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High Pass Filter (HPF) and Low Pass Filter (LPF) Mega Thread

#1,343
Stumbo said:
@The Bass Clef:
I know this thread is old, but for the sake of information, I’m pretty sure that the more recently made CMD 121P combos must have gone through a little change since the one that you had years ago Jimmy.

I just picked up an Indonesian-made one (from 2014) off the classifieds here, and the first thing I noticed was that nasty hissing tweeter.

I looked online to see if that was “normal” (which it is for this amp) and if I could just disconnect it. I found out it was safe to do, but I also saw your post above about it having no highs at all afterwards, so then I figured I’d just have to live with it and use the VLE to get rid of the ugly tweeter noise.

The problem was, while the VLE did get rid of the tweeter ugliness, I also found that it had a bit of a negative effect on my overall tone - I was muddier and starting to get lost in the mix now.

So I researched a little more, and found several posts from people who disconnected their tweeter and said it was way better now.

That convinced me to try it out, so I pulled the wires off mine and I found that my 12” main speaker is most definitely operating full range.

I do have to crank the “High” EQ knob on the amp now if I want to get more of the crispy highs, but they are there, and at least now I’m cutting through the mix again (the VLE is turned back down to where it isn’t making me sound muddy anymore).

Another thing to mention... I didn’t even bypass the crossover like I read many others did. I found a couple posts saying that the CMD 121P doesn’t really have a true crossover, it’s really just a high pass filter for the piezo, and the main woofer is wired full range from the factory. And I found this to be the case with mine.

So... now I’m thinking maybe the older combos actually had a true crossover in them (that cut off the highs to the 12”, as well as cut off the lows to the tweeter) that would have needed to be bypassed. That would explain why your combo didn’t get the full range to the 12, and mine did.

Did you ever try bypassing the crossover, or did you just disconnect the tweeter? It seemed like you enjoyed the VLE turned up, so maybe it wasn’t worth the effort for you to dig in there and bypass it.

I know you’ve moved on from this amp long ago Jimmy, but for future readers, I figured I’d let em know that disconnecting my tweeter made it a way better amp.


@JimmyM:

Well that's good to know if they did fix that. I honestly can't remember if I bypassed the crossover network or not. I may not have. I think I decided it was a PITA to do it.

Let's put it this way...I tolerated the VLE doing the highs cut more than disconnecting the tweeter But I actually thought the VLE was the best thing about Markbass amps,

and I wanted something similar in a tiny effect pedal, and that led to the Broughton Low Pass Filter, which along with the subsequent High Pass Filter and the combo HPF/LPF are a couple of Josh's best selling pedals.

I really didn't hear the VLE acting on the amp. I guess it's possible but I don't remember it that way.
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I have an older, Italian-made CMD 121P. Disconnecting the tweeter on mine did not neuter the highs -- the woofer appeared to run full-range. I spoke with a gent (years ago) in the main Markbass service center and he said that the crossover was not a true crossover but just an HPF for the tweeter. Whether or not it was always thus, I don't know.

I ended up installing a Monacor tweeter in place of the piezo (there's a thread about it somewhere on TB) with an on/off switch for the tweet. A definite improvement -- smoother, more subtle but more clear, and much less hissy. Unfortunately, the head has been cutting in-and-out for awhile, so the combo doesn't get used anymore but, when it's working, it's a good sounding combo.

Balog said:
It seems like a number of people in this thread were asking about EU-friendly options. This looks to be an fdeck clone, but it's made in Ireland so that may help some folks.

Rafferty HPF Pre 2 Bass Preamp / Adjustable High Pass Filter / Phase Switch Custom Color
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Zbysek said:
Thank you, I would be one of those Europeans..:)
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There's a gent on TB (forget who at the moment) who's served, I think, as a sort of "unofficial importer" of the fDeck pres for EU folks. Don't think there's any affiliation with @fdeck, but I believe that he's posted a few times in the thread on the fDeck HPFs.
 
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#1,350
Zbysek said:
That's exactly the kind of person I am looking for... Thank you
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How about this kind: VONG-Filterung – Schalltechnik_04 ?
Yel_wink.gif
 
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#1,351
Zbysek said:
Thank you, I would be one of those Europeans..:)
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Me too. Import tax and postage lead me to ask my amp Tech to knock one up from available schematics. I'm currently trialing the prototype. First impressions are good. It had a super effect on a hard pushed combo on my larger rig I got a lot of perceieved highs when engaged. I ready found the tone a bit bright so trying to work around that. A big help for detuning that's for sure. More attack in the sound but with pick a bit to much with fingers it's just right.....if he decides to make them available for sale I will let you guys know....
 
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#1,356
dabis said:
View attachment 3229005

I spend building mine about 3 hours. Best option I found here in Europe.
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Got the same, except I bought the housing drilled and completly painted. I am no DIY fan either but with Julians complete and idiot prooven sets (prooven by me !) you can't go wrong. And if you still manage to fail Julian is very helpful and even repairs it for you.
 
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