i have send it 2 mails , no response yet
Strange, I got qucik response...
You can maybe try here: Ogonowski.eu - profesjonalne transformatry do wzmacniaczy lampowych
Just to let you know that after completing the second mu-SIT monoblock and setting them up I proceeded to audition more carefully vs the two single ended valve amps (300b and 6c33) I also have made. Pre was an Aikido (John Broskie) with 6h30 and 6cg7.
Some preliminary points:
1. The 8 SITS I bought have very variable characteristics as I already mentioned in a previous post. I rechecked with more careful installation on the heatsink this time. Basically I set up my PS to 2amps constant current mode and I varied the bias between -1 and -5 volts , noting changes in Vds. Essentially this gives you the Gain of each device. I was surprised to see a variation between about x2 to about x6. That is more than 200% variation in gain characteristics!! Fortunately there were two sets that had similar characteristics which I used but still the two amps have about 1db or so difference in gain which is a bit academic and I did not really notice in practice.
However be warned that if you just order two 2sk82 you might get two VERY different vfets.
2. Even with the two matched vfets when I adjusted for lowest distortion I ended up with one sitting at about -4 V bias and 3 A and the other at -5.8 V and 2.4 A.
Anyway with two big film in oil 100uf on the output (this SIT feeds full range speakers only down to 100hz the rest below 100hz is with a powered sub) the sound is really good on the same playing field as a good SET and very probably better. In fact I do prefer them over my SET amps now that they are dialled in and without electrolytics on the output. More precision without losing any of the SET musicality. I would not recommend them with non SET friendly speakers because I noticed a lot of higher order distortion on the distortion analyzer when pushed nearer their output limits. So if you have speakers of 96db sensitivity or more this amp is really great and you do not have to keep replacing those super expensive valves every couple of years (although I believe the 6c33 is very cheap compared to some 300Bs)
Some preliminary points:
1. The 8 SITS I bought have very variable characteristics as I already mentioned in a previous post. I rechecked with more careful installation on the heatsink this time. Basically I set up my PS to 2amps constant current mode and I varied the bias between -1 and -5 volts , noting changes in Vds. Essentially this gives you the Gain of each device. I was surprised to see a variation between about x2 to about x6. That is more than 200% variation in gain characteristics!! Fortunately there were two sets that had similar characteristics which I used but still the two amps have about 1db or so difference in gain which is a bit academic and I did not really notice in practice.
However be warned that if you just order two 2sk82 you might get two VERY different vfets.
2. Even with the two matched vfets when I adjusted for lowest distortion I ended up with one sitting at about -4 V bias and 3 A and the other at -5.8 V and 2.4 A.
Anyway with two big film in oil 100uf on the output (this SIT feeds full range speakers only down to 100hz the rest below 100hz is with a powered sub) the sound is really good on the same playing field as a good SET and very probably better. In fact I do prefer them over my SET amps now that they are dialled in and without electrolytics on the output. More precision without losing any of the SET musicality. I would not recommend them with non SET friendly speakers because I noticed a lot of higher order distortion on the distortion analyzer when pushed nearer their output limits. So if you have speakers of 96db sensitivity or more this amp is really great and you do not have to keep replacing those super expensive valves every couple of years (although I believe the 6c33 is very cheap compared to some 300Bs)
Yes I used the 500r pot but I have only experimented with it when adjusting for lowest distortion. It always ended up in the middle in both amps. I have not experimented with it acoustically yet. What is your impression of its acoustic effect?
Anyway there are so many variables, bias, current, voltage etc that also change relative to each other that trying to optimize by ear would need a whole year of auditioning.
Anyway there are so many variables, bias, current, voltage etc that also change relative to each other that trying to optimize by ear would need a whole year of auditioning.
Here's a pic of me checking the power supplies on my SIT. More to follow soon!
Regards,
Dan
Very nice looking... Are you using Vishey BC caps for PSU?
Here's what I purchased for PS capacitors.
4pcs CDE 75V 37000uF Computer Grade Bus Capacitors New | eBay
Regards,
Dan
Fair enough.I think Mike wants to see the article on paper- AudioXpress or Linear Audio?