Euphonic Audio's Doubler (and v2) has notch filtering and variable phase on channel 2. It doesn't have a strict HPF. After literally playing hundreds, if not thousands of gigs- I feel the HPF is way over-rated. I have invariably sought more depth and low end than trying to get rid of it. That's both upright bass and slab...the EA Doubler is squeaky clean in its power and can really show off your slab's sonic signature. For upright, using a Lifeline pickup at reasonable (with drummer) volume- it can sound like my bass, but I like to play loud so it becomes a harmonic rich big ass "bass guitar". I guess my answer to HPF is turn the cabinet backwards or fire it into the floor (with a gap, of course). These are effective in getting a few more dB out of a microphone (Ear Trumpet Nadine). Right now at my studio, I have an old Peavey 2-15, a Headliner 410 and the EA NL210 driven by the Doubler at 2 ohms. I did it because I can, but I only really use the NL210 when I rehearse with the band. Last week, the mando player asked "is that the bass or plugged in?" (that's a victory).
Doubler does have adjustable HPF. Both the original and II.
Re. the HPF on the Doubler II, I inquired with Euphonic Audio back in 2017 and got the following responses from Gary there (excerpted here with his permission):
The slope of the HP filter is 6dB. The freq points are 20Hz, 50Hz, and 80Hz. For electric bass, set the switch to 20Hz and leave it alone. For upright bass, try the 50Hz and 80Hz settings to see which one works best to help eliminate feedback.
Both channels have their own switch settings. [[Invalid or Expired Link Removed], the frequency for the HPF is set independently for each channel via internal DIP switches.]
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Thanks, Gary.
Do you find the 6 dB slope sufficient for speaker protection with aggressive electric? Is there some other sub-sonic protection in place? I've always been of the steep HPF school, but am open to other possibilities if they work.
Do you know the slope of the HPF on the original Doubler?
...Finally, do you think the Doubler would work well with amplified cello? My own doubling would likely involve electric bass and cello [Editor's note: The amplified cello thing hasn't happened yet, but never say never.] more than doublebass, but doublebass is a possibility, too.
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Hello again, Mark.
There is additional LF rolloff built into the front end of each channel that has been shown to work quite well. Between the two stages, there is plenty of protection.
I am not a fan of steep filters because I feel it affects the pureness of the sound; only use what is required. Plus, the PC board in the Doubler unit is so packed full of parts there is no room to embellish the circuitry any more.
If I recall correctly, the original doubler had a variable filter from 50-150 Hz approximately, and was the same slope. We removed the trim control for the filter to make room for the switches and the optional 80Hz boost on each channel.
Yes, the Doubler will work well with cello. We even have players using it for electric violin. It is a full range preamplifier, so it is very versatile.
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I went on to ask some more annoying questions about the effects loop and signal routing, but, re. the HPF, 1) There's something there. 2) There's some additional, baked-in roll-off in the front end (not necessarily a bad thing), of which I don't know the slope or the means by which it's accomplished. (Gary did say that a similar roll-off was present in the front end of the other EA amps.)
Where and how the low end is rolled-off, exactly, the upshot of it is this: When I played the Eich T-900 (mentioned earlier as having very open deep lows -- Thomas Eich has said that it does not employ an HPF, but I would be surprised if there was not some sort of subsonic protection present) back-to-back with Mike's hot-rodded Doubler I (which should be similar in its HPF approach, if not identical) at similar volumes and trying to dial-in similar sounds, through a couple of MAS 18s (which go pretty low -- -3 dB points somewhere in the 30s), I did not find the low end of the Doubler to be lacking or anemic. It didn't have the very deep-feeling lows of my GBE 1200 with the LF Extend dialed fully down (or the at least-as-deep lows of certain tube amps), but I didn't get that "something's missing" sense that I sometimes have with other compact amps.
Conversely, with the Eich, there was a lot more visible cone-movement. I got good sounds with that amp, live, but felt that I needed to bring more cab to feel safe than with, for example, my Kustom KXB500. When I asked about the amp's HPF, I was concerned that the shallow slope in the specs would result in something that both sounded anemic in the lows and failed to protect the speakers very well.
While I haven't owned a Doubler (and, strictly speaking, haven't played a Doubler II) and might refine my opinion if I got to spend some real time with the amp, what I've experienced of V1 suggests that what EA has in place is both effective at speaker protection and manages not to rob the amp of too much low-end impact. Your more extensive experience, @Sambo, would seem to suggest the same.
