AX84 BBS

Amp Parts and Kits

Doberman Music Products, LLC offers a variety of parts and kits

Can't get rid of Hum/Buzz on my build could it be my House?(by LuisG)

Tue, 16 Mar 2010 16:25:51 -0400

Hello guys, First of all I want to really appreciate all the help I have been getting on finding out why My P1-EX build can't stop huming at when I turn the gain up. Here is the thread where I am following up on that issue: [link] I was doing some research on the net and I came across people getting hum because of house wiring ground loops. I live on an apartment building so this could mean other units ? who knows! I am exploring the possibility of this being the case because so far nothing has worked on getting rid of my hum (tested shielded wire, humdinger, changing the tubes, C4 power cap and even putting my heaters on a 6 volt battery) How can I test if my hum is comming from the ground on my wall socket? I have 3 amps, the P1-EX, Vox VT50 (hum on high gain models) and a Roland microcube (does not hum at all but that amp is not DC adapter has no ground leg). I have a Gibson with humbuckers and a monster cable.. I came across this video on Youtube [link] where they talked about this device called the Hum X by EBtech that is suppose to fix hum from the ground line of the wall. It has good reviews but I am skeptical. So here are a few questions regarding this issue: 1) Does anyone have any kind of experience with this sort of problem in a house? 2) what kind of test can I run? 3) If this is the case can anything be put into the amp so that the ground on the amp does not suck this interference? thanks Luis

Output Transformer Question(by rockyo)

Tue, 16 Mar 2010 16:02:21 -0400

I am planning to build a High octane amp this summer but because of availability issues, The best transformer I could find was a 10W 5K-7K primary impeandence. Is it ok to use it? Will the power output be reduced?

Anodized Chassis(by Brian S)

Tue, 16 Mar 2010 15:06:21 -0400

I am thinking about setting up an anodizing line foir my chassis and wondering a couple of things. Would there be any interest in colored chassis? If you had to pick say three colors, what colors would you be interested in? Thanks Brian

Gothic Ring layout?(by sdp1234)

Tue, 16 Mar 2010 14:49:00 -0400

I like the layouts that I use not for low to medium gain amps but I was thinking of using a Gothic Ring type layout for upcoming hi gain amps. Problem is that I really do not like working with tag strips and I'm not very good with tube sockets. Here is what I was thinking: First I'd try it using narrow single row turret boardseyelet boards instead of the tag strips. Then I only have to deal with the sockets. Next I was trying to think of a way to put holes in a board and fit it over the preamp sockets and have very short flying leads directly to the tube socket. I realize that this probable defeats a bit of the logic around the layout but just trying to find something different that will work. Any Ideas?

Turret / printed circuit board(by tgray)

Tue, 16 Mar 2010 14:39:17 -0400

I have a question about turret boards... I'd like to explore the possibility of using a hybrid printed circuit board with turrets. I made one of these that worked but I'm wondering about the long term reliability of such a board. I have a fairly complicated amp and not a whole lot of space in the chassis, so I'm looking for ways to make the board smaller and to avoid having so many wires. I tried using the back or bottom of the turret board to route wires from place to place but wires on the bottom of the turret board tend to fall out when you solder a connection to the top. This will be hard to see once you've got everthing wired up. To get away from using wires I tried using a 1/16th inch copper clad board that I patterned an interconnect layout and etched the pattern into copper. Then I beefed up the copper traces with a thick coat of solder. Then I glued the copper trace board to another plain 1/16th inch thick board for a total board thickness of 1/8th inch. I then drilled holes for turrets and staked them in place. The board then becomes a hybrid turret / printed circuit board with turrets making contact with the traces on the bottom side. This technique works but I'm worried about long term reliability. Has anyone every used this technique who would care to make a comment? tgray

Tube types and brands for my upcoming Firefly build (by Justin Pfenning)

Tue, 16 Mar 2010 14:29:04 -0400

I'm new to the board, and preparing for my Firefly build. I have purchased everything I need, except tubes. I was going to grab some JJ's or Ruby's, but I wondered what sound difference an NOS or used old tube made compared to the new ones. I have a couple DIY tube amps and preamp in a stereo, and I'm amazed at the sound difference between tubes. You guys have any expireances you would like to share? Also, do the 12ax7's need to be matched? I think I read on hear that you can swap a 12at7 in place of the 12au7. Is that right? Thanks for the input and great board. Justin

Me visiting the USA: NY and SanF!(by jasperoosthoek)

Tue, 16 Mar 2010 14:25:30 -0400

The last day of this month I'll be flying with a colleague from Amsterdam to New York! It's my first time in the country, glad I waited until I was past 21. I'm planning to go site seeing there for a couple of days. Enough to see: statues of liberty, Brooklyn bridges, empire state buildings, ground zero, the whole bit. April the 4th we're going to San Francisco for a conference until the 9th. We'll be staying in San Francisco till the 14th. We're planning to rent a car and go to Yosemite national park. Anyone know of any nice concerts or other musical events that happen to take place during those days? And is there anything I shouldn't miss in San Francisco? Jasper

Saw Steve Morse Saturday Night(by Doug H)

Tue, 16 Mar 2010 14:22:36 -0400

He just did a short tour of Florida and we caught him Saturday night at a little theater that's about 5 minutes from my house. What a great show. Just as good or better as the last 3 or 4 times I saw him. Took my 15 yr old son (wife stayed home this time) and he was blown away. He did a short opening set with Sarah Spencer, his "Angelfire" project. She has a lovely voice and his acoustic playing complimented her nicely. Then he did his "Steve Morse Band" set with Dave La Rue and Van Romaine. And I was once again reminded of why this guy is one of my top favorite guitarists. It's not just his guitar talent, which is formidable, but his composition and arranging skills that are so stunning. No one works a three-piece like he does. His stereo rig looked like a giant boom box. 2 Engl's sitting on a rack, with a 4x12 topped by a p.a. cabinet on each side. The p.a. was for his acoustic I presume. He sounded great, as did the whole band. What a great show.

60 H or 120 Hz Hummm(by Spartan)

Tue, 16 Mar 2010 13:52:35 -0400

This is my 1st tube amp build. I had a sporadic squeal at first (I think it was a coupling problem)- anyway, I redid the boad since the 1st one was pretty sloppy. Good news is the squeal is gone, but the amp has more humm then I would like. Can anyone tell me if this is 60 Hz 120 H or something else? Thanks, [link]

Two Interesting Possibilities(by surfshoptom)

Tue, 16 Mar 2010 13:51:00 -0400

I have two chassis. I don't know what they were. They're identical with two exceptions. They both have three tube sockets - a 7-pin and 9-pin. One has a second 9-pin and the other an octal. And they have different output transformers. They're tiny things. They're 8.5 x 4.5 x 1.5 inches. I think they'd have to be point to point. There's no room for a board. The PTs are stamped TR-196 and they have serial numbers. The chassis with the octal has a TR-212 OT. The other is a TR-210. The fronts have six holes - 3 for pots, one for a small slide switch and two others. I'd like to build or have built two guitar amps. Maybe a Fender 5F1 or 5F2 circuit. Where can I put some pictures? Would it help to have pics? What are your thoughts? I've built a P1 and an HO. I also built one of those obscure, crazy LX2H 1/2w amps. Anyone want to build these for me? How much?

So I just realized something important, wrt amps tone and finger(by DutchMarco)

Tue, 16 Mar 2010 13:39:48 -0400

Tone really does come from the fingers (or the pick, if you prefer). I had ben listening to an old recording I made in the band practice room, and beside me cringing, I have something useful to say about it (No, I won't let anyone listen to it to judge for theirselves, read on for the why). During the singing I was comping with little distortion (as one does), the amount of distortion was quite low enough, but I tried to control the amount of distortion with my atttack. this resulted in a feeble-sounding attack. instead I should have turned down the guitar's volume (or maybe use a switch somewhere - like a 200k resistor to ground or something, either on the guitar or in a pedal (of my own making?) and keep up the powerful attack which does sound bestest to my ears (I believe that that's what people mean when they say 'tone is in the fingers' - by that I can not-modestly sayI had quite good tone - add that to a Champ circuit mated to a 12" speaker, and my tone must have been awesome, except when comping because I didn't want to reach down to the amp and widdle the knobs when switching between comping and lead! so I put too much confidence in the much-hailed touch sensitivity of tubes.

old '63? johnson celestion(by cameron nicklaus)

Tue, 16 Mar 2010 13:33:21 -0400

a friend found and bought this amp on craigslist. [link] we are having a hard time finding much info on it. we found one page on google that shows some ones collection of johnson amps and catalogs but no tube compliment or schematic info. anybody have any more clues?

FX loop done with mixed results(by Nick Zannis)

Tue, 16 Mar 2010 12:43:53 -0400

Used the fx loop from: 6V6 PLEXI SE Rev 2 by Mark Lautizar 3/3/2005. Been wanting to do this for years and finaly tried and it worked but introduced noise into an otherwise quite amp. Amp is now an SEL with a few differences. Chassis is stock P1X and is a bit tight so I used terminal strips bolted onto the preamp tube mounting screws. It was tight and tedious, and I tried to run signal wires perpendicular to PS wires. Got more hum; and, the squeal I got rid of before is now back. Going to go chopstick this thing carefully. Thinking I would just need a bigger chassis to spread thing out a bit. Anybody ever get an effects loop into an SEL or HO? And what does it look like layout wise?

JCM800->EL91 idea/questions(by t mod)

Tue, 16 Mar 2010 11:47:31 -0400

Hi all! Inspired by Bancika's 5W SLO I've been looking at utilizing a pair of EL91s for a low wattage PP combo for some time, and I've gotten a bunch of epi Valve jr, chassis laying about. After reading about Iain's diezel-mods to a JCM800 pre, [link] I've decided to look into grafting a jcm800 pre into and an EL91 PP Pa into the valve jr chassis. Basically I've got three worries I hope to address before I start drilling: 1) B+ voltage for PA. EL91 has a Va max of 250V, whereas the JCM pre calls for 334V-390V. Being low on real estate I've been thinking of adding a Zener/power-zener/mosfet circuit between the negative side of the two first filter stages and connecting the cathodes of the power tubes to the junction between the zener and the caps. The zeners would make sure that the power tubes only see a voltage drop of 250V, whereas the B+1/B+2 node is at 400V wrt circuit ground. Obviously this would demand raising heaters, but I'd do that anyway. Am I missing something here? 2) Signal hitting the EL91. With a PI tailored for EL34s i would expect the signal level to be way to high for EL91. Anyone know the input signal swing needed for driving EL91s? I'm thinking of using 12at7 (or preferably 6n1p as they are cheaper) as PI, but I guess I may have to play with voltage dividers as well... 3) Will I have any chance at all getting this to behave in a valve jr chassis? Now, I like a challenge, but I'm a little worried the chassis might be a little too small to give me a fighting chance at defeating squeal/feeback no matter how much thought and trial/error goes into layout. On the other hand, I've seen drop-in boards based on the HO, so I guess it should at least be possible... Any thoughts?

October Studio Build(by RickB)

Tue, 16 Mar 2010 11:41:28 -0400

Well, I was going to build the P1-eX, however the tone of the October sucked me in. I know this is not a recommended first amp, but... I just couldn't help it. The october just has the tones that I really like. I realize there are more parts in the october and more chances for screw ups, I realize that I may get this built and have to debug and futz with it. But, thats ok. I'm up for the challenge. I will simply take my time. Double check each joint prior to solder, check after each solder.

First build, annoying questions(by Evil Armada)

Tue, 16 Mar 2010 10:39:35 -0400

Just routing wires now but something got my attention. How the hell do you wire up the custom doberman transformer, nothing tells me how. The site gives me specs for each wire but Im a noob. Also what do you do with the extra transformer wires. I cut them pretty short but they are still in the chasis. Is that okay? Routing these wires is giving me a headache. Almost finished though

Heat resistant caps maybe?(by JeffW)

Tue, 16 Mar 2010 09:11:02 -0400

Interesting little snippet. [link]

Low power on a build, questions(by Soundmasterg)

Tue, 16 Mar 2010 07:16:09 -0400

Hello, I've been working on a clone of a Vox AC100 for awhile. I added a second high gain channel to it, and I mix both channels at the first triode of the phase inverter. The inverter is a seesaw paraphase, using a 12AU7, and for the first triode I have another half of a 12AU7 in parallel, with half the value of plate resistor and cathode resistor of a normal single triode. The output section has four KT77's with about 470v fixed biased and 440v or so cathode biased. It seems low on power as I'm only getting about 50 watts out or so. I'm thinking the phase inverter isn't driving the power amp enough, though I'm not sure why. The circuit I used is exactly the same as what Vox used, with the exception of the parallel triode setup. The OT is a Vox AC100 clone that I got from Heyboer. I have no idea why the power is so low....I was thinking it should be about 80 watts cathode biased and 100 watts fixed biased. Does anyone have any ideas about what I can try to look for? Greg

What does blocking distortion look like?(by Soundmasterg)

Tue, 16 Mar 2010 07:04:47 -0400

I was wondering what blocking distortion looks like on a scope? I think I have some in the clean channel of my VOX AC100 build, but am not sure. I'm also not sure how to find it, if I indeed do have it. This channel is identical to the single channel in a VOX 80-100 version of the AC100. The only difference is in the first stage of the seesaw version of the paraphase phase inverter, where I added another triode in parallel but with a seperate grid to mix the other channel in. I also added a master volume right before the phase inverter with the added 100k grid stop. When the master, gain, and treble controls are maxed, then I hear a bit of farting out on low notes, especially when they are hit hard. I know I could just start popping in grid resistors and/or reduce gain, change cap values, etc., but I'm trying to use this as a learning experience. Anyone? Greg

22awg solid core wire in the UK(by Michael Mo)

Tue, 16 Mar 2010 06:02:46 -0400

I am looking to buy some rolls of solid core wire from a UK or European supplier. it needs to be 22AWG, min 600v insulation and the insulation must be at least 0.4mm thick. I can get 26awg wire plenty at ~ �6 per 100m reel but the insulation thickness does not meet CE regs. I have found some at Farnell, see link below, but its �10 for 30m!!!.. .anybody know of a cheaper source? [link] thanks Mike

Preamp wiring(by LuisG)

Tue, 16 Mar 2010 03:17:08 -0400

My P1-EX has a lot of hum when I have the gain up [link] as you can see in this video. I am trying to figure out how to make the hum go away, I think is on the preamp because the gain makes it worst Here is a pic of the preamp wiring [link] I was told that is less than ideal. By looking at Merlins book and site I see how he suggests wiring it [link] but by his pic I see that its no the last preamp stage but more like a middle one. So in my situation what can I do to make it better? should I twist the white all the way to the greens edge and then go through the socket or around the socket like the builders guide says? What about the other wires in the socket? should I make them longer and point them towards the outside of the socket twisting them like Merlins book ilustrates? of just point them outside? Everything is so close there on the build :( One last thing I noticed on the builders guide is that the HO has a resistor on the grid and the shielded wire seems to be grounded on both sides of the line. Is shilded wire supposed to be grounded on both sides? Thanks Luis

12AT7 vs 12AX7 PI(by tgray)

Tue, 16 Mar 2010 02:02:05 -0400

I just went through a lot of unnecessary work on a 50 watt pp build because of bad 12AT7 tubes. If you can believe it, I purchased 3 12AT7 tubes from 2 different stores and all three of these tubes were bad. I was getting poor sound, squealing, low volume, etc... and all of that went away when I put in a fourth tube. All of the 12AT7 tubes were sold under the brand of groove tubes, however, there was a sicky label on the tubes when I took them out of the box. I peeled the label off and there was no marking on the tubes, no indication of the tube type. I thought this was odd but used the tubes anyway. I thought the odds of getting three bad tubes would be pretty slim so I wound up looking elsewhere in my amp build. I spent a lot of time replacing sockets, resoldering joints, replacing components. etc... I'm pretty disgusted with the situation, but on the other hand I'm glad the amp works. By the way, does anyone know why 12AT7 is preferred for PI triodes? My guess is that it has lower gain and it's purpose isn't to add gain, merely to split the phase. tgray

Fireworks inside my tube(by kristjanb)

Tue, 16 Mar 2010 00:18:59 -0400

Hi everybody this is my first post. I just finished my P1-extreme and everything is working and sounding good except when I crank it I get arching inside the power tube. I have tried another tube and the same thing happens. I am using JJ EL34L. The voltage is running kind of high. On the plate it is 392v, 386v on the screen grid, and the bias is just under 27v. I made the PT and the OT myself (following good instructions) so that could have something too do with this. I will have to find out if that OT is working like it should, I just wanted to post here first to see if the voltage is too high. I want to put adjustable bias in but I can�t find a 2W trimmer here in Iceland:) My english is not very good, so sorry:) Thanks!

Someone has to fess up(by Pete Trippe)

Tue, 16 Mar 2010 00:11:04 -0400

I figure this has to be an AX84 member. ;) [link]

HO has too much buzz(by Lou Glorfeld)

Mon, 15 Mar 2010 23:15:20 -0400

I just took my HO down stairs and did a direct comparison with my Marshall JTM 30 to check the noise level. There is no doubt that the noise from the HO is excessive. The maxed out Marshall gives a very loud 60Hz hum but the maxed out HO gives an even louder buzz which I guess is 120Hz + other noise. I am about to replace the fake filter caps, so I thought I would also try and replace my somewhat questionable homemade shielded cable with some good teflon shielded cable I just got from Apex Jr. Any other suggestions would be appreciated. Here are a few pics: [link] [link] [link] It was suggested that I should try and move the wires around on pins 2 and 7(grid pins) of the preamp tubes. I tried to move them, but because my wiring is so tight there is not much to move. I could lower the value of my grid stopper more but I doubt that would help much. Just for interest sake I put a good 47 Mfd 450V cap next to a fake 50 Mfd cap. Note the amp is at least fine with both gains set at 7 and the volume up to about 50%. Past this point the extra noise starts to become annoying. No surprise, but the intensity of the buzz is completely dependent on the gain controls.