I think when it states "each line output" means each channel. The resistors at the output don't change the DC offset so I can't see how any output (line or HP) will be different from the other (same channel)
Also I see that the VR1 trimmers are there only for the DC offset. After continuous power up the voltage across R10 one channel has reached 1.2V exactly and stable but the other channel has reached 1.187V. I hope this difference of bias should be good enough for going ahead with the offset.
Not a problem, with this kind of difference (according to Salas, I had also a slight difference)
Go ahead, with out opamp installed, adjusting the DC offset with trimmers. Expect the offset to drift a bit like 5mV. At the end put the opamp on.
Almost there...
Go ahead, with out opamp installed, adjusting the DC offset with trimmers. Expect the offset to drift a bit like 5mV. At the end put the opamp on.
Almost there...
99mA vs 100mA bias between channels is 1%. Are you joking? 😀
We can't even match phono Riaa capacitors that good with confidence on budget test equipment 🙄
We can't even match phono Riaa capacitors that good with confidence on budget test equipment 🙄
Hehe just that it is a Salas board 😉
Coming to the DC offset with the input shorted I am unable to set the offset anywhere close to 0, it will always drift like from say 0.1mv to 100mv and not stable without the opamp installed. Looking at the guide I think its normal so I have powered down and will install the opamp and then recheck the offset.
So both preamp and shunt reg survived one rail polarity reversal. That's why there was fault current resembling a short. No damage... You are a lucky man 🙂
Try with the trimmers to make dc offset vary the least possible before installing the servo op amp. That's the thing. Maybe you could do better. Don't haste.
Its the current limiting on the BiB that mainly saved the day. 0.1mV to 100mV offset play before op amp, are you sure? Maybe to 10-15mV max?
Too much drift, +/- 10mV would be OK without opamp and <1mV when installed.
Tea Bugs matching was always accurate, don't know what to assume.
Make another attempt to adjust the offset with trimmer and report back
Tea Bugs matching was always accurate, don't know what to assume.
Make another attempt to adjust the offset with trimmer and report back
He better also check there is normal Vbe (0.6V to 0.7V) on Q1 & Q2. To make sure the mirror transistors are OK after the PSU reversal incident.
I am still awake its 4AM here 😱 and my Sennheiser HD-598 are rocking from the HP output. I found one issue with powering the mesmerize source selector board from the BiB DC output along with the DCG3. The positive voltage drops to 9.6V and their is no music playing, it took sometime to figure out that the source selector board is drawing more power, hence I took out 0,12V AC from the transformer and powering the AC-In of the source selector and voila the music started playing again.
The offset is around 0.1 to 0.2mV during idle as well as playback with no drifting at all.
The offset is around 0.1 to 0.2mV during idle as well as playback with no drifting at all.
One question regarding the volume pot of 20k impedance. If I am using a Arduino based LDR volume controller board, then do I need to install the volume control before the DCG3 or after? Does it makes a difference, the reason being that if installing after DCG3 then I need to short the RK27 pot wiring on the source selector board based on Salas pointing out earlier whereby I do not want to use this board as volume connections.
So its completed and running smoothly on my HP. I am yet to connect to my Sony VFET2 amp which I will do it tomorrow.
Regarding the earthing connections, I have the BiB PSU common ground connections to the chassis which in turn is also connected from the chassis point to the IEC earthing. So this chassis point acts like a star ground. But when the common ground of the PSU are connected to the chassis I see that the DCG3 does not switch on the LEDs. I think somewhere shorting is happening, so the question is where do I now connect the PSU grounds to the chassis common star point connection?
Regarding the earthing connections, I have the BiB PSU common ground connections to the chassis which in turn is also connected from the chassis point to the IEC earthing. So this chassis point acts like a star ground. But when the common ground of the PSU are connected to the chassis I see that the DCG3 does not switch on the LEDs. I think somewhere shorting is happening, so the question is where do I now connect the PSU grounds to the chassis common star point connection?
Before. If after, you end up with a high impedance output. Cancels the DCG3 except for its gain. Also in doubt if the LDR can handle the voltage swing it can deliver to it in case of an odd event.
Always ground to chassis (if you have to do that due to hum) from one point only. In this case wire from one channel's HP OUT GND point to chassis. Don't modify the BiB sections wiring in any further way. They common on their way to the DCG3. There is very long cabling going around in your build in general, I hope that the rails are still clean. Missing an oscilloscope check there. You could have the BiBs nearer to the DCG3.
Sennheiser HD 598 is nice. You never replied the voltage drops across the BiB constant current setting resistors R101 R201 and their chosen values. Those would answer your current limit setting via Ohm's law. You don't want to have set very near above the load's idle draw and must also allow for possible peaks. On the other hand since its already driving a 50Ω headphone their now CCS settings should be generally coping.
Savvas called Michael "Tea Bugs" 😀
Yes Salas, I've been following M's ordeal, good thing it all worked out for him, congrats M!
On mine I ended going using a Goldpoint 50k. Much better balanced sound than with the 25k, I used the 25k in the DCB1. I just ordered my new HP's, Fostex stuff we'll see how they sound with the DCG3.
Yes Salas, I've been following M's ordeal, good thing it all worked out for him, congrats M!
On mine I ended going using a Goldpoint 50k. Much better balanced sound than with the 25k, I used the 25k in the DCB1. I just ordered my new HP's, Fostex stuff we'll see how they sound with the DCG3.