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Tube-I-zator Professional PCB

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#281
Funny that Lukasz Fikus is trusted by so many of us to have discovered a miracle output stage when he has made so many mistakes.

I am reassured by your listening impressions, Oliver, and quite excited to hear it. To build this, I sold my DAC, so am now listening to my excellent system through a horrid Sony minidisc player, used as a dac, with a distinctly op-amp sound. Yeurch! My hi-fi has never sounded so horrible, if I'm honest. All good motivation 😀
 
#284
Sure, I really don't mean to criticise him, as I find his site perhaps the most honest, readable and interesting personal hi-fi site I have found on the web, and I am sure this circuit is very good indeed, but surely he will be inviting distortion with such a high i/v value and output voltage, no?
 
#291
Hi Salas. Thanks for responding.

Is R1 the current adjust resistor? Resistor numbers are not noted on the PCB, nor do we have a schematic in this thread. I have just looked at your HV shunt thread to check, and it seems that the schematic shows R1 to be a current adjust, but that it should be a 1W resistor, and also that the mosfet is an IRFP9240, whereas this one is using a 9610, like I already said, so I can only refer you to Oliver's PCB photos on page 20 of this thread.

Current adjust is an audio type 1/4 watt PRP, rated at 56R with 1.855v across it.
 
#294
LucasAdamson said:
Hi Salas. Thanks for responding.

Is R1 the current adjust resistor? Resistor numbers are not noted on the PCB, nor do we have a schematic in this thread. I have just looked at your HV shunt thread to check, and it seems that the schematic shows R1 to be a current adjust, but that it should be a 1W resistor, and also that the mosfet is an IRFP9240, whereas this one is using a 9610, like I already said, so I can only refer you to Oliver's PCB photos on page 20 of this thread.

Current adjust is an audio type 1/4 watt PRP, rated at 56R with 1.855v across it.
Click to expand...

LucasAdamson said:
Correction - had it on for about an hour now - fairly warm, so no worries, but nowhere near as toasty as the other transistor (840), which I am feeling may need a bigger sink for longevity. Photos coming...
Click to expand...

That is R1, and the 9610 is indeed in the newer schematic. If it is running low current like 40mA even 1/4W will do. 1W is there because R1 maybe chosen for whatever current. You should always allow 25mA for staying in the reg above your top consumption in the served audio circuit. ICCS=VR1/R1. Now you got 33mA. The 9610 has 30V across as you report when the 840 has 150V. Guess which one owes to be hotter. The 840 will be significantly less hot when the reg will be loaded and the shunt current will be routed to the load for its most part. Know your full consumption+25mA and choose R1 for each application in brief.
 
#295
Thanks again Salas.

So, if I am pulling 33mA with this 56R:

Allowing 25mA for the shunts gives me 8mA for the both tubes, which is good I think - this is current to voltage buffer tube, and if I remember correctly it only pulls about 3mA per channel.

I will re-sink that 840 though. :hot:

Here's some nice pics of losing my tubes virginity:

TDA1541A_DAC_8.jpg
[/IMG]

TDA1541A_DAC_7.jpg


TDA1541A_DAC_6.jpg


TDA1541A_DAC_2.jpg
 
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#297
a little update: just swapped the boards, same exact results, adjusting the trimmer result in the same behaviour (Vin=Vout-2v approx.)
any ideas??? i followed exactly the print on the pcb for components positioning.. i'll post a close up, perhaps i'm missing something...

edit: added pics
 

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#300
That's your problem most likely. Softer leds, less difference between Vgs-3XLeds, starvation. Calculate a resistor for 40mA. Having 1.12V across the 56R? Make it 27R. Know your now voltage drop across 56R (R1).
 
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