I should have said that the scope trace is basically as it has been so nothing new there. I have yet to burn a CD for the MP3 fikles in post 101.
With the power OFF, each of these points should read directly to ground (a dead short). This means left and right RCA outputs should read short at the socket with power off.
I am afraid I am struggling a bit with this now. I have located two 2K7s and with the power off they appear to be a dead short with the signal pin of the RCAs...however either resistor to either RCA gives a continuity beep. If the machine is off is what you said here not relevant?
"Direct continuity (0.00 ohms, a short circuit) will be because of the shorting action of the muting relay. That is how it works, shunting all the output pins to ground when power is off."
I have burnt the 10hz to 400hz sweep but not used it yet.
"Direct continuity (0.00 ohms, a short circuit) will be because of the shorting action of the muting relay. That is how it works, shunting all the output pins to ground when power is off."
I have burnt the 10hz to 400hz sweep but not used it yet.
That all sounds correct. Only one end of the resistor should give a continuity beep to the centre pin of the RCA. That same end should also beep to the outer ground part of the RCA as well with the power off. That is because the relay contacts are closed and placing a short circuit across the socket to give a perfect mute.
Ok I have scoped the good and the bad. I looked up which setting was going to give the highest sensitivy and I used t-V/Div and it gave me 0.5ms 0.4v and 0.2v/div. The readout gave numbers with a Y next to them or it could be a stylised V for volts. I am not able to decipher the results which I split into 30s chunks.
Good Player. Using one set of speaker outs from amp
30s - 480Y
1.00 - 886
1.30 - 848
2.00 - 733
2.30 - 668
3,00 - 565
3.30 - 488
4.00 - 430
Bad CD6 from L Ch RCA
30s - 372
1.00 - 366
1.30 - 372
2.00 -372
2.30 - 379
3.00 - 379
3.30 - 379
4.00 - 379
Good Player. Using one set of speaker outs from amp
30s - 480Y
1.00 - 886
1.30 - 848
2.00 - 733
2.30 - 668
3,00 - 565
3.30 - 488
4.00 - 430
Bad CD6 from L Ch RCA
30s - 372
1.00 - 366
1.30 - 372
2.00 -372
2.30 - 379
3.00 - 379
3.30 - 379
4.00 - 379
Interesting. That's a curious set of results... at face value the output from the CD6 looks the most even. The voltage output should be the same at all the different frequencies and for the CD6 it pretty much is.
One player is done using RCA output though and one speaker output which makes comparison unequal.
That CD6 result from the RCA looks exactly where it should be though. It would not matter if those were millivolts (and that is what they will be from the RCA) or volts such as 3.72, 3.66 3.79 etc, they are all pretty much equal.
366mv to 379mv (lowest result to highest result) is just 0.3db different in level and that is well within measurement variability. Based on that and if the other channel were the same then the output would appear to be 'flat' at low frequency.
Only phase inversion of such a signal (one channel inverted compared to the other) would give low bass on listening,
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If you look back at post #101 it was really measuring using your meter rather than the scope that I had in mind... might be worth still trying that method as outlined in the post,
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Also if you have the RCA's wired back up then give the player another listen and see if it still seems to have low bass. If it does then switch the amp off, reverse the speaker wires to one speaker only, and then listen again.
Does it now sound better or worse?
One player is done using RCA output though and one speaker output which makes comparison unequal.
That CD6 result from the RCA looks exactly where it should be though. It would not matter if those were millivolts (and that is what they will be from the RCA) or volts such as 3.72, 3.66 3.79 etc, they are all pretty much equal.
366mv to 379mv (lowest result to highest result) is just 0.3db different in level and that is well within measurement variability. Based on that and if the other channel were the same then the output would appear to be 'flat' at low frequency.
Only phase inversion of such a signal (one channel inverted compared to the other) would give low bass on listening,
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If you look back at post #101 it was really measuring using your meter rather than the scope that I had in mind... might be worth still trying that method as outlined in the post,
--------------------------------------------------------
Also if you have the RCA's wired back up then give the player another listen and see if it still seems to have low bass. If it does then switch the amp off, reverse the speaker wires to one speaker only, and then listen again.
Does it now sound better or worse?
When I tidied up the wiring I said that on the L channel the wire to the + solder point on the PCB was blue and the red in the - position which I corrected.
Give it another listen before you do any more testing. If it still sounds wrong just swap the wiring to one speaker and listen again. If the feed from the PCB was reversed the phase would be wrong.
To use a quote from the 80s or 90s....Bass....How Low Can You Go?! Well the bass is back! There is a small issue with some intermittent noise on the L channel (sounds like white noise) which comes and goes and may be a result of original or later poor soldering as pressing the L grd tab seemed to stop it. I will check the tightness of the RCAs to the Grd tabs.
IMO the confused wriring on one channel looks to have been done in the factory and perhaps the reason it was only £20. It could also be the reason I didn't use it and shelved it. It must have been over 20 years ago I bought it and as we get older........etc etc
I will get the RCA outs sorted properly and then re-solder the XLRs and see if they follow the ususal pinout layout.
IMO the confused wriring on one channel looks to have been done in the factory and perhaps the reason it was only £20. It could also be the reason I didn't use it and shelved it. It must have been over 20 years ago I bought it and as we get older........etc etc
I will get the RCA outs sorted properly and then re-solder the XLRs and see if they follow the ususal pinout layout.
I wondered if it might be 🙂
It sounds like you had a phase inversion. If you were to swap the wires over now to one speaker it should 'recreate' the fault you had if that was the case. Also with phase inversion vocals loose the ability to form a good image between the speakers and will seem to come from 'both sides' rather than a central image.
Get the ground right on the XLR's and then wire both outputs the same. As long as both channels are wired the same then phase is preserved.
If both are wired 'the same' but both happen to be reversed then phase is still preserved but 'absolute phase' is not. Absolute phase is often considered not very important and you are unlikely to hear any difference. It just means both speaker cones move in instead of out and vice versa.
You are very welcome. Its been an interesting one and best of all you have been determined to carry on with the testing as we tried to find out what was happening 🙂