Experiment with sub amp

[Tim G.]

I have been tinkering around with some H and U frame subwoofer setups with my Straight 8's that have been sounding pretty good.  To this point I have just been using a spare plate amp to power this sub but think it might be time to get serious and build an amp dedicated to driving sub.

I was thinking that trying to keep topology similar to the paramours would be good (maybe doesn't matter?) and stumbled across this schematic:

http://www.audioasylum.com/forums/magnequest/messages/497.html

So a triode strapped 6v6 parafeed, that should match nicely in to the system right?  I'm not that familiar with the math involved but that should be about 10-15 watts right?  I have read what I can from the 6v6 competition but couldn't find too much on the actual topology or schematics for the contest entries but they looked pretty cool!

System is a Foreplay II -> Paramours -> Straight 8's  (which by the way the latest crossover design takes to a whole new level)

Thoughts, Comments, Suggestions?

 

[Doc B]

That's only going to give you about 2 watts. We're starting to work with a parafeed 6550 design and I have been using a rather non-optimal triode strapped version that gets close to 10W. So far I am liking what is does on my woofers which run from 250Hz down. The long term plan is to see what we can do about getting more power out with different output stage designs.

 

[Grainger49]

How about a 6C33CB mono block?  It will take pretty beefy transformers to feed it, but can be pretty powerful.

 

[Tim G.]

Well that really doesn't seem to be the way to go does it!  I guess I don't completely understand the power calculating from this design versus just a single ended design. 

The 6550 setup sounds interesting, but I'm not familiar with the 6C33CB tube that you mentioned Grainger will have to do some research on that one. 

So what are the thoughts on any "synergistic" advantages to trying to go parafeed?  A worthy requirement, or not neccessary?

Thanks for the quick responses!

 

[Grainger49]

For what it is worth, tubed sub woofer amplifiers are few and far between.  This is one of the areas where solid state amps shines.  Power/current into low impedances with high damping factors are for the most the forte of sand.

The 6C33CB is used in a number of Balanced Audio Technology (BAT) amps.  It is physically big and has a bunch of current needed for the plate (550mA) as well as the heaters (3.3A at 12.6V).  A pair in push pull produce 55 WPC at 8 ohms.  IIRC, Borbely Audio used to make a SET with it.

 

[Doc B]

I think that S8s on tube amps and a sub with a solid state amp would be OK. In fact that is what is running in my HT right now. Cross the sub over at about 50-60Hz. I'm using tubes in my main system because the woofers go up to 250Hz, where the better lower midrange sound of tubes can start to become apparent and better blend with the midrange amp.

 

[ironbut]

I have a big 6550/kt88 PP amp driving my Magnepans. And while it's certainly not the last word in the mids/tweeters, what it does in the upper to mid bass is outstanding. To me, there's something special about the sound of these tubes in the mid/upper bass, namely a very organic roundness and smoothness especially when the sound is cranked up. I've heard some really nice subs driven with ss and in the very lowest registers, I don't think they can be beaten. But when the controls are set to anything above 60Hz or so, my pleasure meter starts to dip.
Now, I can't say that what I'm enjoying is accurate or right, but it's good enough so I'm not concerned whether it is or not. And I guess that's one of the luxuries of being an end user.

 

[Tim G.]

Well that certainly gives me some good info to go on, sounds like a tube version might be a larger project than I thought.  I might just sample some solid state options.

Thanks!

 

[corndog71]

I built a single servo sub kit from GR Research.  Get the woofer and servo amp and you can follow the plans posted there or do something different like I did.

http://www.gr-research.com/index.asp?PageAction=VIEWPROD&ProdID=139

This might be the last sub you ever get.  It's powerful and extremely fast.  Very musical sub.  All you have to do is build a well-braced cabinet with 1.5-1.8 cubic feet of volume.

 

[Grainger49]

Rob,

Is that "cabinet" a stack of wooden donuts?  Would it work similarly using a fiber core?  That is easy enough for most to do without woodworking tools.

 

[corndog71]

Yeah, I started with a 4'x8' sheet plus another 1/4 sheet of MDF from home depot.  About $35.  I'm no woodworker which is why I opted to build a tube-shaped cabinet - no straight lines or square issues to worry about.  All you need is a good plunge router and a circle jig.  Maybe a few other tools. 

The bottom 2 are solid discs and the rest are 14"OD rings.  It wasn't too difficult but still was a lot of work. 

Not sure what you mean by fiber core. 

 

[Dyna Saur]

Would a "fiber core" be the same thing as the "Sono Tubes" which are normally  used as forms for pouring cylindrical concrete footings?  They come in a variety of diameters. Just think "very thick and strong cardboard tubes".   I have  believed that they could have some interesting  speaker-building possibilities.


/ed B in NC

Builder and owner of 1 pair "stock"  Paramounts, 1 pair of upgraded  Paramour IIs, two SEX amps (one upgraded, one bare essentials), two FPIII (one stock, one 6SN7 and step attenuator modified) , one somewhat modified  FP II,  one stock  Seduction, and two Quickies (and coming soon,  one Crack). 

 

[Grainger49]

Rob, think of a toilet paper inner core on steroids.

Ed, Yes, my experience with them were for center cores winding non-woven material or paper into 4' or 5' diameter rolls 12' wide.  I would guess the same companies making the cores I used make the ones that are used for concrete forms.

 

[Skip Pack]

If you take two sonotubes of different diameters leaving about 1-2" of
airspace in between them when one's inside the other, you can put on
end caps and then foam the airspace. It's ultra-rigid, and fairly light.

Skip

 

[corndog71]

While that might work in practice, the cabinet may end up resonating too much to make it worth it.  This sub/amp combo is reference stuff and deserves the best enclosure you can give it.  It'll easily hit 20Hz with a -3dB in the teens.  The amp has a lot of flexiblility too.

If building one is too intimidating you can always buy one from the guy who designed the amp.


http://www.rythmikaudio.com/F12G.html

 

[Grainger49]

Rob,

Are you familiar with the tubes we are discussing.  They are rigid enough to hold yards and yards of concrete.  They also sustain many pounds of pressure from material wrapping around them. 

Seriously, pretty stout.

 

[corndog71]

I am familiar with them.  Like I said, they may very well be rigid enough to make an enclosure, they may not be ideal for a subwoofer enclosure due to their resonant properties.  If they resonate in the audible range then they will not be very accurate for audio use. 

I've actually seen subwoofers made with these tubes before.  I would say if you were using less expensive drivers and electronics then go for it.  For all I know they might work just fine.  FWIW my tube sub despite 1" thick walls vibrates more than I anticipated.  The plans given on GR's website are for very stiff enclosures.  There's an alternate "sandbox" version which has a box within a box with sand-filled walls that is so dense you can't feel ANY vibration from the cabinet.

I can certainly appreciate saving on labor and materials but if you look at some of the best speakers out there you almost always find a well-braced and very dense cabinet.  There are some aspects to physics you just can't cheat.

Of course you can try it and see how it sounds.  If it works, let me know.  Maybe try the tube within a tube and fill it with sand in between.  So long as you have the correct volume you're fine.  And get some poly-fil for the inside as well.  About a pound should do it.