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Removing Limiter From An Amp

Trdat

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I have the Chinese Version of the SoundTown ST that has been measured here on ASR. Mine is the Sinbosen 4 channel K4-450 amp which I presume is the same as the Sountown. I can see from the measurements that the power down low is very very weak and the use as a subwoofer amp is not feasable. I am guessing there must be some kind of limiter for the lower frequencies.

My question is twofold, can an oscillator or a technician test how much power the lower frequencies are producing? And if there is a limiter how hard will it be to remove that from a Class D amp? Of course not DIY I am talking about a professional.

I have contacted Sinbosen to ask them if there is a limiter and I have recieved absolutely no reply. I have sent several messages, called, emailed and no one replies even to a greeting. Usually I have superb experience with Chinese customer service other than the poor English(that is understandable) but on this occasion and with company that is up and coming and farely large it is weird regarding their effort in having some type of ongoing customer support.
 

staticV3

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can an oscillator or a technician test how much power the lower frequencies are producing?
Yes. You can measure output power with an oscilloscope.
Some kind of speaker dummy load would be helpful for this
 
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Trdat

Trdat

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Yes. You can measure output power with an oscilloscope.
Some kind of speaker dummy load would be helpful for this
And what do you reckon can the limiter be removed? If there is a limiter that is, it could be that the frequency power is just oddly shaped. Amir in his comments mentioned that there could be some kind of limiter.
 

staticV3

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And what do you reckon can the limiter be removed? If there is a limiter that is, it could be that the frequency power is just oddly shaped. Amir in his comments mentioned that there could be some kind of limiter.
I have never designed, built, or even modified a class d amp before, so I don't know if such a limiter could be modified or removed entirely. I wouldn't even know where to start on that one.

If you manage to contact Sinbosen however, then I'm sure a graph showing THD+N vs output power at 1kHz and 20Hz would be hugely beneficial for explaining your problem.
The measure and graph part is the one I'm comfortable with.
 

Grotti

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And what do you reckon can the limiter be removed? If there is a limiter that is, it could be that the frequency power is just oddly shaped. Amir in his comments mentioned that there could be some kind of limiter.
If there's a limiter, it could be installed for a reason. Just saying......
 
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Trdat

Trdat

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I have never designed, built, or even modified a class d amp before, so I don't know if such a limiter could be modified or removed entirely. I wouldn't even know where to start on that one.

If you manage to contact Sinbosen however, then I'm sure a graph showing THD+N vs output power at 1kHz and 20Hz would be hugely beneficial for explaining your problem.
The measure and graph part is the one I'm comfortable with.
There was a sheet with graphs that came with it and the measurements are all above par but we know that is not the case according the review here on ASR.
 
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Trdat

Trdat

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If there's a limiter, it could be installed for a reason. Just saying......
I get that, but I want to use it for a subwoofer amp and if its 20watts at 20hz I dont see a point plus as it measures so badly I don't see me using it for any other purpose. To be honest I bought it for subwoofer duties and going off the ASR review it defintely can't be used for that purpose.
 

Vladimir Filevski

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My question is twofold, can an oscillator or a technician test how much power the lower frequencies are producing? And if there is a limiter how hard will it be to remove that from a Class D amp? Of course not DIY I am talking about a professional.
You don't need to measure it again, Amir measured it. Output power at 20 Hz is non-existing, with a good chance the same lack of power will be at 30 Hz also.
Limiter maybe can be removed by a professional, but it will cost you more than to sell your amplifier and to by a proper one.
 

tomtoo

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I get that, but I want to use it for a subwoofer amp and if its 20watts at 20hz I dont see a point plus as it measures so badly I don't see me using it for any other purpose. To be honest I bought it for subwoofer duties and going off the ASR review it defintely can't be used for that purpose.

If it looses so much power at low frequences, this could be also a problem of the PSU. Sell it, get a amp.
 
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Trdat

Trdat

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You don't need to measure it again, Amir measured it. Output power at 20 Hz is non-existing, with a good chance the same lack of power will be at 30 Hz also.
Limiter maybe can be removed by a professional, but it will cost you more than to sell your amplifier and to by a proper one.
Yes it definitely the same one as the manual with the graphs showing the AP analyser are exactly the same.

Thanks for that, I did presume that it would eb non existent as well between 20hz and 100hz.

So it seems it would be a dificult task to remove it.
 
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Trdat

Trdat

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If it looses so much power at low frequences, this could be also a problem of the PSU.
Well power supply can be changed, I can't imagine it being that hard but how do we know it is the PSU? I mean can the technician figure out it is from the PSU...?
 

tomtoo

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Well power supply can be changed, I can't imagine it being that hard but how do we know it is the PSU? I mean can the technician figure out it is from the PSU...?

I good technician can do a lot. If he knows a lot about switching psu's and class d amps. The question would be does it make sense from the financial point of view?
 

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It´s a turd. Throwing more money and time at it is just going to make it a more expensive turd.
Use as is or get rid of it. Move on, buy something proper like a Crown xls, which is also tested here somewhere.


Edit: For example this XLS1502 with DSP
 
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tomtoo

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Let me add maybe a german point of view.

First you need someone that has realy the expertise. They not work for a apple and a egg. So finding the problem(lets imagine it would be the PSU), changing it is easy 4h work. What is in germany easy 400Euro without parts.
 
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solderdude

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This amp is rated at 450W/8 ohm.

I see no reason why this amp would not be suited for low frequencies.
It is possible that besides the temperature protection, over current protection and short circuit protection there is a 'tightly tuned' DC protection circuit that will kick in at constant very low frequencies at high amplitude.
There will not be a limiter and the amp will not have reduced power at 20Hz.

I see no reason why it could not be used as a sub amp.
 

Calleberg

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This amp is rated at 450W/8 ohm.

I see no reason why this amp would not be suited for low frequencies.
It is possible that besides the temperature protection, over current protection and short circuit protection there is a 'tightly tuned' DC protection circuit that will kick in at constant very low frequencies at high amplitude.
There will not be a limiter and the amp will not have reduced power at 20Hz.

I see no reason why it could not be used as a sub amp.
Even though I can see a couple of reasons to NOT use it as a subwoofer amp :) The above is actually not bad advise.
(So I modified my previous post slightly) Depending on your use case the flaws might not be a total showstopper, but for serious HT use its going to suck real bad ;)

Now that you have it, at least try it. You might like the punchy sound from the additional distortion, 50Hz peaking and rolled of last octave :D
On the bright side it does have an (although non defeatable and maybe not 100% intentional) Infrasonic filter which might work well with some ported subs with limited excursion capability ;).
 
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Grotti

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I read the review again: you should sell this unit and buy a better amplifier. To modify it will cost you a reasonable amount of money and you will loose lose warranty.
 
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