Configuring third party subwoofer amp for Pipettes and Subette

[ipetruk]

Hi,

I have a set of Pipettes and a single Subette. I have not yet purchased Sublime, maybe it will happens someday later.

I am trying to use https://fosiaudio.com/products/subwoofer-amplifier-m03-300watts-mono-amp-full-frequency-and-sub-bass-switchable-amplifier with Subette. It has a full monoblock mode and subwoofer mode, where you can tune the cutoff frequency. The problem is that both volume and cutoff knobs are unmarked. They don't have any numbers. I do not know where 70 Hz is that you recommended with Sublime. I do not know how many watts the volume knob gives me. So I have got these:

https://www.amazon.com/dp/B00S8XY2W8

They in theory should have eliminated a single variable out of equation and I would have only have to tune to volume knob. The amp can give 200W with extra power supply, so probably a 160W without it. Plus it is source is my integrated amp pre which is usually operated at 50% of the volume for Pipettes. If power is logarithmic, does it mean that this sub with 50% volume at pre should always operate at less than 30W (roughly), right?

Well, not so simple with those RCA plugs. They have 12dB/Octave slope and it is not documented what slope Sublime has. When I use them via Fosi, Subette barely does anything. If I remove these filter and just rely on Fosi subwoofer knob, I can hear low bass way more in almost all positions, even though it also suppsed to have 12db/Octave slope. But the freequency range is not specified, I could be as well be hearing 500 Hz there. And I am not sure where to put the volume knob because the guide says to keep it easy during the burn in period. That is not very quantifiable.

I have also tried reading the specs of both drivers, from Pipettes (Altair) and Subette (Dayton). Pipette driver seems to drop at 100Hz, and Dayton at roughly 50Hz. Is this a correct reading of the graph? I tried to understand the 70Hz cutoff suggestion. This of course does not take into account the acoustics of the cabinet

I am very inexperiences with subs, so I don't know if it is expected to hear very little form the sub, and mostly have a body feeling from it. Now here are the questions:

1) Should I trust the 70Hz RCA plugs and just get the volume right? Or 70Hz suggestion for Sublime is not universal for other subwoofer amps?

2) How to judge volume levels for Subette? Are there a visual or sonic clues what are "good for initial burn in", "good for long term operation" volumes? I see the speaker moving. Maybe I can play a test track of your suggestion and somehow derive a good listening volume. I can swithc between Pipettes+Subette and Subette-only with one switch on my system. I can also play full range on Subette, tune volume and then switch to sub mode if that helps.

3) Any other suggestions welcome, maybe my approaches are wrong. I plan to get Sublime eventually, but not now, so I wanted to tune what I have at the moment

Other than that the build of both went mostly smooth. Two complications: wire clamps for the Pipette driver were loose and did not hold, had to carefully solder not too melt plastic. Subette did not have this problem, they clicked fine. Subette had very narrow holes in the wood for hexagonal screws for the driver, had to widen them first. Just a feedback, for you to consider improving. Otherwise smooth build, great job overall, I love the speakers!

Thanks,
Igor.

[Paul Birkeland]

Plus it is source is my integrated amp pre which is usually operated at 50% of the volume for Pipettes. If power is logarithmic, does it mean that this sub with 50% volume at pre should always operate at less than 30W (roughly), right?

There isn't any relationship to volume control position and power output, other than turning the volume knob up will result in more output power than you had before (until you clip the amp at least).  The issue is that the source voltage ahead of the amp will have a major influence on power output at a given volume control position, so you can't really make any assumptions.

Well, not so simple with those RCA plugs. They have 12dB/Octave slope and it is not documented what slope Sublime has. When I use them via Fosi, Subette barely does anything. If I remove these filter and just rely on Fosi subwoofer knob, I can hear low bass way more in almost all positions, even though it also suppsed to have 12db/Octave slope.

What's the output impedance of the device driving the Fosi amplifier?  Inline crossover filters like the ones you have are not necessarily the easiest things to drive, and you may be experiencing a lot of insertion loss. 

You should be able to get things set pretty well with an RTA app on your phone.

[ipetruk]

Thank you, I will play a bit with the app. The problem is in the app that phone mic needs to be calibrated against pink noise which will have to be reproduced via some reference system.

I have a other little problem, is this rattle expected?

https://youtube.com/shorts/ROFGV89gqV4?si=odQAZS0XvgrkYwLU

The video is only with sub connected, no speakers. It is normally not very audible in normal music, unless it is very bassy.

It seems to be in the driver. I don't know if I should try to remove it to see if maybe wires are rattling.

[ipetruk]

I might have in fact overtightened the gasket here, not sure if it is possible to recover or put an extra gasket

[Paul Birkeland]

Thank you, I will play a bit with the app. The problem is in the app that phone mic needs to be calibrated against pink noise which will have to be reproduced via some reference system.

There are apps that will be relatively well calibrated if your phone is adequately supported.  I can't help with the rattle, as I'm not yet a Pipette owner.

[ipetruk]

It is a Subette that is rattling.

I was thinking it was gasket, or seal, or something. It does not look like it is a gasket, it seems too seal fine

But I think it is a rubber that is rattling on the driver. Lightly touching it makes it stop rattling. Just trying to understand is it normal or not. Is the driver damaged? If rubber part is damaged, can it be glued, or does the driver need to be replaced?

[ipetruk]

Here it is working slightly pulled out from the cabinet

https://youtube.com/shorts/lbqC8L1MeTY?si=gxmhZoTnKWXzxD7q

I have a feeling it is that yellow cloth making a "sail in the wind" sound. Do you observe this with your units?

I do realize the drivers will not get enough air pressure resistance when the cabinet is opened, but I am only trying to troubleshoot where the sound comes from. Many things can go wrong, for example it could be a defective driver, or the load could be higher than supported, etc.

Again, this is my first subwoofer in my life, so I don't really know how is it supposed to work and if rattle is simply a subwoofer honestly moves at super low frequency

[ipetruk]

Hi,

Please let me know if this looks like a faulty driver and it falls under https://bottlehead.com/our-guarantee/, or is there something else I can test?

I have invited a friend who knows more about speakers and he does suspect it can be a faulty driver, otherwise the rest of the speaker is absolutely fine and seals well. Power is also not an issue.

Thanks,
Igor.

[Doc B.]

I am just back from a weekend away and saw this. That video sounds more like a rattle than a wind sound to my ear. My first thought in these cases is usually to check the internal wiring to see if it is rattling against a part of the cabinet or driver. I understand that you hear the probem stop when you touch the surround of the driver. That is often simply because you are restricting the travel of the cone when you do that, so not as much energy is available to move whatever is responsible for the noise.

I would suggest removing the driver and gently pushing on the flat "cone" just a couple mm to see if there is any noise like scraping sounds or rattling when it moves slowly. If you don't find any noise check to see if the wires may have been buzzing against the driver or cabinet panels, then put it back in the cabinet and fasten it down and try playing music through it again. If it doesn't fix the problem let us know at [email protected] and we can get a replacement for you to try.

For crossover frequency you want something around 70Hz. Try swapping polarity of the subwoofer cables at the speaker binding posts and use the connection that gives the most bass regardless of the connector colors. That is the proper phasing between mains and sub.

[ipetruk]

Thanks. I did check that, it is very strange. It makes no sounds from the wires or from the driver moving slowly, but as you can see on the latest video, the driver itself rattles when removed from the cabinet the same way as inside of the cabinet. And wires do change position when it is removed like that, it is still rattling. I'll send an email to [email protected].

Also thanks for the polarity suggestion, I will try that once the subwoofer is fixed.

Igor.

[ipetruk]

Hi,

A new driver arrived and it does not rattle. It does rattle a bit like at 3% of the previous driver, completely inaudible when listening to music. Thanks!

To give more power I tried preamping Fosi. That has given a tremendous effect. The bass is deep and strong. Basically my integrated amp that powers speakers controls volume on the pre-out and that volume happens to be too low. My listening volume for speakers is 50%, probably that drives pre-out level lower too. When it goes to 160W powered Fosi that makes volume very low even with Fosi volume at 100%.

I have had a separate preamp that can make 20db gain. Adding it to subwoofer chain produces a very powerful bass from Fosi even at 40% of Fosi volume (remember, before it was weak at 100%).

I wonder when I eventually build a Sublime amp, does it have a built in gain? Or does it's volume go from 0-35W based on normal RCA line level input?

[Doc B.]

Yes, the Sublime amp does have a level control on it so you can match levels to track with the main speakers. I can't speak to every amp, but with a Stereomour or S.E.X. amp the gain of the Sublime is adequate for the Subette to easily match the output level of the Pipettes. This is with the speaker output of the Stereomour or S.E.X. amp connected to the RCA input of the Sublime - a perfectly good way to connect the two that is described in the Sublime manual.

I looked back at your original post and realized I failed to address a couple of points. The 70Hz crossover frequency between the Pipettes and Subette has been deteremined by a lot of measurements, not by open air specs on a spec sheet. The Mark Audio driver does get down to around 70Hz in the Pipette cabinet. And the filter circuit in the Subette amp seems to help the Subette get down below 50Hz pretty well.

There is no doubt that the system can be driven into a bit of distortion if pushed hard. It's a small system using small drivers and physics is what it is. I have found that the power levels of the S.E.X. or Stereomour are such that the Pipettes go into a bit of distortion when pushed hard at just about the same level as the Subette running on the Sublime. The system will never play as loud as, say, Jagers with our upcoming big amp. But it will work very nicely at average listening levels.

[ipetruk]

Thanks.

I think I need to make sure my assumptions are correct. I assume there is some "standard" RCA voltage level that usually goes between interconnects. For example between DAC and the amp. Was it 2V or 4V? Please let me know if I am wrong in this statement. I know it is too general, but say we take 10 DACs, I expect their RCA output at max volume be in the same ballpark.

I have my integrated amp pre-out that I can only assume outputs "standard RCA" voltage at max volume. But I don't listen at max volume. This means that my integrated amp outputs only a fraction of that. That's why my 160W Fosi barely moves 35W Subette driver. When I add an extra "middle man" pre-amp with high gain, suddenly it all works perfectly and Fosi does not even need to be at max volume. It's like pre-out of the integrated amp is a problem
 

This is with the speaker output of the Stereomour or S.E.X. amp connected to the RCA input of the Sublime - a perfectly good way to connect the two that is described in the Sublime manual.

If Subette expects a speaker amp output into it's RCA, that can be well higher voltage. For example which voltage would S.E.X. or Stereomour output when Pipettes are playing at listening level? If that is like 10V, but my integrated amp pre outputs 1V, that's a huge difference and I will need to have an additional gain box in the chain to power Subettes with Sublime

I suppose I could connect speaker output of my integrated into Sublime, trying to replicate your suggestion. The level must be correct because it powers Pipettes simultaniously. Do you suggest trying that? I just haven't heard of connecting speaker outs to RCA inputs before. But if it is designed for it, then it must work with a third party amp that works well with Pipettes already

[Doc B.]

PJ once told me "Engineers love standards. That's why there are so many different ones."

Connecting the speaker level output of the main speaker amp to the input of the subwoofer amp is predicated upon the idea that the speaker output impedance of the main speaker amp is very low and the input impedance of the subwoofer amp (i.e. the subwoofer amp level control) is relatively high. That makes the load of the subwoofer amp on the main speaker amp output pretty insignficant relative to the more demanding low impedance load from the main speaker that is in parallel with the subwoofer line input.

Of course you must have a way to adjust that level coming from the main speaker output as it goes into the subwoofer amp. It sounds like you are using a power amp to run the Subette. So you would still need some sort of level control - like you are using on your preamp - to trim the level into the subwoofer coming from the speaker output of your main amp. The Sublime amp has a level control like this.

Typical DAC level output is oft quoted as 2V rms . Or peak. Or whatever. In the real world DAC output levels are all over the place. And that's just one part of the puzzle. The gain of every stage in the preamp and amp circuits influences this tremendously as does the relative sensitivity of the main speakers vs. the subwoofer. And those amp and preamp gains are also all over the place.

And so while I can offer pretty exact level settings for when our amps and speakers and subs are all used together, using different amps (or speakers) mixed with our stuff really becomes a smoke it and see kind of proposition. It's not just our products, that's pretty much true any time you mix any amps, preamps, speakers, etc.