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Chronicling my journey into low power and open baffle

MKG

MKG

Elvish-mark’d abortive, rooting hog
This will be an ongoing thread, chronicling my journey into lower wattage amps and open baffle speakers.

It may split off into just one of those if the other doesn’t catch my fancy.

I recently measured the output of my amps at my typical listening level and realized that I was using significantly less than one watt out of the 650 watts in my system (2x 300w mosfet mono blocks and a stereo 25w/channel tube amp.)

Long story short, while I’m not getting rid of any of my higher power gear, I’ve decided to see what lower power / flea watt amps and more efficient speakers can do.

To start, I’ve got a pair of Wild Burro Betsy drivers on the way. They haven’t arrived yet so I can’t say anything about them.

As far as amps go, I’m starting with a Dumont Emerson 719/720. New caps are on the way for it, as well as a couple resistors and a 5y3 rectifier tube. Based on my AK search engine skills, it’s a SE EL84 design- but its circuit is designed to power a tuner as well, and swapping out the original 5u4 for a 5y3 and using a 120 ohm resistor at r82 will apparently help me get voltages correct and avoid the red plating issues others have had.

Amp is still sitting unmodified and drivers haven’t arrived yet, so I’m not sure where this will go.
 
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In my tube system I' powering open baffles that I made with a Decware zen amp [2 watts] 4 ohm,I forget the efficiency rating but I'm really pleased with the sound.
They have two Dayton 10in. and a Dayton tweeter,sorry I forget the model no. Those Betsy's your getting are the way to go. I do boost the bottom end just a taste with a sub,it's a cool set up.
 
Funny, lately I've found myself enjoying lower powered tube amplifiers.
Both low powered SEP's and PP. I can't really explain it yet. Less junk in the signal path?:dunno: I have some drivers waiting for an OB build myself.
Good luck and enjoy the ride, I am! :thumbsup:
 
If you want the mids to shine 45's are the way to go if speakers are up to the task. OB doesn't shine unless everything comes together. More power always suits low frequency best. Bi-amp
 
The EL84 is a pentode. Do you know if the amp is wired triode, pentode or Ultra Linear? Triode will give less power. Some really like the triode strapped pentodes and direct heated triodes. Wired pentode or UL will give you a bit more power and after listening to both, pentode and UL seem to have a better bottom end to my ears. My 35wpc push pull amp can be switched to triode mode. To my ears it sounds thin and lacking that bottom end punch. Adding a powered sub or helper woofer can really help also.
Vocals sound nice though.
 
MKG said:
I think it’s UL? I need to do some research so that I know the difference. :D
Click to expand...
I have a 300B SE triode amp, I have a SE UL amp l really like. I tried it triode strapped and wired pentode. I left it UL, it sounded best to me. It was very close to when it was wired pentode though.
 
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5F358FA6-466D-45B7-98AA-06E9C6B0B7F5.png 46B46F74-5A1D-4688-8B77-A83ECA2655B9.jpeg Most of the bits arrived to rebuild the little dumont Emerson 719 tube amp!
Pile to the right are things I already had on hand. While this thing takes a 12ax7a, that pair of tubes is actually for my Lowrey organ pull tube amp.

I should have paid more attention to the dimensions of the caps- it’s gonna be a bit of a squeeze to get those in there. Also, apparently I completely forgot to order an iec power input module- gonna hafta temporally steal one from an old pc power supply.

Still waiting for the 5y3 to arrive- I have a 5y3gt on hand that I’ll probably use to try this out tonight, but without a tube tester I have no idea if it’s any good. I really need to pick one of those up sometime soon.

edit- forgot to add pictures.
 
Yeah, I went through the same thing when I built my speakers using high efficiency drivers. I'm finding low wattage single ended amps give the most transparent, and natural sound I've ever experienced without losing detail.

I swear by the 6WPC Wavebourn Edelweiss-3 power amp, and I've a 2.5WPC Chi-Fi Pass Amp Camp Amp inspired amp as well which is just spectacular. Even better than my 1969 Hood amp.

Even though only one of these amps is tube they're all single ended class A designs.
 
Was a tight fit, but all new caps are installed. Won’t fire it up yet- I still need to replace r82 with a 120ohm resistor. I have multiple 1w 120ohm resistors, but it calls for a 2w, and I’ve got 5w on the way.

There’s not a lot of room under this thing, so unless I build a higher wooden base, I’m not sure that I can fit the typical emi/rfi filtered iec power input that I usually use for my builds.

If it sounds decent I’m totally up for that- but for experimenting I may just direct wire a 3 prong plug with an inline fuse.

Betsy drivers should be arriving soon, I’m probably gonna buy some wood tomorrow so that I can get to work on the baffles. I’m going to start with the basic design on Wild Burro’s project page, and do some research and deviate from there.

6B7F18C1-6E73-4D4A-AFDF-3B47F15A4B7F.jpeg
 
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Started on the same journey a couple of years ago, haven't looked back yet. Single ended triode and pentode amps when done right and matched with good OBs just flat nail the mids. I very rarely ever listen to box speakers anymore.
 
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My OB journey began with the single driver Betsy's in folding wings and then I reduced the size of their baffles and added helper woofers. Driven by low power SET amps with solid state power for the woofers, I've never looked back.

PB230008.jpg
 
Enlarged a hole in the amp chassis and made a new hole. Larger hole was for a panel mount fuse, new hole was for an o-ring and power cable. Can’t fire it up until that damn resistor arrives.

8F6C7CCE-2CA0-4765-BB99-59BF0966B117.jpeg

Betsy drivers should arrive on Thursday. I’ll be buying some wood and building the recommended design the same day.

In the meantime... research.

I’m not typically one to blindly experiment- I like to have at least a basic understanding of why I’m doing what I’m doing.

That basic understanding allows me to modify things and experiment in a productive way. It saves me lots of money and frustration.

I’ve been struggling to find information on open baffle speaker design- I’ve found lots of stuff that says, “use this driver and cut things to this size”, without any explanation for why- unlike enclosed speakers. I’m fairly well versed in those and have or can find lots of books and calculators to figure out everything from enclosure size to port size to how much “stuffing” to shove in it. I even have a fancy dats v3 measurement device that can tell me driver specs so that I can make sure my design is up to snuff.

Info doesn’t seem as readily available for open baffle design theory, or maybe I’m using the wrong search terms. The article below is the first one I’ve come across that starts to give me useful info. Do any of y’all have any other useful articles/links/calculators focused on open baffle design theory?

http://www.hi-fiworld.co.uk/loudspe...udspeakers-open-baffles-and-bass-part-15.html
 
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