Plate Amp Guru Needed

[NEO Dan]

Anyone have the ability to calculate custom rumble filter/bass boost resistor values?
I have a 300-794 and the stock filter has the amp -12db@10hz.
I'm looking for some boost at 10hz BassBox sez' the filter fc I need would be between 9hz-12hz with Q of 1.0-1.1.

My guess is R26= 1meg and R27=220k.
Is there a way to calculate the actual values i'd need, an Excel spreadsheet?

I also need help doing this on a BASH 500, but thats another post.

Thanks
Dan

[neildavis]

Provided Link: Excel calculator


> My guess is R26= 1meg and R27=220k.
> Is there a way to calculate the actual
> values i'd need, an Excel spreadsheet?

Change the capacitor values in the link to .1 (cells C2 and D2) to match the values on the 300-794. Then play with the resistor values to get the desired Fc and Q. A ratio of 4:1 for R27 to R26 results in a Q of 1, so if you are trying to get an Fc of 10Hz the nearest standard values would be R26 = 82K and R27 = 330K. The values you picked result in an Fc of 4.

[NEO Dan]

First off, THANK YOU VERRY MUCH!!!

Do I need to change some caps too? Your the first to mention caps. I have a 300-794. On the board C10 is a 4.7uf 50v and C11 is a green Chicklet looking cap marked 104J 100v(almost imposible to read it's crammed in a tight spot)I dunno what the value actually is.

Will this Excel file also be usefull for modding the 500 watt BASH amp?

Thanks again
Dan

[bill]

The 104 before the J is the value in picofarads, 10 followed by 4 zeroes or 100,000 pF. That's the same as .1 microfarad, which is what Neil said it was.

What Neil doesn't know about plate amps probably isn't worth knowing. Follow his instructions and you'll be fine.

HTH,
Bill

> First off, THANK YOU VERRY MUCH!!!

> Do I need to change some caps too? Your the
> first to mention caps. I have a 300-794. On
> the board C10 is a 4.7uf 50v and C11 is a
> green Chicklet looking cap marked 104J
> 100v(almost imposible to read it's crammed
> in a tight spot)I dunno what the value
> actually is.

> Will this Excel file also be usefull for
> modding the 500 watt BASH amp?

> Thanks again
> Dan

[neildavis]

Provided Link: Rumble filter


The resistors and caps are part of a Sallen-Key high-pass filter (aka "rumble filter") that most all subwoofers use. There is a short discussion of this circuit in the page that refers to the mini-spreadsheet: see the link below, and look at the schematic where it says "High Pass F = 39Hz".

Usually you don't need to replace the caps, but if you are trying to achieve a really low Fc it might be advantageous to change the caps so that the resistor values don't get too large. Sometimes it is easier to replace the capacitors rather than the resistors (especially if the resistors are tiny surface-mount units), but it doesn't really matter which get replaced, so long as you achieve the Fc and Q that you are trying for.

The caps for the Sallen-Key HPF are the "Chicklets". 104J is 100,000pf, or .1uF.

The Bash amp should have a similar circuit, but without the schematic it may not be easy to find.

Keep in mind that there are high voltages in that amp and if you don't have the right tools and the appropriate experience this simple change could be a life-threatening experience (in other words, I can't give you any more help than this).

[envisionelec]

> What Neil doesn't know about plate amps
> probably isn't worth knowing. Follow his
> instructions and you'll be fine.

> HTH,
> Bill

Easily one of the most knowledgeable persons I've met to date. I usually don't feel like a complete moron in someone's presence.

[neildavis]

Nah--you were just impressed because I guessed at your weakness for pecan pie. Actually, I was wrong--I thought you'd go for the chocolate. :>)

[NEO Dan]

So I shouldn't lick my fingers and touch the fuses? : )~ Just kidding, I'm checked out on HV

Thanks a bunch for the info

[baldemargarcia]

> First off, THANK YOU VERRY MUCH!!!

> Do I need to change some caps too? Your the
> first to mention caps. I have a 300-794. On
> the board C10 is a 4.7uf 50v and C11 is a
> green Chicklet looking cap marked 104J
> 100v(almost imposible to read it's crammed
> in a tight spot)I dunno what the value
> actually is.

> Will this Excel file also be usefull for
> modding the 500 watt BASH amp?

> Thanks again
> Dan

Nice little spreadsheet. It will help for the BASH amps as well. The 300W BASH uses 0.15uF caps, and the 500W BASH uses 0.22uF. The resistors of interest are listed on the PE website. If you need help locating the resistors on the BASH amps, just ask and I can send you some pics.

NOTE: Using this spreadsheet and the known component values, the 500W BASH appears to have a 30Hz, 1.2Q filter in place. But some folks here have reported having useable output down to 15Hz, which is hard to explain (room gain?). So maybe there's been a change in the resistors used. Might want to verify what you have before modding.

[NEO Dan]

Thanks

Now everyone I know will get there subs built, no more excuses. LOL