A SIT is a votage controlled resistor unlike other FETs hich are voltage controlled current sources. I think it is a voltage source amp unlike lhquam's Teaser F6C which is a current source amp with a higher Zo.
Feedback to the primary [ground] leg of the transformer will be type Black but not Schade or Pass; which will reduce its intrinsic good distortion that makes its unique sonics
Biasing the SITs with one dual rail power supply like in F6.Is it just me or does the pitcure of the working amp have very little parts count?
I see 4 SIT TO-3s, two Jensen transformers and 4 lab power supplies. What's the catch?
Or, is that just it: small parts count?
Ok, I just saw the video on youtube.com. Amazing.
I do not know the answer; but maybe minimize the number of PSUs. Most important with any # of PSUs is to protect the SITs. Vgs for each SIT must be on before applying its Vds.Dont you want the flexiblity of 4 power supplies?
How about a soft-start for the SIT 23v power supply to slow them down?
I don't know if it truley applies, but I'm doing that with CL-60s on the L'amp v193.
Problem with this is turning it on and off in a short time span. How long does it take for a CL-60 to cool off and provide resistance again.
At any rate, I understand what you are saying. Thanks.
One dual power supply for pp SIT amp
I agree that a delay or a soft start is needed. The attached picture is the concept circuit to bias the SITs. Note the following
I agree that a delay or a soft start is needed. The attached picture is the concept circuit to bias the SITs. Note the following
- One dual plus and minus ~33 V PSU is used.
- The source of each SIT is connected to its attendant power rail with a 10 Ohm power rheostat.
- At time zero [before applying power], the large decouple electrolytic cap is fully discharged, and the delay switch is open so as to put the soft start resistor in series with it.
- At power turn on, ~1 Ampere rushes through each 10 Ohm and generates a 10 V voltage drop riding on top of that of each source port which is +/-23 V.
- Simultaneously, the wiper of the 10 Ohm rheostat applies the prescibed Vgs. For example, the gate of the P-channel SIT sits at the target plus 8.4 V above its source voltage of 23 V.
- Once the voltage across the decouple capacitor reaches 9 V, it is safe to short [with shorting switch] across the resistor in series with the cap. The safety scheme like that shown by Zen Mod [#11] will be adaptable and/or applicable here.
- The full effect of "decoupling" the source resistors is fully enabled. The amp is ready to play music.
Attachments
2SK82
why not some 7908, similar to Mike R's LAMP hookup.
http://www.mouser.com/ds/2/149/KA7908-189842.pdf
http://www.mouser.com/ds/2/149/KA7908-189842.pdf
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separate issue , isn't it ;
however , just to spoil part of Buzz's happiness :
I have a 5 fillar version playing nicely
Tea-Bag: Juma used two PSUs; +/-51 V for the front end which also developed the complementary +/-Vgs for SITs. The second +/- 25 V PSU was their Vds. Zen Mod maybe emphasizing the best approach is to adopt 2 PSUs like he and Juma used [Post #11]. Rothacher's SIT amp used two PSUs, and that works. 7908 for the N-SIT and the complement of 7908 for the P-SIT will work.
really whatever is warming ya heart ........ but 8V from 7x08 isn't enough
it demands something as zenner in gnd tail , to elevate output voltage to , at least , 15V or so
in that case - 7x15 or 7x18 or , even better , 7x24 is way to go
though - be sure to (additionally) load output of that reg with at least 15mA (led string or resistor )
in my sketch I drew 30V biasing nets , just to cover all possible Sony SIT ranks ( can't remember which ones I have at home ; most probably the same as Juma have , being from same purchase )
it demands something as zenner in gnd tail , to elevate output voltage to , at least , 15V or so
in that case - 7x15 or 7x18 or , even better , 7x24 is way to go
though - be sure to (additionally) load output of that reg with at least 15mA (led string or resistor )
in my sketch I drew 30V biasing nets , just to cover all possible Sony SIT ranks ( can't remember which ones I have at home ; most probably the same as Juma have , being from same purchase )
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My mistake Zen Mod I was not clear. The PSUs I described for Tea-Bag are referenced to the power rails and not to ground. They float on the rails as shown in the amp's schematic. Although 7909 is called a fixed negative voltage regular it still can be configured to have an adjustable output to tweak Vgs.
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