Solid state amp to drive field coil woofers? Thoughts?

Apr 1, 2018
37
11
13
Ohio
#1
Team--

I had a custom pair of high efficiency field coil open baffle speakers built...full range with augmenting super tweeters and woofers. I'm using DSP to crossover the Supravox 400 EXC woofers at about 100 and its measuring well and sounding great. The woofers are absolutely improving the overall sound no matter what amp I'm driving them with, but I'm hearing a difference in each and every amp I'm trying, so I know they are responding to the amp changes, and so I am curious as to amps that are going to make the "best" bass with them. They are very efficient drivers themselves (the whole speaker is over 100 db we believe), so it's a somewhat unique situation given the efficiency plus the field coil aspect, so I don't know that a lot of us on this forum have gone down this path.

Right now I'm using a SimAudio Moon i7 (about 150 wpc) to drive them, and it sounds fantastic, and that amp is performing this duty much better than my SIT3, a PrimaLuna HP with KT150s, and a MiniDSP plate amp I was using to drive the woofers on my previous pair of similar open baffles (the prototype).

So my question, I guess, is this...does anyone have a solid state amp they have owned or heard that was magical in the lower octaves? I am really reaching here, as I said the SimAudio already sounds really great, and I'm not sure I want to spend $10K on a different amp just to squeeze out a tiny bit more bass magic...but this forum exists for that reason.

Any thoughts? I would love to stay under $5K used if possible, but if you know of a magical amp for me, please don't let the price stop you from shouting it out.

thanks crew...
 

dcathro

Well-Known Member
Sep 16, 2016
84
58
83
Melbourne, Australia
#2
Hi,

I am not answering your question, but would suggest you say what is important to you in the bass. Is it weight, slam, speed, articulation, tonality, etc.

By the way, what are your other drivers?

I just posted a thread on my field coil speakers
 
Apr 1, 2018
37
11
13
Ohio
#3
That's a fair question, and I guess i would answer it as dynamic, tight, musical, and realistic tone vs. big bold to the side of over-emphasized. I know some people prefer a bigger, harder hitting bass to augment, but I'm more about tonal accuracy combined with the right speed and dynamics, maybe at the cost of not going as low or having quite as much chest thump?

My full-range drivers are Rullit Super Aeros in this pair. I had the speakers custom built...Rich has actually built me 3 pairs of fully custom speakers over the years, and a 4th single mono. We've used Rullit full-range field coils in two of the stereo pairs and the mono, and 604Es in the 3rd stereo pair. All have been open baffle as that has worked the best in my spaces vs. boxed or horned. We then worked with a great amp builder for custom power supplies for the field coils and I have been super happy with those as well...fully adjustable which is nice to tweak with different amps used.

I am very happy with these particular Supravox drivers, but we were disappointed with a full-range pair from them that we tried in an earlier prototype...I don't remember which ones we tried but could find out I'm sure...sounds like you modded ones from them?

I will check out your other posts on the field coils...I too have become quite a fan.
 

dcathro

Well-Known Member
Sep 16, 2016
84
58
83
Melbourne, Australia
#4
Hi Parsons,

I thought with open baffle, speed and articulation would be things that you want to focus on.

The Rullit drivers always look beautifully engineered, but I have yet to hear a pair.

Can you post some pictures of your setup?

I am intrigued by your custom power supplies. I am just using large Agilent industrial supplies for the bass, and lab supplies for the widebander. This is an area that I want to work on. Everyone says that Tungar supplies sound the best.

Cheers

David
 
Apr 1, 2018
37
11
13
Ohio
#5
I worried about that with the open baffles as well, but they don't have any perceptible speed concerns at all...if anything, I would say that they sound even quicker than previous setups I've owned. I can't prove this, but I think the field coil setup, when properly done and powered, contributes to that.

I am travelling today but will send some photos when I'm home tonight or tomorrow.
 

dcathro

Well-Known Member
Sep 16, 2016
84
58
83
Melbourne, Australia
#6
I worried about that with the open baffles as well, but they don't have any perceptible speed concerns at all...if anything, I would say that they sound even quicker than previous setups I've owned. I can't prove this, but I think the field coil setup, when properly done and powered, contributes to that.

I am travelling today but will send some photos when I'm home tonight or tomorrow.
Sorry, I meant that they are strengths that you want to preserve and accentuate.
 

dcathro

Well-Known Member
Sep 16, 2016
84
58
83
Melbourne, Australia
#8
Wow, looks like a fantastic setup! The workman ship on the speakers is stunning.

Is Treehaus Audiolab a company?

The power supply looks neat. Are there dials to control the voltage/current?
 
Apr 1, 2018
37
11
13
Ohio
#9
Thanks, sorry the photos weren't great--I had trouble uploading a couple others for some reason.

Treehaus is a relatively new brand, yeah. I don't even think he has a site up yet...but I have contact info for him obviously if you were interested in contacting him. I met Rich (the owner/builder) on a couple forums, and after about 6 months of interactions, I had him build me my first pair of open baffles with Rullit drivers, which he had used with a couple of other builds (and for his own speakers, I later learned). I've gotten to know him very well as a result, and after the first pair was such a success, he has since built me 2 more pairs of stereo speakers and one mono. A have been incredibly satisfied with each build...easily an understatement.

As you noted, Rich's work is over-the-top and always exceeds my expectations, both from a sound quality perspective and from a build quality and aesthetics perspective. He is incredibly easy to work with, super knowledgeable, and builds a very bespoke product, which I thought was awesome as I have been pretty picky with designs, and definitely with sound quality. He has been very patient with me, and we changed the design and parts list for a couple key items while testing the sound of the drivers in various enclosure designs. As mentioned in a previous post, we tried Supravox full-range drivers in the first pair, but in comparing them to 3 sets of Rullits we had, we decided to go with the Rullits as the mains in 3 of my 4 sets of speakers (we used 604Es at my request in one pair).

As part of the first build, he introduced me to Radu Tarta, who has built me 3 field coil power supplies and has built me 3 amps (so far)...similarly, his work is fantastic in the same regard as Rich's, and he also does a great job with custom work. And yes, Radu has built all 3 of my power supplies to be adjustable within the appropriate ranges of the drivers, which is awesome and works to really tune each field coil driver to amp changes and personal sound preferences...I would never have a power supply built without this feature, honestly. I had a solid state power supply built for the Supravox woofers (at Radu and Rich's suggestions), and he built a tubed hybrid (I think hybrid?) for two sets of Rullit full-range drivers. Rich helped Radu determine the tech and look of the power supplies and amps on my behalf, so that was a huge help to me, not being super technical.

Rich also helped with my discussions with Oleg Rullit in terms of determining what levels of full-range field coils I wanted for each build...also a very welcome help.

As I read my glowing review, I should also note I have ZERO financial affiliation with either Rich, Radu, or Oleg, but I certainly stand up as a very satisfied customer of all of them, and have met Rich and Radu in person during the process of the builds, and each are super guys too. Oleg was great to communicate with as well.
 
Jan 29, 2012
1,818
1,052
520
#10
Thanks, sorry the photos weren't great--I had trouble uploading a couple others for some reason.

Treehaus is a relatively new brand, yeah. I don't even think he has a site up yet...but I have contact info for him obviously if you were interested in contacting him. I met Rich (the owner/builder) on a couple forums, and after about 6 months of interactions, I had him build me my first pair of open baffles with Rullit drivers, which he had used with a couple of other builds (and for his own speakers, I later learned). I've gotten to know him very well as a result, and after the first pair was such a success, he has since built me 2 more pairs of stereo speakers and one mono. A have been incredibly satisfied with each build...easily an understatement.

As you noted, Rich's work is over-the-top and always exceeds my expectations, both from a sound quality perspective and from a build quality and aesthetics perspective. He is incredibly easy to work with, super knowledgeable, and builds a very bespoke product, which I thought was awesome as I have been pretty picky with designs, and definitely with sound quality. He has been very patient with me, and we changed the design and parts list for a couple key items while testing the sound of the drivers in various enclosure designs. As mentioned in a previous post, we tried Supravox full-range drivers in the first pair, but in comparing them to 3 sets of Rullits we had, we decided to go with the Rullits as the mains in 3 of my 4 sets of speakers (we used 604Es at my request in one pair).

As part of the first build, he introduced me to Radu Tarta, who has built me 3 field coil power supplies and has built me 3 amps (so far)...similarly, his work is fantastic in the same regard as Rich's, and he also does a great job with custom work. And yes, Radu has built all 3 of my power supplies to be adjustable within the appropriate ranges of the drivers, which is awesome and works to really tune each field coil driver to amp changes and personal sound preferences...I would never have a power supply built without this feature, honestly. I had a solid state power supply built for the Supravox woofers (at Radu and Rich's suggestions), and he built a tubed hybrid (I think hybrid?) for two sets of Rullit full-range drivers. Rich helped Radu determine the tech and look of the power supplies and amps on my behalf, so that was a huge help to me, not being super technical.

Rich also helped with my discussions with Oleg Rullit in terms of determining what levels of full-range field coils I wanted for each build...also a very welcome help.

As I read my glowing review, I should also note I have ZERO financial affiliation with either Rich, Radu, or Oleg, but I certainly stand up as a very satisfied customer of all of them, and have met Rich and Radu in person during the process of the builds, and each are super guys too. Oleg was great to communicate with as well.
I’d love to see the rest of your system. The speakers and the power supplies look fantastic.
 
Jun 13, 2013
11,629
2,449
603
E. England
#11
Parsons, there is a dealer a few miles from me running Maxonic field coils from Japan, a little tasty at £80k+. I believe powered by Soulution SS.

Are you aware of the Maxonics? At 100dB+ efficient, they surely cry out for medium power triodes.
 

Atmasphere

[Industry Expert]
May 4, 2010
968
180
455
St. Paul, MN
www.atma-sphere.com
#12
Since the speakers are open baffle, an amplifier with a low output impedance is likely to cause a bass rolloff. Open baffle speakers generally use tighter suspensions and are supposed to be loaded by the room/baffle combo. So I would recommend an amp with a higher output impedance, but one that also has the bandwidth and speed you are looking for. This might be tricky to do with solid state! But if you are set on that, then Nelson Pass has done some experimenting in this area and has built solid state amps employing current feedback to raise their output impedance.

Our amps are zero feedback but owing to direct coupled outputs, have full power to 2Hz so no phase shift at 20Hz. The best tube amps with output transformers tend to have a 5Hz cutoff- so phase shift below 50Hz is common- that robs you of impact IME.

Beautiful setup BTW! I'm really curious about that field coil midrange. I run field coils in my speakers, but the midrange drivers are horn loaded.
 
Apr 1, 2018
37
11
13
Ohio
#13
Parsons, there is a dealer a few miles from me running Maxonic field coils from Japan, a little tasty at £80k+. I believe powered by Soulution SS.

Are you aware of the Maxonics? At 100dB+ efficient, they surely cry out for medium power triodes.
No, I'm not, but super interested to read about them. Would love to hear what you think of them if you get a chance to hear them. That's considerably higher $ price point that I'm capable of!
 
Apr 1, 2018
37
11
13
Ohio
#14
Since the speakers are open baffle, an amplifier with a low output impedance is likely to cause a bass rolloff. Open baffle speakers generally use tighter suspensions and are supposed to be loaded by the room/baffle combo. So I would recommend an amp with a higher output impedance, but one that also has the bandwidth and speed you are looking for. This might be tricky to do with solid state! But if you are set on that, then Nelson Pass has done some experimenting in this area and has built solid state amps employing current feedback to raise their output impedance.

Our amps are zero feedback but owing to direct coupled outputs, have full power to 2Hz so no phase shift at 20Hz. The best tube amps with output transformers tend to have a 5Hz cutoff- so phase shift below 50Hz is common- that robs you of impact IME.

Beautiful setup BTW! I'm really curious about that field coil midrange. I run field coils in my speakers, but the midrange drivers are horn loaded.
Ralph, thanks for the post. I actually own your M60 3.3s, but have been running them in another system. I will definitely pull them out and give them a try here on these woofers...Rich (who built these speakers) actually suggested the same thing to me this past weekend while I was out of town, so I haven't had a chance to try them yet!

I tried the SIT 3 (I own that too) from Nelson, but perhaps I need to look up further his his Pass line...the SIT 3 didn't quite have the grip I was looking for.

BTW, I acquired a Cary SA-200.2 (one of their two current-model solid state amps) while on my trip, and it's doing very, very well at driving the bass woofers, so it's currently in the driver's seat.

thanks all...
 

dcathro

Well-Known Member
Sep 16, 2016
84
58
83
Melbourne, Australia
#15
Thanks for the information on your speakers Jay! The photos look great, but I would love to see some shots from a distance.

I love your approach - not mainstream!

A few questions:
  • how many powers supplies do you have, and are they all the same?
  • did you compare different power supplies.
  • What voltages do you run the different drivers at?
  • how do you cross over from the full range to the tweeter
  • Are you running the Rullit and tweeter passive and the bass active with dsp and a separate amp?
  • how smooth are the Rullits in the upper octaves? - I have been wary of wizzers.
  • which Supravox widebander did you try?
  • How did the Rullits compare with the Supravox widebander?
  • Did you compare open baffle bass with sealed/ported?

Thanks

David
 
Apr 1, 2018
37
11
13
Ohio
#16
  • how many powers supplies do you have, and are they all the same? I have one solid state for the woofers, and one tube hybrid for the full-range--they are customized for each driver type by Radu Tarta
  • did you compare different power supplies. in an earlier pair of Rullits, there were hospital grade power supplies used, but I never heard them
  • What voltages do you run the different drivers at? I've been running my Supravox woofers between 12-14v pulling about 5A (their range is stated 9.5-14v), and the older modded Rullit drivers are much higher at 105v, pulling 85 milliamps
  • how do you cross over from the full range to the tweeter. a simple first order passive at like 15K I think
  • Are you running the Rullit and tweeter passive and the bass active with dsp and a separate amp? yes
  • how smooth are the Rullits in the upper octaves? - I have been wary of wizzers. they are insanely smooth--especially the Super Aeros, but I always felt that even the Classics were quite smooth
  • which Supravox widebander did you try? a don't know, can try to find out (we bought them used on eBay I think)
  • How did the Rullits compare with the Supravox widebander? much, much better according to Rich
  • Did you compare open baffle bass with sealed/ported? not with the open baffle up top; the sealed box prototypes Rich tried included a bass driver in one iteration, but I don't think I ever heard them with the bass drivers included
Here are some system shots as requested:

BF9D59D3-9A3B-4D09-99FE-CAE6CC05569A_1_105_c.jpeg FD155830-67EB-4E01-BA37-A246F2957A0C_1_105_c.jpeg 35B04C19-CC88-4E97-8D49-AA89BCDB5B71_1_105_c.jpeg 7E694855-1C11-4B5F-8BE5-5B9560B832CB_1_105_c.jpeg 60DDF25C-E564-4F3B-9088-B7C333B397E9_1_105_c.jpeg 974EF7A8-CA14-404A-A39C-753292D77F14_1_105_c.jpeg 1FF97296-309E-4A16-9F0B-8482CDBC84B9_1_105_c.jpeg E5BF6306-0E55-4BDE-B007-40003657E162_1_105_c.jpeg 5B2BE68C-A5D1-4AD9-8F23-F6EEAA0A1607_1_105_c.jpeg
 
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dcathro

Well-Known Member
Sep 16, 2016
84
58
83
Melbourne, Australia
#17
Hi Jay,

Thanks for your reply. I love the pics. I like the way they have used solid timber for the speaker baffle. I also love the look of your roo, it looks big and really solid.

It is interesting that the Supravox bass units pull 5A at 12-14V, my bass units only pull 1.5A at 12V.

Do you notice a big difference in tone when you change the voltage?
 

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