Using Aktiv Stereo cards with non-Linn amps
Posted: 2019-04-09 09:59
A few weeks ago, a pair of Keltiks crossed my path, and although I hadn't planned of getting any just yet, I couldn't help myself and went and bought them anyway. I already have a pair of Keilidhs I've been planning to turn active, so I already have more amps than I can use right now. My original plan was to use a miniDSP to make a sort of diy Exakt system.
However, the speakers came with a set of Aktiv Stereo cards which I figured I could use to start with. Now these are made to fit in Linns AV5125, 2250 and LK85/140 amps, which I don't have. So I thought I could put together my own Tunebox. The first thing I found was a thread on this site where Fredrik suggested the voltage required to supply power to the cards are around 20 Volts. Well it turns out that I can get +/- 21V from the pre-amp section of my old surround amp. So now my plan is to put the cards in the amp and hotwire them there and then use four channels to run the isobarik woofers, and send the other channels to two external amps.
And now to my problem. And I have to make a n00b alert here, since I'm not formally trained and experienced in electronics. I don't want to ruin any cards or amps so I have breadboarded the cards to see if they work as they should. So I connected them up and measured the voltages. There are check points on the board marked 0V, -15V and +15V. But when I feed the cards 21V I only measure between 7,5-10V on the check points for the different cards. Why is this? It would make sense that I get the stated 15 Volts right?
When I trace the cards I can see that they first pass two parallelled 470 Ohm resistors before entering the LM317/337. So when I measure before the resistors, I do get 21 V on the boards. But between the resistors and the regulators it's down to 10-12 Volts. AFAIK the regulators would need a few volts higher supply than their regulated output, right? What am I missing here?
However, the speakers came with a set of Aktiv Stereo cards which I figured I could use to start with. Now these are made to fit in Linns AV5125, 2250 and LK85/140 amps, which I don't have. So I thought I could put together my own Tunebox. The first thing I found was a thread on this site where Fredrik suggested the voltage required to supply power to the cards are around 20 Volts. Well it turns out that I can get +/- 21V from the pre-amp section of my old surround amp. So now my plan is to put the cards in the amp and hotwire them there and then use four channels to run the isobarik woofers, and send the other channels to two external amps.
And now to my problem. And I have to make a n00b alert here, since I'm not formally trained and experienced in electronics. I don't want to ruin any cards or amps so I have breadboarded the cards to see if they work as they should. So I connected them up and measured the voltages. There are check points on the board marked 0V, -15V and +15V. But when I feed the cards 21V I only measure between 7,5-10V on the check points for the different cards. Why is this? It would make sense that I get the stated 15 Volts right?
When I trace the cards I can see that they first pass two parallelled 470 Ohm resistors before entering the LM317/337. So when I measure before the resistors, I do get 21 V on the boards. But between the resistors and the regulators it's down to 10-12 Volts. AFAIK the regulators would need a few volts higher supply than their regulated output, right? What am I missing here?