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Simplistic NJFET RIAA
Simplistic NJFET RIAA
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Old 2nd September 2014, 11:33 PM   #13391
LucasAdamson is offline LucasAdamson  United Kingdom
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My calculations for 30v are 30 /230 *240 = 31.3VAC * 1.41 = 44.1VDC less diodes etc.

A 33 VAC Tx comes out at 48.5 VDC. Hmmm
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Old 2nd September 2014, 11:49 PM   #13392
Salas is offline Salas  Greece
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But the Airlink 230/30+30 gave 46.5+46.5VDC because we barely load it to its true current ability. I would order same secondaries and VA model from same manufacturer as Marra if in your shoes. Because all unknown factors are already tested. I would only ask them if they offer magnetic shielding peripheral band as an extra option.
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Old 3rd September 2014, 12:09 AM   #13393
LucasAdamson is offline LucasAdamson  United Kingdom
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Quote:
Originally Posted by stajo View Post
Thank you. Indeed it is to be a DCB1 buffer preamp with the FSP as integrated RIAA. Akouo select & volume with a Muses 72320 chip.

It doesnt show at the pic but the boards are actually piled up to the final height so the legs are about right. Ill solder them when its fixated.

I am to fodder the alubox with thin ply and fodder the heatsinks even more so they only radiate to the outside.

The DCB1 will have its own foddered compartment with heatsinks with the same principle.

Plus a separate PSU box with a lot of different voltages in the umbilical cord connecting the two.
Stajo,

It looks like a very practical solution. My only question is, if you are to have a separate power supply unit feeding the unit by an umbilical, isn't it better to bring DC into the pre-amp with the umbilical, rather than AC? The DCB1 has onboard rectification. Are you planning to move the rectification off the DCB1 board and into the PSU box?
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Old 3rd September 2014, 12:20 AM   #13394
LucasAdamson is offline LucasAdamson  United Kingdom
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My matched pairs of 2SK170BL are as follows:

6.60 mA pair
6.89 mA pair
7.07 mA pair
7.39 mA pair
7.47 mA pair
7.52 mA pair
7.62 mA pair
8.12 mA pair

They were, however, all tested with 9v, back when building DCB1, F5, etc.

I also have a near match at 9.80 / 9.96, which when I retested at 22v, came out at 10.31 / 10.50 which shows that voltage is critical to evaluating IDSS.

Should they all be retested please, and if so at what voltage?
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Old 3rd September 2014, 12:53 AM   #13395
Salas is offline Salas  Greece
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Use 10V for your re-testing confirmations if you got a variable PSU. Leave each one sample enough minutes on power until it stops climbing on the reading.
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Old 3rd September 2014, 12:56 AM   #13396
LucasAdamson is offline LucasAdamson  United Kingdom
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OK. Yes they can sometimes climb for about 5-10 minutes as I remember, which complicates testing. Doesn't the actual voltage they will encounter in the circuit matter though?
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Old 3rd September 2014, 01:29 AM   #13397
stajo is offline stajo  Sweden
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Quote:
Originally Posted by LucasAdamson View Post
Stajo,

It looks like a very practical solution. My only question is, if you are to have a separate power supply unit feeding the unit by an umbilical, isn't it better to bring DC into the pre-amp with the umbilical, rather than AC? The DCB1 has onboard rectification. Are you planning to move the rectification off the DCB1 board and into the PSU box?
Yes. I make a pre reg filter C-R or C-L in the PSU-Box and plug directly on to the onboard C.
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Old 3rd September 2014, 01:30 AM   #13398
Salas is offline Salas  Greece
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Quote:
Originally Posted by LucasAdamson View Post
OK. Yes they can sometimes climb for about 5-10 minutes as I remember, which complicates testing. Doesn't the actual voltage they will encounter in the circuit matter though?
Practical test:

10V K170BL 7.48mA (3 minutes are enough)

9V same sample 7.44mA

They will not encounter more than 9-10V VDS in circuit.
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Old 3rd September 2014, 11:33 AM   #13399
Marra is offline Marra  United Kingdom
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Quote:
Originally Posted by Salas View Post
That's nice bcs the Decca is peculiar. So, given the trafo was loaded, it should have about 1.35 full wave rectification ratio DC/AC in this app. Is it 80-100VA rated model?
I went for the 120VA as it was only a couple of pounds difference and added an interwinding screen.Didn't bother with the Goss band as the power supply is in a separate case so I didn't think it was necessary.
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Old 3rd September 2014, 01:37 PM   #13400
AndrewT is offline AndrewT  Scotland
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Will do once I sort out photobucket.
Attach your pics.
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