Members Ryan_F Posted April 1, 2009 Members Share Posted April 1, 2009 I had ordered a bunch from El34world.com Good site to order from, you can order in 1-foot increments. Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted April 1, 2009 Author Members Share Posted April 1, 2009 Here's the Hi/Low mod. Man...drawing that up in Paint was ROUGH. With the way I have it wired, the amp is on the High gain channel when there's no power to the relay (switch is open). To make it default to clean, just swap the Normally Open connections with the Normally Closed ones. Link to comment Share on other sites More sharing options...
Members SirJackdeFuzz Posted April 1, 2009 Members Share Posted April 1, 2009 i have lloked soooo many times into a VTM . . . so this might be the ideal place to ask !Is there any mods out there in VTM-Mod-Land, that increase the low end and make it (((looser))), like that of a Green Electric USA or MATAMP GT1 ?All info very welcome !Thanx Guys Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted April 1, 2009 Author Members Share Posted April 1, 2009 You could try increasing the values of the coupling caps (C2 and C3) and Cathode-bypass cap (C5) and adding a cathode-bypass cap to V2A in parallel to R9...you could also increase the value of C15 and C16 to filter out more treble and shift the frequency response lower...but you'd also be decreasing gain. (All caps are located on the preamp board) Link to comment Share on other sites More sharing options...
Members Ryan_F Posted April 1, 2009 Members Share Posted April 1, 2009 Thanks for the diagram! What value of EL cap did you use, and what voltage is your relay? I'm using 6V relays, but I have a half-wave rectifier as found on them JCM2550 schematic. Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted April 1, 2009 Author Members Share Posted April 1, 2009 I've got a 470u cap and 12v relays. I'm thinking about throwing a 1K bleeder resistor in parallel to the cap as well...that thing stays charged for a WHILE after you shut the amp down. Link to comment Share on other sites More sharing options...
Members Ryan_F Posted April 1, 2009 Members Share Posted April 1, 2009 I have the same issue with my system. I'm using a 220u cap, I can switch channels a few minutes after the amp shuts off. I'm tempted to mod this weekend... I like how you made it so the relay is off while on high gain, and on with low gain. Thats what I did with my "two channel" mod. I noticed a bit of noise if I had the relay activated on high gain channel. Link to comment Share on other sites More sharing options...
Members SirJackdeFuzz Posted April 1, 2009 Members Share Posted April 1, 2009 Originally Posted by Sixtonoize You could try increasing the values of the coupling caps (C2 and C3) and Cathode-bypass cap (C5) and adding a cathode-bypass cap to V2A in parallel to R9...you could also increase the value of C15 and C16 to filter out more treble and shift the frequency response lower...but you'd also be decreasing gain.(All caps are located on the preamp board) WOW - thanx for the fast response !If a simple (read cheap) mod will do just that, then i am about to hunt down a 60W VTM head asap !I am not too worried if i loose some gain, as this amp has more than i need anyways !I take it any good amp tech will be able to do such a mod, correct ? Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted April 1, 2009 Author Members Share Posted April 1, 2009 Definitely...we're talking less than $10 in parts and about a half an hour in soldering. Link to comment Share on other sites More sharing options...
Members Ryan_F Posted April 1, 2009 Members Share Posted April 1, 2009 Let us know how the tweaking goes. Link to comment Share on other sites More sharing options...
Members SirJackdeFuzz Posted April 1, 2009 Members Share Posted April 1, 2009 Originally Posted by Sixtonoize Definitely...we're talking less than $10 in parts and about a half an hour in soldering. Bloody Hell . . . $10.00 for an amp like this with a more pronounced and looser bass response - what a bargain !!!Thanx Again man Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted April 1, 2009 Author Members Share Posted April 1, 2009 The hardest part will be finding the right values of caps to add...which is why I recommend getting a soldering iron and practicing with it so that you can make the swaps yourself. Change something and see what it does...don't like it? Change it back. Like it? Change something else. That's all there is to modding, really. Link to comment Share on other sites More sharing options...
Members Ryan_F Posted April 1, 2009 Members Share Posted April 1, 2009 When experimenting with different value caps, try one, then pick another one that is either quite a bit lower or higher valued. You should be able to tell to what end of the spectrum you need to pick a cap value, and at least narrow down your testing. Same with resistors. If you have some alligator clip wires, you can do off-board quick interchange of parts. The only other tips is, dont blow up your amp, burn your fingertips off, forget where a part you took out came from, ummm... what else have I done... Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted April 1, 2009 Author Members Share Posted April 1, 2009 Originally Posted by Ryan_F If you have some alligator clip wires, you can do off-board quick interchange of parts. Damn...GREAT idea!Why didn't I think if that? Link to comment Share on other sites More sharing options...
Members SirJackdeFuzz Posted April 1, 2009 Members Share Posted April 1, 2009 Originally Posted by Sixtonoize The hardest part will be finding the right values of caps to add...which is why I recommend getting a soldering iron and practicing with it so that you can make the swaps yourself.Change something and see what it does...don't like it?Change it back.Like it?Change something else.That's all there is to modding, really. Originally Posted by Ryan_F When experimenting with different value caps, try one, then pick another one that is either quite a bit lower or higher valued. You should be able to tell to what end of the spectrum you need to pick a cap value, and at least narrow down your testing. Same with resistors. If you have some alligator clip wires, you can do off-board quick interchange of parts.The only other tips is, dont blow up your amp, burn your fingertips off, forget where a part you took out came from, ummm... what else have I done... GOTCHA . . . thanx guys Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted April 4, 2009 Author Members Share Posted April 4, 2009 UPDATE: I've been tweaking my 2-channel mod, and I can't get rid of the last bit of noise. It seems as though whenever I connect the taps to supply heater current to my relay power supply, it causes a noticeable hum...even when the relay isn't connected. Also, it makes the same hum no matter where I connect the power taps...be it V1 or V4, and whether or not the preamp volume is at zero or maxed. I don't think it's a shielding issue, because I've tried using shielded wires, too. At this point, I'm a bit stuck. I may have to install an additional transformer to provide 12VAC to my power supply circuit. Link to comment Share on other sites More sharing options...
Members Ryan_F Posted April 5, 2009 Members Share Posted April 5, 2009 I used the relay power circuit as indicated Here on this marshall 2550. Look in the middle of the schematic, where it says "to heaters" You can omit R30, R31, the LED between those two resistors, the "pull boost switch" (mounted on font panel so you dont need a footswitch to control it). Make sure to isolate all connections in this circuit from the chassis. If you put anything to ground, youll have issues. You'll need to use 6V relays in this setup. You can use a bigger value cap also, but I wouldnt go too much bigger. I replicated this exact schematic in several different amps, with 100% perfect results. The biggest issue I have seen happen is that the footswitch jack is connected to the chassis, which is very bad. Its not blow-stuff-up-bad, but it will cause noise issues. Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted April 5, 2009 Author Members Share Posted April 5, 2009 I'll have to try that...maybe my full-wave rectifier is causing the weirdness. Link to comment Share on other sites More sharing options...
Members Ryan_F Posted April 6, 2009 Members Share Posted April 6, 2009 Yay plexiglass!You can also see the switch near low gain input for the bright cap on/off, the silver knobs are for gain channel, and the red knobs are for clean channel (pre/post gain), and the red LED for channel indicator. Between high eq and the DIP's you can see the switches controlling the "saturation" resistors i posted on here earlier. Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted April 6, 2009 Author Members Share Posted April 6, 2009 That plexi panel looks pretty badass! And I tried ripping off the 2550 switching supply, and it didn't make any difference...I still got the same noise as when using the full-wave rectifier. Although, FWIW, the noise created by the switching power supply is less than the noise in my Boss GE-7...so it's not really that noticeable...but it's the principle of the thing. I think I'm just going to break down and throw in a dedicated 12V transformer to power my relays and keep the two power supplies completely separate. Link to comment Share on other sites More sharing options...
Members Ryan_F Posted April 6, 2009 Members Share Posted April 6, 2009 Thats really strange you are having such issues. I guess it didnt add enough noise for me to notice too much. My VTM has a low, but constant noise floor that kinda irritates me. I'm about 90% sure that its caused by stuff I have plugged in front of the amp, cuz with no cable plugged in, it has ZERO noise. It's probably not a terrible idea to keep the two power supplies separate, as the heaters arent designed to have that much more stuff loading it down. I messed around with the low gain channel, and I really cant find any use for it. I like the clean channel I hacked into mine FAR better than the low gain. It can sound completely clean, or nice and chimey with the clean gain maxed out. Next step is to make separate EQ... Not likely to do that as I have no room on the faceplate for more knobs. Any ideas what I should etch into the plexi panel? And input on color of lighting? I dont want the etching to be too complicated, but enough to make it look fancy with lighting behind it. I was thinking of carving a VTM in some gothic style lettering. Link to comment Share on other sites More sharing options...
Members Ryan_F Posted April 6, 2009 Members Share Posted April 6, 2009 Some Interesting Links:http://music-electronics-forum.com/s...&highlight=vtmhttp://music-electronics-forum.com/s...&highlight=vtmhttp://music-electronics-forum.com/s...&highlight=vtmhttp://music-electronics-forum.com/s...&highlight=vtm Not all of the information is 100% correct, but I have a ton of PM's regarding those threads so I can answer questions. Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted April 8, 2009 Author Members Share Posted April 8, 2009 SUCCESS!I installed an external transformer to power my relays, and now the VTM is silent!...Well, no more noisy than it was BEFORE the channel-switch mod. Link to comment Share on other sites More sharing options...
Members Ryan_F Posted April 8, 2009 Members Share Posted April 8, 2009 Congratats! Link to comment Share on other sites More sharing options...
Members tedmich Posted April 8, 2009 Members Share Posted April 8, 2009 Originally Posted by Sixtonoize SUCCESS!I installed an external transformer to power my relays, and now the VTM is silent!...Well, no more noisy than it was BEFORE the channel-switch mod. glad its fixed...you noise may have come from the floating ground PV uses for their heaters, its 47ohm above true ground by using a flame proof (47FP) resistor :(its R14 in my Bravo, R28 in the VTM)there are a lot of tone mods in the switchable cathode bypass caps the VTM tweaks from the DIP; higher cap values boost to a lower freq, and the boost can be attenuated with series resistors, or a pot. Bypassing up to 22uF at C5 and C10 will bring the boost WAY low for more bass (too much may fart out though..)See the valvewizard guys stuff on cathode bypass for some neat ideas: http://www.freewebs.com/valvewizard1...Gain_Stage.pdfVTM/Ultra and Bravo tone is all about the cathode bypass Link to comment Share on other sites More sharing options...
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