Hannes,
Got the board a couple of weeks ago and the parts I didn't have in my boxes arrived today.
I'm looking at using the Zetex ZTX651 transistors in place of the 2SC2547s, at least I can get them at Digikey and be sure they are not fakes.
I am curious about one thing... all of the shunt regulators I've seen use a 2 or 3-terminal current source in line with the active rail (positive or negative). You use the 180R/1w resistor there. Any reason not to replace that with a 2-terminal current source set to about .3a?
Greg in Mississippi
Got the board a couple of weeks ago and the parts I didn't have in my boxes arrived today.
I'm looking at using the Zetex ZTX651 transistors in place of the 2SC2547s, at least I can get them at Digikey and be sure they are not fakes.
I am curious about one thing... all of the shunt regulators I've seen use a 2 or 3-terminal current source in line with the active rail (positive or negative). You use the 180R/1w resistor there. Any reason not to replace that with a 2-terminal current source set to about .3a?
Greg in Mississippi
RIAA cap orientation
h_a, I bought the RIAA caps from you, am using the new board and have a question. I notice the small silver colored RIAA caps have a black line around on end. Assuming they are not polarized, (or are they?) do they have a preferable orientation? If so, should the end of the cap with the line around it be next to the circular silk screen on the board, or towards the "hole end" where the caps other wire would go?
Abundance of caution and all that,
Thanks,
Russellc
h_a, I bought the RIAA caps from you, am using the new board and have a question. I notice the small silver colored RIAA caps have a black line around on end. Assuming they are not polarized, (or are they?) do they have a preferable orientation? If so, should the end of the cap with the line around it be next to the circular silk screen on the board, or towards the "hole end" where the caps other wire would go?
Abundance of caution and all that,
Thanks,
Russellc
If my old data books are correct the black band indicated the lead connected to the outer foil, this should be connected to the lowest potential point.
The reason given was that the outer most part of the foil has an effect of screening the capacitor.
In this case the black bands should all point in the direction of R3 (390R).
Sharif.
The reason given was that the outer most part of the foil has an effect of screening the capacitor.
In this case the black bands should all point in the direction of R3 (390R).
Sharif.
OK then, I figured the black band meant something. Not polarized, so towards R3 it is.
Russellc
Sorry for my late reply, for some reason I didn't get a notification for new posts in this thread 😉
But I see you already got excellent help from Sharif!
The provided polystyrene caps are not polarized and the line indicates indeed the outer foil.
But I see you already got excellent help from Sharif!
The provided polystyrene caps are not polarized and the line indicates indeed the outer foil.
I finished building it yesterday and had a very late night listening to it, I was very impressed by the sound quality and how revealed it was with difference cartridges.
Just one thing when I power it up and checked the 40V I've got 43.2V is this OK?
Sharif.
Just one thing when I power it up and checked the 40V I've got 43.2V is this OK?
Sharif.
You have more that 50v on input ?
I installed some sokets made from ic sokets to have the posibility to test different kinds of transistors.
Instead of polystirenes i installed wima fkp2 and i'm still thinking if i should replace those wimas with polistyrenes.
I installed some sokets made from ic sokets to have the posibility to test different kinds of transistors.
Instead of polystirenes i installed wima fkp2 and i'm still thinking if i should replace those wimas with polistyrenes.
I've measured 43.2V across the STP55NF06, I currently using a Farnell bench power supply set at 50V. (just rechecked with my DVM and the Farnell psu is read 50.1V)
Just notices RP1 on the schematic is 180R and on the BOM it 270R?
Sharif.
If RP1 is 180 or 270R is not relevant but the final voltage (43.2v in you case) is decided by RP2 and Rp3 and Led Vf. I will come in more details tommorow or you can search few pages back when i had some similar problems and some very kind guys (Hannes is one of them) explained to me how to adjust RP2 and Rp3 (this is a voltage divider) value in relation of Led Vf to set final voltage.
What voltage do you measure across led ?
What voltage do you measure across led ?
I've set the psu to 48V and checked the led there is 1.6v across it.
Across the SENSEV & SENSEGRD I measured 42.7v and on pin 3 of the THS4031 1.5V
I've just read the post at 125 and 126 and notice you changed RP2 (25K5) to 22K?
Sharif
Good news Sharif. Practically you matched the Led Vf to voltage set by voltage divider. (pin 2 and 3 of opamp).
Here are a few photos of my build.
Simple psu using a 20va transformer was a very tight fit.
Main board with a three transistor series regulator for the 48v dc.
Rear panel layout.
Rear panel assembly with a straight through connection and two switchable low pass filter at 500Hz.
This will allow for the extra 1-1.5db eq that needed for the Phillips GP390 ceramic cartridge.
Sharif.
Simple psu using a 20va transformer was a very tight fit.
Main board with a three transistor series regulator for the 48v dc.
Rear panel layout.
Rear panel assembly with a straight through connection and two switchable low pass filter at 500Hz.
This will allow for the extra 1-1.5db eq that needed for the Phillips GP390 ceramic cartridge.
Sharif.
Very nice work Sharif !
What case did you used for preamp ? I'm still searching something not so expensive and suitable.
What case did you used for preamp ? I'm still searching something not so expensive and suitable.
This is the one I've used, I have see the cheaper on the web you may have to do a search.
1455N1601 - HAMMOND - Enclosure, 1455 Series, Extruded With Metal End Panels, PCB Box, 53 mm, 103 mm, 160 mm, Aluminium | Farnell element14
Great work Sharif! Really nice!
The red boards fit straight into the Hammond case, for the green boards one needs to be a little creative 😉
The red boards fit straight into the Hammond case, for the green boards one needs to be a little creative 😉