# New amps at CSS...



## favelle

Yung SD300 300W, 200 and 100. Question though, does anyone know if they have a HPF and if so, what is it set at?


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## bgarcia17

This is completely a guess on my part, but seeing as these are the same amps that PE now sells, and that they are the models without bass boost, I will say the HPF is likely to be about 20Hz with no boost, meaning a nice slow roll-off. Maybe one of the CSS guys has the scoop from Yung, and can tell us exactly what it is.


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## favelle

That's what I was thinking. Do have any info on the PE versions? As they would likely be identical, like you say...


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## bgarcia17

What type of info? Info for these is really limited, even PE seems to be a bit in the dark about full specs. Bob from CSS likes them though, and feels they have more power than the BASH. You may have noticed that these are simply a lower power version of the 500W model, so info among them all is likely true for them all. Only the 300W and 500W have speaker-level inputs.

I ordered the 200W (with boost) model from PE, to trace its pre-amp circuitry. They seem to be very well made, but are a pain if you have plans for customization. Everything is glued and sealed, the components are surface mount so modding requires removal of the board. I did find the boost circuit, and it DID NOT have the 6dB boost as noted in the specs. The spreadsheets I use show it's a little under 3dB of boost-age.  Not sure I'd buy another, since I like having the option of changing my amps' response as I move them around to different designs.


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## favelle

I guess the only info I'm really interested in is the high pass filter and what its set at. If its at 25hz, then these things are no good for my purposes.


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## bgarcia17

I'd say you're good to go then. I expect these to be flat down to 20Hz, just like the 500W model.


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## calem91

bgarcia17,

Sorry I know this thread is a but old, but I just bought the Yung SD300-6 by accident and I saw that you managed to find the bass boost circuit? Do you know if it would be possible turn off the bass boost or remove the circuit entirely?

Calem


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## bgarcia17

Calem,

You can turn off the boost circuit, or even remove it all together. The bigger question comes down to your ability to remove the board from the amp so you can work on it. Take a look at it and notice all the yellow sealant/glue that they use to hold the board to the metal plate (along with mechanical hardware). If you think you can physically remove the board, and are comfy working with a soldering iron, I can tell you how to mod the boost circuit.

Note that your warranty will be void if you attempt these mods. I had a bit of a tough time just removing the board; it's kinda difficult to pry all that glue off with the limited space in the assembly. But it can be done.


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## calem91

That would be great if you could point me where to go to remove the circuit. I agree, it is messy, but I have had a fair bit of experience working with a soldering iron.


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## bgarcia17

I'll get you component values and locations so you can get flat response down to about 10Hz. How does that sound? Or any other frequency that you prefer. Just let me know.


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## alphaiii

bgarcia17 said:


> What type of info? Info for these is really limited, even PE seems to be a bit in the dark about full specs. Bob from CSS likes them though, and feels they have more power than the BASH. You may have noticed that these are simply a lower power version of the 500W model, so info among them all is likely true for them all. Only the 300W and 500W have speaker-level inputs.
> 
> I ordered the 200W (with boost) model from PE, to trace its pre-amp circuitry. They seem to be very well made, but are a pain if you have plans for customization. Everything is glued and sealed, the components are surface mount so modding requires removal of the board. I did find the boost circuit, and it DID NOT have the 6dB boost as noted in the specs. The spreadsheets I use show it's a little under 3dB of boost-age.  Not sure I'd buy another, since I like having the option of changing my amps' response as I move them around to different designs.


I'm curious if all boost models have the less than specified boost. A difference of 3db vs 6db boost can make a big difference in low end response and driver excursion when in WinISD models of various drivers I've tested, so it'd be important to know what the actual boost really is.


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## bgarcia17

I wondered the same thing, but I wasn't about to buy a different model just to see.  And my findings were based on just the one HPF circuit I found. I never got to finish tracing the rest of the preamp, all them dual-ganged pots and stuff hurt my head. I'd be surprised if there was more boost added within the phase, lpf sections (as it'd have to be the same Fc), so I'm pretty sure that's all there is. Maybe someday I'll finish what I started.


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## calem91

That would be great. I'm going to be tuning my sub to about 28hz, but I just wanna get rid of that awful spike that the amp has.


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## bgarcia17

Here you go. Once you have the preamp board removed and in your hands, hold it component side up with the adjustment pots facing away from you. The HPF components are located in the upper left hand side area, right near the LED. Verify (hopefully) that C4 and C5 are .22uF (markings u22j or such). That would be a good sign that your amp uses the same board as I suspect. Now, the numbers:

for Fc = 28Hz, Q = 0.7, R8 = 18.3k, R23 = 36.6k.
for Fc = 28Hz, Q = 0.9, R8 = 14.4k, R23 = 46.5k.
for Fc = 8Hz, Q = 0.7, R8 = 64.6k, R23 = 126.7k.

I'd recommend the second set of numbers for your design, but you can check them in your simulation software. The values don't have to be exact; if they're reasonably close I doubt your system will suffer badly. Good luck!


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## calem91

Thanks for that! I did locate C4 and C5 and they are .22UF. If I could ask a couple more questions i think i will be able to get this mod underway.
I don't really understand the theoretical part, if you could please try to explain how this mod works in reducing the 6db spike, maybe i will be a bit more confident in doing it? Also, what type of resistors are these? thick film resistors? and do you have any retailers or suppliers you would suggest getting them from?

Many thanks!


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## bgarcia17

Did you know a speaker in a box can be thought of as having a filter type of response? Like when the optimal sealed box is suggested the Q response of the system is aimed at being .707. That because, a response with a Q (which is damping factor) of .707 gives you the flattest frequency response. If you put that same woofer into a smaller box, the response then has a higher Q, which gives you a bit of a peak in response. In a bigger than optimal box, the Q is lower than .7, which gives you a drooping type of response. Model your woofer in box sizes like this and take note of the response and corresponding Q values.

Now, that is pretty much the same way it is with electronic filters. Remember, a woofer can be modeled this way because it is just a combination of electronic components that result from its electro-mechanical parts. Haven't you noticed how t/s parameters include Q values? Anyway...I'm digressing a bit.

Boosts in circuits like this are set by using high Q filters. It is commonly applied to the high-pass filter in the preamp, which is also sometimes called a subsonic or rumble filter. So all we have to do is locate the filter in the preamp, find its associated components, then use a simulation spreadsheet to tailor it to our needs. It's usually easy to find, as the filter uses two identical caps, and they are also a different type of cap. All them blue caps in our amps are used for the critical audio processing circuits, so I just had to find the matching pair then trace them to the op-amp that was using them, then find the resistors that are also part of the circuit. Per your request, I used the spreadsheet to give me the resistor values needed to get the Fc and Q's I needed. Note that a Q of .7 means that Fc is 3dB down from the flat response. I personally think that's a bit low if your box has response capable of that without issue, so I gave you a Q of 0.9, Fc 28Hz. That means that there will be a slight bump at frequencies above 28Hz, but nothing at all significant. If your box simulator can model the filter, you'll see what I mean. So in a nutshell, we're just reducing the Q of the filter to flatten the response and get rid of the boost.

As for components, any type of resistor that you can find will work. These are thin-film, I believe, but that's not necessary. You can even replace them with regular resistors once you bend the legs. I bought a resistor kit long ago from Radio Shack, but now I buy components from Digikey. Not sure what's available where you are, but any electronics parts supplier should have what you need.

This spreadsheet here has the ability to show you changes in response with active filters applied.

http://audio.claub.net/software/jbabgy/WBCD.html


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## bgarcia17

I forgot to ask...can you measure your present resistors and tell me their values? I'd like to plug them into my filter spreadsheet to see what response you presently have. Thanks.


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## calem91

Thanks bgarcia17,

I feel i better understand what I am doing now, I was not aware you could 'electronically' tune your sub aswell!  I don't currently have the equipment to test resistance levels, but when I get my tester I will let you know.
Thanks for all your hard work!


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## calem91

I should mention that this will be a vented box tuned to 28hz so there will be a bit of a boost anyway, I am just concerned with the cone excursion and port air velocity. I have tried to model the filter using WinISD (the spreadsheet does not seem to work for me). I used the parametric EQ to simulate the filter and put an Fc of 28 and Q value of 0.9 with a 3db gain. Is this correct? There still seems to be a boost and very high port air velocity.


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## Mike P.

Which driver are you modeling?


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## calem91

Peerless 830952 12" in a 1.5 cubic ft. box.


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## bgarcia17

Not sure how your build progressed, but we found some new things to note about these Yung amps.

Make sure to see this thread for all the details:

http://www.hometheatershack.com/for...ubwoofer-plate-amplifers-8.html#axzz2IjQJ0oyq


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## soldering iron

If you are going to use soldering iron I would suggest to use temperature controlled soldering iron. Temperature of this iron can be precisely adjusted with the front panel temperature control knob.


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