Hi Delange. The current through the 47.3R increases very slowly over a period of about 40 minutes.
I'm repeating this right now. I got 1.32V with pot wound down. Spent 5 minutes trying to get 2.74V (all the while the voltage tending to increase). Finally nailed the initial value, averaged over 10 seconds. Now, after 30 minutes I'm measuring 3.05V. Elector says I should not be concerned if it reaches 90 mA = 4.2V.
This process is not very satisfactory. I'm currently some way off 90 mA and I could have 50% error for all I know.
Please don't reject advice from other contributors, Q-Watt builders or not. It just leaves us all poorer and reliant on too few words from Elektor to get by.
If I had nailed my initial value immediately, when the junction temp was increasing at the highest rate, I would probably be reading 4V now not 3V...
So in the steady state (warm) should the quiescent current be 30mA or 60mA?
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3.05 volts over the 47 ohm resistor is about 65mA. Deduct 30 mA from the relay and you have about 35 mA which is fine.
I guess there is also the original potmeter at play: it is not easy to adjust very precisely with such a pot.
If that is the value you measured after abut 40 minutes I would say your Q-Watt is ready for action.
Don't worry I'm not. Its just that one particular annoying guy that I'm ignoring. His only intention is to create confusion and he always knows everything better. There seem to be al lot of DYI-Audio users who are ignoring him for the very same reason. One could say he his notorious... 🙂
If you use the Elektor process with the 47 ohm resistors in the power supply leads then you need to read about 60mA in the positive supply lead.
This means the the bias current is 30 mA when you read 60mA in the above process and that is exactly what you need.
I would say congrats, your first channel is up and running !
Sorry, Popchops,
it was a discalculation by me by the factor of 10. The correct values are 12 mV or 13,2 mV, respectively, at a bias current of 30 mA.
Best regards!
Just want to remind you that Elektor is offering some discount on the Q-Watt kits, valid until July 8th.
Best regards!
Best regards!
https://www.elektor.com/q-watt-110656-71
Price indicated in Sterling is £82.95 reduced to £69.95 or €79.95 euros.
2 days, 7 hrs left!
Price indicated in Sterling is £82.95 reduced to £69.95 or €79.95 euros.
2 days, 7 hrs left!
I also bought them at 80 Euros (a while back). Great amplifier; very happy with the performance.
I'm now starting a new amp project: Apex SR200.
I wouldn't dream of it... 🙂
There is a (very lengthy) thread here: http://www.diyaudio.com/forums/solid-state/173462-studio-reference-amplifier.html
This thread is, as threads on Apex designs sadly use to be, quite derailing, or, in Ray Davies' words, »a mixed up, muddled up, shook up world« :-D.
Best regards!
You are such a bad influence delange 😀
I can't stop listening to my Q-Watt, so consequently my case still has no feet.
Pops.
Indeed it is.
I've made a habit of taking notes in notepad while reading the thread.
Mister Apex spits out a lot of designs, which is great. But the result is that one thread is filled with different designs / models and it gets difficult to keep track of everything.
The SR200 looks like an interesting amp and that is why I decided to built it.
Thanks... I do my best 😛
Well it is a great amp. It gets daily use over here. I'm very pleased with my Q-Watt's.
Nah it's shocking.
The cheap Maplins stereo pot is so badly balanced that even after I trimmed it in the nominal position I get massive imbalance when I reduce volume.
I have an off the shelf Tisbury passive preamp in the post with stepped attenuators. Basic functions but exactly what I need.
You can't DIY for their price... even building a properly balanced attenuator is costly.
Pops.
The cheap Maplins stereo pot is so badly balanced that even after I trimmed it in the nominal position I get massive imbalance when I reduce volume.
I have an off the shelf Tisbury passive preamp in the post with stepped attenuators. Basic functions but exactly what I need.
You can't DIY for their price... even building a properly balanced attenuator is costly.
Pops.
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