Simplistic NJFET RIAA

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#3,081
R6 50R trimmer is to adjust DC offset?

In the channel with 7.2V I tested the DC offset & is changing between +1 or +2 mA & -1 or -2mV, very very good numbers without adjusting nothing?

Really I am very happy, I have ahead a superb design, Salas thanks again to sharing with us, tomorrow if weather let me finally I hear the phono.
 
#3,082
No, with that we will match the output levels. For now, set those trimmers, so you got 10V DC under R10 6k2 on Q2 drain pin on each channel. What you see for ''DC offset'' is what the DVM reacts on really nothing, since this is an capacitor coupled circuit.
Do you have a photo that shows it full so I can see your wiring?
 
#3,083
I remember 25 years ago mine trip honeymoon was Greece, I visit the touristic places & I enjoyed but the best remember remaining aren't the History, Museums, Restaurants, etc. The best remeber is that all people was very kind & friendly still have in mind.

So you remembered me how kind are greek people.

Sorry for OT.
 
#3,088
Yes 10V there. Normally 12V on Q3's collector. When R1 is 3k3. Trimmer must pass 10mA at 330mW, I suggest you make it a 1W fixed resistor at a point, as designated in the circuit. Since you put it there, it is very handy to match first stages voltage, so the LEDs will not make much difference. R17 and Q6 Idss determine the current through LEDs. Are you having same mV across both R17's?

P.S. Very good components I see. What kind of resistors?
 
#3,090
Tomorrow I will test if I have same mV across both R17's

Rload, R2 & R4 are all Shinkoh

R9 & R17 Koa Speer as per your advice

R1 I will change for Xicon carbon film 1W

R3, R5, R7 & R8 all are Takman Pink carbon film

R10 & R11 both are Xicon carbon film

This is mine first approach, after depending the sound I will upgrade with better components if I can.
 
#3,096
Channel 1
Leds V OK
1.5mA through them. OK to keep the dissipation of Q6 low due to 45V B+.
R10 on Q2 point, working, play with the trimmer under Q2 and go up to 10V
R1/Q3 Arrange for 11.5V your ''R1'' trimmer.

Channel2
LedsV a bit hot.
Is this R17 220R for sure? Measure that resistor. If yes, there must be some wrong connection and 4.5mA runs, that is why your LEDs pick up Vf. To be due to such high Idss difference between this Q6 and the other channel's is unlike. Compare other channel's connections.
R10/Q2 looks cut off. See if it can go 10V with ''R6'' trimmer, if it will not respond there is something wrong.
R1/Q3 works. Bring up to 11.5V with trimmer.
 
#3,098
The guys with Hypno or Mez say that those Leds are very steady for Vf readings and you can avoid buying too many BTW. http://www.diyaudio.com/forums/pass-labs/145201-building-symmetrical-psu-b1-buffer-109.html

Yes they fit for the Riaa too. But the reason you got more voltage in one channel is because you run much more current through them in the second channel. Check if that 220R R17 is correct value and if its connections are the same with the Jfet of the 7.2V Leds reading channel. No need to change the ones you got already.
 
#3,099
Channel 1 is ok
LEDs 7,35V
R17 345mV
R10/Q2 10V
R1/Q3 11,5V

Channel 2 is wrong
LEDs 7,86V
R17 between 1.070mV till 1.081mV (resistor value is ok 217 ohms)
R10/Q2 max adjust with R6 trimmer go till 0,11V
R1/Q3 11,5V

I used for Q6, one channel 10,24 & the other channel 10,25 Idss
 
#3,100
Check Q6 connections to be exactly like in the OK channel. If identical, change Q6. Also check all connections around first stage to be identical to the OK channel before changing it. R10/Q2 some problem there too. Can be connections.

P.S. How much voltage from R7 to ground and from Q5's drain to ground on the OK channel? So to know if output buffer is doing well too and to keep it as whole board a reference to fix the other channel.
 
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