Quan, i think it is just so you get both signal and ground close to each other so you can twist the output wiring all the way.. the 5R resistor will be bypassed since you connect to the output side of it which makes it possible to go direct from the buffer board if you want.
Otherwise i don't think there will be any trouble taking the output from the buffer board - but you only have one ground connector (at the input) so you have to solder two wires there (in an out).
But it certainly looks better at wiring it back to the paradise board 🙂
But it certainly looks better at wiring it back to the paradise board 🙂
As pdul says, the output needs to go back to the main PCB - otherwise the servo is lost ;-(
The absolute accuracy is not important, as any old semiconductor guy will tell you , but the relative accuracy - matching between the transistors, and from channel to channel. It is a little tricky though since we are dealing with NPNs and PNPs (at least in the input stage), thats why I prefer the little circuit from teh assembly guide since it can do both, just reverse the supply.
Better to make your own hfe measurement set-up. I made mine 5(pnp)+5 (npn) channels, so I could put 5+5 transistors and measure them in the same time (same temperature, conditions etc.) Without that, it would have been impossible to get 2000 sorted.
Sorry for those who asked for matched transistors, I have a little 2 months old baby, don't have time to verify again the transistors and to put apart the sets. When I'll have the completed sets, I'll let you know - if anyone interested anymore.
Emil
Sorry for those who asked for matched transistors, I have a little 2 months old baby, don't have time to verify again the transistors and to put apart the sets. When I'll have the completed sets, I'll let you know - if anyone interested anymore.
Emil
Yes, no oscillations now🙂 The boards are cased up now although I haven't optimised the earthing, still need to read up and understand the best way to do it. I haven't been able to listen yet for various reasons so I'm going to leave the Paradise powered up for a week or so until I sort out my turntable and make space for the two full width cases. One thing I found after putting the boards in the case was that the DC offset on the output has dropped dramatically, now it's around +/-10mV which is good!
One thing I noticed recently was the pre-regulator buzzes quite a bit, I'm wondering if it's DC on the mains making the coils buzz. Anyone else out there using the pre-regulator found this?
two of my pre-regulator transformers buzzes too. I tried a isolation transformer but no difference. So i don't think it's DC mains offset.
galac
galac
The Hammonds buzz a little, the common mode chokes and the 'box' transformers should not. Did you make sure they were all super pressed down to the pcb while being soldered in place?
Yep, they were nice and snug although I'll go back and check to be sure. It's not like the buzz you get from a toroidal, it's a higher pitch. That said it's impossible to be sure which devices it's coming from, if I had to commit I'd say it was the chokes but, as you rightly say, they shouldn't really be making any noise. With the lid on the case I can still here it from, say, a metre away. I'm guessing I won't be able to here to hear it once it's in the rack. The two huge Canterbury traffos in my HackerNap are far noisier anyway when the mains is dirty.
The hammonds and the cmc's are dead silent. The transformers are soldered accordingly - they even did not change the buzz if there's some pressure on it. I think it's only a bad production batch or failed quality control.
Hi guys, i installed the Calvin buffer today and ran into some problem. I am not able to adjust the offet to zero. The offset stuck at 22mV on one channel ,the other one at 28mV. I am using the trannies from GB, and used the values as per update build guide. Any suggestions?.
Quan
Quan
Thats odd, the adjustment range should be pretty large in both directions.... Are you sure you put the JFETs in the right locations, maybe the two JFETs from the lower half (right hand side of the PCB, looking at it from the input side) are swapped?
Hi Alfred , i did triple checked the jfets prior to soldering as per the build guild. I am listenning to it at the moment. May be i should check it again and report back. Everything as per boards value except the output transistors are 2SA 1930 with cc 200pF.
quan
quan
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Hi Quan
Did you check the pin out for the 2SA1930?🙂
I think you may find that they are reversed compared to the 2SA1381 so can’t easily be used.
I was thinking of using the 1930 but after checking the Data sheet decided not to for the above reason.
I bet that if you change the OP transistors that all will work well.