MarkBassChat

No, it's exactly the oposite: the center conductor cannot be shorted with shield. As I mentioned earlier, you can also put a piece of paper between contacts of the input jack. Have you read it? Mark

Yes, it will work. You can put a piece of e.g. paper between contacts of the input jack. I will work in the same way as a dummy jack. Mark

The input jack is shorted to the ground when there is not plug inserted. So a parallel input will be also shorted and the preamp will not work unless you insert a "dummy" jack into the front socket. Why do you want to do this? Maybe an angled jack will help. Mark

If you look at the photo of the Icepower 125ASX2 module: [url="http://www.icepower.bang-olufsen.com/en/news/news?id=20"]http://www.icepower....news/news?id=20[/url] you will se a fuse (in the bottom-right corner). Check if it's not open. Of course the amp has to be disconnected from mains power supply - but you know this, right? If changing the fuse does not help, it means that transistors on the PC board are shorted. This can be fixed but requires some advanced skills (desoldering high power SMD components - without destroying the board). EDIT: here: [url="http://www.icepower.bang-olufsen.com/files/solutions/icepower125asx2_datasheet_1_1.pdf"]http://www.icepower.bang-olufsen.com/files/solutions/icepower125asx2_datasheet_1_1.pdf[/url] you have slightly better picture. FH200 symbol in the bottom-left corner. Mark

If you are in contact with technical guy from Marshall, it's the best source of knowledge. Ask him about it. Ideally, you should replace all valves because the one that are still good have different parameters than the new one. And you should use a matched set of valves. If you consider that this is too expensive, other possibility is to sent your good valves to someone that has a valve-meter and ask him to select additional two valves with similar parameters. I personally never heard of matching valves by measuring grid current. You need to know what is anode-cathode current of the valve. This can be measured by breaking a wire between cathode and the ground and puting a DVM in this place (and measuring the current). This may be not that easy but in this way you may match valves on your own. BTW, 87mV on V6 looks bad. This is either a bad valve, or a typing mistake. Mark

[quote name='rushers' timestamp='1352511244' post='1864191'] Thanks to my own idiocy I managed to 'blow up' my Amp head by switching the input voltage from 320 to 115 on the back of the amp....while it was on.[/quote]I think that you meant 230V and not 320. Ideally, one should learn from other people's mistakes. In your case you have to learn from your own mistakes and £218 is the cost of learning. I hope you will never try to do it again . My suggestion is to open the amp and make a photo of the power supply module. It is switching power supply (most probably together with a class-D power amp). I don't know which module it is there but usually such modules have a fuse on the circuit board and mayby this is just a matter of replacing the fuse. It may be not that easy since sometimes the fuse is soldered to the board. The price that you got is for replacing the module and not fixing it. But maybe it can be fixed. If you post the photo, I may try to tell you what could be the problem. Edit: I wonder if you find that this is Bang & Olufsen Icepower 125ASX2 module, which has a (removable) fuse and all that has failed is the fuse? In this case you would be very lucky and you could fix the amp on your own. Mark

The mains power voltage in different countries has nothing to do with class-D power amp. It has to do with power supply of the amp. If the amp uses "classic" power supply (with big transformer like Aguilar SC500) you need to adjust the amp (or in the worst case to replace the transformer). If the amp uses modern switching power supply (SMPS), then it depends. For example, some models of Eden amps will work with any voltage between 90V and 260V. And other (e.g. WTX500) need simple adjustment in the power supply module. So in general it depends on the model of the amp. Luckily this information is in the amp's manual. It meas that you need to read the manual. Of course, if you buy the amp in Europe (e.g. MarkBass) , it will be already adjusted to the mains voltage in your country. Mark

Sometimes you may use a contact cleaner, sometimes a sharp knife, and sometimes you need to replace the jack. Mark

You can easily verify what exactly is the problem by plugging the bass into the Power Amp input. You can also plug the bass into the Effect Return input. Or plug the Preamp Out -> Jack-Jack cable -> to another power amp. It can be caused by many issues; dirty Effect Return jack, or problems with power amp bias. Make the tests and report what you got. Mark

I needed a photo of the preamp and not the pot cavity . The preamp on the third photo looks lite typical old Ibanez preamp build with 3 inductors. If the problem is not related to the issue mentioned by Luke (desintegreted foam isolation), then the problem is with the preamp. And it can be easily fixed because it is very simple. Tantal capacitors in this preamp (little blue bulbs - photo #3) are components that quite often fail in old equipment. But don't replace anything until you know it failed. Another posibility is a lost of contact in the connectors between the preamp and pots and pickups, or failure of any of the pots. The guy who is going to fix it should have no problem finding what's wrong with the preamp. This preamp (when fixed) sounds different (some poeple say: better) than modern preamps - due to inductors used in the equaliser circuit. Mark

TonePump is a preamp with a very strong signal. If you get weak signal, there must be some wiring mistake. Check it again with the wiring diagram. The trick is that every single wire has to be connected properly, not 99% of them . If you cannot do it on your own, find someone in the neighbourhood who can fix it. Mark

Make a photo and I'll try to tell you whether it can be fixed. Mark

I think that you meant switch mode power supply (SMPS) - it has nothing in common with digital. Clearly the problem is related to the amp - most probably to the power supply. Due to the complexity of the power supply it is quite often replaced and not fixed when it fails. Fixing it is possible but time consuming - which makes it more expensive. So the fact that service replaced the board (instead of fixing it) is quite normal. But I'm confused with what you wrote: [quote name='muso'] They've been very helpful but have been unable to trace any fault with the unit regarding the loss of volume.[/quote] How this is possible? This is a basic task to be done and in fact it is very simple (using a generator and an oscilloscope). I would say that they rather didn't want to spend any time on this task. I would contact Markbass Italy directly saying that official service in UK cannot help you. They could be interested in finding what exactly was the failure. At least I would try. Mark

It's very simple but not that simple as you think. A potentiometer is a 3-terminal resistor and you have to connect all 3 terminals and not only 2. A potentiometer is a voltage divider exactly as the two resistors that are used in the chorus. The slider of the pot should be connected to the pad where two resistors are connected. EH just didn't consider such a mod to be interesting enough to justify increased costs - you will test whether they were right or not. As I mentioned before, in order to avoid 0-100% adjustment, you may use 2 additional resistors in series with the pot. Of course you need to have some soldering skills and schematics reading will be also benefitial. So start with the schematic of the effect first. Mark

Dry and wet signals in this chorus are mixed with two resistors (22k and 20k as far as I can tell), so the solution is to remove them and replace with e.g. 47k linear potentiometer. To avoid situation that you can change the mix from 0 to 100% (this is not needed since you can simply switch off the chorus if you need 0% wet signal) I would put 2 small resistors in series with the pot (e.g. 4.7k). This will change the range to 10 to 90% which should be OK for you. Mark

I you get any parallel looper pedal (e.g. like this one: [url="http://www.amptone.com/bossls2.htm"]http://www.amptone.com/bossls2.htm[/url] ) , you will be able to do it without any mod and furthermore it will work with any effect. Mark

If you don't use tweeter, then it's probably not tweeter. Take a look at the crossover. If something is melted, you cannot un-melt it - you have to replace the component. First, you have to find out what exactly is wrong. Mark

In all cases, which I heard of, the hot plastic smell was caused by a plastic component in crossover that started melting due to high power delivered to the cab. Most probably it's something similar in your case. Just open the cab and look at the crosover board inside. You can also take a look at the tweeter (if there is one in your cab). Mark

The solution is very simply; you have to put a thermistor in series with primary winding of the power transformer (Ampeg also uses this solution). Similar to this one: [url="http://uk.farnell.com/ametherm/sl22-5r012/thermistor-series-sl22/dp/1653457"]http://uk.farnell.com/ametherm/sl22-5r012/thermistor-series-sl22/dp/1653457[/url] You just have to make sure that the maximum allowed current (for the thermistor) is equal or greater than the maximum current drawn by the amp. For me 5 Ohms and 10-15A should be OK. And be sure that you know what you do - this part of the amp is connected directly to the mains power. Mark

Regarding the transformer: the photo is not perfect but it seems that you have 2 secondary windings (3 red and 3 orange wires on the right) and the primary winding has only 2 wires (black and blue wires on the left). So it seems that this is US domestic version (117V) - you have to buy a new transformer, or rewind this one to use it with 230V mains supply. I think that rewinding shouldn't be to expensive - you just have to find out someone who can do it. The other problem requires some understanding of electronic schematics. If you cannot fix it, give it to a tech. With Peavey similar problems are often caused by non-contacting plugs. You can check every plug in the amp whether it's not oxidized. You can also investigate the problem a little bit more; you can check whether the problem is related to the preamp or the power amp. I'm sure that there is power amp input jack; by pluging there an external preamp you can check which part of the amp fails. Mark

You can buy any switch, disconnect the wires from the old switch, connect the new one and see if this helps. Noisy amp may be something else related e.g. to old valve (I don't remeber if there is a valve - in TD650 there is one). Mark

I'm glad I could help. Regarding the lower gain of the active channel I must admit that I could make a mistatke. Active bass has stronger signal than passive. The preamp for active bass has lower gain than the passive in order to keep the output signal send to the speaker on the same level. Sorry for the confusion - somehow I didn't understand the problem correctly. Maybe it's because I never used active input, or -15dB pad, even when I play with active bass. Most active basses sound better with passive input (unless they have huge signal - then some attenuation is needed - I met only 1 such bass, it was Spector). Mark

[quote name='yann' timestamp='1342387377' post='1734239'] I think that no other jack than the (high) input one has ever been used on this amp,[/quote]It does not matter whether the jack was not used, or not. It's not about dirt from a jack but rather oxidized metal - it happens also when the jack is not used. Mark

[quote name='yann' timestamp='1342352370' post='1733534'] (I did ask Peavey Greece for a change form 110- 220v but they asked for 250 euros plus taxes plus worktime, this would make the amp "golden"...)[/quote]Check which version of the power transformer you have (just count wires on the primary side). Export version has 4 wires and in this case changing supply voltage is easy. [quote name='yann' timestamp='1342352370' post='1733534'] Anyway,i've noticed that the active channel was in loudness much lower than the passive one, and the serviceman said "it's usual,actives are lower that the passive sects",a thing i didn't believe cause i've worked this amp a lot back in the '80s...[/quote]It's rather the other way round - it's good you didn't believe him (is he a serviceman???). [quote name='yann' timestamp='1342352370' post='1733534'] The active channel started cut offs and scratches,and sometimes going up to the real loudness it should be...[/quote]This is quite often caused by dirty Return jacks. Just plug a jack-jack cable from Send to Return jack and see if it helps. [quote name='yann' timestamp='1342352370' post='1733534'] Ps: Anyone has an original footswitch,i'd like to buy it! [/quote]As far as I remember this footswitch consists only of two switches and 4 wires - you can buy any 2-switch footswitch and change the wire (and the plug). Mark

This is most probably non-contacting Effect-Return jack. Quick and dirty solution is to plug a Jack-Jack cable into Send and Return effect loop. If this fixes the problem, you may start asking who can fix, or replace the jack. Mark