MoFo

For the three and more legged things
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ed
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Re: MoFo

Post by ed » Tue Feb 05, 2019 11:43 pm

Ah pathos, I'd almost forgotten.
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IslandPink
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Re: MoFo

Post by IslandPink » Wed Feb 06, 2019 11:31 am

Umm... OK...
So, what makes this more successful in high current solid state ?
Just remembering my last use of a by-pass in the shunt-reg supply, and what I simmed on LT Spice that seemed to explain why it might sound bad.
"The bass is the king of the instruments - it has no known natural predator" (Wobble)

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Re: MoFo

Post by Nick » Wed Feb 06, 2019 12:39 pm

IslandPink wrote:
Wed Feb 06, 2019 11:31 am
Umm... OK...
So, what makes this more successful in high current solid state ?
Just remembering my last use of a by-pass in the shunt-reg supply, and what I simmed on LT Spice that seemed to explain why it might sound bad.
Its the best of the available compromise. If you could have a 22000uf film cap it would probably sound better, but you can't, so the next best thing in my experience is to use a 1uf or more cap across the electrolytic. It may be a regulator will work with just a small film cap on the output, but I have not tried that. Also, consider that the PSRR of a solid state amp may be very different to a valve one.

One of these things is not the same as the other.
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Re: MoFo

Post by IslandPink » Wed Feb 06, 2019 3:36 pm

OK - could be partly a difference between SE and PP, as it seem most solid state amps are PP or relatively low demand on the PS ? ( which I suppose is PSRR )
"The bass is the king of the instruments - it has no known natural predator" (Wobble)

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Re: MoFo

Post by ed » Wed Feb 06, 2019 3:49 pm

I understand the bypass scenario(or at least the hf/spike rejection bit) but why would a film cap be better in the heavy duty section?

hold that question...I'm revising ESR and ESL
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Re: MoFo

Post by Nick » Wed Feb 06, 2019 4:35 pm

ed wrote:
Wed Feb 06, 2019 3:49 pm
I understand the bypass scenario(or at least the hf/spike rejection bit) but why would a film cap be better in the heavy duty section?

hold that question...I'm revising ESR and ESL
Yes, there is that, plus electrolytics tend to be less linear than film caps
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Re: MoFo

Post by little eddy » Thu Feb 07, 2019 9:45 am

Nick wrote:
Tue Feb 05, 2019 8:29 pm
Also try adding film bypass caps on the electrolytics.
As per Nick's Rankin valve book, rather than just add as a bypass cap, was thinking of adding the 4u7 film cap at the end of the filter chain as a small Pi filter with a 0.1R resistor.
Thorens TD-125 & 'Snail' phono/pre, NAS/SBT, CS4398 DAC, Rocky KT66 amp, still messing with OBs.

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Re: MoFo

Post by Nick » Thu Feb 07, 2019 10:15 am

Seems like a good way of increasing the impedance of your supply.
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Re: MoFo

Post by little eddy » Sat Feb 16, 2019 5:08 pm

Time to stop meddling and do some listening.

If this were a boxing match, I am quickly heading towards the heavyweight division at an unexpected 18kg for just 12.7W.

Additions include microwave transformers, moving original chokes into the power supply and film filter caps as suggested by Nick, (only had polyester MKT1813s to hand).

The only things I've left to consider at the moment is supplementing the heat sink capacity and trying different film caps both on the input, and also bypassing the 6800uF output electrolytic.
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Mofo film cap small.jpg
Thorens TD-125 & 'Snail' phono/pre, NAS/SBT, CS4398 DAC, Rocky KT66 amp, still messing with OBs.

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Re: MoFo

Post by IslandPink » Sat Feb 16, 2019 6:13 pm

If I can ever find a second Audyn 4.7u/100V KP-SN, I will send you the pair. I've been poking around while looking for other final bits for the amp, but so far no success.
"The bass is the king of the instruments - it has no known natural predator" (Wobble)

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Re: MoFo

Post by little eddy » Mon Feb 18, 2019 11:43 pm

Distortion falls as bias current is increased but might a higher Idss also provide an audible difference (I remember increasing the current with 6SN7s in SRPP made a huge audible improvement, at least to my ears)?

More current means more heatsink so it's not a cheap/easy thing to do if it's unlikely to provide any sonic improvement.
Thorens TD-125 & 'Snail' phono/pre, NAS/SBT, CS4398 DAC, Rocky KT66 amp, still messing with OBs.

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Re: MoFo

Post by little eddy » Mon Mar 11, 2019 1:05 pm

Sacrilege
cpu heatsink small.jpg
PWM controller with temp sensor on the water from China, so then we'll see how much dissipation can get out of one of these things without too much noise.
Thorens TD-125 & 'Snail' phono/pre, NAS/SBT, CS4398 DAC, Rocky KT66 amp, still messing with OBs.

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Re: MoFo

Post by Ray P » Thu Mar 21, 2019 8:08 am

I've just ordered a pair of MoFo boards from the DIYAudio store. I'm not sure I really need another amplifier but I'm intrigued by it's simplicity and based on some basic assumptions about what i could use with the MoFo circuit I have pretty much everything I would need, apart from the Hammond chokes, to do a cheap breadboard build. My assumptions are;
  • To use an LT1083 regulated supply or, alternatively, a cap multiplier for each MoFo board's power requirements.

    To use the 6SN7 driver stage from the 6C33C project as the basis of a driver stage for the MoFo
Image

Thoughts?

Reflecting on this and relating it to my 13E1 project and possible open baffle direction, with a little effort maybe this would be good for the bass driver on a bi-amped OB - just a thinking out loud...

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Re: MoFo

Post by Ray P » Thu Mar 21, 2019 6:54 pm

little eddy wrote:
Tue Feb 05, 2019 3:53 pm
Found a guy in Swinton with a number of different models for sale that I could go and test. Picked these up for £10 each.
Any chance of a pointer; as I haven't got any suitable chokes it probably makes sense to get something cheap and, possibly(?) better. Only problem is I'm down in the South West.

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Re: MoFo

Post by little eddy » Thu Mar 21, 2019 9:39 pm

Ray P wrote:
Thu Mar 21, 2019 6:54 pm
Any chance of a pointer; as I haven't got any suitable chokes it probably makes sense to get something cheap and, possibly(?) better. Only problem is I'm down in the South West.
I bought the XB-800-2024 MOTs off slease-Bay from here and he offers free shipping that's great for very heavy items, (2 left): https://www.ebay.co.uk/itm/XB-800-2024- ... ctupt=true

Quite cheap compared to branded ones larger than 2A. I went and tested a few and these had the lowest DCR of what I tried, around 2R. I'm sure these tested at above 100mH so no issue with bass response.

The one thing I would suggest is that the MOT eats up voltage and available power so if you want more than say 12W, I would suggest a transformer higher than 18V if conventionally aspirated.

I have a supply voltage of 21.7V to the pcb, so running with 1.7A I have just under 13W output. Dissipation is theoretically 31W. I would really like to run at say 2A so should really have bigger heatsinks than the 0.53 C/W ones I bought, hence me looking at the cpu heatsinks with fans.

If it's for the bass then perhaps the SMPS or laptop supplies would be OK as very easy to build. I had a faulty one that sidetracked me for ages but you probably need around 24V if using MOTs. This is my idea for a bi-amped OB as I now have 2 pairs of Mo-Fo pcbs.

I'm currently playing around with the Mo-Fo capacitors, both input dc-decoupling and bypass ones around the output 6800uF cap. So far not found an ideal combination but when building, you may want to leave the legs on C2 then you have the option of bypassing. Because I am not yet happy with a choice of input cap, I am glad I have a transformer output from my pre with the option of the signal injected directly across R3, so again I left the resistor legs uncut on the underside of the pcb.

Also I had trouble with the screw terminals being very tight in the pcb holes, and also the screw heads seem to wear even though I've been careful tightening and loosening cables. I just used about 1" lengths of wire on the 2nd pcb and solder the wires to the ends of them and insulate with heatshrink.

Mike.
Thorens TD-125 & 'Snail' phono/pre, NAS/SBT, CS4398 DAC, Rocky KT66 amp, still messing with OBs.

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