Actually this is not the first clone, but it is going to be the first with the new boards. On this one I'd like then to try some other interesting modifications (Lavardin, etc).
The other clones I have built were already very good sounding, one of them has eaten a Krell KAV 300 in a direct comparison
I'll keep you guys informed!!
Ciao!
Paolo
Hi,
but the problems are only related to different measurements or there is also a problem when sit there and enjoy the music with a cold beer?
Ciao!
Paolo
C9
Hi Fab!
Thank you for your useful reply! Now I have a clear picture.
The loading of the VAS stage using this scheme should be only in the high frequency range, or it could also impact the useful bandwith operation?
The power supply ripple increase is due to the increased current required for this stage connecting this resistor, right? Will increase also the dissipation of the driver transistors? In any case, using a regulated power supply should solve the problem, right?
Ciao!
Paolo
Hi Paolo
C9 is not a Cdom but a "shunt lag" compensation (VAS shunt to ground). The DH-200 does not use Cdom Miller cap but C9 and RC networks in the collector load of the input stage for frequency compensation scheme. Some schools of thoughts say that Cdom is not good for audio and some other schools say that shunt compensation (C and/or R to shunt VAS to GND) loads to much the VAS stage. The DH-200 frequency compensation scheme uses a small C9 and the rest of the compensation (except feedback compensation) is done in input stage. So, it may be one reason why the DH-200 sounds good. Putting a 20k in parralel extend the open loop bandwidth of the amp but at the price of Power supply ripple increase. So, there is no free lunch.
However, 20K is a high value which should limit the perpectible effect on ripple generation.
Fab
Hi Fab!
Thank you for your useful reply! Now I have a clear picture.
The loading of the VAS stage using this scheme should be only in the high frequency range, or it could also impact the useful bandwith operation?
The power supply ripple increase is due to the increased current required for this stage connecting this resistor, right? Will increase also the dissipation of the driver transistors? In any case, using a regulated power supply should solve the problem, right?
Ciao!
Paolo
Hi,
I've refurbished (or should I say restored) few DH-200, I can tell you that the difference is huge. AFter all this years, a lot of components are aged, and of course there are a lot of tricks that, meanwhile, are worth doing.
I'm not a class D amplifiers fan, this heavily biases me from supporting your intention of using the Hafler chassis for such a project.
Ciao!
Paolo
It depends on the cap value but the laoding VAS problem is real. In the case of the DH-200 the loading is small even with adding 20k to the existing C9 which is not a very disturbing value. The power supply ripple possible increase is an effect of the extention of the bandwidth to a higher frequency value because at the same time you also reduce the open loop gain at low frequency (including 50, 60, 100 or 120Hz) which reduces the Power supply rejection ratio of the amp. However, having said that, I have myself added a 15k resistors between VAS and ground for both polarity of amp and I can not observe a perceptible increase in ripple (but not really measured though...). The regulated supply sure helps in a lot of manner but not in reducing the loading of the VAS transistors. I think I made good publicity of the regulated supply for the front end pcb of this amp in this thread if you have noticed...
Ciao!
Fab
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hello!:
It's been several years since my last vist-back to post 204!. Quite few others have since. Latest post #827! to haflerfreak R u tweeking a XL280? to mlloyd1 I find your mods very appealing as I'm short on time w/5 kids and another coming. Though I know which end of a soldering iron is up, I lack the experience & expertise of the rest of you guys. I can handle swapping caps, resistors, wire, & diodes.
I've revamped my purpose for my XL 280s since my last stretch of visits here-Home Theatre! I have 4 of them! Specifically, use one amp each to bi-amp my left*, center*, & right channels* maximizing channel separation, etc. The 4th powering my surrounds full range*; a Mackie 1400 covers the sub.
* I'll tweek this one also
Back to the good stuff about Haflers. I'm certain they need a bias "tune-up." Some other specifics: use the right channel** above** 2Khz, the left channel** below** 2K**. I plan to use 4th order HP/LP "E" filtering
W/ these** in mind, the only other mods that I think could net me the results I seek could be completely separate, tailored left/right PS filtering & rectification for both the front end and final stage.
Tailored being add'l recitfication & PS filtering for right channel(s), channel, upgraded filtering & recitfication for the left. Space may allow for a "T" transf with multi windings and higher VA ratings.
With ove 800 posts to sift through (I read many of them) I'm still at a loss for ideas & some specifics. mlloyd1 you nailed the resisitor(s) mods, thanks. And thanks in advance to all of you for pursuit of this fun/insane hobby!
It's been several years since my last vist-back to post 204!. Quite few others have since. Latest post #827! to haflerfreak R u tweeking a XL280? to mlloyd1 I find your mods very appealing as I'm short on time w/5 kids and another coming. Though I know which end of a soldering iron is up, I lack the experience & expertise of the rest of you guys. I can handle swapping caps, resistors, wire, & diodes.
I've revamped my purpose for my XL 280s since my last stretch of visits here-Home Theatre! I have 4 of them! Specifically, use one amp each to bi-amp my left*, center*, & right channels* maximizing channel separation, etc. The 4th powering my surrounds full range*; a Mackie 1400 covers the sub.
* I'll tweek this one also
Back to the good stuff about Haflers. I'm certain they need a bias "tune-up." Some other specifics: use the right channel** above** 2Khz, the left channel** below** 2K**. I plan to use 4th order HP/LP "E" filtering
W/ these** in mind, the only other mods that I think could net me the results I seek could be completely separate, tailored left/right PS filtering & rectification for both the front end and final stage.
Tailored being add'l recitfication & PS filtering for right channel(s), channel, upgraded filtering & recitfication for the left. Space may allow for a "T" transf with multi windings and higher VA ratings.
With ove 800 posts to sift through (I read many of them) I'm still at a loss for ideas & some specifics. mlloyd1 you nailed the resisitor(s) mods, thanks. And thanks in advance to all of you for pursuit of this fun/insane hobby!
...but the xl-280 produced the best null.
What's a null? I know how it relate to math?
new pcb
yes, of course, as you can see in the picture of post 817 there is also a new pcb
Ciao!
Paolo
Might be nice to replace Haflers butt ugly pcb too
yes, of course, as you can see in the picture of post 817 there is also a new pcb
Ciao!
Paolo
ok, thanks for the explanation
And what about its benefits about sound?
The regulated supply sure helps in a lot of manner but not in reducing the loading of the VAS transistors. I think I made good publicity of the regulated supply for the front end pcb of this amp in this thread if you have noticed...
Yes, and I've put this mod with an high priority in my list
Ciao!
Paolo
P.S.: have you found those results by simulating the amplifier (or a part of it)?
Unfortunately, it is hard for me to tell since I made several mods at the same time....
I have not gone through the "before and after" listening for this single mod... Personaly I prefer to have a known passive load for the VAS instead of an unprecise high impedance load which varies with the butterfly effect....What specific results?
Thanks
VAS loading
Hi Paolo,
This is electronic base knowledge that loading a VAS or any actice device degrades its linearity. Of course, some loading is always mandatory for a circuit to work. It is just when we put EXTRA loading with no great benefit in return that it should be avoided. It is always a compromise. There is an optimal value and 15k ohms may not be considered an extra loading for the VAS medium power transistor type used in the DH-200/220 amp.
You can try to simulate it but I do not trust completely simulators or the models used for simulations...but I have access to simple simulator only like Microcap 6. There may be better simulators available.
I have observed one benefit for adding the 15K oms VAS loading in case you regulate the supply of the front end (with no additional voltage supply increase for the front end) like I did. Indeed, it provides a load when transistors turn off while powering off the amp and it avoids small (but hearable) "clicking" noise at output of speaker.
Fab
Hi Paolo,
This is electronic base knowledge that loading a VAS or any actice device degrades its linearity. Of course, some loading is always mandatory for a circuit to work. It is just when we put EXTRA loading with no great benefit in return that it should be avoided. It is always a compromise. There is an optimal value and 15k ohms may not be considered an extra loading for the VAS medium power transistor type used in the DH-200/220 amp.
You can try to simulate it but I do not trust completely simulators or the models used for simulations...but I have access to simple simulator only like Microcap 6. There may be better simulators available.
I have observed one benefit for adding the 15K oms VAS loading in case you regulate the supply of the front end (with no additional voltage supply increase for the front end) like I did. Indeed, it provides a load when transistors turn off while powering off the amp and it avoids small (but hearable) "clicking" noise at output of speaker.
Fab
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25W class A output mosfet-diff input- JLH converted amp
Hi Tony
See at:
jlh-fabclassapoweramp (fabaudio)
...check my 25W class A output mosfet-diff input- JLH converted amp into a DH-200 chassis...
Hi Tony
See at:
jlh-fabclassapoweramp (fabaudio)
Hi Fab
Thanks Fab!
Ciao
Paolo
ok, I don't get the news so far....
so your judgement is based upon the capability of the driver transistor?
I do not trust them completely either, I'm just trying to find the better way to validate a reasoning...
This can be nice, but it is not the main purpose of the mod
Thanks Fab!
Ciao
Paolo
Vas....
Sorry if I may have confused you a bit and this is my fault. C9 is really the one that can load the VAS because it represents a short circuit at high frequency. The parallel 15k ohms only affects the open loop gain in relation to frequency - thus the feedback factor at low and mid frequency is reduced (less good) but it is increased at higher frequency (good).
In conclusion, you can play with the parallel resistor to adjust the open loop gain in relation to frequency. Install it for both polarities VAS. 100k will not do much effect since it is higher than the impedance of the driver stage - already seen by the VAS. Lower than 5k is probably reducing too much the overall performance of the amp (at least for THD) since the VAS gain will be reduced to less than 50 ((5k ll driver) /100)!
Good luck and Thanks
Fab
Hi PaoloHi Fab
ok, I don't get the news so far....
Sorry if I may have confused you a bit and this is my fault. C9 is really the one that can load the VAS because it represents a short circuit at high frequency. The parallel 15k ohms only affects the open loop gain in relation to frequency - thus the feedback factor at low and mid frequency is reduced (less good) but it is increased at higher frequency (good).
No, see my explanation above.
I know.This can be nice, but it is not the main purpose of the mod
In conclusion, you can play with the parallel resistor to adjust the open loop gain in relation to frequency. Install it for both polarities VAS. 100k will not do much effect since it is higher than the impedance of the driver stage - already seen by the VAS. Lower than 5k is probably reducing too much the overall performance of the amp (at least for THD) since the VAS gain will be reduced to less than 50 ((5k ll driver) /100)!
Good luck and Thanks
Fab
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Hi Fab!
I have done my homework and seen the explanation on Self's book about shunt leg compensation, that actually is just as you told me. Seems that I have to read this book all over again, I'm missing some points...
I'll come back then with a lot of questions!
Thanks Fab,
Ciao
Paolo
no, Fab, it's my fault, seems I still don't have the right global picture
I have done my homework
and seen the explanation on Self's book about shunt leg compensation, that actually is just as you told me. Seems that I have to read this book all over again, I'm missing some points... I'll come back then with a lot of questions!
Thanks Fab,
Ciao
Paolo
from post #23
I have a device* to convert unbalanced to balanced. My [SURROUND] amp** has 35' interconnects hence my interest in "balanced drive.".
* Applied Research & Technologies (ART) ** XL280
TO Fab: your reply was change some resistors and some thing about inverted input. Can I get some details? thnx tony
I have a device* to convert unbalanced to balanced. My [SURROUND] amp** has 35' interconnects hence my interest in "balanced drive.".
* Applied Research & Technologies (ART) ** XL280
TO Fab: your reply was change some resistors and some thing about inverted input. Can I get some details? thnx tony