AX84 BBS

Amp Parts and Kits

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

Octal Fatness D*mble- Wow...(by Doug H)

Sat, 04 Feb 2012 15:52:35 -0500

Years ago, David Jones posted that he modded his Octal Fatness 2nd and 3rd stage into a D*mble ODS overdrive circuit. You tweak the 2nd stage, add the interstage divider, and convert the buffer into a gain stage. I was planning on cannibalizing this amp into a SE Wreck. So iI thought while I was waiting on parts I'd give this a try. Wow, just Wow...is all I can say. This is the most nearly perfect DIY tweak I've tried yet... This little magic overdrive circuit does the trick- effortless juicy harmonics under complete control of your fingers. All it needs is a little less gain and more headroom. I will tweak the interstage divider for that. It's a drive control trimmer on the ODS- maybe I'll just use a trimmer too. But this thing is so smooth and cool sounding. I thought it would be harsh with the g12h30 but no worries, even with the PRS which is bright. Using the bright switch I can turn down the guitar for great semi clean with the preamp gain not too high. I may have to get more parts to do this other amp now...

RE: MIDI Footswitch(by dsmith)

Sat, 04 Feb 2012 15:38:41 -0500

Yes, please do share. I'd be very interested. -Dale

RE: Suggestion for blues amp?(by David Staepelaere)

Sat, 04 Feb 2012 15:05:17 -0500

Hi Steve, Yes I got the schematic yesterday and it is pretty readable for the most part -- thanks! I do have a couple of quick questions though... 1. What is going on at the bottom side of the 500k volume pot (top channel)? I suppose it should simply be a connection to ground, but it looks like it is parallel with something else (like a cap?) but I'm not sure. 2. Do you know voltages at either B+ or the PT secondary? 3. The resistors on the input tubes seem kinda high (330k/510k plate, 2.2k cathode) especially considering the triodes are in parallel. Is that right? (This is not so much a question about reading the schematic, rather my understanding of it.) 4. Do you mind if I scan it and post a link? Of course I would crop out your FAX info. Thanks again. David

RE: MIDI Footswitch(by 3rdof3)

Sat, 04 Feb 2012 14:58:59 -0500

I'd LOVE info! I control my switching via LDRs as it is and would love to be able to utilize midi instead of ground lift switching. 3rdof3 at gmail dot com Thanks!

RE: More Gain!(by JeffW)

Sat, 04 Feb 2012 14:58:49 -0500

On 02/04/2012 @ 14:04, Christopher R Wise wrote : im looking at the doberman amp site and its says their kit is 20 watts, so if i go with a different power tube it will lower the output power rating? --

It says that tubes are included and gives no option so I would email them and ask if there are optional tubes etc. but yes, changing the output tube and biasing it properly will give you a different power rating. If that is your plan I would have them send you the variable bias option.

RE: References in RDH4(by PhilS)

Sat, 04 Feb 2012 14:32:01 -0500

Look at p. 1368 of RDH4. You are looking for the Sept 1942 Electronics published by McGraw Hill. 15.9....15 is volume number and 9 is the month?

RE: More Gain!(by Christopher R Wise)

Sat, 04 Feb 2012 14:04:17 -0500

im looking at the doberman amp site and its says their kit is 20 watts, so if i go with a different power tube it will lower the output power rating?

References in RDH4(by Henry Ramsey)

Sat, 04 Feb 2012 14:32:01 -0500

Anyone know what magazine or article the reference in RDH4 chapter 15 "Cutler,S. "Audio frequency compensating circuits" Elec. 15.9 (Sept 1942) 63" actually refers to? I assume that "Elec. 15.9" is a magazine edition and 63 is a page number, but the abreviation doesn't tell me enough. Which magazine? Electronics or electrical seems obvious enough, but it's too generic to search from and gives me thousands of irrelevent hits in google. My local library may have old magazines in their closed stacks if I know for sure which one to look for. I have to be specific though or they're not going to help. Due to funding cuts the librarians are all unwilling to be helpful like they used to be. If you don't know neither do they. :-(

RE: More Gain!(by Kursad K)

Sat, 04 Feb 2012 11:16:55 -0500

On 02/03/2012 @ 10:03, Chris Hurley wrote : I've been surprised in the digital realm by how much low end you can lop off and still have something that sounds like a cranked amp. 300hz? sure.

Well, 3000hz works too. It's the slope of the eq curve that matters as the cut off frequency is increased beyond a certain point. Software lacks obviously audible problems like hiss and hum and that's why it is possible to do things that seem to be beyond what is reasonable with analog circuits. So instead of obviously audible problems one finds himself dealing with not so obvious ones such as why that sandyness in high gain tones cannot be eliminated completely. Kursad

RE: Turning a Heathkit EA-3 amp into a guitar amp(by Wick Man)

Sat, 04 Feb 2012 10:41:14 -0500

I live in Raleigh NC if anyone closer is interested in taking on this project. If not Steve I will contact you. Thank you very much!!

RE: Turning a Heathkit EA-3 amp into a guitar amp(by steve25)

Sat, 04 Feb 2012 10:30:13 -0500

I could take it on for you in a month when I get out from under the amps I am currently working on. Where do you live? I am in NY, other folks on this site who might live closer to you and do the work also could save you on shipping charges if they chose to take in on. You can email me at smag25ra5@yahoo.com

RE: Turning a Heathkit EA-3 amp into a guitar amp(by Wick Man)

Sat, 04 Feb 2012 10:04:41 -0500

Hi Steve-I tried the Radio Shack suggestion a long time ago and the results weren't good at all. Would you be willing to take on this project as maybe a head for a decent 8 or 12 inch speaker enclosure? I just don't have time and have wanted to do this for the past 2 years or so. Thanks!!

RE: Turning a Heathkit EA-3 amp into a guitar amp(by steve25)

Sat, 04 Feb 2012 09:54:07 -0500

You can use it right now as a guitar amp, just take a drive to a Radio Shack store and pick a adapter to go from 1/4" female to RCA male. This will allow to plug in your guitar, the question is where, as the Phono input may be a little too hot and break up early, and the tape input will be a little low on gain. One easy cure might be to pull out the 12ax7 preamp tube and pop in a lower gain 12au7 tube,this change alone may let you use the Phono input. Other conciderations would be for the power supply filters, as at that amps age they should be changed out even though they may work now. Old filters can change And end their lives very fast at times by just going into blow the fuse mode, other times a 120 cycle hum will thru the speaker will get worse and worse by the day! Other factors to concider are how good are the original tubes.Most home audio use preamp tubes hang in there well, but the two EL84/6BQ5 output tubes and the 6CA4 recitifer tube may be weak by now. Also the amps tone circuit range may not be to your liking, but 20 bucks worth of parts and two hours worth of labor charges can fix that too!

Turning a Heathkit EA-3 amp into a guitar amp(by Wick Man)

Sat, 04 Feb 2012 10:41:14 -0500

Hi- I'm fairly new to this site but wanted to see if anyone would be interested in making a decent guitar amp from an old but working Heathkit EA-3 amp? I believe it is 14 watts RMS and I'm willing to pay whatever. Please provide a costs estimate of time and materials if you would consider taking on this project as well as your background with amplification. Thank you very much.

RE: Daisycutter'ish SE AMP(by Asdain)

Sat, 04 Feb 2012 09:02:16 -0500

Aaaand some more changes,.. some small Tonestack Tweaks (thanks randy for the tip) and a 500k Volume Pot. [link]

RE: mini pc's (by AdamM)

Sat, 04 Feb 2012 08:25:30 -0500

You can use a usb joystick as expression controller.

RE: More Gain!(by mhelyar86)

Sat, 04 Feb 2012 07:47:59 -0500

As the SEL page says "KT88/KT77/KT66/EL34/6L6/6V6 Power Tube in Class-A Single Ended Configuration provides a range of output wattage selections." Most of those valves aren't going to be more than 10W single ended. My amp has a single ended EL34 and it runs at around 7W. So you don't have to use a KT88 just becaose that's the example in the schematic.

RE: Daisycutter'ish SE AMP(by Asdain)

Sat, 04 Feb 2012 06:39:21 -0500

I tweaked it some more, for instance i added a Zobel network across the OT primary to smoothen out the highs just a little bit. I also decreased the second stage cathode resistor a little to give it a tad more raw sound and recalculated the Voltages... Here the link: [link]

RE: mini pc's (by Kursad K)

Sat, 04 Feb 2012 03:11:02 -0500

Btw my amplitube-like toy has a new reverb which seem to sound nice through headphones [link] that shows what would be possible on these units if they had good audio interfaces and no power supply noise.

RE: mini pc's (by Kursad K)

Sat, 04 Feb 2012 02:27:26 -0500

On 02/04/2012 @ 01:58, markie83 wrote : for around the house I think a guy could pull it off but trusting it in a gig is a whole other ball came. : : I am the computer goober at work and I will tell you if you are going to run a full fledged OS on this thing you will need a real keyboard mouse etc because something always comes up and flying blind is not a place you want to be in a gig. : : now can it be done properly? I think it could but the only way I would trust it would be with a custom rolled OS to fit the need....I would probobly use linux setup in a bare-bones setup like they do on routers and other embeded equip but with all the audio stuff preconfigured and your effects program set to run on bootup....then comed interfacing with the effects program, not to mention being able to switch through and costomize multi-effects etc. : : the big problem is you are going to have to spend TONS of hours getting the software to do what you want...and for me anyway programming at that skill level is beyond me. : : what you need to ask yourself is what sounds are you going for and what your budget is. I would also guess you are probobly going to dump way more cash in this than you think. Those mini-itx boards always temp me because the mboard+cpu combos are usually cheap but if you need a mini touchscreen monitor or other accessories your going to wake up $400-$500 into this thing by the time you are done. I have not priced a pod/modeler so I couldnt tell you what they cost off the top of my head but I bet you could still get alot of effects for $300 (which is probobly the extreme minimum I see this project costing). : : Personally I have been buying the Behrenger pedals and have been real pleased with them all (especially the wah)...at around $30 ea $200 bucks would get you 5 or 6 pedals....no muss no fuss and you have more effects than you can use at one time and not sound like a spaceship. : : just my .02 --

Well, I dont really consider it reliable enough for gigging. In any case I cannot play good enough to gig, and I do already have a pod and an expression pedal that I can connect to amplitube, so that's just hobby. Everything I'm trying to build already exist in some cheap to buy form. So mini itx just seemed to be a nice toy to play with. Just that. The toy is nice, but its power demand is not. Kursad

RE: mini pc's (by markie83)

Sat, 04 Feb 2012 01:58:25 -0500

for around the house I think a guy could pull it off but trusting it in a gig is a whole other ball came. I am the computer goober at work and I will tell you if you are going to run a full fledged OS on this thing you will need a real keyboard mouse etc because something always comes up and flying blind is not a place you want to be in a gig. now can it be done properly? I think it could but the only way I would trust it would be with a custom rolled OS to fit the need....I would probobly use linux setup in a bare-bones setup like they do on routers and other embeded equip but with all the audio stuff preconfigured and your effects program set to run on bootup....then comed interfacing with the effects program, not to mention being able to switch through and costomize multi-effects etc. the big problem is you are going to have to spend TONS of hours getting the software to do what you want...and for me anyway programming at that skill level is beyond me. what you need to ask yourself is what sounds are you going for and what your budget is. I would also guess you are probobly going to dump way more cash in this than you think. Those mini-itx boards always temp me because the mboard+cpu combos are usually cheap but if you need a mini touchscreen monitor or other accessories your going to wake up $400-$500 into this thing by the time you are done. I have not priced a pod/modeler so I couldnt tell you what they cost off the top of my head but I bet you could still get alot of effects for $300 (which is probobly the extreme minimum I see this project costing). Personally I have been buying the Behrenger pedals and have been real pleased with them all (especially the wah)...at around $30 ea $200 bucks would get you 5 or 6 pedals....no muss no fuss and you have more effects than you can use at one time and not sound like a spaceship. just my .02

RE: Stereo Preamp(by Kursad K)

Sat, 04 Feb 2012 01:36:15 -0500

On 02/03/2012 @ 02:11, Kursad K wrote :

On 02/02/2012 @ 22:02, BSharp wrote : : Everyone seems to have missed the concept. I'm not trying to engineer a digital effects unit, I would use an off the shelf box like a DigiTech for that. : : : : I'm wanting to build a stereo preamp with an effects loop that then drives either a tube power amp or my existing Trace Elliot stereo power amp. : : : : So basically: Stereo input switchable to mono input that bridges both inputs, something that allows for drive, tone controls, prescence, into an effects loop, with a master volume at some point. This then either plugs direct into a power amp Oor the effects. : : : : Second separate idea. Recently I've started theorizing an all tube guitar amp with an output low enough to drive a power amp. How would you get the power amp saturation and harmonics with say for example, a 12AU7 as the power tube output. Obviously this is not meant to drive a speaker cabinet. : : : : Okay so it's just a very low output version of an amp that drives a power amp so the output would be like 1 volt. : -- : :

: : Saying "I want to build a digital effects style tube preamp with stereo outputs" imply that you want to build the whole thing. It doesn't really sound so strange because it's possible after all, just not easy. : : So if you want to build a preamp with an effect loop, or perhaps with a stereo effect loop, that's easier. If it's not an high gain one, it's even better (from building ease perspectve:-) ) : : Kursad : : : --

It looks feasible if the hardware is a pc [link] but there are a few issues to be solved... Kursad

RE: mini pc's (by Kursad K)

Sat, 04 Feb 2012 01:20:04 -0500

On 02/04/2012 @ 01:15, Kursad K wrote : : #1 is bad enough:) perhaps can be solved by using a dc-to-dc converter. I dont know how much doese they make.

The sentence above should rather be "I dont know how much noise they make" Kursad

RE: mini pc's (by Kursad K)

Sat, 04 Feb 2012 01:15:02 -0500

On 02/03/2012 @ 23:13, markie83 wrote : ok I dont mean to be a debbie-downer...If you really want to try this give it a shot but what I see as a problem is: : : #1 pc power supplies make more emi noise than Rosanne Barr with a microphone....I cant even listen to AM radio with a computer going in the same room alot of the time. : #2 keyboard mouse & moniter...you will need to put them somewhere. : #3 you will need a really good sound card with full duplex : #4 getting the software and hardware to work together without latency is a total b**** (realtime kernels, jack audio interface, etc) : #5 the signal processor software itself...there are some free ones out there but I have not played with them much. : : for my money I would just get a pod or something similar...however if you really want to try this I would set it up on a computer you already have and see if you can get it going before you start buying gear. : : ....good luck : --

#1 is bad enough:) perhaps can be solved by using a dc-to-dc converter. I dont know how much doese they make. #2 can be replaced by a few pedals attached to the parallel port, maybe an expression pedal can be attached too using some a/d converter to make things like wah wah. That's not a simple circuit though. [link] #3 is a problem #4 probably can be solved on a specific -lucky- board, but not all. #5 some effects are not too difficult, these are delays, chorus and reverb. I've done all of these but probably not the best of them. some simple distortions can also be done without claiming it models this or that amp. So that's it. Some of these mini pc's can be real cheap, but they are power hungry, come without decent audio, and if the power supply is also noisy, then.. "good luck" is a good response. Kursad

RE: Changed to 6N7 vs 6SN7(by Henry Ramsey)

Sat, 04 Feb 2012 01:05:30 -0500

I changed to what should be the stock 6N7 configuration per the original schematic. I still have an imbalance w/ large signals. I put my finger on the instrument channel jack and the first section gets 65VAC and the paraphase gets only 35VAC. BUT, I'll see if I can live with it. I now need to go back to working on the tone controls. I'm considering switching that stage to cathode follower and converting the tone controls to a normal treble/bass setup.