening through HD650s. If anything, people say they're a little smooth for rock compared to Grados. Since I tend to prefer a quicker, sharper sound, I was severely tempted to get some Grados instead. But I managed to find some frequency charts for the two and discovered peaks in the Grados high end that I expect are the cause of their brighter sound. Looking at the frequency plots alone, I decided that the HDs were probably better. I didn't like the idea of having such defined spikes in the frequency response (that was exactly the reason for spending £££ on an decent pair of headphones in the first place, I was getting t'ed off with the ringing in my ears after getting them treblerised by cheap headphones), so bought the HD650s and figured that any lack of brightness I'd make up for with a quicker amp. I like the full ear cushions as well.
Got to say, the HD650s certainly aren't too smooth for me and I listen to a lot of rock and electronic music. If I was using the Grados, I think I'd probably not like the treble. I'm tempted to say that people who find the HD650s laid back perhaps have a bit of a slow system powering them.
The AD843s really bring things forward compared to the OPAs. I was listening to the guitar solo from Daft Punks Digital Love and really noticed big differences in the underlying sound of bends. For example, guitars had sharper, more defined distortion with the ripping, tearing, cutting crunch sound I like and played harmonics really shine through. The OPA was close, but definitly not better.
I tried it out with a few more tracks, like Alanis live and Goldfrapp and for both, even though the OPA was close, the AD843 gave a tiny bit more precision and life to the sound.
With more treble on the Grados I was looking at, theres a slight possibility the AD843s might be too bright, particularly if you like a more mellowed out sound. But it's splitting hairs. And there is a big price difference. In fact, I seriously doubt I'd pay that much for a pair over the ADs.
If you find the AD843s too quick, you could always try offsetting it by mellowing out some other components.
I'm kind of curious about what's going on with the AD843, it seems to be missing from ADs product table, but it's page is still up. I've emailed them to see what's happening.
I'm going to try out some others but am using the cmoy layout from TS at the moment, so may also have a go at the buffered design. Has anyone tried both? Is it worth the extra effort? Since I'm using HDs, which have 300 ohms of impedance, I'm guessing a buffer won't make such a big difference as it might for low impedance phones.
Given the simplicity of the cmoy, I think I might go crazy and use some AN tantalum resistors or something similar...
Try this one http://www.sjostromaudio.com/_unsql/hifi/qrv05/ sounds MUCH BETTER than Buf634...
I'd like to try the Sjostrom buffer, but this is where my knowledge gets very deficient. How would I connect it to the Tangent Pimeta board? It appears to require 15v of current, x2 for stereo, so does that mean it needs 30v of power *in addition* to the 24v the Pimeta would run on? And would a 634P be sufficient for the ground channel, or would I need three of these suckers?
I'm guessing it's just way over my head (for now). I can solder and have basic understanding of how audio circuits and components work together, but I dunno...
I'm guessing it's just way over my head (for now). I can solder and have basic understanding of how audio circuits and components work together, but I dunno...
The QRV5 can run from +- 6 to 24 V DC with chosen transistors.
Just like Pimeta.
Just leave out BUF634 and connect the QRV5 to in and out,and connect the + and - supply.You can use the Buf634 in the powersupply.
Just like Pimeta.
Just leave out BUF634 and connect the QRV5 to in and out,and connect the + and - supply.You can use the Buf634 in the powersupply.
An externally hosted image should be here but it was not working when we last tested it.
http://www.diamondstar.de/dDB_overview.html
This discrete diamond buffer implementation was designed for the Millett tube hybrid. It works in a PIMETA, too. There was a post about this at head-fi.org, and there have been group buys of the PCB at headwize.com (and possibly head-fi.org).
This discrete diamond buffer implementation was designed for the Millett tube hybrid. It works in a PIMETA, too. There was a post about this at head-fi.org, and there have been group buys of the PCB at headwize.com (and possibly head-fi.org).
Yes,it works too,if you can find Pcb´s.I found 2 at head-fi.org
will try them later.
There will probably be a GB of these in march.At least thats what the counstructor said.
http://headwize.com/ubb/showpage.php?fnum=3&tid=6711&fpage=9999&action=subscribe
will try them later.
There will probably be a GB of these in march.At least thats what the counstructor said.
http://headwize.com/ubb/showpage.php?fnum=3&tid=6711&fpage=9999&action=subscribe
I've decided to try the QRV5. With a little research I see it's not beyond me at all, really.
The only problem is finding the transistors:
BC860C "PNP 45V 500mA 0,25W 150MHz Hfe 160-400"
BC850C "NPN 45V 100mA 0,25W 300MHz Hfe 420-800"
Those exact model numbers are listed as "obsolete" on Mouser. And I can't seem to find another model that matches those specs exactly, for either. Anyone know of a probable source for these?
Surprisingly all the parts for two QRV5s costs about the same as four BUF634Ps...
The only problem is finding the transistors:
BC860C "PNP 45V 500mA 0,25W 150MHz Hfe 160-400"
BC850C "NPN 45V 100mA 0,25W 300MHz Hfe 420-800"
Those exact model numbers are listed as "obsolete" on Mouser. And I can't seem to find another model that matches those specs exactly, for either. Anyone know of a probable source for these?
Surprisingly all the parts for two QRV5s costs about the same as four BUF634Ps...
Care to explain this?
While you´re at it,what does the ground channel do?
I mean theres allready a railsplitter..
http://tangentsoft.net/audio/pimeta/misc/schematic1.pdf
Ryssen said:
L or R is a potential difference to virtual ground voltage level. Just as either channel has to generate that voltage precisely, the ground has to, as precisely, maintain the difference.
The railsplitter is to tie the mid-point supply reference to signal ground, but then the buffer to isolate it by dumping the output current back to the rails instead of the reference from the railsplitter. For each L or R channel *action*, the ground buffer channel has to react to maintain the drive voltage through the load.
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