Looking for advice on replacing my amps

I skimmed through the posts and I have a chance to pick up a Sunfire loaf inversion model the 300w model not the signature it's an hour and a half drive to check it out. I asked the owner (a woman I think) if I'll be able to test it out when I arrive and asked if she knew of any issues. She says it was in a house they bought or sold but she removed the amp and it was working. I asked if any protection lights were on before I looked through the mail to see if it had anything like that. She said when it's plugged in it does nothing. I figured it should at least light up the front screen (the power draw meter) what should be happening on power up? I told her to check the main AC fuse to be certain it's not blown. I've not heard back yet.
 
When you talk of 40 year old amps that's what I have right now 2x qsc 3500 series 3 amps. For years I had 1 hot channel during idle, I never turn them off and the hot channel would cool down during music playing, after 7+ years of it being hot it started entering a hot warning during idle pretty often. I checked the bias and set it up after replacing the all 3 pots on the hot board. It was tricky because I don't have a distortion meter but have a scope and noise generator. I got the input and output signal to match and it ran cool.

But when I had the board out I pulled the good board out too to reference the traces to be sure some solder joints were not overlapping where they shouldn't because the hot board has already been repaired before I got it and I'm sure that's why they sold them (it was a church). When I put the good board that was not touched back in it would not latch the speaker relay. The led light stayed red as if it had a start up issue and checked DC at speakers and saw nothing.

I tested the relay and it was fine. I removed it from the board to test it. I tested various parts that were in the start up path and found no issues. I tested the board and then it would not light the red led or the rear board led that is the power on delay led . Tested the led and it was good. The charging cap is good and all parts around it were good. I pulled the Q17 and Q18 and tested them and saw they read on and that's really all I could do was verify they operated on the tester food enough to show some numbers and the 3 leads functioned

I pulled the zener diode that switches the red LED to green ay start and it should have turned green but instead when I power it up the led still had no red light or green but when I turn it off I hear the speaker relay latch quickly and then it turns off normally with the switch delay. There is power running through the circuit and I don't understand why. I would think that the ptotect light should be a sign that the power isn't going to the boards of the speaker latch should engage and the leds both front and back should have power. The circuit isn't that complex and I've done tests every single part on the board other than the B2 the B1 tested fine but the B2 is hard to get to and I'd probably end up removing a bunch of other stuff to be able to remove it and put it back without destroying anything on the part or board. I've checked voltages at points where I know they should be and the only issue seems to be the voltage at the front and rear LEDs being low. Like 2.2v and the turn on delay circuit should go up to 7 volts to charge the C7 that gets voltage from q17 ot q18 base to turn on the rear led for delay never gets charged but the charging cap tests within 1% it's only 10v 100uf nonpolar cap. I've tested all diodes and big ceramic resistors , replaced big caps and still nothing lights up the indicator LEDs.

If I leave it on the board will get hot at idle like the other one used to. Setting the bias down to zero doesn't change anything. Those pots are terribly hard to adjust. It's either too little or way too much but makes no difference. I tested the voltage controlling resistor or thermal resistors both in the bias circuit and on the heat sinks and they do respond. The zener diode can't be tested but the manual says it can be lifted and it should still work since it just directs the opposing voltage once the voltage is over the existing voltage on the other side. So it should be getting the led voltage or current needed to change it but it never gets enough.

That's why I have decided to look for new amps, I can't keep tearing stuff off the board and expect the copper traces to take it. I already had to fix one spot on the top where a hidden trace came up with a big cap.

I picked up a Grady deal on another qsc gx5 that had similar specs on paper but is a completely different amp with SMD parts and small chips with the noisiest fan I've ever heard, amp looks new inside and out. I put a 60Ω resistor on it and it's much better. The GX5 seems to do fine on my woofers and I have the input settings at about half the way compared to when I used the 3500?

I have tested woofer load at 2.2Ω. I did try out using 3 old (50 or more years old) bgw 150 amps one in stereo for panels band 2 in mono on woofers and when my source input cord got slightly pulled out of my phone it made the typical loud noise and one of the bridged amps turned off. After inspecting it, I found it was repaired and they mixed up two of the transistors where the middle one is different than the others and I removed all trans and tested them. All good I replaced them but the board wants to cook 2 big 0.22Ω resistors and I put it aside for now since I have 5 of those BGW amps fixing it isn't worth my time.

I have been using the 3500 on highs and the gx5 on woofers but since I got it on Friday night I haven't been able to crank it up. I typically play it during the week to avoid bothering my neighbors. They work during the day. So I can't say how it sounds with volume. But it does ok at lower maybe 80db or higher levels even with the fan slowed it's cold to the touch and so is my 3500.

I'm writing this as I wait to hear back from the seller but I'm almost certain that the carver amp must have an issue if it's not turning on or lighting the power meter. Thats really what I need to know, does the meter light up when it's plugged in or does it require a signal to turn on with auto sense? This model doesn't have bypass for auto sense.
 
I also have a chance to pick up 2 audio control Architect 2 channel amps for $50 each but they're even further away than the carver and all these amps are about the same age. The audio control are only 80wpc and are bridgeable and are rated at 2Ω with 125wpc bridge into 4Ω is 250w RMS 200 dampin. They also have a 7 band eq built in each amp which is weird.

I'm thinking of getting them too since they're fan less and can run the panels without any problem. In fact all amps I've tried can drive them to loud levels without a problem. I have also tested an old Peavey CS400 amp and disconnected its fan just to find out it's good for about 30 seconds at low volume before it thermals. I replaced the fan and added an outboard (mounted inside the case) power supply to power the 12v fan with 8 volts and it works and sounds fine but it's huge and the fan is noticeable even when slowed and a quiet fan is used. It's mounted right on the rear panel, the GX5 is in the center so it's less prominent.

Any help on the carver would be nice since I think $250 is a decent price. I did see a 2400 for $500 and another for $850. I'm not sure how much better theyd be over what I'm already running but having 2 nice amps that are better looking would be nice if I'm going to go with something new.

I see that some carver have fans? I can't recall which. There are 3 Ashley amps locally but they're huge and have 2 fans in the 250w x2 amps and 1 big one in the 100w x2 model. So even at a good price they're not going to work.

I can't believe they get $30+ for a quieter fan when I paid $100 for an entire amp with a fiberglass case that's like new. I can't justify another $30 for a fan. Fans are free in my world.

I'm currently looking for a sound activated switch to control amp fans , preferably one that has a threshold setting to be able to set the turn on and turn off by volume of noise it heads with maybe a delay as well so it's not cycling constantly and stays off longer during quick low volume sounds or noises.
 
Last edited:
TimD said:
Crest was another outstanding unit before Peavy got their hands on them as well. (Never much cared for QSC).

Solid as a rock, and fully modular making field maintenance a breeze. A full channel changeout is sub 10 minutes . . .

A guy from Audio Analysts told me that part of the sales pitch was the sales guy holding one in the air and dropping it on a concrete floor, and they always worked. I own 12, and I can see why . . .
Click to expand...
They should have made a fucking turntable too then! LOL!
 
You must log in or register to reply here.
Back
Top