Beiträge von d95err

    I've built a G-02 Animal kit I purchased from Musikding. It sort of works, but the gain seems to be way too low, when comparing to clips of the real G2. I've tried both with silicon diodes and with various germanium diodes. The diode type makes a difference (silicon results in more gain), but the original is supposed to get lots of gain with germanium diodes. With germanium diodes, my build can barely get a slight overdrive even with a medium-high pickup (EVH Wolfgang).

    I've double checked the component values and can't find any errors. The voltages check out more or less (transistor voltages listed below). I did some tests with my scope and a signal generator to investigate the gain of each stage (I removed the clipping diodes for this test, to be able to see the unclipped gain of each stage). I also did some SPICE simulations of the stages:

    Stage 1 (buffer 1) - gain 1 (as expected)
    Stage 2 (buffer 2) - gain 1 (as expected)
    Stage 3 (boost) - gain 2 (too low, simulated: 4.5)
    Stage 4 (clip 1) - gain 5 (too low, simulated: 10)
    Stage 5 (clip 2) - gain 15 (too low, simulated: 25)
    Stage 6 (recovery) gain 8 - (seems OK, simulated: 7)

    Stage 3 seems to be the most suspicious part, but I can't find any component errors. I replaced the Q3 transistor, but there was no significant change.

    Transistor voltages:

    Q1 E: 4.79 B: 5.29 C: 9.04
    Q2 E: 5.33 B: 5.83 C: 8.93
    Q3 E: 0.19 B: 0.78 C: 4.65
    Q4: E: 0.20 B: 0.77 C: 4.71
    Q5: E: 0.04 B: 0.62 C: 3.90
    Q6: E: 0.99 B: 1.17 C: 5.34

    Any help will be much appreciated!

    Re: Only analog is good ... but it's necessary to choose the best!!!

    Zitat von DanE


    Vorbis: Sorry, but a J5 cannot have more gain than a Peavey Classic 30. The J5 has a single EL84 SE and the Peavey has 4 EL84s PPP in its power amp.

    The poweramp has nothing (or at least very little) to do with how much gain the amp has. In both these amp, gain comes primarily from the preamp. The J5 has lots of gain available and so has the Classic 30 lead channel.

    My M15 will easily go into AC/DC territory on both channels (although it will be very loud when you get there on the Clean channel...).

    The Crunch channel will have a bit more gain (distorsion) than a regular Marshal Plexi, because of less attenuation between the stages, lower voltages and no negative feedback in the poweramp. If you add a cathode decoupling cap to the second gain stage you get even more gain.

    Re: Can I use a PC fan in my M15?

    You don't necessarily need 12V to power a 12V fan. Using a lower voltage will just make the fan run a bit slower. This can actually be good, because you'll get less noise from it. So, try powering it from the heaters and you'll have plenty of current available. A simple half-wave rectifier (single diode) and a fairly big low-voltage filter cap should do the trick.

    Re: how to modify m15 to accept 6v6?

    I think the only change (except for changing to octal sockets) would be to change the cathode resistor to an appropriate value.

    Check some 6V6 tube data sheets, they usually contain recommended cathode resistor values for various lplate voltages.

    According to this: http://www.mif.pg.gda.pl/homepages/fran…084/6/6V6GT.pdf
    a cathode resistor of about 250 ohms should work in the M15.

    (I haven't tried this, so don't take my word for it...)

    Re: So why "boutique" amps are so expensive?

    How many hours did it take you to finish your amp? How many amps could you produce in a year with that rate? What price would you have to set on those amps to earn a living?

    Boutique amps are not expensive.

    Are they worth the price? Well, that's another and very subjective question.

    Re: Burned resistance in G2 power suply board

    Without knowing the schematic or anything, my guess is - you have the wrong polarity on a filter capacitor. I did that on my M15Mk1 and I got smoke from a powersupply series resistor.

    Check the filter caps (again) and make sure the negative end is connected to ground.

    If that's the case, you should probably replace both the cap and the resistor just in case. They could have been damaged.

    Re: More highs for m15mk1

    You can't add more treble, but you can always remove more bass. Try a "bright" cap on the volume control. Somewhere between 100-500p is a good place to start.

    Otherwise, try a brighter speaker. The speaker accounts for a very big part of the sound of the amp.

    Re: 2 questions about the G2: headphone output and which small speaker is best?

    A headphone or recording output needs speaker simulation to sound good. That's fairly difficult to do in a tube circuit.

    I've seen some schematics for passive headphone taps for amps, but they've been in experimental stages and requires rather difficult to find inductors.

    I would use a dummy load on the amp, and get something like the Behringer GI-100 (DI box with speaker simulation). You can run the signal from the GI-100 to a line input on an I-Pod, stereo or just about anything that has a headphone output.

    I had my first gig with my M15Mk1 last night. I mostly play at home, so this was also the first time I could really let it sing at full power.

    After I first took it to rehershal in the beginning of the week, I noticed a really bad hum problem. I had to work really hard during the week to pinpoint it. Eventually it turned out to be something in my relay-circuit that caused the problem so I simply ripped it out. It didn't really matter much, because I almost only use the "Clean" channel.

    After that, the amp was dead silent. Definately the most quiet guitar amp I've ever had. Any noice I could hear came from the guitar. With the Strat pickup selector in the hum-cancelling positions it was completely quiet. You could almost not tell that the amp was on. The hum from the monitors and PA was much louder.

    I run the "Clean" channel with the volume knob straight up (12 o'clock). This gave me a wonderful warm and compressed sound with a touch of overdrive on the attack. I could then easily use the guitar volume to fine tune the sound.

    15W perfect for this gig. It was a large hall that can seat about 400 dinner guests. The volume was perfect for stage levels. I could hear myself and everyone else perfectly. The amp was micked to get a bit extra push into the hall, but I'm not sure that was really necessary. The main part of the sound definately came from the amp itself.
    I then used my Fuzz Face (DIY of course) when I wanted a bit more distortion, and my MOSFET (clean) boost to push it up for solos.

    The result was perfect! This is the first time in my life that I could really feel that - yes, this is exactly how I want to sound. When I played solos, I could let the tone speak for itself rather than trying to hide it with too fast licks or tricks. I could just grab a good note and let it ring...

    I had lots of people coming up after the gig commenting on my tone and lots of questions about the amp ("What IS that amp? Is that some kind of old vintage brand?...) :)

    Really amazing to play a gig with a *real* amp.

    Re: How far will the M15 go??

    Zitat von Intoxicate


    Could you please explain more detailed where you connected the bypass capacitor?

    Connect a 0.68uF capacitor paralell to the cathode resistor on the second gain stage (R12). Just like on the first gain stage (R7/C7).

    This will add about 6dB of gain on the treble and mids. Not a big change, just a little bit more bite.

    If you find that this mod makes the bass "fart out" a bit when cranking the amp, try lowering the value of the coupling capacitor after the first gain stage (C6) to reduce bass a bit. Start out by trying something like 0.0022uF. If that's too bright, you can just solder another cap in paralell to it to increase the value.

    Good luck modding!

    Re: A15, matched tubes?

    Matched tubes is really only useful in Hifi amps. In a guitar amp, there are so many things that make the poweramp more unbalanced than unmatched power tubes. For instance, most components are usually 5% tolerance or worse. Tolerance errors multiply, so the chance of getting both sides of the poweramp matched are very small indeed.

    In a typical fixed bias push-pull output stage (like in the A15) there is an inherent imbalance because of negative feedback entering one half of the phase inverter. This is sometimes compensated for (rather crudely) by using different plate resistors on the phase inverter, but it's still quite a big imbalance. Probably much greater than the difference between unmatched tubes.

    So even if you do put matched tubes in, it's not certain that would make the poweramp more balanced (it could even become less balanced. since the difference between the tubes could accidentally be compensating for the inherent imbalance).

    Now, I wouldn't mix output tubes from different manufacturers or so, but I wouldn't spend extra money for matched tubes.

    Re: 100w attenuator

    Browse around the Trainwreck forum at http://www.ampgarage.com and you'll find a schematic for Kevin Fisher's Airbrake. It's a simple resistive attenuator that is supposed to work fairly well. I think it should be able to take 100W if you get large enough resistors.

    However, how much is it you want to attenuate? If you want to take the level down just a little bit, an attenuator can work OK. E.g. if you want to take the volume down 6dB or so (making your amp effectively 25W).

    If you want to get down to "bedroom" or "don't disturb the neighbours" volumes, you simply can't do it well with a 100W amp. You can get the volume down, but it will sound like crap. In that case, it's better to get (or build!) another amp. Max 5W and THEN add an attenuator...

    Re: How far will the M15 go??

    I've built an M15. The amount of gain depends a lot on how high you are willing to push it in terms of volume. If you can really crank it, you'll get lots of gain.

    The "Clean" channel has surprisingly much gain if you crank it. It will get you to AC/DC for sure.

    The Crunch channel has even more gain of course. You can increase it even moreby adding a cathode bypass capacitor on the second gain stage (like on a Plexi). You may have to decrease the coupling cap a bit to handle the higher gain though. (I put this on a switch so I could select between "Bluesbreaker" and "Plexi" modes).

    With this simple mod (one cap) and hot humbuckers, you'll get into EVH territory if you crank it.

    Just remember, 15W cranked is *really* loud. You'll need that poweramp distortion to make the M15 sing. If you want distortion at "bedroom" levels, I'd go for the A15.

    Re: Adding a tube tremolo to M15Mk1

    Zitat von futurama


    Why so complicated ?

    Basically, the only thing you need for a tremolo is a low-frequency
    oscillator and a LED/LDR-pair. No need to provide an extra channel.
    The oscillator can be tube-driven or (more economic) a Timer-IC.

    Do you need a tremolo, a third channel or an additional tube :) ?

    The 18W tremolo is very different from a simple LED/LDR tremolo. It works by modifying the bias of the first preamp stage in a rather complex way. It will modulate, not just the amplitude of the signal, but also gain, headroom and frequency response. Even the depth control of this tremolo is interactive, since it changes the cathode resistor of the first gain stage. So even when it's off, it affects the sound.

    Some say that it is the best sounding tremolo out there...

    But, for a really simple tremolo, the easiest solution is a solid state oscillator and an LED/LDR, perhaps driven by the unused 20V tap on the PT.

    Re: A15 problem

    I had a problem with a smoking resistor in my M15Mk1 once. It turned out to be a filter cap that was wired with the wrong polarity.

    Don't know if that could be the problem here, but at least it's something to check for.

    Re: My M15 is complete

    Zitat von MAD


    Hey, that amp and speaker box really looks great, but the guitar :o

    Didn't I mention I did all those mods to make the amp perfect for my old worn nylon-string... ;D

    Zitat


    I'm looking forward to hear some soundsamples ;D

    It'll have to wait for a while, because right now I'm packing up most of my musical gear while preparing to sell my appartment. In January though, I will have a house with a big basement where I can make as much noice as I want!!!

    I've finally decided that I have to call my M15 build complete. I simply don't have time to make any more changes, since I've just bought a house...

    Some pictures:

    http://hem.bredband.net/runeson/elektronik/madamp-1.jpg
    http://hem.bredband.net/runeson/elektronik/madamp-2.jpg
    http://hem.bredband.net/runeson/elektronik/madamp-3.jpg

    This was my first tube amp build. To begin with, this was supposed to become the "Ultimate" guitar amp, but as the build has progressed it has more and more become a prototype platform for me to experiment so I can learn more. Perhaps I can build the "Ultimate" amp next time... ;)

    I made a lot of mods to the original design, including:

    • Power Scaling - switchable with two positions - High/Low. Low is at about -9dB
    • Post-PI Master Volume - dual 1M pot with 100p bright-caps
    • JTM45/Super Lead switch. Push-pull switch on the Crunch volume that adds a .68uF cathode cap to the second gain stages and switches in a smaller coupling cap. I also removed the master on the crunch channel
    • Relay remote controlled channel switch. 5V relay powerd by heaters, transistor activated relay.
    • Negative feedback - four position switch (off-some-more-lots)
    • Conjunctive filter on the poweramp - smooths the treble a bit when switched in
    • Line Out with volume control (Firezog style)
    • 50W dummy load resistor switched in when no speaker is connected
    • Variable hifi L-Pad one the speaker cabinet
    • Bright-switch on the speaker cabinet (inserts a bright capacitor across the L-Pad)

    As you can see from the mods, I put a lot of effort into quieting this thing. I really needed to be able to run it at appartment level (not necessary anymore though...)

    It all seems to work quite well. The combination of Power Scaling, master volume and L-Pad makes it possible to really control the output level while retaing a fairly good tone. I haven't been able to make much A/B testing yet though.

    I'll try to get some more pictures and perhaps a few soundclips. It may have to wait until I've moved into my new house though.

    Re: M15MK1 FOR BASS?

    If you want more volume (enough to play with a band), you simply need more power. While 15W should be loud enough for guitar (at least with efficient speakers), it simply won't be enough for bass.

    Bass frequencies sound mushy or muddy when distorted. Therefore a bass poweramp needs to run fairly clean. Clean power means higher power. Guitar amps can get away with less power, because they can run the poweramp into heavy distortion (cutting out a lot of bass to avoid sounding like mush).

    For a reasonably loud band you'd probably need 50-100W (tube) or 100-200W (solid state). 100W+ tube amps have very large and expensive transformers so it's not as interesting for the DIY community. This is why you don't see many bass amp designs on DIY sites.

    Martin has a bass preamp kit coming soon though. That and a solid state poweramp (or simple bass amp) should sound great!