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MarkBassChat

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Everything posted by MarkBassChat

  1. Switching from 9V to 18V does not provide any extra boost. It provides only some more headroom which is not the same as extra boost. So switching from 9V to 18V does not make much difference/sense. Mark
  2. Nice tutorial.It seems that previously you mentioned that you could not remove the knobs. What was the problem? Mark
  3. Check this video: [url="http://www.youtube.com/v/AJ1B4vVXZTI"]http://www.youtube.com/v/AJ1B4vVXZTI[/url] to see/hear the difference between piezo and magnetic pickups sound. Mark
  4. This usually happens when you replace output transistors without replacing driver transistors, or bias circuit. But a tech should know it Mark
  5. I think that I mentioned that I did it once. It's not easy but once you start doing it, you will do it. It takes less than 1 hour and you waited already 4 days :-(. This is the amp I was fixing - all modules were removed from the enclosure, including front panel. [attachment=134879:RH450.jpg] Mark
  6. Information from: [url="http://www.voxamps.com/valvetronix/vt-series/"]http://www.voxamps.com/valvetronix/vt-series/[/url] : "By using the optional VFS5 foot switch you can switch programs, turn reverb or other effects on/off, or make speed/tap settings using your foot. This is a great advantage when you're creating sounds or performing live." Why do you think it's mono? Mark
  7. Which exactly model you have (there were at least 4, or 5 different models of the amp)? The one that I know uses VFS5 footswitch, which requires a stereo cable. The footswitch contain electronic circuit and it cannot be replaced with a footswitch of other manufacturer. How do you know that the one that you have uses mono jack? Mark
  8. Being frankly I don't remember (I was fixing the amp 2 years ago). You have to know that this is very advanced amp - switching power supply, class-D power amp, digital pramp, figital front panel. And opening it is also not that simple. Try to remove the torx ones and see if this is enough. Regarding the knobs - it depends which ones are already removed. Why can't you remove all the knobs? Are they glued? If you post a photo of the amp, I may try to remember which screws I removed. But you can just feel it. Mark
  9. [quote name='big rob' timestamp='1368304032' post='2075581'] Maybe your right but tc are sending me the replacement buttons and say its just a case of opening it up and popping off the old and replacing with the new ones. Someone must have opened one up, would really appreciate the help it anyone has. [/quote]Yes, you just need to open the amp and replace the buttons. The most tricky part is opening the amp. As far as I remember I had to buy a hex key or even a torx key to do it. Mark
  10. I hope that you are joking about dropping the amp from from a great height. If the amp works correctly (sometimes), then this is just a minor problem, maybe just a dry joint, as mentioned. Or maybe a problem with the volume pot. I wonder how it is possible that Marshall couldn't fix it. Maybe they just couldn't reproduce the problem in their lab. Mark
  11. Be warned that the amp contains dangerous voltages and there is no room for mistakes when you deal with such voltages. Previously you said that the amp blew the power fuse when you disconnected the power amp module from the pre-amp. In the last post you said exactly the oposite: when you disconnected the power amp, the rest of the amp is working. Which way is it? I think that the second post is more accurate. First you have to identify modules in the amp: the preamp, the power amp, the power supply and the transformer (part of the power supply). I susspect that what you are doing is disconnecting the power amp from the power supply (correct me if I'm wrong). In this case the preamp works (you can check that the valve is glowing and you have signal both of the Effect Send output as well as on the DI output). The Power LED os on and the fan is working. This proves that the preamp and the power supply (including the transformer) is OK. This means that the power amp is shorted (output transistors). And in this case I'm sorry but it is too difficult for a novice to desolder the transistors. Appart from the output transistors quite often driver transistors fail (along with the quiescent current regulator). So my advise is to confirm that you disconnect the power amp from the power supply (and not from the preamp), verify that the preamp is working, check the output transistors for shorts (with a digital multimeter) and that's it. If the transistors are shorted, the only thing you can do is to take it to a tech. If you are not sure what you are disconnecing, make a photo and post it here. Also make sure that the fuse that you had previously is of the correct type: it should be 4A - slow blow. Sometimes people use fast fuses and this is the whole source of the problem. Mark
  12. Failed power supply, or the power amp. The most frequentlt the problem is caused by shorted output transistors. Mark
  13. If they are active (and it looks like they are), you are not measuring the resistance of the pickup but just a resistor on the output of the preamp. Mark
  14. I don't know why you have no sound with the power amp but the power amp clip light suggest that one low voltage rails (either +15, or -15V) is missing. Can you measure the voltage on Zener diodes (after large, white resistors) in the power supply? I'm only guessing but I would start with this measurement. Mark
  15. This is clearly related to the preamp. Either there is something wrong with the preamp itself, or with wires soldered,or plugged into the preamp. In any case you can take a look at the preamp with a magnifying glass. If there are plugs (from pots to the preamp), check that they are OK. If you cannot see the problem, ask a tech to service it. Mark
  16. Nice bass. It uses standard MEC 2 band active electronics (preamp). And when you pull the volume pot, it bypasses the preamp. I assume that the bass works correctly in passive mode, but it does not work in active mode. Simply speaking the preamp is not working. This can be either the battery, or the switch in the push/pull pot, or non-contacting wires. Do you have any multimeter to check at least the battery connection? Did the preamp work previously? Can you make a photo of the preamp? Mark
  17. Now I think that for 18V (2x9V battery) it is better to have two circuits and monitor each battery separately. It's because of the fact that with this configuration you can use a new battery (9.6V) with older one (e.g. 8.5V). With one circuit monitoring 18V you would replace two batteries even if only one of them needs to be replaced. But the main purpose of such a circuit is to avoid battery replacement when it is not necessary. Here is the circuit I built. It consumes only 30 microampers when it blinks (when it's not blinking it's much less). It's due to the fact that it blinks only for few miliseconds within a second. It starts blinking when battery voltage drops below 8V. Edit: I'm not able to attach a picture of the circuit. There is something wrong with both basic and flash uploaders. I'm getting an error "No file was selected for upload" but the file is selected. It's in jpg format - I assume that this format is allowed. Mark
  18. If the valves were glowing white, this may e a problem with the power supply. New valves will not solve it. Is the amp switched properly to 230V,or by mistake it is switched to 120V? But in this case it would most probably blow the fuses. I think the amp needs a tech. Mark
  19. [quote name='BassPimp66' timestamp='1355500655' post='1899334'] I thought it worked by shaving off some lows and making the sound relatively trebly. [/quote]That's not correct. Here you have a high-pass filter with a pot in parallel, which you may consider all-pass filter. So switching the filter on causes that more high frequency signal gets to the output. Low frequency signal is passing through the pot. This is very well explained by Bear of the Bass above. Please read it. Mark
  20. [quote name='BassPimp66' timestamp='1355437488' post='1898537'] Now... assuming this is correct. Can I mod the preamp, replacing the capacitor with a 300 PicoFarad? If I run the same formula, I get a cut-off frequency of 53 Hertz. All in all, I hope to achieve a shift in the cut-off frequency to make the preamp sound less bright. [/quote]I'm sorry but most of your assumptions are false. First of all, when the bright switch is on, the 10MOhms resistor is not used. The capacitor "works" with upper part of the pot. The purpose of the resistor is to avoid "click" when the switch is turned on. You can replace the capacitor with any other value but when you replace it with 300pF, it will increase high frequency boost so the preamp will sound [u]more[/u] [u]bright[/u]. To make it sound [u]less bright [/u]you have to decrease its value, or just turn the Treble pot down, or, if you have a tweeter in the cab, turn off the tweeter. And keep reading wikipedia: you are not interested in cut-off frequency in this case. You are interested in high frequency boost, or cut. Mark
  21. Clearly something failed in the amp and it was not fixed and tested by "Barry something". You can only check whether external preamp (e.g. from 450W SS amp) works (or not) with the power amp from V4. Most probably it won't work. This would indicate that the power amp in V4 still needs to be fixed. If you have some electronic skills, you can check bias of the output valves. Here is how to do it: [url="http://www.dustyend.com/finnbass/oxblood_stuff/V-Type_V4_instructions.pdf"]http://www.dustyend.com/finnbass/oxblood_stuff/V-Type_V4_instructions.pdf[/url] Mark
  22. I'm talking about a jack socket. if you look at any jack socket (even at the one provided by yourself), there is a conductor which connects to the tip of the jack plug. On your photo it's just to the right of the orange line. When there is no plug in the socket this conductor is shorted to the ground with another conductor which is below this one (it's not visible on the photo). What you need is to make that these two conductors are not shorthed together. You can achieve it but putting any isolator (like paper, wood, fabric) between those two conductors. In the evening I can make a photo but it is so simple (to do, not to explain). In this case you don't need any jack plug in the front of the preamp. Mark
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