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PostPosted: Thu Nov 29, 2007 6:57 am 
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Hi Carlos,

"class D amps are very speaker dependent and frequency response changes according to the impedance of the speakers it is driving"

Yeah, there are a lot of bad class d amps and many of their failings are found to be euphonic.

That could be what Jocko meant, though I'm not sure if that one in particular is responsible for the sense of greater width. Either way in relation to UCD it doesn't apply at all. It does have a flat and load invarient frequency response, as we all know. Yet the same statement of "wider soundstage" might apply to it too if noise prone electrolytics are used. It seems to be a very rare electrolytic cap that is so well damped mechanically that it isn't prone to this form of noise I describe.

So that's why I make it a point to say, the new Hypex caps are not guilty of this crime and as a result the natural ambience comes through untainted for a change. If anything it sounds a lot more like a well behaved non switching amp than ever before. Some people appreciate a euphonic mess though, and it's only to them that UCD HG's would disappoint.

Come to think of it now, most of those bad class d amps you described arent' even linear across the audioband when driving a resistive load. That might make the soundstage seem wider as it's lost height. Maybe that's what he meant by frequency response, but it doesn't apply here.

BTW my EQ is actually a DSP, and I can mimick even more characteristics of bad components with that if I wanted. I never said it was desirable, but it can be interesting to see what it takes to make it sound just as bad, and even nicer to turn off that processing after. I can't imagine why you'd want to be stuck with that all the time.

PS:

The treble is accurate and convincing, the pitch is very good. I find the amp most capable, but the audiodock needs something.... like a garbage bin. Not to mention the high's in most recordings suck pretty bad. I listened to a few jazz recordings from Telarc in flac format the other week and was blown away by how convincing it was, despite the rest of my system. It's not my type of music but it sure was an experience.


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PostPosted: Fri Nov 30, 2007 11:37 am 
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carlosfm wrote:
Chris, I think Jocko mentioned frequency response because class D amps are very speaker dependent and frequency response changes according to the impedance of the speakers it is driving.


CarlosFM[Frequency Modulation, just kidding dont get upset]

The Class-D amps which implement POST-FILTER FEEDBACK SCHEME donot suffer from Load Dependant Frequency Response..........for example UCD is a post filter feedback amp whose frequency response remains constant with all recommended loads......

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PostPosted: Fri Nov 30, 2007 2:09 pm 
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Kanwar wrote:
CarlosFM[Frequency Modulation]


That's a natural association indeed.
Gotta check what frequency am I tuning today. The pilot tone is wistling in my ears.

Kanwar wrote:
The Class-D amps which implement POST-FILTER FEEDBACK SCHEME donot suffer from Load Dependant Frequency Response..........for example UCD is a post filter feedback amp whose frequency response remains constant with all recommended loads......


Yes, that's it.

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PostPosted: Sat Dec 01, 2007 6:46 pm 
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carlosfm wrote:
Kanwar wrote:
CarlosFM[Frequency Modulation]


That's a natural association indeed.
Gotta check what frequency am I tuning today. The pilot tone is wistling in my ears.

Kanwar wrote:
The Class-D amps which implement POST-FILTER FEEDBACK SCHEME donot suffer from Load Dependant Frequency Response..........for example UCD is a post filter feedback amp whose frequency response remains constant with all recommended loads......


Yes, that's it.



It is for UCD at least, not all feedback loops are created equally, so I dont' think it applies universally, some folks make a mess of it.

That particular effect seems to be one of strong euphony though, it's disgusting but I'm not sure if you could really say it is responsible for a sense of "greater width". Either way I lump such things together as undesirables.

I think there at least a few other amps out there that hit the mark of faithful reproduction aside from Hypex but they aren't DIY oriented or affordable, and as such I will likely never hear them.

Cheers


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PostPosted: Thu Dec 06, 2007 8:54 pm 
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Hi,

For those who wish to stuff their emptry CRD pads for a little extra performance, and are too frightened to re arrange their modules as I have previously recommended in order to get the tweak done for free, or aren't capable of finding an alternative current source..

I have found a direct source for the SST511 CRD via Linear Systems, and they are willing to sell them in small volumes at a cost of 4.75 USD each.

You may contact Eli at emanis@sympatico.ca for them.

Please don't go wasting his time by asking him if he thinks the amp will sound better with them... this is manufacturer direct and he's there for taking your order only.

Cheers


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PostPosted: Thu Dec 06, 2007 11:00 pm 
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TragicallyDistorted wrote:
For those who wish to stuff their emptry CRD pads for a little extra performance, and are too frightened to re arrange their modules as I have previously recommended in order to get the tweak done for free, or aren't capable of finding an alternative current source..

I have found a direct source for the SST511 CRD...


You would have a much easier task with a J511 or 1N5314, instead of using a 3-pin SMD device (where you have to short two pins).

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PostPosted: Thu Dec 06, 2007 11:24 pm 
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carlosfm wrote:
TragicallyDistorted wrote:
For those who wish to stuff their emptry CRD pads for a little extra performance, and are too frightened to re arrange their modules as I have previously recommended in order to get the tweak done for free, or aren't capable of finding an alternative current source..

I have found a direct source for the SST511 CRD...


You would have a much easier task with a J511 or 1N5314, instead of using a 3-pin SMD device (where you have to short two pins).


Not really. The modules already have the footprints for the SST511, waiting to be stuffed. So it is the cleanest way of getting the job done, but it's not like there aren't options for the more adventurous of course.

Throwing the part onto the pads is likely to be easiest for most people, and the third pin will help some of them get it properly oriented (not everyone can read a datasheet or knows up from down). So for the simplicity of it, the cost of the SST511 may prove worthwhile to some.

I have used the SST511 deadbug style but only because I already had them and wanted to put them to use. I can't say I recommend doing that but it is a good way to kill a day and frustrate yourself.


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PostPosted: Tue Dec 11, 2007 11:20 pm 
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Just to confirm the efficiency of adding CRD on the right pads to overpolarize the LM4562 to the positive rail. On my UcD 400 HG HR amp built in dual mono, I choose to put off the BDX 33-34 (preregulator) and feed the HxR directly from the auxillary output to HG mono Hypex ps (as was adviced by Hypex for the AD). I just changed the 7812 7912 regulators on board for7818 7918 as one needs 15,5v at HxR entry. Therefore, I could move the sst511 T40-T41 to T29 T26 and the desoldered 22µ cap were used to filter the entry of the supply line from HG mono. The results are extremely good : the sound is cleaner and more musical while retaining dynamics. Basically these amps are very good, but after that mod, the sound is as fluid as the best tubes while being much more precise and punchy. It is really worth trying. You need a thin soldering iron, thin solder, some desoldering braid, a lightened magnifying glass and a little of calm. I have been interested into HIFI for at least 40 yearsr and it is equal to the best sounding amps I ever listened to. DC coupling the UcD 400 HG HR improves image, but the magnitude of the change is less than working on LM4562. I begun with this easy mod.
One could desolder the HxR from the amp board to put them on the HG mono board after getting off the 78-7912 regulators. Therefore, they can power directly the LM4562. Desoldering these 5 pins regulators is not easy and there is not enough space to cut their wires properly. Should this have been possible, I would have done this way and could have the CRDs and 22 µ caps left unused. Both solutions separate the supply of the op amp and the power amp.
Without Chris advices, these mods would not have been possible. My next move would be to modify my first UCD400 AD amp exchanging the AD8620 for a biased LM 4562 (the AD is biased to the negative rail, one has to change the 2 CDR from the pads.
My system consist in a Passlabs x2,5 preamp, CEC XL51XR and Lavry DAC DA10 for CD, Tannoy GRF. The tuner is Luxman T530 and for black disks Thorens TD126 DL103 Aqvox.
BTW with the GRF, even before mods, I would not say that these amps lack bass. Bass are present, very fast and natural, varying with the source. They remain after the mods (of course).
Sorry for the bad English being French (near Brest).
Philippe


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PostPosted: Wed Dec 12, 2007 10:21 am 
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TragicallyDistorted wrote:
Hi,

For those who wish to stuff their emptry CRD pads for a little extra performance, and are too frightened to re arrange their modules as I have previously recommended in order to get the tweak done for free, or aren't capable of finding an alternative current source..

I have found a direct source for the SST511 CRD via Linear Systems, and they are willing to sell them in small volumes at a cost of 4.75 USD each.

You may contact Eli at emanis@sympatico.ca for them.

Please don't go wasting his time by asking him if he thinks the amp will sound better with them... this is manufacturer direct and he's there for taking your order only.

Cheers


Chris,
Many thanks for sharing one possible source for SST511s :) Although I saw it a day too late. I found some old stock (Vishay) on the Farnell Newark site which also happens to stock Rubycon ZA/ZL series in copious quantities. Managed to get 10 pieces of SST511 for US$19 including local taxes. Will be popping them in soon for the Class-A Bias tweak on my 400HG/HxR based monoblocks ;)

Btw, do you know what make are the audiophile grade Hypex decoupling caps and the reason for a drop in the value? I recall Jan-Peter commenting somewhere that they are 220uF/100V - it seems like the cap value has been dropped from 470uF in the AD version where some tweakers had reported better results with a 680uF Panasonic FC.

P.S. This happens to be my first post here. I have followed your experiences with UcD modules since your DIYAudio days. Have enjoyed reading and appreciated your insights and deep knowledge in the UcD modules.


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PostPosted: Thu Dec 13, 2007 3:56 am 
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Philippe, thanks for sharing :good:

I'll show my method for doing the aux supply in the comming months, and discuss the results here as well.

It's actually hard to say which has the most effect though, in the end they all work together. If you did the CRD first and the DC coupling later you'd be likely to think the complete opposite of what made the most difference. I tend to think the biasing has greater benefit than it ever did before, because everything else is already so clean. It just cleans up a little haze, better defining every little detail, improves focus and depth. Worthwhile if you like that sort of thing.

Jack:

Very unusual, you must have gotten the last few. People have been looking for those for some time and they have been unavailable. Newark in Canada has some but like others, you can only buy a minimum quantity of 1000. I just checked Farnell and it's the same story, out of stock. Lucky you!.... we're not going to suddenly find 990 of them available on Ebay, are we?

"Btw, do you know what make are the audiophile grade Hypex decoupling caps "

No idea whatsoever.

"and the reason for a drop in the value? I recall Jan-Peter commenting somewhere that they are 220uF/100V - it seems like the cap value has been dropped from 470uF in the AD version where some tweakers had reported better results with a 680uF Panasonic FC."

They are 220uF 100Vdc. As Jan Peter said in that same post you mention, they were chosen for their superior sound quality, and of course excellent specifications. As you noticed the value is reduced, but they deliver far more. There are other factors in consideration than the mere capacitance alone. If you think increasing the value of it is a good idea, think again. You will only skew the synergy of things, and it wont' be good. They are sized within the constraints of the module. With this good a cap, it hurts performance none at all, but I think it just stresses the already important requirement for good wiring in class d.

Rest assured, I have experimented extensively with those electrolytics and you already have some of the very best out there. There is no tweaking required at all, and non desirable beyond what was discussed here. It is just that optimal already, which was the whole point to the new version. Be like a good artist and know when to call your painting finished.

Best Regards,
Chris


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PostPosted: Sun Dec 16, 2007 2:57 pm 
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Hey Chris!

Thanks for your comments about the decoupling cap. Coming from you, I'll take it at face value ;) - not that I was planning to change them anytime soon - was just wondering about the reduced value vis-à-vis the previous attempts to improve the sound quality on the AD version.

I checked back with Farnell folks about the availability of SST511s and indeed it's completely gone. I just can't believe my luck that I managed to get the last 10 pieces off them - normally I'm never so lucky :grin:

They don't know when more stocks or replacement stocks will be in, but I've put in a request to be notified by e-mail if fresh stocks come in. I'll report back here if I hear anything.

Spare time in the next few weeks (kinda hard with all the partying thrown in ;) ) will be spent on the Class A mods and some PSU improvements especially the 12V supply to LM4562.

Thanks again and Happy Holidays!


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PostPosted: Fri Jan 04, 2008 9:47 pm 
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I used the Christmas break to modify my 400 AD amp. It was already DC coupled and the op amp powered by the Hypex ps. Now, I put two good quality caps (BC036 47 µF) on both + and - just at the entrance of the external wire coming from the Hypex ps. It did some good. Then, I exchanged the AD8620 for the LM4562, moving the sst511 on the positive rail (they were on negative side for AD). The work is a bit difficult, but with a thin iron soldering and solder, it can be done if you have some experience on smd components. The result is really worth trying: the treeble and high mid are richer, less aggressive, much more natural without any loss in definition. Despite this mod, the 400 exAD (400LM?) is still not so good than the 400 HG with the previously described mods. However, its quality-price ratio is probably higher. One last interesting mod could be to get rid of the 78-79xx reg in the ps supply and use super regs. But this mod would cost about 100 $. As it is my first class D amp proto, and the 400 HG is so fine, I will not go further with the 400exAD and I am going to sell it. But I want to share this experience. If you have UcD 400 AD amp, consider DC coupling, external powering of the op amp and exchanging AD8620 for LM 4562 without forgetting of exchanging rail for CRD. In addition, the LM is not expensive, DC coupling is free, and, if you have Hypex ps, external powering is free and afetr all that you have another amp.
Thanks to all the contributors on various forums including of course Chris. I am now able to have a better appreciation of the fantastic work Bruno Petzeys have done on the modulator.
Season’s greetings to all from Brittany.
Philippe


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PostPosted: Sat Jan 05, 2008 10:57 am 
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Hi Philippe et al,

The reason for the extra caps on the HG in your case was because of how you chose to power it via the auxiliary supply. I thought it a good idea to have some local bypass /storage cap pre HXR regulator even though it has some small amount on board the HXR, it isn't likely to be very much, and then it just helps you get away with practical wiring issues, like zero length. As you discovered the pre HXR regulator caps do not bypass the HXR's but the zener in their onboard pre regulator and they will not serve dual function, so you're left with the choice of relocating the HXR to the HG supply and relying on a very well wired sense outputs to correct for any error, or leaving them on board the HG modules and adding a small external bypass electrolytic of good quality, if your wires are more than a few inches long for instance.

I have yet to try that personally though, but your ears liked it.

On the AD the situation is a little bit different since there you don't have any HXR to feed, and all the regulation is on the HG supply since you made use of the aux supply on it. You're feeding the local bypass cap for the input stage directly with it, and adding two more close to the input stage will only parallel them in a likely very inelegant way.

So the difference you hear from that will be from a number of areas, ~halving the total capacitance down to ~10uF from 22uF, with some loop area inductance in between forming a no doubt ugly filter of some sort, the mix of characteristics between the two types of caps, likely with the stock cap prevailing as it's closest, and perhaps a bit of a mess in the complex impedances.

Try to stick with a single quality cap in this case.

Unless of course I misunderstood what you did and you simply replaced the caps that were there with the BC036, which would be my recommendation (or some other high quality cap if you have a favorite and find it a good mix, but _this is where the nightmare begins_).

The modded AD will never sound as good as the HG, the differences are too many and some just too drastic. I will get closer than most will have the chance to though as my modded AD's contain the Hypex caps already and it is one of the big factors I think. I will also be using HXR's with them, the sand is already the same where it counts, and I will not bother with other passives for awhile, like the resistors in the feedback and gain setting resistors of the input stage will stay stock, for now.

I suspect whatever difference between them that's heard will, in my case, be easily ruled by implementation, things like completely different PSU's for instance will likely set the pace.

If I were to mount one of each, HG and modified AD, side by side on the test jig and powered them from the same supply, I'd expect them to be voiced almost identically, or too close to really tell between speaker variation and placement and such. The real difference between those wouldn't be perceived on the test jib because it will amount to their ability to reproduce the stereo image over anything else like voicing, where the HG's higher quality parts should give it a slight edge.

My view though is that for anyone with plans to get HG quality out of an AD, you can forget it, without the Hypex caps you'll never even get close, they are that big a factor, and for the time, effort, and money it would cost (especially if you're the type to reach for black gates or other jewelry) save up and get the HG's and be done with it. Unless it's just being done for the experience, go for it, but don't beat it to do thinking you'll ever reach the HG's level of sonic excellence.

As for myself, I have been concentrating my efforts recently on the bottleneck of my system, the audiodock. I've managed to uncover the big bottleneck in it and with the parts that were already on hand, two full days and nights of trial and error and listening, aaand a very sudden and unexpected arrival of some PPS sample caps that were requested over six months ago, and completely forgotten about, (Merry Xmas Wima) I have blown the door right off the thing.

It's not 100%, probably 85% up from 40 though. I am veeeeeeery happy! The sound is extremely coherent and together. Focus doesn't come through well on my particular speakers but it's there stronger than ever by far. The slightest nuances in the details can be heard, people in live crowds talking and yelling all around you, and when they whistle it sounds like it's from in the room somewhere and not some faint whisp off in the distance.. freaky.

The last little bit of vibrato can also be clearly heard as they just run out of breath, all things that were just lost before.

The very best part though is something that's burnt my side since day uno. Coherency in the high's were non existant. In the early days it was partly due to the poor onboard regulation of the AD modules (Hypex told ya to use AUX supplies for a reason. the 180's by memory seemed to manage better though), biasing the zener helped that a great deal but it was still not fully together and I knew the audiodock was to blame from partial improvements to it over time. So I've finally got that aspect of it fixed and the high's are incredible, nice flat response, great position, awesome extension/decay/air, couple that with a set of BC036 caps on the outputs and the air will be enough to blow you right away.

I find there's some haze though due to the characteristics of some of the components I used, and I think now with another handful of new and different components and values, coupled with what I've learned in recent weeks, I can blow the door off it completely, maybe, but if this is as good as it gets for the hardware I'm stuck with I will be most content.

Imaging is holographic like I've never heard, and it has the ability to mess with your mind in the way things get projected around, the depth to it is seemingly limitless, and coupled with the ability of the HG modules it's a real dream system at this point, finally.

So the goal now will be to clean it up just a little bit more and render it completely and utterly terrifying with how convincing it is.

Oh and (yaaawn) the HG modules are still stock aside from DC coupling and additional biasing.
I "may" revisite one or two little things on them once the audiodock is finished though... since the source has changed so drastically it seems reasonable to revisite things. With the HG's being such a solide reference I've been revisiting many things in the audiodock and with excellent results, often entirely different from before, they speak the truth, and have allowed me to make great headway when before I was swimming upstream.

BTW I scored a new toy as well, two complete P6201 probe kits for my scope. Not exactly the twins I was saving up for but hey, the deal was too good to pass up and it seems they both work. :yahoo: Next is a 7L13 plugin, or a signal gen. Seems like it's a good idea to wheel and deal on ebay over the holidays, when people are thoroughly sauced.

I guess I'll include a few pictures to show how I plan on spending some of my time these next few months.

If you should see some green electrical tape used on my amps, well, it is a test jig, 3X + recycled connectors and I'm running out of interconnect :beee:


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PostPosted: Sat Jan 05, 2008 11:01 am 
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The old jig with the new modules


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PostPosted: Sat Jan 05, 2008 11:07 am 
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Old jig again


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