Elektor-Giant 1000W

[togo]

Hello!

I hope someone of you can help me with the following problem:

Does anyone rember to the giant 1000 from elektor?

I have biult this amp but it makes some trouble.
First of all i had to replace the original 2SK135/2SJ50 to the 2SK1058/2SJ162. Then i had to biult up a new PCB to fit the schematic on a 100x300mm card. The new layout is very similar to the original from elektor except that i mounted all MOSFETS and the voltage regulators on the same heatsink. Next i built the security schematic from the giant 2000 also from elektor, because its better then that one for the giant 1000. After that i tested the amp. Everthing works fine till the relay in the outputline conected the speaker to the amp. I hear a little hum and when i switch the amp off the relay falls after 5ms. In this time period, a very nasty and loud noise comes from the speaker.
Does anyoune built up this amp and made the same experience with it in the power-off sequence?

thx

PS: if you need more information, please ask.

[nigelwright7557]

Originally posted by togo
Hello!

I hope someone of you can help me with the following problem:

Does anyone rember to the giant 1000 from elektor?

I have biult this amp but it makes some trouble.
First of all i had to replace the original 2SK135/2SJ50 to the 2SK1058/2SJ162. Then i had to biult up a new PCB to fit the schematic on a 100x300mm card. The new layout is very similar to the original from elektor except that i mounted all MOSFETS and the voltage regulators on the same heatsink. Next i built the security schematic from the giant 2000 also from elektor, because its better then that one for the giant 1000. After that i tested the amp. Everthing works fine till the relay in the outputline conected the speaker to the amp. I hear a little hum and when i switch the amp off the relay falls after 5ms. In this time period, a very nasty and loud noise comes from the speaker.
Does anyoune built up this amp and made the same experience with it in the power-off sequence?

thx

PS: if you need more information, please ask.

Schematics would be helpful.

Most amps give a thump through the speaker on turn off unless there is cctry to stop this.

[togo]

Thank you for your interest.
Here is the original schematic of the giant (gigant).

[Netlist]

Originally posted by togo
except that i mounted all MOSFETS and the voltage regulators on the same heatsink.

Are the regulators and mosfets well isolated from the heatsink?

/Hugo

[togo]

Oh yes of course with mica and between thermal grease.

[nigelwright7557]

Originally posted by togo
Hello!

I hope someone of you can help me with the following problem:

Does anyone rember to the giant 1000 from elektor?

I have biult this amp but it makes some trouble.
First of all i had to replace the original 2SK135/2SJ50 to the 2SK1058/2SJ162. Then i had to biult up a new PCB to fit the schematic on a 100x300mm card. The new layout is very similar to the original from elektor except that i mounted all MOSFETS and the voltage regulators on the same heatsink. Next i built the security schematic from the giant 2000 also from elektor, because its better then that one for the giant 1000. After that i tested the amp. Everthing works fine till the relay in the outputline conected the speaker to the amp. I hear a little hum and when i switch the amp off the relay falls after 5ms. In this time period, a very nasty and loud noise comes from the speaker.
Does anyoune built up this amp and made the same experience with it in the power-off sequence?

thx

PS: if you need more information, please ask.

I think the problem is just the capacitors in the PSU discharging and upsetting the amp cctry.

I have numerous amps both home built and bought in that give a thump on power up and power down.

My own designs use a microcontroller to hold the relay off for 3 seconds on power to get rid of the power up thump.

I suppose I should have added a mains detect cct that also detects when the mains goes away and then I can disconnect the speakers quickly.

[togo]

What is the PSU and whats the meaning of cctry ?

I don't have a problem in the power up sequence.
The problem is the power down sequence.

I made some new meassurments on my amp:
When i switch off the amp, the +90V on the input of IC1 (7808) jumps from +90V down to +70V. The same happend on the output of IC1. Here the voltage jumps from +80V to +70V.
From +70V i meassure a slow unloading curve from the cap.
Why does it jump so steep from 90V to 70V ?
Is it in context with the diodes D17, D5 (D18, D6) ?

The schematic is over 25 years old so i ask myself: Are the diodes D17, D5 (D18, D6) on todays voltage regulators 7808 (7908) necessary?

[nigelwright7557]

Originally posted by togo
What is the PSU and whats the meaning of cctry ?

I don't have a problem in the power up sequence.
The problem is the power down sequence.

I made some new meassurments on my amp:
When i switch off the amp, the +90V on the input of IC1 (7808) jumps from +90V down to +70V. The same happend on the output of IC1. Here the voltage jumps from +80V to +70V.
From +70V i meassure a slow unloading curve from the cap.
Why does it jump so steep from 90V to 70V ?
Is it in context with the diodes D17, D5 (D18, D6) ?

The schematic is over 25 years old so i ask myself: Are the diodes D17, D5 (D18, D6) on todays voltage regulators 7808 (7908) necessary?

PSU = power supply unit.
cctry = circuitry.

[ntropy]

Hi Togo

One possibility would be that when you turn off your amp, a sparc builds up on your power switch which causes all sorts of ugly EMI interferences with your amp. I had exact this phenomenon on my DIY active speakers.
I got rid of this by installing a simple snubber (RC-Glied in German) in parallel to the power switch. Just make sure the snubber is at least rated for 250VAC. I would try a value like 22nF and 100ohm.

http://en.wikipedia.org/wiki/Snubber

Or you can use a so called "X2" capacitance instead of the snubber, again I would use a value like 10...47nF, maybe maximum 100nF:

http://www.wima.com/DE/mp3x2.htm

To test if it's really caused by the switch, you can switch off your amp by just unplug the wall plug. Then the nasty sound should be smaller.

Hope this helps
ntropy

P.S.: your relais falls of in 5ms, not 5s?

[ntropy]

PSU = power supply and cctry is just short for "circuitry".

The diodes D17, D5 (D18, D6) are just standard protection diodes for the LM7808, you can find them under "typical applications" in all LM78xx datasheets.

That you have a steep jump from 90V to 70V is a bit strange. How big are your capacitors in your power supply? (how many uF)