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Simplistic NJFET RIAA
Simplistic NJFET RIAA
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Old 19th August 2018, 12:53 AM   #17221
Salas is online now Salas  Greece
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Simplistic NJFET RIAA
Quote:
Originally Posted by aive View Post
Progress so far - phono boards cased ready for testing. XLR sockets just because my downstream gear is all balanced and I am too lazy to make a custom cable :P

No case for the PSU yet, size it up after I get the trannies.
Neat
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Old 19th August 2018, 01:12 AM   #17222
aive is offline aive  Australia
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Originally Posted by Salas View Post
Neat
I bought the RG174 from ebay from one of your old posts - it's very delicate to work with >< I'm still not happy with how its soldered to the connectors. Doesn't seem to draw in solder very well. Oh well, case work is the worst part :P
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Old 28th September 2018, 09:33 AM   #17223
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Hi Salas - my transformer finally arrived and I powered up the unit and set bias quite easily.

When I inject 1 khz sine and view output on my CRO I notice a gain difference (photo).

IMG_7392.jpg

What's the best way to fix this issue?

Thanks for your help in advance Salas!
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Old 28th September 2018, 10:28 AM   #17224
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LOL never mind Salas, my PC was the cause of the imbalance! It's perfect channel matching
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Old 28th September 2018, 10:34 AM   #17225
Salas is online now Salas  Greece
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Simplistic NJFET RIAA
Which is due to excellent matching of active components between channels since there is no overall feedback loop in this circuit to fix the gain
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Old 28th September 2018, 11:37 AM   #17226
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Hehe thanks Salas - Teabag did all the hard work :P

I just need to case up PSU so earthing can be sorted and I’m done. Just tested with turntable then and there’s some minor hum as no connection to mains ground has been made yet. Still sounded very nice! :P
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Old 28th September 2018, 11:59 AM   #17227
Salas is online now Salas  Greece
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Simplistic NJFET RIAA
Is your transformer magnetically shielded? If not, make the raw DC umbilical long enough to can place the two boxes apart in some good distance.
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Old 29th September 2018, 04:06 AM   #17228
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Nah it’s not shielded. I’ve mounted the PSU components and wired the grounding. No hum whatslever!

Just to check - I originally biased with VR2 but then My rail voltages were just over 1V apart between channels. So then I used vr2 to adjust rail voltage of higher rail channel closer to about half a volt difference then used vr1 to get tp1 tp2 same as other channel. It took a lot of turns of vr1 - is this ok?
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Old 29th September 2018, 04:39 AM   #17229
Salas is online now Salas  Greece
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VR2 is the control for the regulator's general rail output voltage and VR1 acts as fine rail adjust exclusively for the input stage if needed. So the rest of circuitry can still run on closer rail levels between channels. Thus you utilized those two trimmers properly.
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Old 29th September 2018, 04:46 AM   #17230
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Awesome thanks!
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