Aato, nice shot and good to see the build commencing - keep us posted on your progress.
Do you have all the power supply components in hand too? Which power transformers did you go for?
Do you have all the power supply components in hand too? Which power transformers did you go for?
Thanks Zman, Yeah I went with Antek 20v 400VA, I know it is a bit smaller than recommended but we'll see if I can get away with, also went with 20v rather than 18v because I m planing to use cap multiplier.
good eye 😀. Yes they are for now, I ordered the wrong ones, will keep them for testing purposes before I change it to suggested ones.😎
Unfortunately, I am still waiting on Pats Connexion to send my items. I placed an order almost 2 months ago over $300 value and no answer yet. All do they mentioned back then they are out of 10uF Clarity caps and will take 2 or 3 weeks. I check the stock and them still out of it. Until I receive my order I can not do anything.
I have tested same green Vishay Fernice wirewound ones on Alpha. They definitely increase distortion in the feedback position. Best are Panasonic ERX Metal thin film. Carbon film works well too but hard to get precise values.
Looks like higher wattage metal thin films is not generally easy to come by.
Anyhow I matched the heatsinks to PRPs, 😀
Attachments
Nice looking heatsink !
You could have used first batch of pcb which was red color too.🙂
You have difficulty to locate MRA5 resistors?
Fab
Thanks 😀
I couldn't find any when I ordered rest of the parts from mouser, But looks like they have it now 🙂
Wanted to order off ebay but it was like 3$+ for each, so I went with wirewound for time being.
thanks zman 🙂
Not Holding Bias After Cool-down
All:
Having a strange issue. I bias the amp to 0.063 mV (1.25A) and near zero offset. Let is sit for a couple of hours and all is good...bias remains fixed, sounds fantastic. I then shut it off, let it cool down completely, re-power and let it come up to temperature. The bias has settled in at 0.044 mV (0.88A). I re-biased and did the same test with the same results.. the bias will not come back to original set point. Could this be an issue with the thermistor? Suggestions anyone?
Steve
All:
Having a strange issue. I bias the amp to 0.063 mV (1.25A) and near zero offset. Let is sit for a couple of hours and all is good...bias remains fixed, sounds fantastic. I then shut it off, let it cool down completely, re-power and let it come up to temperature. The bias has settled in at 0.044 mV (0.88A). I re-biased and did the same test with the same results.. the bias will not come back to original set point. Could this be an issue with the thermistor? Suggestions anyone?
Steve
Hi
Yes definitely strange....looks like it is maybe over compensating in temperature.
Of course you must adjust the bias without music playing to get DC bias reading.
I think you have a different thermistor package which makes a direct very good contact with heatsink. When I made the adjustment for resistors values it was for the thermistor part of the BOM where the contact with heatsink is not direct. You may try to have your thermistor not directly in contact with heatsink. The goal is to have a stable voltage across TP7/V+ and TP8/v-.
Otherwise we may have to change some resistors values to correct temperature compensation. It is normal that the bias would vary of about 5-10% between different days though but not that much as in your case. At boot -up it will always be a lot lower but should gradually increase to target bias since it is class A...
Keep us informed.
Fab
Yes definitely strange....looks like it is maybe over compensating in temperature.
Of course you must adjust the bias without music playing to get DC bias reading.
I think you have a different thermistor package which makes a direct very good contact with heatsink. When I made the adjustment for resistors values it was for the thermistor part of the BOM where the contact with heatsink is not direct. You may try to have your thermistor not directly in contact with heatsink. The goal is to have a stable voltage across TP7/V+ and TP8/v-.
Otherwise we may have to change some resistors values to correct temperature compensation. It is normal that the bias would vary of about 5-10% between different days though but not that much as in your case. At boot -up it will always be a lot lower but should gradually increase to target bias since it is class A...
Keep us informed.
Fab
I no longer have the documents because the lightning (thunderstorm) grilled my PC (television and other electronic devices) but remember it would not be rather 63mV for bias adjustment and not 0.063mV?