Roland Cube 60D Humming - Page 1
Forum section: electronics / repair

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 02, 2019, 04:43:40 pm
content: Hi all.First time posting here. Because I am genuinely stuck repairing my amplifier. A Roland Cube 60D solid state amplifier.The symptoms:There is a very loud hum coming from the amp which sounds to me like 50Hz from the mains and it is at full volume.There is no audible signal from the guitar.None of the knobs, switches or jacks change the sound or adjust the volume of the hum in any way.So I have found the schematic diagram and started with the power supply.I am experiencing an AC voltage on all the +DC rails but no AC on the -DC rails. I am sure this is not right and might indicate the cause of the fault.I have checked the bridge rectifiers using the diode test mode on my multi-meter and can confirm none of the rectifier diodes are shorted or open circuit.I have attached the power supply schematic with the voltages I can see labelled on it. Can anyone please suggest what to check next and where this AC signal might be getting onto both of the primary +DC rails?All voltage readings are taken with respect to the center tap ground on the transformer which is connected to mains earth.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 02, 2019, 05:42:10 pm
content: Please note that the 86VAC reading on the output of BD1 bridge rectifier was mis-typed as 86VDC.Please see corrected image.

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 02, 2019, 09:47:15 pm
content: Your AC voltage measurements look, errr..., nuts!What reference point did you use for your measurements?

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 02, 2019, 10:17:56 pm
content: I thought so too. That's why I am confused.As stated at the end of OP the reference is the center tap / mains earth.

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 02, 2019, 11:19:38 pm
content: Oops, sorry I missed that...Just in case check that the point you actually set your DMM ground lead to has continuity to the transformer centre tap, frame ground and DC ground.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 03, 2019, 12:26:14 am
content: Hi, yes. The multimeter ground lead was crocodile clipped to the chassis and if you check the schematic, the chassis ground is connected to mains ground, and the mains ground is connected to the centre tap of the secondary windings. So all the grounds are the same.I will take some more readings with a friends Fluke DMM tomorrow if I can borrow it, but mine is usually fairly accurate.My theory:As far as I can see, the problem is that the AC voltage is leaking onto the two positive DC rails somehow. This I think is causing the problem with the hum because it is applying AC to the positive reference of the op amps and messing them up including the power amp IC.

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 03, 2019, 10:06:12 am
content: I have looked at the schematic and seen that, earth, and secondary ground should be the same.I still think something is wrong with your measurements though and would check that reality conforms to schematic...You can't measure 7V AC on a 3.3V regulator and have a mainly working device... In that sort of case you should see/smell smoke.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 03, 2019, 10:18:47 am
content: that is what I thought which is why I am confused There is no smoky smell and the digital part of the amp seems to work fine judging by the indicator LEDs.Unless the regulator is switching on and off to protect itself perhaps? But it seems to be rectifying the AC too by the look of the voltage drop.Do you think that both the bridge rectifiers could be leaking AC? Or perhaps a diode or tranny on the 'mute_ac' line?

author: Synthtech
author_rank: Regular Contributor
timestamp: October 03, 2019, 10:40:22 am
content: Cracked tracks or solder joints on the filter caps?

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 03, 2019, 05:07:13 pm
content: Quite probably solder joints, although I have had a good look with a magnifying glass and there are none that I can see obviously cracked or crusty looking. Also I have tried prodding each component with a pencil to check the joints and nothing seemed to change the signal, crackle or other such noise.I have a LCR meter but I ideally do not want to start de-soldering everything as it is all SMD and some of the power supply caps caps are under a big blob of white concrete like glue which I cannot seem to shift.Although if it were filter caps, thinking about it, how might the AC then be getting past the bridge rectifiers?

author: Renate
author_rank: Super Contributor
timestamp: October 03, 2019, 10:13:39 pm
content: You're not going crazy.Your meter is lying to you.Some meters use a blocking capacitor on the AC ranges, some don't.Yours uses a diode in the positive flowing direction and some sort of filtering/averaging circuit.Proof?Find a clean 12 VDC supply somewhere, put your probes on it in the normal directionOn the 20 VDC range it will read 12 VDC.On the 20 VAC range it will read 20 VAC (or something).Reverse the probes (still on the AC range), it will read dead zero.

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 03, 2019, 11:35:12 pm
content: So that's the explanation... The multimeter AC "polarity" would need swapping to read the AC on positive DC voltage rails.I wasn't aware such designs existed, are those very cheap meters usually?

author: SilverSolder
author_rank: Super Contributor
timestamp: October 03, 2019, 11:42:07 pm
content: Quote from: paul_g_787 on October 03, 2019, 10:18:47 amThat seems like a pretty good guess, intuitively. Imagine what the amplifier IC would do if its "Mute" line was jiggled at 50Hz...I would carefully check every component along the 'mute_ac' path. Shorted diodes, dried capacitors, that kind of thing.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 01:11:30 pm
content: Quote from: SilverSolder on October 03, 2019, 11:42:07 pmNow that has made me think1 Yes if this part of the circuit was faulty then the mute could be turning on and off very fast, and AC will probably get amplified by the poweramp and make the horrible sound I am hearing.I think the purpose of the circuit at the top of the previous schematic is to delay the turn on of the op amps and the power amp for protection.Now, bear with me, thinking out loud here.If you look at the attached analogue schematic you can see the MUTE line is being used to turn on a bunch of NPN transistors (shown in green) which short the OP amp ICs to ground. This would mute the output from those op amps.Then there is the P_MUTE (shown in blue). This is connecting to the mute pin of the LM3886 Power Amp IC.According to the datasheet:Pin 8 Open or at 0V, Mute: OnCurrent out of Pin 8 > 0.5 mA, Mute: OffSo I think that to bring this IC to mute it is being switched by the power supply to -12V, therefore current will flow out of pin8 and turn 'on' the IC.So the purpose of the circuit at the top of the previous schematic I think is to delay the turn on of the op amps and the power amp for protection.

author: SilverSolder
author_rank: Super Contributor
timestamp: October 04, 2019, 01:45:33 pm
content: Yes, the idea is probably to delay turn-on until the power supply has stabilized, and perhaps also to quickly mute things when power is switched off.Some products don't have this kind of circuitry and make a bump/noise in the speaker when turned on/off. So it looks like the Cube 60 is well designed!

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 02:42:23 pm
content: Quote from: SilverSolder on October 04, 2019, 01:45:33 pmApart from it is broken lol

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 03:22:38 pm
content: Quote from: Renate on October 03, 2019, 10:13:39 pmthanks you were right. I took all the measurements again with the meter both ways round and no AC voltage.Tried with my friend's Fluke DMM and that doesn't have this problem.Although my £4.99 meter is only 0.1V of from his. Go figure.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 03:48:53 pm
content: So I tested all the components in the muting circuit. No shorted diodes or trannys. Resistors and caps all read in tolerance as far as I can see. The P_MUTE output seems fine at -12v which turns on the power amp.I am not sure why the MUTE output is the 4.5v though. This is turning on all the transistors to mute all the the op amps in the pre amp circuit.Probably why I have no sound from the guitar.OK so see attached the power supply output measurements taken with the Fluke DMM. All measurements reference to ground as before.The mains input voltage at the time of taking the measurements was 244VAC.As you can see the transformer winding are perfectly balanced on both sides and read the same on both sides of ground.I cannot find a datasheet for the transformer but it is a ST-11785 (Roland part code SD000469) if anyone knows what it's output is supposed to be? To me it appears to be 2x30V and 2x15VAs you can then see after the rectifier BD2 on the bottom circuit the voltages are less balanced for some reason? Both rails are shifted by approx +1v relative to the labelled voltages.Then after the three regulators the output voltages are pretty much perfect.Then looking up at the voltages after BD1. The positive voltage is around 8 volts too High! These rails are used solely to run the power amp. this definitely doesn't seem right.

author: Renate
author_rank: Super Contributor
timestamp: October 04, 2019, 04:11:20 pm
content: Step 1: This thing is humming loudly. Disconnect the speaker.Step 2: Measure the voltage on the speaker output wire.Step 3: If it were very negative see if your mute voltages all changed to non-muted. See if the -30V supply has jumped to -40V.Step 4: Use the headphone jack and see if something works.Edit: Note that 30V (transformer RMS) * 1.4142 (sqrt(2) peak factor) - 0.7V (silicon diode drop) = 41.7 VDC

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 04:17:21 pm
content: Quote from: Renate on October 04, 2019, 04:11:20 pmThanks will try those steps but shouldn't there be a load on the amplifier? I have always been told to not power up amps without a load.

author: Renate
author_rank: Super Contributor
timestamp: October 04, 2019, 04:23:23 pm
content: Old tube amplifiers with output transformersmighthave high flyback voltages without a load.Old transistor amplifiers can usually tolerate no load without any problem.New IC amplifiers have plenty of protection built in.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 04:55:21 pm
content: Quote from: Renate on October 04, 2019, 04:23:23 pmWell I have no idea if this amplifier does have this kind of protection or not, or if it is working correctly so I will play it safe and leave the speaker connected.Speaker shows 8.1Ω DC resistance so appears good.I checked the voltages at the speaker terminals using the fluke meter and there is no AC signal but there is 16.5VDCFluke meter: -16.5VDC 0VACFluke meter in reverse polarity: 16.5VDC 0VACCheapo chinese meter: - 16.6VDC 0VACCheapo chinese meter in reverse polarity: 16.6VDC 36VAC

author: Renate
author_rank: Super Contributor
timestamp: October 04, 2019, 05:17:06 pm
content: So, as I guessed the amplifier is putting out -16VDC. It shouldn't.You're putting 2 amps (16V/8ohm) through the speaker at 16V for 32W of heating.I would not do that. You're cooking the speaker.Either your amp IC is blown or else the DC feedback is seriously screwed.You're not going to be able to troubleshoot that with the speaker cooking.You're also dragging down the -40V supply so that you can't tell what's really going on.If you feel really heartbroken running the amp without a load, put alightload on it, maybe 50 ohms.You'll still need better than a 5W resistor.Then go and check the -40V supply to see if it's recovered.Check all the pins on the LM3886.A 12" speaker costs more than a $5 IC.You're also dissipating another 30W of heat on the amplifier IC too. Did you notice that?

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 05:31:34 pm
content: Quote from: Renate on October 04, 2019, 05:17:06 pmWould a 100Ω 50W resistor be ok to use in place of the speaker? i have one spare.It was the +30V DC supply that was reading too high at 39.4V not the -30V supply.Should I try disconnecting the + and - 30V wires from the power amp PCB and see what the voltage on the power supply is then?

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 05:38:44 pm
content: Also, I forgot to mention, I tried the headphone jack. It starts silent, then is starts to hiss very quietly, the hiss gets louder and louder. Then there is a small 'pop' and it is silent again until the amp is turned off. Some capacitor somewhere I would say.Will try headphones with an input.Although looking at the schematic, the signal goes into a ADC which is connected to the CPU, then there is a DAC which connects to the headphone / line-out op amp.Seems a little poorly thought out to me. Analogue - > digital -> Analogue. Especially if one wanted to hook line out to a PA system, it would be not as good as taking analogue straight out.

author: Renate
author_rank: Super Contributor
timestamp: October 04, 2019, 05:40:29 pm
content: As I explained above, there is no "+/- 30V supply".There is a +/- 40V supply and the minus leg is being dragged down to 30V.That's because you're supplying 60 Watts of power, 1/2 being dissipated in the amplifier IC, half in the speaker.100 ohms is fine by me.You'll see the minus supply go to the correct -40VDC.Then you can try the headphones.The headphones are not going to work correctly until you fix the -40V which is screwing up the mute.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 05:46:57 pm
content: Quote from: Renate on October 04, 2019, 05:40:29 pmThat makes more sense! Thanks. Will try that and post back.According to the datasheet. the LM3886 (Power amp) is has these features:50W cont. avg. output power into 8Ω at V CC = ± 35V|V+| + |V-| max of 84V / min of 24VOutput protection from a short to ground or to the supplies via internal current limiting circuitryOutput over-voltage protection against transients from inductive loadsSupply under-voltage protection, not allowing internal biasing to occur when |V EE | + |V CC | ≤ 12V

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 06:25:44 pm
content: Right some progress! Please see attached v3 diagram with the new voltages.With the light load connected, the voltages are much more stable on the power rails and on the mute lines which now appear to be working fine.I tried the headphones and this is what happens measuing the voltage on the MUTE line and listening to the headphones.At power on it is immediately 11.6VThe headphones hiss slightly for approx 1.5 secondsThen the headphones start to hum at 50Hz. Immediately the hum starts to gt louder as the voltage starts to drop.Once the voltage drops to -4.4, the hum immediately stops and the headphones are silent.

author: Renate
author_rank: Super Contributor
timestamp: October 04, 2019, 06:43:20 pm
content: So, it's all non-muted now.Have you tried to play guitar to the headphones?

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 07:30:00 pm
content: Yes all non muted.Although when the amp is turned on, but before the mute turns off, there is 35VDC across the input jack. Also there is 9vdc across the tuner output and 76vdc across the line-out.Once the amp un-mutes these all go to 0V.Then I tried a guitar input, I have a sound from headphones although the sound is very distorted even on clean with all effects off.The tuner and line out outputs sound fine, perfectly clear output and the effects all work beautifully.

author: Renate
author_rank: Super Contributor
timestamp: October 04, 2019, 08:29:49 pm
content: Well, as long as the line out is clean we can skip the headphones for now.(Have you used the headphones previously and did it work fine?)With the 100 ohm still in place, what's the voltage on the hot end of it? (I'd guess -20VDC or so)?Find the junction of R15, C11 and pin 8 of IC6.Check the voltage, it should be minus a couple of volts.Ground that point and see if the voltage on the hot end of the 100 ohm goes to zero.Remove the ground.Measure carefully and exactly the voltage on pin 9 & 10 of IC6.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 04, 2019, 08:34:53 pm
content: Quote from: Renate on October 04, 2019, 08:29:49 pmNo never tried the headphones before.Will try as you suggested tomorrow. Thanks for all the help so far

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 05, 2019, 12:03:52 pm
content: Quote from: Renate on October 04, 2019, 08:29:49 pmOK just done the voltage measurements.All voltages below are DCVoltage across output load =-42.2Vvoltage from IC6 pin 8 to ground = -3.1VVoltage across output load with IC6 pin 8 connected to ground =-41.5VVoltage from IC6 pin 9 to ground =-9.6VVoltage from IC6 pin 10 to ground =0V

author: Renate
author_rank: Super Contributor
timestamp: October 05, 2019, 12:41:14 pm
content: Yup, it looks like the low transistor in the output IC is shorted.Grounding the mute pin switches out the input stage and uses a separate stage whose only purpose is to DC balance the amplifier to zero volt output.There's a 1% chance that the lower clamping diode D21 is shorted.With the 100 ohm disconnected, measure:Between the output & the +40Between the output & the -40Check with the "ohms" setting (one way) and the "diode" settings (both ways).

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 05, 2019, 03:45:35 pm
content: Quote from: Renate on October 05, 2019, 12:41:14 pmI tested across D21 in both directions. Dead short. So I removed D21 and out of circuit it seems fine and measures 601.Also tested D20. In and out of circuit it measures 603 so I'd say it is good also.With D21 still out of circuit I checked between Pin3 of IC6 and the - rail of BD1 bridge rectifier. Dead short both ways.Tested the output + cable and there is a short to -40V with 16Ω resistance. Tested this with the DMM leads both ways.Tested output + with +40V and there is no connection and infinite resistance. Also with leads both ways.So the LM3886 is duff then. But the question now is why did it fail?

author: SilverSolder
author_rank: Super Contributor
timestamp: October 05, 2019, 03:50:03 pm
content: It could have failed due to a manufacturing flaw when it was made - something that can take years to surface.I have seen them stand up to incredible abuse (120 watts continuous for hours on end with no quibble), but I have also seen some fail under less extreme conditions. Sh!t happens.They are really good chips, basically. Solder another one in, and let'er rip! :-)

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 05, 2019, 04:14:24 pm
content: Quote from: SilverSolder on October 05, 2019, 03:50:03 pmBefore replacing it I would like to hear what Renate has to say about it. I want to make sure I don't blow up the new IC straight away in case there is another fault which caused the IC to blow.Although, just looking at the schematic, what if previous owner connected their mixer to the speaker instead of the line out jack? The jacks are right next to each other and are very hard to tell apart.Surely this would blow the power amp IC?When I got the amp given to me (for free so I hope I can get it going) I was told " lent it to a friend for a gig and it came back like this".

author: Renate
author_rank: Super Contributor
timestamp: October 05, 2019, 04:24:30 pm
content: SilverSolder is right, stuff happens.Most of the IC amps today are pretty bombproof.Even a short to ground doesn't annoy them too much.When removing multiple pin devices, I always like to destroy them.I cut the leads off as near the body as I can.Sometimes I even use a Dremel tool.Then I can unsolder the leads individually.This saves wear and tear on the PCB.You can look at the headphone driver now if you like.The obvious thing would be if the op amps were missing one leg of power.They could be blown too.If somebody had plugged a cable from ext speaker out to headphones out....

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 05, 2019, 04:47:16 pm
content: Quote from: Renate on October 05, 2019, 04:24:30 pmYes I tend to cut off legs on faulty components too. I usually dob them with some red paint as well, I have a box of broken electronic bits that might make some good artwork one day haha.Moving on...Is it safe to run the amp without the IC to fault find further? Or shall I replace it first?As for the op amps, they are all on the 12/-12V regulated rail. Do you think they could be affected? I guess I could test for direct shorts on them. What say you?What about the speaker. It still measures 8 ohms on the DMMbut could it be damaged? It doesn't push in and out very much but i can't feel the coil rubbing either.And headphone circuit. What to test first?The last few DIY repairs I have done all tend to be shorted silicon components. Are modern silicon components just rubbish or something?

author: Renate
author_rank: Super Contributor
timestamp: October 05, 2019, 05:05:08 pm
content: It's mostly a question of how quickly you can get a replacement IC and your choice.I'm impatient, so I'd remove the IC, clean the board up and go on to the headphone.Of course, removing & replacing the amplifier IC in one go would save some effort.This would also give you a guitar amplifier that you can feed into *something* while waiting for your part.The headphone opamp only costs a dollar, so I think that I'd just order one.Did you use stereo headphones and did both channels sound the same?

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 05, 2019, 05:35:49 pm
content: Quote from: Renate on October 05, 2019, 05:05:08 pmIt will take approx 5 days to get one. The cheapest I can find is £5.50 GBP without waiting months for one from china.I don't mind removing the old IC first. Just wanted to check I wouldn't damage anything by not having the IC in circuit..at you mean about connecting headphone and speaker jack. Could easily have fried both!Yes, both channels on headphones were distorted. I see that the headphone op amp is a dual package with both channels in parallel. A NJM4556AM is £4.75 in the UK! But only £1.50 for 5pcs from china. And people wonder why everyone doesn't buy British.I'll remove the power amp IC6 now and then with it out, test the IC17 voltages.If both are faulty I might as well get both from china and wai patientlyt. I do have another amp I can use for now.

author: Renate
author_rank: Super Contributor
timestamp: October 05, 2019, 06:28:20 pm
content: Well, whatever you do, be sure to write us an epilogue some time.We get hooked into these things and like to know how it ends.This thread caught my attention because I have a Fender Acoustasonic 40.It worked mostly fine, but the turn-off popped.They had put in a circuit for that, but it didn't work well at all.I ripped it out and put in my own uP monitoring the +28V supply.It uses both mute and standby in timed sequence.I replaced the power LED with a red/green that shows what the uP is thinking.[Hmm, I tried to post a photo, but it didn't work.]

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 05, 2019, 06:39:55 pm
content: I will keep you postedThank you again for all the help. I have learnt a lot and would not have managed to get this far without your help.Just managed to remove the IC. Bloody fiddly thing. Half the legs bent one way and half the other so I had to snip one half then bend it upright.Just checked pins 3 and 4 and yes dead short between them.This video clip illustrates my last 10 minutes perfectly!https://youtu.be/c1QcjsjjtRcJust having a cup of tea then will check the headphone op amp voltages.RE: replacing the IC. Can I use some of my Arctic Silver CPU heatsink paste I used on my gaming computer?

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 05, 2019, 07:25:38 pm
content: OK, I just checked the headphone circuit and there is +11.6VDC coming out of both tip and ring on the jack!!!!!!You can clearly see this on the op amp output pins 1 and 7.Voltages of IC17 pins:1. 11.16V2. 9.81V3. 9.72V4. -11.84V5. 9.72V6. 9.80V7. 11.16V8. 11.79VAlso there are no direct shorts from pin 1 or pin 7 to the + or - 12V rails. And i cannot find any direct shorts between any pins on IC17.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 05, 2019, 09:18:41 pm
content: Have taken voltage readings from the headphone circuit. Had a think about it but still cannot work it out.Both the left and right channels share a common input and both have the same problem with the voltage on the output and the levels are exactly the same on both channels.C175 and C180 are blocking the DC which is why the line out is working great.So the problemmustsurely be after those two capacitors.It also looks like the voltages are being divided by the feedback resistors and also the biasing resistors, so I would hazard a guess that the unwanted voltage is coming from the highest point which is from pin 1 and 7 of the IC.So unless I have missed something; I can only conclude it must be something internal in the IC. What do you think?

author: SilverSolder
author_rank: Super Contributor
timestamp: October 06, 2019, 12:10:15 am
content: I think your diagnosis is right - that chip is probably fried.The voltage at the inputs 3 and 5 should be zero volts... those pins are inputs connected to ground via R157 / R163, so no significant voltage should be present there.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 06, 2019, 02:33:56 pm
content: Well I finally manged to remove the damn headphone IC!First time I have de-solder a SOP8 IC and I am in no hurry to do it again! Very fiddly. Much harder than installing and SOP8 IC.I have tested the voltages now it is removed and there is 0v on the inputs and outputs now! So it was indeed the IC.Will order replacements fro both ICs and post back once they arrive.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 06, 2019, 03:26:22 pm
content: I have some questions:1. Would a TL072CDR be a suitable replacement for the faulty NJM4556AM? I ask because I already have one.2a. What is the white greasy compound used on the LM3886TF? It is still wet so is non-setting.2b. Is this the same stuff used on computer CPUs? I already have some arctic silver. Can I use that?

author: Renate
author_rank: Super Contributor
timestamp: October 06, 2019, 05:31:36 pm
content: You need a NJM4556AM because it can drive a low impedance load.My philosophy is that any heat sink compound will be fine.Most older things used standard zinc oxide, that white, greasy goop.You can get fancier, silver containing or those rubberized thingies.I'm sure somebody has a strong opinion on this, but I don't.I think that somebody did a test using spit!It worked fine, but tended to dry out.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 06, 2019, 06:00:03 pm
content: Quote from: Renate on October 06, 2019, 05:31:36 pmOK thanks. Will have to have a shop around then. Otherwise a chinese order and a month waiting it is.

author: SilverSolder
author_rank: Super Contributor
timestamp: October 06, 2019, 10:23:06 pm
content: Mouser seems to have some in stock.By the way, I have an old Cube 15 here, loved to bits! :-)

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 10, 2019, 10:09:25 pm
content: Well my ICs came in the post and after some fiddly soldering with the SOP8 I can now confirm all is well and working great.I checked the voltages for good measure and all is good. 0VDC on the op amp outputs and 0vDC on the speaker output.Headphone are clear sounding and the Power amp is back to working order.Thanks everyone for the help and advice!

author: SilverSolder
author_rank: Super Contributor
timestamp: October 11, 2019, 10:15:56 am
content: Winner, winner, chicken dinner!

author: Renate
author_rank: Super Contributor
timestamp: October 12, 2019, 10:52:46 pm
content: Yea! Glad to hear it.(Here's that photo of my power monitor mod on the Acoustasonic 40.)

author: paul_g_787
author_rank: Frequent Contributor
timestamp: October 28, 2019, 05:14:10 pm
content: Quote from: Renate on October 12, 2019, 10:52:46 pmQuite a neat looking mod if I do say so.The Roland amp is still going strong. Quite a loud amp for 50W.

author: Renate
author_rank: Super Contributor
timestamp: August 04, 2020, 12:41:22 pm
content: Just a little update on my power monitor/muting controller that I mentioned above.It worked just fine and nothing had changed, but I noticed that if I turned the amp on with the volume and the reverb cranked I'd get a pop and a whoosh.With the reverb turned off this didn't happen.I guess the real way would be to put a proper reset/mute signal on the reverb chip (was it a VC1? I forget).Instead, I just extended the power on qualification time to 1.5 seconds.So now when you turn it on, the red LED flashes three times (at 0.5 second intervals) then the green LED goes on.It's nice to have a guitar amp that doesn't go "whomp".I guess that purists would say that a guitar amp HAS to go "whomp".

author: m3vuv
author_rank: Super Contributor
timestamp: August 05, 2020, 06:16:33 pm
content: it hums because it doesent know the words!!