xerxes
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Post by xerxes on Dec 13, 2006 11:36:13 GMT
In a recent comparison of my little Pimeta amp to my WNA MKII, I prefered the Pimeta; it seems to have a bit more bite and pazzaz. I listen to headphones a fair amount and I think I'd like to get an amp a step up from the WNA and Pimeta. The only real criteria are that it must sound very good, work well with Sennheiser HD650s and cost no more than £500.00 ~ $1000.00 USD. I had a look around Head-fi, but to be honest it wasn't much help, someone will claim an amp is the best thing since sliced bread, someone else will say it's rubbish and generally the whole thread deteriorates into a mud slinging match, and in the end you're none the wiser. Given a budget of £500.00, what would you buy and why?
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Post by PinkFloyd on Dec 13, 2006 14:18:38 GMT
In a recent comparison of my little Pimeta amp to my WNA MKII, I prefered the Pimeta; it seems to have a bit more bite and pazzaz. I listen to headphones a fair amount and I think I'd like to get an amp a step up from the WNA and Pimeta. The only real criteria are that it must sound very good, work well with Sennheiser HD650s and cost no more than £500.00 ~ $1000.00 USD. I had a look around Head-fi, but to be honest it wasn't much help, someone will claim an amp is the best thing since sliced bread, someone else will say it's rubbish and generally the whole thread deteriorates into a mud slinging match, and in the end you're none the wiser. Given a budget of £500.00, what would you buy and why? First question would be..... what do you feel is lacking in the WNA MKll / Pimeta and would it be improved if you threw £500 at another amp? No point in just spending £500 on an amp and calling it a "step up" unless you know what it is you're stepping up to. Is it more bass you want? better seperation? more musicality? or just and amp that looks like £500? Before you get rid of the WNA MKll... what PSU are you using with it? If the switch mode crap wart that comes with it then you're missing out on a helluva lot of performance there, and I mean a helluva lot, what opamps amps are you running under the bonnet? If LM6171 then you're also missing out on a helluva lot of musicality, they're clinical and analytical sounding to the point of being boring..... nothing like how music should be presented. If you're running LM6171 then that means you're also using output caps directly in the signal path, again.... you're missing out on one helluva lot of music with these things in situ. For a few quid you could replace the LM6171 with AD-843, remove the output caps (jumper across the pads) feed it with a proper regulated PSU.... you have just jumped up from an OK amp to an absolutely mind blowing amp and saved yourself that £500. I spent ages with the MKll and, believe me, it can sound anyway you want it to xerxes
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xerxes
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Post by xerxes on Dec 13, 2006 14:55:51 GMT
Hi Mike,
In comparison to the Pimeta, the WNA sounds very slightly soft and wooly, the Pimeta is a bit snappier. It's not a night and day difference, but there is a difference.
I'm not dead set on spending £500.00 just for the hell of it, I just wondered what others thought and what I could get within this budget.
The WNA is absolutely stock, with the LM6171s, as Built by WNA, and yes I have the standard PSU, although, if you remember, I also built a battery PSU for it. The battery PSU is an improvement over the little mains PSU, but it's not huge, and not as big a difference as going from the WNA to the Pimeta.
Your suggestion of changing the OP-Amps and removing the output caps sounds interesting, is that all I need to do? The output caps are the big blue Evox Rifa Polyproylene caps, correct?
What difference should I expect in sound terms by removing the caps and replacing the LM6171 with the AD843?
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Post by PinkFloyd on Dec 13, 2006 15:21:27 GMT
Your suggestion of changing the OP-Amps and removing the output caps sounds interesting, is that all I need to do? The output caps are the big blue Evox Rifa Polyproylene caps, correct? No, incorrect. The big blue caps are the 4u7 input caps, if you run AD-843 then you can safely dispense with these as well as the output caps which, if stock, will be the 470uF yellow Nitai caps. Both the input and output caps strangle the sound but are necessary with the LM6171 due to the massive DC on the output. The AD-843 have extremely low DC as they're FET chips (+/- 1mV typically) so can be used without these horrible in / out caps in the signal path. Send me a pic of your MKll and I'll confirm what you need to change. Night and day improvement. More musicality, a warmer more fluid presentation.... basically more of the music and less of the pastuerised, politically correct, analytical, emotionless, lacking in soul sound of the LM6171. Hopefully Whitey has socketed the LM6171 so rolling will be easy. Do you have the lamps fitted inside too? if so whip them out and replace with zero ohm links or axial ferrite inductors.... they also go toward dampening the potential of this great amp. No wonder you want to change it if you're using that rank switch mode PSU that comes with it....... URGH! Throw that right in the bin and get yourself a half decent 24V regulated supply, my calex is up for grabs if you're interested (24V linear regulated) housed in a funky neon blue see through enclosure ;D Seriously Owen, a lot you can do to improve the MKll for very little expenditure, it's a case of subtracting parts rather than adding them here The bullet proof in / out caps are not required with a FET opamp and the lamps are not required period. I'd tend to go AD-843 throughout (one in all IC positions including rail splitter) though you can use a slower chip like the OPA134 in the splitter if you want an even warmer sound. Much you can do with this amp to greatly improve the sonics.
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xerxes
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Post by xerxes on Dec 13, 2006 16:26:28 GMT
Here we are: You can see a really big picture here: www.tdsf.co.uk/Xfeed/WNA02.jpgI bought the MKII only about 5 or 6 months before WNA shut up shop, so it would have been one of the last. It doesn't have the lamps, it has ferrite beads instead. In any case what do you reckon?
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Post by PinkFloyd on Dec 13, 2006 20:33:32 GMT
Here we are: You can see a really big picture here: www.tdsf.co.uk/Xfeed/WNA02.jpgI bought the MKII only about 5 or 6 months before WNA shut up shop, so it would have been one of the last. It doesn't have the lamps, it has ferrite beads instead. In any case what do you reckon? Yep, no problems. Remove the LM6171 and replace with AD-843 (you may also want to try OPA 627) Once you have AD-843 in place it's safe to dispense with both the input caps and the output caps. The input caps are the, as suspected, PHE426 4.7uF Blue ones and the output caps are the, as suspected, yellow 470uF Nitai ones. Jumper across input cap pads with a zero ohm link. Do the same with the output cap pads... see photo: I have jumpered across J1 (input cap position) on the underside of the board which is why you don't see the links in the photo. I used AD8065 which I soldered onto a browndog converter in the above photos (another opamp you may want to try) There are lots of tweaks you can try with the MKll and all of them most effective over the stock belts and braces design. Some here: www.rock-grotto.co.uk/wna-MKll-tweaks.htmYou can even try bypassing: Zobel Network: Loads for you to try Owen If using AD-843 it's a good idea to have a read of the AD-843 data sheet www.analog.com/UploadedFiles/Data_Sheets/AD843.pdfI fitted a 2u2 polyester between pins 4 to ground and pin 7 to ground on my MKlll.... not a big difference doing this (if any) but something you can do if you want. If you can't be arsed with it Owen then by far the cheapest and easiest tweak to your existing LM6171 setup is to add a feedback distributor. This simply involves fitting a 330K resistor across pins 2 and 6 of the LM6171... improves the musicality of the bass and adds a touch of welcome warmth and smoothness to the sound whilst retaining all the good aspects of the LM6171 sound. I prefer to solder them directly onto the pins as shown here... one I made earlier Dr White explains the Feedback Distributor: Adding the 330k resistor reduces the gain of the LM6171 from open loop to 330. This increases the bandwidth of the LM6171 gain block so that the global negative feedback loop is effective out to higher frequencies. The high frequency distortion is thereby reduced. This is a standard nested feedback arrangement which I have been using in my mos125 power amplifiers for years. In the latter case there are three rather than two nested feedback loops. I suspect that the reduction in transient intermodulation distortion resulting from this arrangement is more important than the reduction in high frequency harmonic distortion. I was interested to hear that it seems to be generally agreed this improves the bass definition as well as leading to a smoother overall presentation.That should all give you a bit of food for thought Owen, enough to get started with anyway
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xerxes
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Post by xerxes on Dec 13, 2006 22:06:01 GMT
Hi Mike,
A couple of questions:
Am I right in thinking I can just plug in these alternatives, AD843 or OPA627, without any other changes. My power supply is 24v isn't that too much?
You suggest replacing all three LM6171s with AD843s, does that go for the OPA627s as well?
I'm a little worried when you describe the AD843 as warmer. As I said, I find the the WNA a little to soft and wooly. So if that's warm as in more guts, more grunt, richer texture that's a good thing. If it's warmer as in mellow, soft, dull, that's a bad thing. ;D
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Post by PinkFloyd on Dec 13, 2006 22:53:10 GMT
Hi Mike, A couple of questions: Am I right in thinking I can just plug in these alternatives, AD843 or OPA627, without any other changes. My power supply is 24v isn't that too much? You suggest replacing all three LM6171s with AD843s, does that go for the OPA627s as well? I'm a little worried when you describe the AD843 as warmer. As I said, I find the the WNA a little to soft and wooly. So if that's warm as in more guts, more grunt, richer texture that's a good thing. If it's warmer as in mellow, soft, dull, that's a bad thing. ;D Warmer as in more grunt, richer texture and guts. Remember that 24V gets split into 12V per channel by the rail splitter. AD-843 and OPA627 are fine with 12V. You can mix and match with a different opamp in the splitter to the opamps in the amp. ie: opa627 in the splitter, 2 x AD-843 in the amp.... or AD-843 in all positions, opa-627 in all positions.... it all depends which ones you think sound best. Generally, the faster the opamp in the splitter the better but, as I say, a slower opamp in this position can add a bit of wooly warmth to the sound. Whatever you do, don't use the LM6171 anywhere if you dispense with the in / out caps.... it'll oscillate like mad.
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Post by PinkFloyd on Dec 13, 2006 23:46:18 GMT
If it's grunt your after xerxes then essential you increase the quiescent current by 25%. If you're doing this it's a good idea to fit small heatsinks on the transistors as upping the quiescent current increases their core temperature from about 60 centigrade to 80 centigrade. Another very cost effective tweak which really does add some balls to the MKll. Dr. White explained why: Increasing the quiescent current means that the output stage doesn't switch from class A into class AB operation until later in the day when it is pushed very hard by low frequency, high voltage swings into low impedance headphones. This is why you hear the improvement in bass "gruntAll the tweaks I list here have been tried and tested over a period of a couple of years and all improve the sound over stock, some to a small degree others to a night and day degree. The only reason most of these never made their way into the stock kit amp was "cost". David White's idea was to supply the standard "bullet proof" kit amp and then it would be down to the end user where he wanted to take it from there. The tweaks I list were 50% mine, 50% Davids but David endorsed all of them 100%. I actually started to get a bit tired of his approach and felt he should incorporate these tweaks into the actual kit amp but "cost" came up again and again. For example he couldn't source the AD-843 in quantity and if he could they would add a lot onto the price. He could source bucketfulls of LM6171 for pennies which is why they made it into the kit amp, that and the reason they actually sounded pretty good compared to the competition at the same price. Upping the quiescent current in the stock amp would have meant supplying heatsinks in the kit... again, added "cost". As good as David was with constantly improving the design and giving lots of good free advice he still had to make a profit from it so, rest assured, there are areas of the amp that can be tweaked that bring about a vast improvement in sonics. The heatsinks you'll need are TO220 types (if you're going to up the quiescent current) I have hundreds of the things kicking about somewhere but, due to the tight placement of the BD139 / BD140 transistors it's necessary to cut them so they'll be a custom fit. You can get the clip on types which provide adequate dissipation: You know I've got the part numbers for these and the part numbers for thousands of other things too...... it's finding them that's the problem! Same with pictures, I've got hundreds of WNA photos (MKl MKll MKlll) but it's got to the stage I've lost track of where they all are and one reason I'm thinking about just throwing the computer out of the window and going back to the simple life..... the stuff that accumulates and the stuff you have to keep on top of is just insane. There should be a few WNA pics here www.rock-grotto.co.uk/audiogeddon/index.html but that's not even the tip of the iceberg. I really must buy another domain name and dedicate it solely to all the pics of amps I've taken over the years.... some of them going back as far as the 1970's...... a lot of work involved and, as I said previously, I'll either do it or just throw the computer (literally) out of the window and take up bird watching. Anyways xerxes, I'm rambling now so will shut up. That £500 amp you were talking about...... I know what I would do, I'd save £450 of that and spend the rest bringing the WNA into the land of the living This is the best advice I can give and hope it turns out to be "sound" advice. No point throwing £500 away when you don't need to. After the mad Christmas postal rush is over send me your Meier HA1 MKll, I'll get that up and running for you free of charge so don't hammer it just yet Mike. Hammer time!
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Post by PinkFloyd on Dec 14, 2006 0:07:19 GMT
Just looked at the pics of your WNA MKll xerxes, I'm being pedantic now but I'd (If it were mine) lose those cruddy latching sockets immediately and hard wire the input / outputs directly to the board. They make it easier to take the old girl apart, for sure, but if you're happy with the tweaks then lose them and bolt the hatch down for good... they are another weak point in the signal path and far from good quality latching connectors either. David waffles on about the benefits of gold plated headphone sockets in the manual (another thing I disagree with strongly) yet he then proceeds to fit these shitty tin plated latching sockets all over the board...... nope, lose them and hardwire directly to the pads.
Mike.
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xerxes
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Post by xerxes on Dec 14, 2006 6:54:54 GMT
OK Mike, I've ordered the parts, although £50.00 was a bit optimistic, try doubling that, and that's without going anywhere near an improved power supply. I don't have a circuit diagram or any documentation with the WNA amp, so I might need a bit of help identifying some of the components C4, R5 etc. as the labels on the PCB are covered by the existing components. Do you have a picture of the bare board somewhere? Fingers crossed, this will give me the lift I'm looking for. I know it's not a guaranteed indicator of performance, but given the price difference the WNA really ought to out perform the Pimeta.
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Post by PinkFloyd on Dec 14, 2006 20:11:28 GMT
OK Mike, I've ordered the parts, although £50.00 was a bit optimistic, try doubling that, and that's without going anywhere near an improved power supply. eh? a hundred quid? what the heck have you been buying, gold plated resistors? Somewhere online but don't know where, scanner is broken so I will take some photos of the manual and e-mail them to you xerxes. You'll notice an improvement. Right, off to find that manual.
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xerxes
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Post by xerxes on Dec 14, 2006 21:14:53 GMT
3 x OPA627 comes to ~ £48.00, the AD843s were an "extended range" item at RS, so 3 of them came to ~ £21.00 + £10.00 postage, then there was all the other bits and bobs, for the zobel network, heatsinks etc. You have to remember that I'm fairly new to this game, so I haven't built up a huge stack of odds and ends over many years which will contain a fair chunk of the parts I will need for any DIY job. In any case, whichever op amps I don't use in the WNA I can try in the Pimeta.
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Post by PinkFloyd on Dec 14, 2006 21:50:31 GMT
3 x OPA627 comes to ~ £48.00, the AD843s were an "extended range" item at RS, so 3 of them came to ~ £21.00 + £10.00 postage, then there was all the other bits and bobs, for the zobel network, heatsinks etc. You have to remember that I'm fairly new to this game, so I haven't built up a huge stack of odds and ends over many years which will contain a fair chunk of the parts I will need for any DIY job. In any case, whichever op amps I don't use in the WNA I can try in the Pimeta. Oh xerxes I wish you had let me know before you'd ordered ;D
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Post by PinkFloyd on Dec 15, 2006 14:11:41 GMT
In the process of repairing my scanner xerxes, those diagrams won't be long in coming.
Mike.
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xerxes
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Post by xerxes on Dec 15, 2006 15:30:13 GMT
Hi Mike, I've just had another look at the board, the Zobel network is already in place. So the only thing I really need is to identify R5 and R6 in order to increase the quiescent current. Is the picture above correct?
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Post by PinkFloyd on Dec 15, 2006 16:15:14 GMT
Hi Mike, I've just had another look at the board, the Zobel network is already in place. So the only thing I really need is to identify R5 and R6 in order to increase the quiescent current. Is the picture above correct? Yes, that's R5 and R6. So what you do is replace R5 (the 120ohm) with a 160ohm resistor (or thereabouts) and replace R6 (the 75ohm) with a 100ohm resistor. This will up the quiescent current by 25% Good quality (expensive) resistors whitey has fitted there xerxes.... almost a quid a pop, Welwyn RC55Y with 15ppm temperature coef.... lovely little things like licquorice torpedos The non black ones are 0.1% 15ppm trueohm types, equally as good as the welwyns. Looks like he's fitted 100uF 25V Rubycon caps if my eyes don't deceive me? Nice caps too, going by the colour I'd hazard a guess at Rubycon ZA series?
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xerxes
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Post by xerxes on Dec 15, 2006 17:20:47 GMT
All done: Currently fitted with 3 x OPA627, very nice. The sound is definately "bigger" and more spacious, the sound is definately more "out of the head" than previously. I need to listen to some more stuff, to really get to grips with it, but initial impressions are very postive. Thanks Mike.
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Post by PinkFloyd on Dec 15, 2006 17:51:40 GMT
All done: Currently fitted with 3 x OPA627, very nice. The sound is definately "bigger" and more spacious, the sound is definately more "out of the head" than previously. I need to listen to some more stuff, to really get to grips with it, but initial impressions are very postive. Thanks Mike. Jesus, that was fast xerxes I don't think you need the sinks on the transistors in the rail splitter but, if they fit then why not I'll be very interested to hear what you think of the AD-843 compared to the OPA627. You may want to try it firstly with all AD-843 in all IC positions and then with OPA627 in IC2 and AD-843's in IC1. Give it some time to stabilise (ie: warm up) before evaluating. You're liking it a bit better than LM6171 already then?
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Post by PinkFloyd on Dec 15, 2006 17:58:08 GMT
All done: Currently fitted with 3 x OPA627, very nice. The sound is definately "bigger" and more spacious, the sound is definately more "out of the head" than previously. I need to listen to some more stuff, to really get to grips with it, but initial impressions are very postive. Thanks Mike. Jesus, that was fast xerxes I don't think you need the sinks on the transistors in the rail splitter but, if they fit then why not I'll be very interested to hear what you think of the AD-843 compared to the OPA627. You may want to try it firstly with all AD-843 in all IC positions and then with OPA627 in IC2 and AD-843's in IC1. Give it some time to stabilise (ie: warm up) before evaluating. You're liking it a bit better than LM6171 already then? If you decide you prefer AD-843 then you can fit bypass caps between pin 4 and ground and pin 7 and ground of both IC1 check out the specsheet "grounding and bypassing" section www.analog.com/UploadedFiles/Data_Sheets/AD843.pdf I didn't bother with the tantalum or ceramics on mine just fitted a smallish polyester 2u2.
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xerxes
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Post by xerxes on Dec 15, 2006 18:21:20 GMT
I got cracking as soon as the delivery turned up about 3 o'clock this afternoon. I don't have the AD843s yet, they will probably take a while as they are shipped from elsewhere according to RS.
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Post by PinkFloyd on Dec 15, 2006 18:39:44 GMT
I got cracking as soon as the delivery turned up about 3 o'clock this afternoon. I don't have the AD843s yet, they will probably take a while as they are shipped from elsewhere according to RS. 627 are nice though and hopefully give you an idea where I was going with the £500 thing? Spend £500 and you're not, necessarily guaranteed an amp that will sound half as good IMO. Next on your shopping list is a good regulated PSU... adds another 50% to the sound.
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xerxes
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Post by xerxes on Dec 15, 2006 18:52:33 GMT
I currently have the amp running from 24v lead acid battery pack, which has 5 x 1000uF caps, which Rick suggested would overcome battery powers tendency to reduce dynamics. This has a pass through for the little mains PSU that came with the amp, so I can switch between the mains PSU and battery power, so that I can run from the mains if the batteries need charging, but it also facilitates a quick A-B comparison between mains and battery power.
Battery power sounds better, but only very slightly, you really have to listen for it. That being the case, I wonder how much improvement a better mains PSU would bring, and would it be better than the battery power pack?
Yes they are, is that good?
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rickcr42
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Post by rickcr42 on Dec 15, 2006 23:05:16 GMT
likely totally dependant on how clean your AC Mains feed is more than the acutal power supply which should proivide more dynamics.
The main feaure for going to pure battery operation is to eliminate all the AC riders crap but if you have that area whipped then is actually a better way havng way more power reserves for peak events and that will not change during long seesions unlike a battery that will eventually drain down
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xerxes
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Post by xerxes on Dec 16, 2006 0:12:24 GMT
Any recommendations for a good PSU kit/board/module? Here's a couple I've considered: www.tangentsoft.net/elec/teps/ - no complete kit. welbornelabs.com/psreg.htmI'd sooner buy a kit with all the parts or a completed module. To be honest I find sourcing all the components a bit of chore, in the UK at least, it invariably means buying from several suppliers and all those delivery charges rack up and it ends up more expensive than a complete kit or assembled module.
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