Depends what max output your “normal” preamp can do. Assuming it is an opamp based one that runs off of dual 15v rails, you may get +/-12v easily assuming your gain is there.
Like ZM said, 8Vpp for 1w and 11.1Vpp for 2w.
Just got my MoFo up and running and sounds promising.
Decided to switch to an OTT CRC supply due to a noisy laptop psu (and because I'd bought most of the parts for an F4), and wow what a change.
I feel assaulted and it didn't sound as if it was fed with a valve pre-amp. The detail was astounding with so much grabbing my attention. Bass was great and taught. And the sound stage - at one point I felt I was being flanked and surrounded.
The downside was it was just too 'detailed' especially in the higher octaves, with many of the audible little dings, taps etc on some recordings distracting me from the many positives. I'm hoping that some of this will mellow with further use and there being so many large electrolyics - is this normal and might things settle down? Perhaps some silver interconnects needed at least in the short term to tame things a little!
The other good thing is that at 19V and around 12W, I find myself questioning whether I need to strive for any more power.
But got to get my priorities right so first thing must be to sort out the hum on my 41MP pre-amp.
Decided to switch to an OTT CRC supply due to a noisy laptop psu (and because I'd bought most of the parts for an F4), and wow what a change.
I feel assaulted and it didn't sound as if it was fed with a valve pre-amp. The detail was astounding with so much grabbing my attention. Bass was great and taught. And the sound stage - at one point I felt I was being flanked and surrounded.
The downside was it was just too 'detailed' especially in the higher octaves, with many of the audible little dings, taps etc on some recordings distracting me from the many positives. I'm hoping that some of this will mellow with further use and there being so many large electrolyics - is this normal and might things settle down? Perhaps some silver interconnects needed at least in the short term to tame things a little!
The other good thing is that at 19V and around 12W, I find myself questioning whether I need to strive for any more power.
But got to get my priorities right so first thing must be to sort out the hum on my 41MP pre-amp.
Attachments
Pass DIY Addict
Joined 2000
Paid Member
Ah - welcome to the club! I just love my MoFo being driven by a BA-3. I have many of the same reactions that you do, especially the enveloping sound stage. This amp does seem to coax out more bass than some of my other DIY amps.
I haven't noticed too much detail on the top end as you have. Perhaps this is something specific to speakers or other components in the chain?
I'm running both channels (6A current draw total) from the same 12A Dell power brick and haven't experienced any problems with power.
Got the bug now and after months of looking, finally found some half suitable MOTs.
Primary resistances of the four models I measured were 3 Ohm and over but one pair were slightly lower at 2.1R, nevertheless significantly higher than what some US users have suggested. L>150mH.
Anyway should be able to get around 12.6W so enough and get the benefit of using the small Hammonds in a CLC power supply.
Primary resistances of the four models I measured were 3 Ohm and over but one pair were slightly lower at 2.1R, nevertheless significantly higher than what some US users have suggested. L>150mH.
Anyway should be able to get around 12.6W so enough and get the benefit of using the small Hammonds in a CLC power supply.
Attachments
That's awful high. Cuts audio output power some.
Build as-is. Try. Maybe you won't miss the power you lose.
But the primary is on the outside. With care (bright light, sharp picks) you can free the outside end of the winding and unwind about half of the primary. That's far from optimum, but these MOTs are oversized for our need, a sane-size MoFo won't cook half the primary. Re-figure your bias! on the new DCR.
Take care secondairy voltage of the MOT is ~ 300V with ~ 24V on the primary.
Don't touch it but need isolate secondairy winding help avoid the danger
Just finished one substuting a IXYS IXFK44N50P. A poster a number of pages back had done it. I sent him a PM but never got a response. I just assumed the existing components on the board would be fine. I biased it at 1.80 amp. The idea is to have a more robust output device to handle the extra amperage. I am getting a slow motor board thumping through the speaker with no signal present.
Suggestions?
Suggestions?
I was getting that on power-up on one channel - the culprit was a faulty/noisy laptop supply.
I tried a different power supply with no difference. What I did discover is if I press on the heatsink it stops for 15 seconds. When I take my hand way it speeds up and then settles back to a slow thump. Same thing when I went to remove the power supply power cord. The thump stopped when I held the power supply AC plug end and when I pressed on the AC three inlet adaptor.
I suspect grounding is not optimal. The other amp with the IRFP does not do this.
So, here is where I am now. I decided to put a signal to the amp. As soon as I turned on the preamp, no thumping. Dead silence. I played two full CD's and it sounded wonderful with no noise between selections or change of disks.
I have it back on the bench checking connections etc. I will go to a regulated conventual power supply for both next as well.
Thanks for your input guys.
So, here is where I am now. I decided to put a signal to the amp. As soon as I turned on the preamp, no thumping. Dead silence. I played two full CD's and it sounded wonderful with no noise between selections or change of disks.
I have it back on the bench checking connections etc. I will go to a regulated conventual power supply for both next as well.
Thanks for your input guys.
Mofo Hybrid
This is my version of the MoFo using a tube driver section plus cathode follower section per channel. The heat sinks are not that big so I'm running 22V @ 2A. The heat sinks are pretty warm, but I could probably hold my hands on them indefinitely. Not sure how hot is ok, and it's only been running about 1/2 hour.
I haven't hooked up my main speakers to this yet. Right now just running some small bookshelf speakers. Sounds pretty good though.
This is built on a rack mountable shelf, so at some point I'll put the rack brackets back on it and install it in my free standing rack.
Thanks to the OP for a cool design and everyone who has posted here. Lots of great information.
This is my version of the MoFo using a tube driver section plus cathode follower section per channel. The heat sinks are not that big so I'm running 22V @ 2A. The heat sinks are pretty warm, but I could probably hold my hands on them indefinitely. Not sure how hot is ok, and it's only been running about 1/2 hour.
I haven't hooked up my main speakers to this yet. Right now just running some small bookshelf speakers. Sounds pretty good though.
This is built on a rack mountable shelf, so at some point I'll put the rack brackets back on it and install it in my free standing rack.
Thanks to the OP for a cool design and everyone who has posted here. Lots of great information.
