One way to find out....
Order a few of the bias transistors also. If the bias transistor is intermittently opening (rare but it happens), it could cause the outputs to fail/blow fuses.
When you get it up and running and all of the transistors clamped, keep your scope connected to ch 4 and look for intermittent oscillation. Tap on various parts of the board to see if you can get it to misbehave. Also move all of the switches to see if that causes problems.
Order a few of the bias transistors also. If the bias transistor is intermittently opening (rare but it happens), it could cause the outputs to fail/blow fuses.
When you get it up and running and all of the transistors clamped, keep your scope connected to ch 4 and look for intermittent oscillation. Tap on various parts of the board to see if you can get it to misbehave. Also move all of the switches to see if that causes problems.
Which transistor would be the one for bias?
Also I found another weak point. CH4's RCA shield needed to be re-soldered together. It measured OK but I could tell the connection was only touching and not solid. I went ahead and resoldered the ring of each RCA shield on this amp. it was quick to do.
I put CH1's output transistors on CH4 and will be running some tests against it all this evening.
Also I found another weak point. CH4's RCA shield needed to be re-soldered together. It measured OK but I could tell the connection was only touching and not solid. I went ahead and resoldered the ring of each RCA shield on this amp. it was quick to do.
I put CH1's output transistors on CH4 and will be running some tests against it all this evening.
Is this normal? When I increase the amplitude from the frequency generator the emitter resistor voltage slightly increases. At rest the voltage is 0.000vDC, but when I increase the input voltage from the generator to 0.25vAC the emitter resistor voltage rises to 0.010vDC. The outputs get pretty hot!
I measured voltage of the generator and got 0.003vDC and 0.250vAC meaning the generator is just slightly offset with DC voltage.
Is there something wrong with the offset bias on this amplifier? Both CH3 and CH4 are doing this.
When this channel blows in my car, I'm probably supplying the amp about 1-1.25v of signal from my Pioneer HU, plus the amp's gain was up a little bit.
I measured voltage of the generator and got 0.003vDC and 0.250vAC meaning the generator is just slightly offset with DC voltage.
Is there something wrong with the offset bias on this amplifier? Both CH3 and CH4 are doing this.
When this channel blows in my car, I'm probably supplying the amp about 1-1.25v of signal from my Pioneer HU, plus the amp's gain was up a little bit.
Last edited:
The small transistor under the board, pressed against the heatsink is the bias compensation transistor.
When you have to solder the shields, you have to be careful not to apply enough heat to melt the insulator inside.
I can't say if that's normal, various amplifier designs will act differently. Compare it to the other channels.
Offset voltage and bias current are two different things.
When you have to solder the shields, you have to be careful not to apply enough heat to melt the insulator inside.
I can't say if that's normal, various amplifier designs will act differently. Compare it to the other channels.
Offset voltage and bias current are two different things.
I replaced a bunch of transistors in this amp with new ST outputs and the majority of the driver transistors for channels 3 and 4, plus cleaning and applying new layers of heatsync compond on the tops and bottoms of both the transistors and the mica slivers. In doing the massive rebuild, I also did find a fault with how CH4 transistors were pressed against the heat sync. I fixed it with shimming the screw which was too long with a pair of thin washers and now CH4's outputs are pressed firmly to the sync. So far, the amp is playing on the bench -OK- but I'm affraid to test it out further and harder. At .25vAC input the emitter resistors still measure 0.010 across all four channels. When bridging (or dropping the ohms of the speakers) this voltage doubles to 0.020 at .25vAC in. I guess this could be normal but I'll just have to keep playing and testing. I dont want to rebuild this amp again thats for sure. Its costed me about $30 so far.
There is something fishy with the way stereo, mono, and the internal RCA cross switch. When in mono mode, the manual says I should only use the Right RCA input, but then I only get half volume and only one gain pot works on CH1/CH2. If I use both RCA inputs then both pots work and the sound is louder. Comparing this to CH3/CH4 is odd, because in Mono mode only one RCA needs to be connected and bridging works fine, plus only one pot works.
All switches have good continuity, and the relay in the center appears to be functioning as designed.
Alas, I've tested all components in all four channels and I cannot find the fault if there even is one.
There is something fishy with the way stereo, mono, and the internal RCA cross switch. When in mono mode, the manual says I should only use the Right RCA input, but then I only get half volume and only one gain pot works on CH1/CH2. If I use both RCA inputs then both pots work and the sound is louder. Comparing this to CH3/CH4 is odd, because in Mono mode only one RCA needs to be connected and bridging works fine, plus only one pot works.
All switches have good continuity, and the relay in the center appears to be functioning as designed.
Alas, I've tested all components in all four channels and I cannot find the fault if there even is one.
Last edited:
Welp, I've been playing the amp on the bench with 2 test speakers and a musical source; bridged down the 4 channels to 2 and running the channels at 2 ohms each. Needless to say everything is staying relatively cool or normal operating wise. At high volumes where my test speakers are the absolute weakness the emmitter resistors measure 0.020 vDC. The amp is running through a 5A fuse off the bench battery.
The gain vs number of RCA inputs is a little strange however. I think what I'll do is run the amp as a two channel amp and use RCA split cables running from the fron RCAs of the HU as I think the way the RCA network was designed is a little mis-representing from the manual. If I install it in a car I'll probably have to use the volt meter to match the gains. Seems they are a little all over the place from each other. Its almost like this amp has 4 little amplifiers in one - kinda cool.
I do have to say this little amp sounds wonderful on the bench
its probably one of the best sounding amps I've had the pleasure to work with.
The gain vs number of RCA inputs is a little strange however. I think what I'll do is run the amp as a two channel amp and use RCA split cables running from the fron RCAs of the HU as I think the way the RCA network was designed is a little mis-representing from the manual. If I install it in a car I'll probably have to use the volt meter to match the gains. Seems they are a little all over the place from each other. Its almost like this amp has 4 little amplifiers in one - kinda cool.
I do have to say this little amp sounds wonderful on the bench
its probably one of the best sounding amps I've had the pleasure to work with.
Last edited:
Here is the manual for this amp
http://www.soundstream.com/manuals/AMP/sa_mc_d_class%20a/mc140245/mc140245.pdf
http://www.soundstream.com/manuals/AMP/sa_mc_d_class%20a/mc140245/mc140245.pdf
this amp DOES have 4 amps inside. and when you bridge 2 channels together it is normal to use only one rca jack as input for those 2 channels. the bridging switch disconnects the other channel and feeds one input to two amp channels(one channel inverted). this is how ALL bridged mode amps work.
It sounds like the amp still has some issues. keep working on it. these amps are not flaky or unstable by any means! so if you are experiencing odd problems and weird issues...there are still problems.
It sounds like the amp still has some issues. keep working on it. these amps are not flaky or unstable by any means! so if you are experiencing odd problems and weird issues...there are still problems.
Its like the two gain pots still need to be moved together on the two 'channels in the center of the amp, and also the signal is half that of the good/working bridged channels. If I use both L&R RCAs on the iregular pair the signal will match the other bridged side. I can get the gain/level matching on all bridged channels while having both L&R RCAs plugged into the center-of-amp channels. The gain pots from channels (1/2) and (3/4) have matching sensitivity across the adjustment range. While bridging, Channel 3's gain pot is disabled. I imaging channel 1's gain pot should be disabling as well.
Does it make any difference that this amp has 10K and 20K gain pots? The good/bridged side has 10K pots (channels 3, and 4), and the side thats irregular has 20K pots (Channels 1 and 2). I'd think not; maybe only in sensitivity if any.
You had mentioned on checking the operation of the relay and switches. Is the relay always supposed to activate regardless of any switch positioning? The switches are measuring up with good continuity at the defined position.
Channel 1 is the left-most circuit network. Channel 4 is right-most
Inverted view. Channel 4 on left, channel 1 on right.
Last edited:
I don't know about this amp but in similar amps, the 10k/20k pots wouldn't make much of a difference.
I don't know how the relay is being used here. Have you followed the circuit back from the contacts of the relay to see what they connect to?
Have you looked at the signal on the relay contacts to see if they had preamp level audio on them?
With the amp in 4 channel mode (no channels bridged), is there any single RCA input that will produce audio in more than one channel?
I can't remember if it was this amp... Were there any traces that were cut and you repaired?
I don't know how the relay is being used here. Have you followed the circuit back from the contacts of the relay to see what they connect to?
Have you looked at the signal on the relay contacts to see if they had preamp level audio on them?
With the amp in 4 channel mode (no channels bridged), is there any single RCA input that will produce audio in more than one channel?
I can't remember if it was this amp... Were there any traces that were cut and you repaired?
I was working with this amp about three weeks back and yes there were two items somewhat peculiar on this amp. First, on both the top and bottom of the PCB, the traces directly between the RCA shields of channels 1 & 2 were cut. I didnt repair it, but I did test putting a lead between the RCA shields - no difference. You can see the cut on the bottom of the two pictures above.
The second thing was this amp seemingly could have been missing what I had thought to be a 1N4148 diode near the 3524. You can see the two pads just south of the yellow cap in this photo. I thought a diode would go here because I saw some pics on AmpGuts from Soundstream D series amps. Puting a diode in this spot deactivates the relay but also channels 1&2.
There does not seem to be any audio across the relay. It looks like it's purpose is to activate channels 1&2.
I'll try the single RCA in stereo idea.
The second thing was this amp seemingly could have been missing what I had thought to be a 1N4148 diode near the 3524. You can see the two pads just south of the yellow cap in this photo. I thought a diode would go here because I saw some pics on AmpGuts from Soundstream D series amps. Puting a diode in this spot deactivates the relay but also channels 1&2.
There does not seem to be any audio across the relay. It looks like it's purpose is to activate channels 1&2.
I'll try the single RCA in stereo idea.
Looks like I'm back into working on this amplifier. After rebuilding it back just over 2 months ago, it was running exceptionally well in my car. I never did figure out why the gain controls had to be set differently from channel to channel; but I had just set them with a sin wave and volt meter to match each channel. I had the amp running a 4Ohm bridged (2 ohms per channel) which estimated the output at 2x90w (The amp is 4x35w normally).
This evening I think I overpushed/heated the amp. I was listening to some DJ style music at maximum volume for about ~10 minutes with my friend driving home after getting a good deal at the sound distributor. I turned down the volume after the ~15 minutes or so, said one thing to my friend, and then POP! The left door speaker went out. Amp's channels 3&4 went dead, and also the two 3A fuses poped. Opened her up, and both of Channel 4's output transistors (TIP102/107) are shorted between legs 2 and 3.
The thing is about channel 4 is, its all the way furthest and almost practically at the edge of the heat sync. I wonder if this amp died of natural causes (over pushed) or perhaps there is something else not quite correct?
This evening I think I overpushed/heated the amp. I was listening to some DJ style music at maximum volume for about ~10 minutes with my friend driving home after getting a good deal at the sound distributor. I turned down the volume after the ~15 minutes or so, said one thing to my friend, and then POP! The left door speaker went out. Amp's channels 3&4 went dead, and also the two 3A fuses poped. Opened her up, and both of Channel 4's output transistors (TIP102/107) are shorted between legs 2 and 3.
The thing is about channel 4 is, its all the way furthest and almost practically at the edge of the heat sync. I wonder if this amp died of natural causes (over pushed) or perhaps there is something else not quite correct?
Well, Im not precisly sure, but I bet the way the transistors are sandwiched to the heat sync between the PCB doesnt really help too much. I bet when the amp got hot, the board may have flexed a bit and allowed one of the transistors in Channel 4 to seperate from the sync and really overheat.
I already fixed the amp again and put it back in my car; but not before slightly adjusting the way the transistors get sandwiched. I put a larger washer on the screw holding channel 4 to the sync and used a lot more than the necessary ammount of sync compound to put it back together. Hopefully it will hang in there; but if not then I'll either have to rewire the channels for a 4 ohm load rather than 2, and perhaps think about putting a drill to the heat sync and making the contact points of the outputs to the sync press a lot harder. One more thing I can do it raise my HU's hi-pass crossover just a bit to help keep the low frequency draw off this amp. I had it set to 50hz which is mighty low for 6.5" door speakers and I dont think 80hz will make it sound that much worse off. At 50Hz it sounded so freaking awsome in conjunction with the sub.
At the end of the day, I think this amp is more for clarity and sound quality than for maximum SPL; although it sounded so amazing right up until the very end.
I'll never get rid of this little amp.
I already fixed the amp again and put it back in my car; but not before slightly adjusting the way the transistors get sandwiched. I put a larger washer on the screw holding channel 4 to the sync and used a lot more than the necessary ammount of sync compound to put it back together. Hopefully it will hang in there; but if not then I'll either have to rewire the channels for a 4 ohm load rather than 2, and perhaps think about putting a drill to the heat sync and making the contact points of the outputs to the sync press a lot harder. One more thing I can do it raise my HU's hi-pass crossover just a bit to help keep the low frequency draw off this amp. I had it set to 50hz which is mighty low for 6.5" door speakers and I dont think 80hz will make it sound that much worse off. At 50Hz it sounded so freaking awsome in conjunction with the sub.
At the end of the day, I think this amp is more for clarity and sound quality than for maximum SPL; although it sounded so amazing right up until the very end.
I'll never get rid of this little amp.
Home Depot and Lowes have aluminum stock but it's generally very thin. McMaster and eBay are both good sources for aluminum stock. You can get exactly what you need. I've dealt with Online Metal Supply (Pierce Metals) many times with no problems.
If you haven't done much metal work, read the Basic Metalworking page.
If you haven't done much metal work, read the Basic Metalworking page.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.