it is possible, but ........
arrange DC connection directly between buffer and MoFo, so biasing of entire shebang is made on JFet gate, no need for separate biasing of mosfet itself
so, bummer then, you'll need another buffer - in front of autoformer
or adequately low Rout of preceding stage
search around for "Lazy Singing Bush", even if not confirmed in vivo ( sometimes I'm super -reserved), you can find few details there
arrange DC connection directly between buffer and MoFo, so biasing of entire shebang is made on JFet gate, no need for separate biasing of mosfet itself
so, bummer then, you'll need another buffer - in front of autoformer
or adequately low Rout of preceding stage
search around for "Lazy Singing Bush", even if not confirmed in vivo ( sometimes I'm super -reserved), you can find few details there
hey guys,
tonight I had a silly idea. dunno if its published elsewhrer
I'm using puck-mofos/50v as a balanced amp with a balzenpre. Just with the normal output-cap and they sound very nice.
The thing is: why not using them with an auto-bias-servo and without the caps. Just for the fun of it…and no: caps are not the problem,
I'm just a little bored…
Can that work? The “right” amp has its normal bias-setting. The "left" gets it's bias from the opa. Hoping, that the bias never become negative, a single-ended voltage-supply would do it for the opa...
The irfp250 are just drawn for "help". In reality, they are the well known ixfn140 external on the heatsinks…just like the coils...
tonight I had a silly idea. dunno if its published elsewhrer
I'm using puck-mofos/50v as a balanced amp with a balzenpre. Just with the normal output-cap and they sound very nice.
The thing is: why not using them with an auto-bias-servo and without the caps. Just for the fun of it…and no: caps are not the problem,
I'm just a little bored…Can that work? The “right” amp has its normal bias-setting. The "left" gets it's bias from the opa. Hoping, that the bias never become negative, a single-ended voltage-supply would do it for the opa...
The irfp250 are just drawn for "help". In reality, they are the well known ixfn140 external on the heatsinks…just like the coils...
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hey brennwa,
thanks for your reply.
i`m a little afraid of the thermal runaway, without the servo. The only chance of getting dc at the outputs is the difference between the coils, but not the different vgs/thermal side-effects/...of the mosfets. The coils are more stable in their resistants which triggers the bias on the opposite mosfet, than the mosfet.
...theoretically the servo is obsolete by setting the bias...It just make me feel save and sound
if you can explain my wife, why i had bought big expensive coils, throw them now away and buy new ones...then i will buy the cross-coupled ones
thanks for your reply.
i`m a little afraid of the thermal runaway, without the servo. The only chance of getting dc at the outputs is the difference between the coils, but not the different vgs/thermal side-effects/...of the mosfets. The coils are more stable in their resistants which triggers the bias on the opposite mosfet, than the mosfet.
...theoretically the servo is obsolete by setting the bias...It just make me feel save and sound
if you can explain my wife, why i had bought big expensive coils, throw them now away and buy new ones...then i will buy the cross-coupled ones
Ooh, wow... These sound addictive
Did bias adjustment this afternoon and couldn't wait to try and listen.
Powered by a lab supply, on my test speakers, with an iPad as source through a Korg B1 and a cable mess. Never thought it could sound like this 😁 looking forward to get the MoFos finished and to try them in my main system.
Did bias adjustment this afternoon and couldn't wait to try and listen.
Powered by a lab supply, on my test speakers, with an iPad as source through a Korg B1 and a cable mess. Never thought it could sound like this 😁 looking forward to get the MoFos finished and to try them in my main system.
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Interesting. Earlier posts postulated that a Korg B1 + MoFo wouldn't be such a great match; what is the maximum voltage swing on your Korg B1?
Kind regards,
Drew
First Watt B1 Korg
According to this, the B1 Korg can output 5V but at quite a high distortion level of close to 7%. So only about 3W into 8 Ohm, assuming it is 5 Vrms.
According to this, the B1 Korg can output 5V but at quite a high distortion level of close to 7%. So only about 3W into 8 Ohm, assuming it is 5 Vrms.
I listened to a Korg B1 + MoFo combination for the better part of two months as my main system. I thought it was an improvement over an ACA (better bass response), and the B1K seemed to smooth out the high-end output of my antique Sony CD player, but I don't play loud. I'm now back onto a passive transformer-based preamp with some voltage gain in front of the MoFo. Even cranked to full on I don't get a ton of punch out of the amp, just less distortion than with the B1K. I guess this is a long way of saying that depending on your listening levels, a B1K may be just fine in front of MoFos.
It was a somewhat "sweet" sounding combo - to my ears it sounded very well. I did not play to loud and on 90 dB sensitive speakers.
I have just moved the "finished" Mofos to my main system. on 92 dB sensituve speakers they sound absolutely wonderful
even fed by a B1 v1. Able to play loud enough for normal listening Next is to try with a WBA18 linestage.I think they deserve a more permanent home at some point
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look perfect leave as is ....It was a somewhat "sweet" sounding combo - to my ears it sounded very well. I did not play to loud and on 90 dB sensitive speakers.
I have just moved the "finished" Mofos to my main system. on 92 dB sensituve speakers they sound absolutely wonderful
I think they deserve a more permanent home at some point
Pass DIY Addict
Joined 2000
Paid Member
woody, I see your point. A source follower is inherently very linear, so one might think that the characteristics of the device do not matter very much (SIT vs. MosFET).
There is Ben Mah's Fokin, which uses Tokin as a source follower with a choke load:
https://www.diyaudio.com/community/...-choke-loaded-2sk180-lamp.366312/post-6803744
Also, not long ago, Nelson Pass released the Sony VFET SE amps, which are source followers: https://www.firstwatt.com/pdf/art_diy_sony_vfet_pt2.pdf
I don't know if anyone directly compared a SIT and an IRFP (or similar MosFET) in a MoFo. I once thought about a circlotron, and I compared the SIT/THF51 with MOS/IRFP150 here. They did have slightly different harmonic distortion profiles.
There is Ben Mah's Fokin, which uses Tokin as a source follower with a choke load:
https://www.diyaudio.com/community/...-choke-loaded-2sk180-lamp.366312/post-6803744
Also, not long ago, Nelson Pass released the Sony VFET SE amps, which are source followers: https://www.firstwatt.com/pdf/art_diy_sony_vfet_pt2.pdf
I don't know if anyone directly compared a SIT and an IRFP (or similar MosFET) in a MoFo. I once thought about a circlotron, and I compared the SIT/THF51 with MOS/IRFP150 here. They did have slightly different harmonic distortion profiles.