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In one of our threads the issue came up about whether the Yung SD-200 plate amp has a subsonic filter. In the "Questions and Answers" section on the Parts Express website, someone posted the amp does not have a sub sonic filter.
I heard that it did, so to clarify the issue I went to the source, http://www.yung.com.tw/

I asked: Does the SD-200 has a sub sonic filter, and if so, at what frequency.

The reply was All of our SD-series amplifiers have a sub sonic filter. The working frequency is 30Hz.

I thought it was a mistake and replied: You must mean the sub sonic filter is 20hz, am I correct?

The reply was Our engineer advised that the subsonic filter is 30 hz on all SD-series amplifiers.

EDIT

A Rep from P.E. has stated that the amps are (supposedly) flat to 30 hz and 3 db down at 21 hz, but this needs to be verified.

http://www.parts-express.com/term/yung?srch=yung





 

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Wow thats a shame.
 

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Ouch. That's just nuts, that high of an HPF isn't good for anything besides small box 8" drivers or maybe a wimpy 10". That's going to make the Yung amps impossible to recommend. That is unless they publish info on how to modify the HPF, if the amp design even allows for that. I'd suspect that it might be since there are the models with boost.

It's even laughable. A 500W amp with an HPF at 30Hz, not to mention a 200W or 500W amp with 6dB boost and HPF at 30Hz.
 

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Whoaa! :unbelievable:
I almost pulled the trigger on the Yung 500 last week. I even had my cc in hand since they were on sale for $199 but I spent some money on the kids Christmas gifts and changed my mind.
I'll order the good old BASH 500 when I get paid Friday!
Thanks a lot for the heads up.
 

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That's just nuts, that high of an HPF isn't good for anything besides small box 8" drivers or maybe a wimpy 10". That's going to make the Yung amps impossible to recommend.
Agreed; that makes these amps essentially useless.
 

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I'm the one who ordered the 200W model with 6dB bass boost from PE, and found that there is boost, and Fc does calculate to be about 30Hz. Only thing was that the boost calculated to be only about 2.5dB. I also own the 500W model from CSS, which should have no boost and it was assumed had subsonic down about 20Hz. I'll take it apart and check the resistors to see where Fc is set.

As I warned before, it is not easy modding these. The preamp board is glued pretty well to the steel plate, and must be removed for safe modding due to the use of surface-mount resistors. The BASH is much easier to mod, for sure.

It's interesting that my 200W model had "200-6" written on the pcb with a marker, which I thought was a sign that it was actually as advertised. To me that indicated that it was indeed different from the 'no boost' model, and , even different than the other models with boost. I'm confident that all models use the same preamp board, so now I'm curious to see if my 500W model does extend down to under 20Hz.
 

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Maybe sealed with an 8" or 10" driver, but I sure wouldn't want a forced HP at 30Hz for a 15" or 18" driver.
 

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Note...

A rep from PE (Mike V.) had this to say about the Yung amps...

"Sorry I'm late to the party on this. The Yung SD Series plate amplifiers are flat to 30 Hz, -1.5 dB @ 22.5 Hz, and -3 dB @ 21 Hz. I have no information on modifying this filter and strongly discourage it as Yung has designed the amplifiers to perform to high standards with the filter in place as-is."
http://techtalk.parts-express.com/showthread.php?234409-Yung-or-Bash&p=1869703#post1869703

So if it's -3dB at 21Hz, it'd be more appropriate to call it a 21Hz HFP, right?
 

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I'm the one who ordered the 200W model with 6dB bass boost from PE, and found that there is boost, and Fc does calculate to be about 30Hz. Only thing was that the boost calculated to be only about 2.5dB. I also own the 500W model from CSS, which should have no boost and it was assumed had subsonic down about 20Hz. I'll take it apart and check the resistors to see where Fc is set.
The boost should be at 35Hz for the 200W model...

Do you mean the Fc of the HPF is at 30Hz? Is the boost actually centered at 35Hz as advertised?
 

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Wow, very surprising to hear but excellent information to have.

Thanks for the heads up on these amps Mike.
 

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Yeah, flat to 30 and -3dB at 21 would make it a 21Hz HPF. That's a bit of a relief, though still high compared to the 16-20Hz range that other plate amp HPFs are.
 

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The boost should be at 35Hz for the 200W model...

Do you mean the Fc of the HPF is at 30Hz? Is the boost actually centered at 35Hz as advertised?
One of the spreadsheets I use calculates the highest boost to be at 38Hz. Here are the complete stats based on the components installed in my Yung 200-6.

Fc = 30.139Hz, Q = 1.2
Gain at Fc = 1.59dB
Center Frequency Boost = 38Hz, Gain = 2.408dB
 

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If it truly is only 3 db down at 21 hz then it's not so bad a deal, but this needs to be verified. The first post has been edited to state this.
I assume these stats apply only to the non-boost models? Sorry, too lazy to go the the PE site to see the nitty-gritty.
 

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Well, my 500W from CSS (non-boost) is even more troubling. Once again we do get an Fc of 30Hz, but with much more boost. Here are the stats.

Fc = 30.595Hz, Q = 1.7
Gain at Fc = 4.8dB
Center Frequency Boost = 34Hz, Gain = 5.1dB

So this kind of jives with what Yung communicated. PE is going to have to check some of their amps to see what they really have. I don't know if they've actually measured the circuit response, or if they are going by what Yung told them (which seems to be different than what they told us).

I must point out: MY circuit analysis is only based on ONE clear active circuit that I could find. I traced the board right up to where the signal goes to the level, low-pass, and phase pots. I'm not an expert at circuit design, but I don't believe there is any more HPF type circuitry mixed in there. What I've traced so far looks very typical of what I've seen in other plate amp schematics, except these numbers aren't looking good. I've been tweaking these circuits since back in the early days of DIY plate amps, and seems to me all other circuits were pretty close to what was advertised.

For whatever it's worth, there you have it.
 

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You can re-tune it though, right B?
Then post the mods for others?
Just wondering, I don't have any of these amps, myself.
I know you can do it, though.
 

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In a sealed 12" application, how big of a factor is this higher ~30Hz HPF vs. something with much lower filtering?
There is a lot of useful "rumble" content in the range from 20-30Hz, that's why this is such a concern. Since it sounds like it's actually a 21Hz HPF not 30Hz there isn't as much of a worry.
 
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