Hi Everyone, I was hoping for some advice.
I’m considering a three way speaker build, that goes against my new rule of bi-amping for the bass driver for frequencies below 200hz. Therefore enabling low powered Class A tube and Solid State amps from the lower mid-range upwards.
It’s a 1” dome, 3” mid and 15”woofer. Unfortunately the 15” woofer crossover at 375hz. I like 300B amps and already invested.
Does anyone have experience of using an F4 where it is fed by the tube amp just to power the bass drivers above 200hz (to 375hz ideally but any experience welcomed!) I appreciate it’s a critical frequency range and wondering if this is a viable approach than my usual bi-amping.
I’m considering a three way speaker build, that goes against my new rule of bi-amping for the bass driver for frequencies below 200hz. Therefore enabling low powered Class A tube and Solid State amps from the lower mid-range upwards.
It’s a 1” dome, 3” mid and 15”woofer. Unfortunately the 15” woofer crossover at 375hz. I like 300B amps and already invested.
Does anyone have experience of using an F4 where it is fed by the tube amp just to power the bass drivers above 200hz (to 375hz ideally but any experience welcomed!) I appreciate it’s a critical frequency range and wondering if this is a viable approach than my usual bi-amping.
Thanks 6XS7 for the quick response. I have read that PDF. I’d think it’s a wonderful solution for crossing over at 200hz and below. More curious about anyone crossing over higher, such as my example 375hz. As that’s an important part of the lower mid-range.
I built an F4 to do this on my coincident PRE speakers have dual 12s on a 1st order crossover that does a lot of blending like yours (they're at 125hz, but have significant output up there too). I was using a coincident Frankestein 300b as the driver.
My experience was not great. I lost a ton of coherency. Fortunately, however, that led me to try the F4 with the full speaker and I loved it. Eventually built f4 monoblocks, with external power supplies, and premium parts.
Got a dht preamp for voltage gain into the F4 and love what I hear.
I use my F4 with an aikido high gain tube preamp to drive a 3 way. 1" dome tweeter 4" cone mid, with 10" woofer, passive crossover, maybe 85 dB efficiency, no problems driving it to very loud levels in my living room.
The F4 has a reputation for being very neutral so in theory it should have just been supplying some extra current to the signal from your 300B. Have you any theories as to what caused the loss of coherency?
It was easy to hear it fall apart.
I had high hopes since I purpose built the F4 for exactly that role.
I had high hopes since I purpose built the F4 for exactly that role.
Thanks everyone for the responses.
I’ve had great results bi-amplifying another speaker.
What makes you say that? 1st order? Do you think I’d have an issue with a second or fourth order crossover at 375hz?
I’ve had great results bi-amplifying another speaker.
I have an Aikido, I think I need to just build one and do some testing. Will report back.
This is very interesting, what tube did you end up with and what decisions did you make for your ultimate F4?
Just my personal experience trying it. Unfortunately I don't know enough about speaker design to opine further.
I've got a very simple dht pre built around the EML 50a. I loved the idea of a single-stage voltage gain, but was running the tube too hot and running out of gain (and getting distortion). In the end I put a ba3 stage in my F4 case to get the gain structure right.
Built my dual mono F4 back in July but headed out on a work trip before I got around to posting the results. It's a dual mono PSU using Antek AS-3220, @rhthatcher V8 boards (27kuF caps) w/rectifier & AC inrush boards, and the rest is standard "plain-jane" stuff (back panel kit, Mogami W2381 input wire, 14Ga BNTechGo DC wire, 16Ga BNTechGo AC wire, 14ga BNTechGo chassis ground, XFH 3/8" heat shrink for twisted wires, 3D print transformer seats, 3D printed wire management/separation posts, Modushop 5U/400 Deluxe chassis). Biased per the guidance in this thread and wires are soldered direct to most boards per Zen Mods guidance.
This was my first dual mono. I've barely had a chance to listen to it yet as I need to shuffle stuff around to hook it up in my listening setup, so just posting pictures here to help others visualize what I did to pull it all together. Thanks to everyone who's posted support in this thread and others, @6L6 for making a great build thread, and of course Papa for the enormous generosity to this community!
This was my first dual mono. I've barely had a chance to listen to it yet as I need to shuffle stuff around to hook it up in my listening setup, so just posting pictures here to help others visualize what I did to pull it all together. Thanks to everyone who's posted support in this thread and others, @6L6 for making a great build thread, and of course Papa for the enormous generosity to this community!
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That looks absolutely fantastic! Very nicely done!! 
🙂 🙂 🙂
I like the printed vertical wire tower thingamabobbers.
🙂 🙂 🙂
I like the printed vertical wire tower thingamabobbers.
birdbox,
I echo the sentiments of 6L6 and e_fortier on your DIY F4 amplifier - kudos on your well executed dual-mono build in a single chassis!
I also spot your "transformer seat" and strap on band method in action. 🙂
Enjoy!
I echo the sentiments of 6L6 and e_fortier on your DIY F4 amplifier - kudos on your well executed dual-mono build in a single chassis!
I also spot your "transformer seat" and strap on band method in action. 🙂
Enjoy!
Fugly!
Now, put a dozen of amber leds inside, randomly situated, lit them well, and call it McIntosh!
Now, put a dozen of amber leds inside, randomly situated, lit them well, and call it McIntosh!
Question: If one were to run the F4 at a different voltage, (+- 12V ex.) would the bias circuitry work as is, og would it be necessary to change any values? 
Hmmm… that is a good question. I wouldn’t be surprised if it didn't bias properly with the stock resistor values, but it would be easy enough to try it and find out.
Why do you want to run one at such low voltage?
Why do you want to run one at such low voltage?
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Very nice build, Birdbox! The planning and forethought are evident! Dual mono builds get heavy quickly. I was shocked when I was done with my SissySIT and saw that it was near 65lbs. As I turn old and decrepit in the coming years, there may come a point that I'm not able to lift it and work on it anymore 😉.
One detail that I can't see well in your images: if you have any trouble with hum (excellent work on keeping AC wires tightly bundled), you might be able to solve it with a CL-60 (or similar) between channel ground at the board level and AC mains ground at power entry.
One detail that I can't see well in your images: if you have any trouble with hum (excellent work on keeping AC wires tightly bundled), you might be able to solve it with a CL-60 (or similar) between channel ground at the board level and AC mains ground at power entry.