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Old 30th September 2004, 08:05 PM   #21
zeke is offline zeke  United States
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Here'd the other pdf.
Attached Files
File Type: pdf bogen m330a schem mods powersupplyonly 30sep04.pdf (54.9 KB, 160 views)
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Old 30th December 2006, 12:21 PM   #22
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I realize this was some time ago, but does anyone know how this turned out? My son has the same amp with the same thing in mind. Thanks.
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Old 26th January 2007, 03:53 PM   #23
zeke is offline zeke  United States
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Join Date: Apr 2004
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The Bogen M330A project turned out great. I was very careful about safety and your son must be too. This is important! Make sure everybody reads all the warnings about tube amp dangers. There are plenty of them all over this forum.

For the tonestack, I experimented with the fender 5F6A arrangement, the vox setup and the Baxendall (sp?) design. The fender circuit sounded the best to me and I felt it gave the strongest variation in sound with tone knob adjustment. But, now that Iím used to the Baxendall circuit, I might not change back. Itís a matter of taste.

Keep it simple. Forget the Ďboostí and Ďpreamp outí and other complications. Get the basic amp working right first; you can add the other stuff later.

The standby arrangement works well. I used a properly rated 3-position rotary switch so itís really intuitive: full ccw = off, mid position = standby, full cw = on. I donít have to fiddle with two toggles like on most other tube amps.

Also, forget about trying to have 2 channels. It never quite worked right and there was always a weird squealing at various volume and tone settings. Since I'm not an EE, I never figured out how to resolve it. I eventually eliminated the second channel and now it works really well.

Also, It's LOUD! I use a 2x10" speaker cabinet I made with Jensen speakers (8 ohm, 75W each I think). The amp sounds great and the distortion is really tunable with the combination of master and channel volume controls. Also, I can get really nice feedback by holding my guitar up to the speakers, everything from subtle hums to screaming chaos. You can turn up the channel (preamp) volume and turn down the master for preamp distortion at low volume but the only way to get power amp distortion is to turn the master up. With about medium preamp volume it seems to stay very clean until the master is around half-way up, then it starts to break up. Above that, it starts to get really loud. I rarely have it at max volume because I get phone calls from neighbors. I guess thereís not much worse than loud bad guitar.

Good luck to you and your son. Iíd like to hear how it comes along.
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Old 24th February 2007, 06:31 PM   #24
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Thanks for the reply. We have quite a bit going on at the time and the amp gets drug out every now and then. This may be a summer project. I will let you know if it works out, right now we are trying to resolve a power supply issue - no power to the pre-amp.

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Old 28th February 2007, 05:07 AM   #25
pango is offline pango  United States
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Hi Zeke.
Any chance you have a last last official absolutely done tinkering with it Schematic of your bogen? Or even a jpg? I'm impressed that you went from what seems like complete novice to tearing the guts out and making it into a guitar amp. I'd be interested in seeing what the final layout was, if you have a schem. Thanks!
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Old 16th September 2007, 04:10 PM   #26
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Default Bogen M330A for bass... hums

New member to this forum (love it!) but certainly not new to tube amps. I have a Bogen M330A (from Goodwill for $25) which works well. (Hums too much but that's another topic.) Plug my electric bass into the 'phono' (mag) input (at low volume from the bass) and sounds great! Need to modify the input stage to improve this...

I have grabbed a couple of schematics stating they're for the M330 but clearly NOT mine! It's been a while since I looked inside, but mine has 6L6 PP output, 3 mic inputs, #1 switchable to 'mag/aux' and has a 'speech filter' switch. And as I recall, the tone stack is not boost/cut but bass/treble 'cut' only. (yuk) More resembles the K-15 from what I can tell.

Anyone else have an M330A? (I think so...) What does yours have? Any other schematics out there? (and I have to fix the hum! even hums w/o the tubes, including w/o the 5AR4!)

Mark in Oregon
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Old 4th December 2009, 05:20 AM   #27
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Hello zeke and everyone else in diyaudio land....
I recently converted my bogen m330a as described in this thread...i used your final schematic, and I want to thank you and everyone out there for putting this information out there because the amp sounds awesome now.
I left out the nfb pot and went with the value suggested by Mike (some kind of genius)
Put in the tone stack called "fender" from a widgetlike software called tonestackcalculator

I used the top thre knobs spaces for inputs and added two new for the pre-controls. my inputs squealed at first but i sheilded them with some wire mesh and they stopped.
any way now i have some questions and want to know if i can ressurect this string.....
see i want to include this reverb tank i pulled out of a kenwood jumbojet (kr760 i think) that was in a cccar crash....yeah....well it was just trashed...i have the tank and its driver, pickup, and all other components that it needed everything is mapped out on paper......but i want to power it (b+ 30v) with something from inside the bogen....i am afraid that if i put another xformer in there i will get hum.....(which i have absolutely none!!) couldnt i just voltage drop one of the hv down to 30v and use that? the amp seems to be running a bit less than it is possible what were the "remotes" for anyway....
so there..i can post photos, schems(and mabey trade some schems too...(knight setchell carlson, and then some...)
This thing is kind of hard to distort but thats ok cause i like jazz and reggae and 60's soul and stuff....(the amp is for my guitar player anyway i play sax) and it is LOUD 30 watts dosent describe it....
playing through a 100 watt 2x15 cab at 4ohms with vibrolux? speakers and a tele....
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Old 6th December 2009, 03:52 AM   #28
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Started a new thread
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Old 6th December 2009, 06:58 AM   #29
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