SVTIV Pro Side B out

[Enzo]

Actually, the more Xover notch you have the cooler the amp is running. Most of us will not hear a small amount of it anyway, so leave a bit of notch and se what you get.

[booj]

Ok, my first answer just disappeared, so here we go again.

I'll let you know, Jazz about that idle current. It does seem a bit high at 1 amp. I just tried it again and got the same results.

Another can 'o worms has opened. I'm getting a flat top positive waveform that starts at about 6 watts and disappears at about 35 watts into 4 ohms with a signal driving the power amp directly. After 35 watts the waveform looks normal. This only happens at 4 ohms. At 8 ohms everything is clean and healthy. No change going from about 100 hz to 500 hz.
Maybe the Zeners (D214 - 217), the 1N3070's (D211 - 212), 914's (D210 - D213) or the caps (C211 - 214)?
Additionally, there is no relay delay time. I can look at the scope while turning the power on and the waveform comes up instantly.

Thanks, fellows for your help so far. It's appreciated!

[Jazz P Bass]

The 'flat top positive' may be a driver circuit issue.

[booj]

Both sides work great now. Yay! (I replaced the 10 volt zeners, the 914's, the 1N3070's, the 1uf, and the 10uf caps) BUT... now it doesn't seem to be working correctly in bridge mode. The bridge/mono switch functions normally, I get signal into the preamp A input jack, and the signal from IC201-pin 8 goes to the input B input jack, (confirmed with an ohmmeter) but for some reason, they are the same phase, which makes no sense. So I get the same output from the bridged output jack as I do from either of the sides in stereo mode. I am confused. Anybody got $0.02 to throw in here?
by the way, Jazz, when I use the 5 amp analog meter scale instead of the 1 amp scale, the idle current appears to be under 1/2 amp.

[MarkusBass]

I get signal into the preamp A input jack, and the signal from IC201-pin 8 goes to the input B input jack, (confirmed with an ohmmeter) but for some reason, they are the same phase, which makes no sense. So I get the same output from the bridged output jack as I do from either of the sides in stereo mode.

I wonder how did you check that both signals are in the same phase? With a dual channel oscilloscope, or some other way? This is almost imposible - it would mean that IC201 still works but suddenly it's become non-inverting. Another option would be that the S1 switch does not work at all and you are measuring non-bridged amps during the test. You can also compare the signal phase between the ouput of IC101 and the output of IC201.

Mark

[booj]

I measured the signal voltage between power input jack A and B and it is indeed double the voltage to just one jack, so my assumption that the signals were in phase was amiss. I was jumping to the conclusion that if the output was the same the input must be the same. that being as it is, I'm still left with proper input and improper output. I've changed a whole lot of parts on this puppy. I'll check for something along the lines of bad solder connections on the main board. Thanks for your response Mark.

[booj]

Ok, I think I figured it out. The owners manual block diagram on page 17 shows that to use bridge mode, you must use the center Speakon connector and have the speaker wires connected to 1+ and 1-. the picture shows 1+ going to Ch. A "hot", and 1- going to Ch. B "hot". However the circuit board the connectors reside on are not wired that way. 1+ and 1- of the center connector go to 1+ and 1- of channel A. 2+ of the center connector goes to channel B "hot", and 2- of the center connector goes to ch. B gnd. Of course, I can't find my digital camera to show this.
That means the only way to get bridge mode operation is to connect the speaker wire to 1+ and 2+. It also means if I'm right, the manual is wrong.
I'll hook 'er up with no load and measure the voltage and see what I get.

[booj]

http://www.ampeg.com/pdf/SVT4PRO.pdf

there's a link to the manual.

[booj]

Ok. I have confirmed in bridge mode the amp needs to be connected to the 1+ and 2+. On the same page that comes up in google for the manual is a talkbass forum question about running bridge mode which helps confirm. This is an excerpt "An AMPEG Mono Bridged cable will have the amp end's -1 wire moved over to the +2 terminal and the +1 stays put. When running Bridged the switch is IN."
Thanks again for your help guys. Now on to the next one.