Mofo

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steve s
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#1 Mofo

Post by steve s »

Got these boards from Ray.. (Thanks again ray)
Read up quite a bit and to be honest nearly did not bother to build them.
I'd ordered some of the mosfets and looked at the chokes but in the end ordered the recommended Hammond jobs.
I'd built most of the boards up a couple of weeks ago. The chokes arrived last Thursday so over the weekend got one running just using a 12 volt battery. I've mounted the mosfets on a cpu cooler and fan.. stone cold with the fan on lowest
Anyway it worked on my crappy office speaker. Sounded ok as far as could tell.
This afternoon I set up a couple of 12vt power supplies and a battery for the fan. Soldered all the connectons to the second board. Set it up and running on my crappy office speakers (and my phone going straight into it so low output ) for an hour or so.. all was well.
Tonight I brought it down and it's now on the main speakers. Just fed by the CD player. Much less than a watt of output. But room filling volume..too loud for Ed.
I'm now glad I went ahead with it. it is it is a nice sound. It passed the clapping test with aplumb
(For Steve c ) . The best solid state amp I've built so far. And so simple,
but it needs another stage to drive it and more voltage so anything could happen then.. but at this point I'm very impressed. It seems the backing music is possibly a slighly more recessed than the valve amps, but i'm not really sure.. but it good enough to add a triode to front end and the correct power supply..
Been looking through my books to see what may suit.
Indirectly heated there's the pp3521 /pa1/ mxp41/ ac/p or maybe a dht
I'm not sure.. then thought of some of the battery valves.. the idh valves seem easy..
Last edited by steve s on Mon May 11, 2020 10:56 pm, edited 1 time in total.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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Ray P
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#2 Re: Mofo

Post by Ray P »

This is what I was planning to use on the front end Steve;

http://www.bartola.co.uk/valves/2017/06 ... amplifier/
Sorry, I couldn't resist!
steve s
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#3 Re: Mofo

Post by steve s »

Thanks ray, those valves get good reports. But I'll be using something I already have.
I have a spare pair of nano interstage txs I may incorporate and would néed to match those, but I'm still not sure,
I'll try and keep it all simple to match the output stage.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
little eddy
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#4 Re: Mofo

Post by little eddy »

You're progressing a damned sight faster than I did.
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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izzy wizzy
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#5 Re: Mofo

Post by izzy wizzy »

Ray P wrote: Mon May 11, 2020 10:10 pm This is what I was planning to use on the front end Steve;
http://www.bartola.co.uk/valves/2017/06 ... amplifier/
I use the 4P1L as driver in my GM70 amps. I think Mark uses it to drive a 300B. Nice valve but they can be incredibly microphonic.

You might also consider 2P29L which would also do the job in a similar way and isn't microphonic apparently. I plan to use in a line stage.

Cheers,

Stephen
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Nick
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#6 Re: Mofo

Post by Nick »

For what its worth, I have found several times now that the ECC40 is a good choice for these things, it has a very 2nd only distortion spectra.
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steve s
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#7 Re: Mofo

Post by steve s »

Thanks gents for the recommendations, I've went to bed last night with the valve manual and tablet.. I'm pretty sure I'm going to use the mazda ac/p.. low gain, low distortion where I'm going to use it, it will drive an interstage nicely.
I need a gain of around 5 to cope with low output cds I play. So a gain of around 10 is about right with some room to spare,

I don't want anything in the signal path. Not even the valve.. But there has to be comprimises

I ended up reading this artical which reminded me of the way to go.. triodes, high impedance loads, simple implementation.


http://www.milbert.com/articles/Lynn_Olsen_THD

Thanks again for the recommendations, I heard too many Russian valves to use them.. They are not for me.. Sorry
The ecc40 is a valve I don't have nick, but I was looking at the e182cc. Which is a later computer version
Also the ec82, but there was too much gain not enough current for what I have in mind.
I may have an ec31 but doubt I have a good pair, but short path ac/p 's are plentyfull on my house.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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Nick
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#8 Re: Mofo

Post by Nick »

Nice article. Though I do have a small complaint.

It says:
try and find a transistor circuit that can deliver 50V rms at less than 1% distortion with no feedback!
Well, why would I need one unless I was driving a valve. May as well ask

"try and find a valve circuit that will produce a regulated 30A at 5v".
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izzy wizzy
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#9 Re: Mofo

Post by izzy wizzy »

steve s wrote: Tue May 12, 2020 12:40 pm Thanks gents for the recommendations, I've went to bed last night with the valve manual and tablet.. I'm pretty sure I'm going to use the mazda ac/p.. low gain, low distortion where I'm going to use it, it will drive an interstage nicely.
I need a gain of around 5 to cope with low output cds I play. So a gain of around 10 is about right with some room to spare,
Had a look. If I had some of those, I wouldn't be using 4P1L :)
steve s
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#10 Re: Mofo

Post by steve s »

Had another listen to the bare mofo, must say it is so open sounding, it's dynamic without a hint of grain.
Its close to the illumination of instruments that a good valve brings without all of the expense
I guess easy to spoil the with the wrong driver/pre
I'm going to build this as an all in one to keep the signal paths short and simple
Just going to start looking for the bits for the valve stage this afternoon.. My garage is rather full though.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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ed
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#11 Re: Mofo

Post by ed »

steve s wrote: Tue May 12, 2020 3:06 pm Its close to the illumination of instruments that a good valve brings without all of the expense
I'm feeling quite smug at the moment.....somebody will knock me down shortly I'm sure.

when you've found your valve Steve I won't be able to ignore the thought that I wonder if it will compare to my mofo with a 3x gain opamp at the front...I'm getting right 'ornery in my old age.
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steve s
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#12 Re: Mofo

Post by steve s »

I did not know you had built one ed
Will be great to compare...
Ed
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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Nick
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#13 Re: Mofo

Post by Nick »

I built a F4 years ago. Built a pre for that with a pair of choke loaded 76's. But a op amp at the front would be certainly simpler.
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ed
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#14 Re: Mofo

Post by ed »

steve s wrote: Tue May 12, 2020 3:52 pm I did not know you had built one ed
Will be great to compare...
Ed
it was at the 2018 Owston, and performed admirably until heat got the better of it and it went down on one channel. I was oblivious but Chris mangler pointed it out.

It was this that alerted me to the benefits of decoupling to the extent of using 2 seperate power supplies. I messed about for some time with such exotic solutions as tl431 etc but saw the light in the end. Unfortunately won't be able to compare anything now because it's been repurposed and Mike Head has the chokes.
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steve s
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#15 Re: Mofo

Post by steve s »

Sorry Ed alot goes on at Owston and mofo would have ment nothing to me at the time

I managed to find a suitable transformer this afternoon, I think its a partridge, perfect in every way except for the rectifier windings 4 or 6.3vt at 2 amps. I had to go back to find suitable rectifiers. I came back with a selection of possibles.. all subject to a test, one is a perfect match for the Mazda ac/p if it works
20200512_195722_copy_768x1024.jpg
Fingers crossed.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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