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Holton NXL800 Power Amp Build


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7 hours ago, Eggmeister said:

Would you take it to someone else to have a look at it ?

I could but if the designer doesnt know whats going on then then who will?

 

 

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Im extremely pleased to communicate to you all I think the issues has now been resolved. 👍   So what's transpired from my last post was that i installed bypass caps on the power supply as su

Like this perhaps. 🙂        

Cable arrived today (cheers @Bill125812 👍  ) so I completed the remaining wiring and fired it up!   As someone who also services gear i've taken a few non-audiophile approaches to this build

On 05/10/2020 at 3:19 AM, Tubularbells said:

I could but if the designer doesnt know whats going on then then who will?

 

Sounds like a huge pain in the arse, I'm not sure I'd be as patient as you & I doubt I'd now ever consider Holton going forward.

 

The different value caps he fitted seems sloppy, surely if you had a customer with an issue you'd at least check your remediation work.

 

I'd expect this kind of hassle buying stuff overseas but seems poor form from an Aus manufacturer. Why would he not just send a new pair of modules for you to test.

 

Do you have any option to cut your losses & return for a refund?

 

 

 

 

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On 22/09/2020 at 6:19 PM, andyr said:

But not that fully balanced amplifiers sound better than 'normal' unbridged, unbalanced amplifiers.

Of course not the world isn't so black and white.

 

Not all motorbikes are faster than cars..... etc.

 

 

... but in general, the "argument", they make so getting an improvement is quite sound.   Of course, there's many other ways to skin the cat too.

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On 05/10/2020 at 3:19 AM, Tubularbells said:

I could but if the designer doesnt know whats going on then then who will?

 

 

 

If these travel restrictions weren't in place, I am fairly confident the three of us together would sought out the problem fairly quickly.

 

If you go back to RCA is it ok?

 

Edited by Melon_Head
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18 hours ago, zero1 said:

 

Sounds like a huge pain in the arse, I'm not sure I'd be as patient as you & I doubt I'd now ever consider Holton going forward.

 

Well it could be a lot worse, imagine having to ship a product back to another country.

 

I think it's important we support local businesses wherever possible.

 

 

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17 minutes ago, Melon_Head said:

 

If these travel restrictions weren't in place, I am fairly confident the three of us together would sought out the problem fairly quickly.

 

If you go back to RCA is it ok?

 

Yes quite right, if I could I would have already flown over the strait, to sort this out, I have literally thousands of these DIY amp modules installed all over the world and very happy customers, the incorrect cap installation was me with my almost 60 year old very long sighted eyes. :) We will get to the bottom of what is actually going on.

Thanks to Doug for being an absolute gentleman. :)

Edited by Aussieamps
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If you short the two polarities of the XLR connector to the ground pin with say 100 Ohm resistors does the bias and dc offset change at all compared without the resistors installed?

 

 

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4 hours ago, Melon_Head said:

I think it's important we support local businesses wherever possible.

100% ☝️

 

We also need local businesses to support local suppliers

 

I look forward to reading about how these DIY amps sound, once you have ironed out the bugs!

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1 minute ago, JB82 said:

100% ☝️

 

We also need local businesses to support local suppliers

 

I look forward to reading about how these DIY amps sound, once you have ironed out the bugs!

I have never heard one, but just looking at the output stage and power supplies used, these are serious pieces of kit.

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This should have been an easy fix, all supplied parts completely replaced. Getting to be a bit of a long joke now 

Edited by Sime
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Amps on there way back to Tassie for retrofit and Anthony assures me he will put on his glasses this time 😆

 

What i'd expect (and i'll be sending a message incase Anthony doesn't read this) is for the following to occur as it is becoming quite the saga that neither of us need in our lives right now.

 

  1. Replace input filter cap with correct value
  2. Thoroughly re-test both modules for noise and distortion using balanced inputs  and not just a simple power test injecting a sine wave and measuring output voltage as I don't believe that test reveals the issue
  3. Explain to me what the 2 filter caps are attempting to achieve (across the + & - balanced inputs and across the driver stage transistors) as I don't understand the reasoning behind this approach
  4. Listen to them (preferably using piano as that instrument seems to highlight the issue more than others) to ensure 100% before returning

 

Failing that (and perhaps even better) is to send another pair of modules for me to try as although the issue was occuring in only one it is no longer labeled so can no longer identify which is causing the issue as IMO that would have been the easiest solution rather than the too and fro that is currently occuring.

 

I do not believe my system is at fault  as my speakers (Duntech Sovereigns) only drop down to 3.2 ohm and these amps are supposed to be unconditionally stable into 2 and am now on my second preamp (Modwright LS100 to a McIntosh C22 MkIV) and am using Mogami Gold XLR leads & Mogami speaker cable. That gear should be adequate enough I would hope to not send the amp into a hissy fit.

 

Finally, the reason why I have not given up (and trust me I would have long ago)  is ive heard the potential of this amp and do believe it will sound great once working 100% and do appreciate Anthony's commitment into getting the issues resolved for me.

 

 

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Yeah - I think it should be out and out replacement (and probably should have been earlier than this), especially given that they are trying to mod the design to make it work.

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Maybe I'm pre-empting this a little, but let's try and avoid a public lynching here.

 

It is likely agreed by all this could potentially have been solved easier and earlier, but Holton has a great reputation and as he mentioned, thousands of these units out in the wild with no problems. We are in unusual times and circumstances, so processes are probably not what they normally would be. I would hate to see Anthony's reputation destroyed on here over one unusual case - which to me appears he is absolutely trying to make right. Let's hold the comments about what could or should have been done, and focus on the best possible outcome for @Tubularbells going forward.

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4 hours ago, Tubularbells said:

 

  1. Explain to me what the 2 filter caps are attempting to achieve (across the + & - balanced inputs and across the driver stage transistors) as I don't understand the reasoning behind this approach

 

 

 

I haven't seen exactly where he is placing them, but it would seem from his earlier explanation. he is applying an RC filter at the input to prevent high frequency noise being fed into the amp and then amplified.

 

And across the drivers to enhance stability etc.

 

These are very normal adjustments to make and are commonly used by many manufacturers.

Edited by Melon_Head
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There seems to be a number of points of misunderstand regarding this saga.

 

The first is I am committed to find out exactly what is going on, that is something I have always done for the last 20 years for my DIY amplifier customers.

The reason I have not replaced the modules is I have not found anything wrong with them during both visits to my Lab.

This particular design is a very mature design and as mentioned has been installed into many DIY installations.

I have done tests on the said modules driving them with balanced as well as unbalanced signals to full power into 2 ohm loads with sine waves and square waves

and in one test adding a 1uf MKP x2 capacitor across the 2 ohm load and drove the amplifiers with a square wave at 1khz, 10khz and 20khz . This simulates a very reactive load and it shows a very strong indication of the stability margin of the amplifier to reactive loads. Neither of the modules failed this test.

 

I increased the common mode input filters to approximately 100khz. on these modules they are normally set to around 280khz  added a 100khz differential filter to the input as a blanket filter, not because I believed there is a problem, but as a precaution and hopefully trap any unusual signals that might be causing whatever is actually going on.  

Sadly on the last visit I misplaced one of the differential caps with a high value than what was intended and Doug did not have the required rework tools, so it was thought best to return them to me again to refit the differential filter to the input.

 

While the modules are here I will redo the tests and see if I have missed anything, 

 

I hope this helps people to understand this from my perspective. :)

 

The only other thing I can think of is to add some bypass capacitors to the underside of the PSU Two power boards.

 

The capacitors that were supplied with the power boards are a newer 4 pin type and may require bypassing? 

With my other power boards bypassing has not been needed to ensure amplifier stability.

I have some suitable capacitors that I have coming in for another project I am working on, I will be sure to send some back with the modules.

So Doug can add them to the boards, the PSU Two boards were made with the SMD land pads so DIY's could add them if they wished and experiment.:)

 

  

 

 

 

 

 

Edited by Aussieamps
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Doug did make a point, though ... that sine wave / square wave testing is one thing ... but listening to actual (complex!) music - particularly piano music - is required as well.

 

Andy

 

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1 hour ago, andyr said:

Doug did make a point, though ... that sine wave / square wave testing is one thing ... but listening to actual (complex!) music - particularly piano music - is required as well.

 

Andy

 

When the eyes, and explanations are strained with the other , a good piano recording, can be relied on  to properly test audio equipment.

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As I have discovered in my personal life this year you have to take the good with the bad. 

 

I too am on the tail end of a Holton DIY build. I have to return the amplifier to Anthony with the view to addressing the transformer amongst other issues. 

 

One of the great things about these builds is that you get to extend yourself with something that you wouldn't ordinarily do. Let's be honest, these builds serve as an opportunity for free advertising for the developer as well. 

 

But it wouldn't be a build if there weren't hiccups along the way which both parties need to acknowledge. 

 

What kind of thread do you want? Do you just want to hear about the success stories and create a feel good echo chamber or do you want to hear about difficult moments that both the builder and developer can learn from. Ultimately I think what we all want is an outcome where Doug gets to build an amplifier which is consistent with his expectations and showcases the Holton brand in an honest and positive light. 

 

 

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5 hours ago, wooferocau said:

@Tubularbells   Was / Is the issue resolved as yet ? 

 

Hi received my modules back last week from Tassie and have not had a chance to try it yet. Also received a bunch of surface mount caps from Anthony to install in the power supply to bypass the big caps. Anthony hasn't mentioned whether he has changed/tested anything else so assume he couldn't replicate the distortion im hearing in one channel. @pony-tail has kindly offered to test these on his noise & distortion meter early in the new year which may or may not reveal what I had been hearing but i'm hoping it will be all good now with the last round of mods Anthony performed when he had them the time before last.

 

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Tubularbells,  looking very good sir ! Nice work ! id have to say I've known Anthony for over 23 years and he has always stepped up when an issue has come up and is always willing to help out ! He sure works hard and knows his stuff !!

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  • 2 months later...

Im extremely pleased to communicate to you all I think the issues has now been resolved. 👍

 

So what's transpired from my last post was that i installed bypass caps on the power supply as suggested however low level distortion remained in one channel [sigh]. Ron (aka Ponytail here on the forum) kindly offered to run it through his noise and distortion meter in an effort to try and determine what's going on and alas the problematic channel instantly revealed itself to show a distortion measurement of nearly 3% @ just a few watts of power so armed with this info I passed it to Mr. Holton for further analysis to which he conceded that the best course of action was to build me a fresh pair of modules as apparently  there's a known issue with some of the dual lateral mosfets used (I'll leave it to Anthony to decide whether he wants to elaborate on this or not) however the good news was as soon as I installed the new boards everything was sounding really, really good!

 

Yeah it has drawn out way longer that I would have hoped but do appreciate Anthony for not putting me into the too hard basket who seemed committed to resolving the problem one way or another so that's good news.

 

I'll write more about the sound in the coming days weeks suffice to say my current thinking is this is in the top 3 amplifiers I ever owned so a promising start....

 

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20210216_140311.thumb.jpg.9a7d6db7c6142ca21cd4fe2f703d2515.jpg

 

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Great to hear, @Tubularbells.  :thumb:  And kudos to Ron for being able to reveal the problem.

 

@ghost4man, could a "known issue with some of the dual lateral mosfets used " be your problem, too?

 

Andy

 

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On 19/02/2021 at 10:11 PM, andyr said:

Great to hear, @Tubularbells.  :thumb:  And kudos to Ron for being able to reveal the problem.

 

@ghost4man, could a "known issue with some of the dual lateral mosfets used " be your problem, too?

 

Andy

 

Potentially Andy but the experts that have looked at mine have identified a glaring issue being the transformer which wasn't specked properly. There are other concerns as well but the transformer being changed is a start. 

 

 

 

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22 minutes ago, ghost4man said:

Potentially Andy but the experts that have looked at mine have identified a glaring issue being the transformer which wasn't specked properly. There are other concerns as well but the transformer being changed is a start. 


Ghost4man,

Oh so the transformer from Toroidy wasn’t any good. It was producing the dual  +\-65 Vac ? 

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1 hour ago, Steven Van said:


Ghost4man,

Oh so the transformer from Toroidy wasn’t any good. It was producing the dual  +\-65 Vac ? 

Not quite. The transformer wasn't correctly specked which is why Anthony has agreed to replace. 

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On 19/02/2021 at 4:18 PM, Tubularbells said:

Im extremely pleased to communicate to you all I think the issues has now been resolved. 👍

 

So what's transpired from my last post was that i installed bypass caps on the power supply as suggested however low level distortion remained in one channel [sigh]. Ron (aka Ponytail here on the forum) kindly offered to run it through his noise and distortion meter in an effort to try and determine what's going on and alas the problematic channel instantly revealed itself to show a distortion measurement of nearly 3% @ just a few watts of power so armed with this info I passed it to Mr. Holton for further analysis to which he conceded that the best course of action was to build me a fresh pair of modules as apparently  there's a known issue with some of the dual lateral mosfets used (I'll leave it to Anthony to decide whether he wants to elaborate on this or not) however the good news was as soon as I installed the new boards everything was sounding really, really good!

 

Yeah it has drawn out way longer that I would have hoped but do appreciate Anthony for not putting me into the too hard basket who seemed committed to resolving the problem one way or another so that's good news.

 

I'll write more about the sound in the coming days weeks suffice to say my current thinking is this is in the top 3 amplifiers I ever owned so a promising start....

 

20210219_191141.thumb.jpg.36ab3431c71790dd8fec200d2e382f47.jpg

 

20210216_140311.thumb.jpg.9a7d6db7c6142ca21cd4fe2f703d2515.jpg

 

 

Hmmm.... 3% distortion is IMHO pretty high.  Easily audible to most.  :(

I guess it just goes to prove that measurements do matter.

 

Cheers,

Alan R.

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That truly is great news Doug.  I hope the amp now gives you many years of great music.

 

One thing I don't understand.  How is it that Aussie Amps could not replicate the distortion on one of the modules that Ron identified instantly by measuring?   Surely this is not something customers are expected to do, even if they are DIY.

 

kudos to Ron.

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7 hours ago, metal beat said:

That truly is great news Doug.  I hope the amp now gives you many years of great music.

 

One thing I don't understand.  How is it that Aussie Amps could not replicate the distortion on one of the modules that Ron identified instantly by measuring?   Surely this is not something customers are expected to do, even if they are DIY.

 

kudos to Ron.

Fair call. 

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7 hours ago, metal beat said:

That truly is great news Doug.  I hope the amp now gives you many years of great music.

 

One thing I don't understand.  How is it that Aussie Amps could not replicate the distortion on one of the modules that Ron identified instantly by measuring?   Surely this is not something customers are expected to do, even if they are DIY.

 

kudos to Ron.

 

The quote below is what I sent via email to Doug last week detailing what I have found and why I first did not pickup the oscillation burst, I hope this helps?

 

As I mentioned in the last email, the issue stems back to around 2006 when the Dual Die Lateral MOSFETs first came out.

They were originally manufactured by SemeLab in the UK. A lot of designers back then were having heaps of problems with them breaking into oscillation.

Back then I was doing some design work for an audio company in Nottingham UK, which had a strong connection with SemeFab (The company who manufactures the Dual Die MOSFET’s) in Scotland.

I came up with a fix back then on how to solve the oscillation issue with these devices, which SemeFab implemented the changes into their Die to cut a very long story short it fixed the issue and Profusion eventually got the rights to make the new devices with new mods to the silicon die.

However Profusion in recent times had changed the design which at the time I did not trap, this is because the actual issue only manifests its self at low power levels and high voltage levels, even then its seems around 10 watts of so; above and below these power level it does not happen, so a bit tricky to trap, especially if you think all is well. :o)

This would explain why you were only hearing the distortion some of the time.

Also the issue only becomes an issue when multiple dual die devices are used in parallel at high supply voltages above 80vdc

Anyway the issue this time is fixed by increasing the local capacitance in and around the output stage, it also only effects the N-Channel devices the P=Channel devices for whatever reason are unaffected.

 

To add to this my commercial amplifier designs already have large amounts of capacitance very close to the output stage devices, which is why by default

none of these designs have this actual issue.  Its would be helpful also to point out that this issue is only localized to the NXL800 and only the newer white solder masked boards, the black solder masked versions have no reported issues over the years they have been sold around the world.  

 

 

 

Edited by Aussieamps
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Damn seems ive spoken too soon as a few days back during what was an otherwise enjoyable listening session i began to notice the dreaded distortion in one channel rear its ugly head yet again 😭

 

Its really quite odd as its only appears on some recordings (or becomes obvious anyway) kinda like  a tearing/scratchy sound on the trailing edge of instruments or a bit like a listening to a radio station that is slightly off tune.

 

At first I thought it might have been an issue with the LP I was playing so tried another and same thing so I disappointingly switched off the system hoping it would pass in a day or two's time so today I returned and did some extensive testing comprising of.

 

  • Switching left to right XLRs to see if the distortion issue followed which would indicate an issue up stream
  • Rechecked bias which admittedly I think might have been a touch high as I adjusted the bias to 400mA from cold as I suspect most DIYers would do following the instructions and yep it was about 480mA in both channels so I re-adjusted to 400mA once the amp had warmed up a bit but this made no difference so I tried a bit lower and higher but again the distortion remained.
  • Put back my old amps to see if the issue remained indicating either an upstream issue or a speaker issue but as soon as the old amps were back in there was ZERO issues ruling that out.

 

So ive just sent Anthony a message asking for further assistance, Im sure hes getting tired of this as am I so not sure where to from here im afraid 😔

 

 

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Man!  Heartbreaking to read that...  But nothing on how you must feel.

I really hope it all comes together for you soon Bro.

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Just now, Eggmeister said:

What a mess

 

Yep truly scrambled Sir Egg.

 

Im not lying when I say its affected my mental health greatly (yeah first world problems and all that but it truly has taken quite a toll and has almost made me want to give up on HiFi altogether and just return to my boombox from the 80's and just enjoy the tunes rather than the system as I did then......

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Sounds like you and Anthony have pretty much exhausted all options, and both have tried to resolve without success....

Is it time to call this project quits, return the modules for a refund, and put it down to a system incompatibility issue?

 

Build something else?  Re-kindle that audio flame?

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