DD15 - a tube guitar amplifier
Builder: Pekka Lehtonen
Started: 01.05.2005, last update: 01.07.2006
My long planned tube amp project has finally reached production. After months of planning and comparing I decided to build a slightly modified clone of 0rang3 AD15. Later the amp turned into something a bit different with more preamp gain and negative feedback. This page describes the course of this project. Page is updated every now and then.
Summary
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Testing the amp for the first time. |
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The almost finished amp. |
- Two 12AX7 pre amp tubes
- 12AX7 phase inverter
- Two EL84 power tubes (Push-Pull, cathode bias)
- 5AR4 rectifier tube
- Hammond 125E output transformer
- UralTone power transformer
- Two channels: "crunch" and "more crunch"
- Foot-switchable gain stage w/ separate Gain and Master vol
- Classic / Moders switch for "more crunch" channel
- Gain 1, Gain 2, Middle, Treble, Master 1 and Master 2 controls
- Point-to-point costruction
- Ideas taken from: 0rang3 AD15, JCM800, ODS, SLO, AX84 projects etc...
The Schematic
Current version. This has been the longest lasting revision so far. See notes for more info.
Olders versions:
- 17.04.2006 See notes.
- 26.2.2006
- 13.1.2006 (the R22 was 22k and R20 and R21 were 330ohm)
- 1.1.2006
- Third version
- Second version
- First version
The Beginning
On 24th of april I ordered all the required parts from Uraltone. Well, allmost all anyway. These included a Hammond 125E output transformer, Uraltone TV4 power transformer, two EH 12ax7, two EH el84, a 5AR4 rectifier tube, load of resistors, OrangeDrop capacitors, some Alpha pots and Fulltone knobs. And of course a Hammond steel chassis. See the picture of first "setup".
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Transformers and tube sockets installed |
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Pots and knobs fitted. Lookin good so far. |
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Wiring of the first tube. |
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Tone stack. |
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Phase inverter. |
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Tubes fitted. |
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The second preamp tube Gain stages 3 and 4. |
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Wiring complete. This is the current state of the amp. |
Chassis
I decided to built my amp on terminal strips. A tr00 point-to-point aparatus. And why? Well, not because p-to-p "sounds better" or because it's "the only way (tm)" but bacause I'm too lazy to design a decent tag board layout. After some planning the chassis was drilled on 3.5.2005. Rectangular holes for power switch and AC-jack were "milled" with the good old Dremel. Two holes and two worn out cutter blades...
The drilling went well. It's allways nice to work with good tools. Thank you Jammi! But of course two pots had a bigger bolt than the others so two of the holes are too small. The picture shows the chassis assebled with tube sockets and transformers. I hope my so called layout works.
Wiring
As mentioned, the wiring is done point-to-point. The first stage is now done and it's looking pretty good. But unfortunately it seems that the rest of the circuit won't look as good when finished. Those OrangeDrops were a lot bigger than I thought.
(6. may 2005, 21:34) PI and tone stack allmost done. Not looking too nice any more. Maybe next time I'll take the time to design the layout before building.
Wiring now allmost complete (8. may). Not pretty but seems ok. No ground loops and relatively short wires.
The First Glow
Looks so nice... link
Testing
Wiring was completed on 12th. may. Signal path is nice and short but the wires from PSU to the circuit could be shorter (see the red wires on the picture). PSU capasitors were mounted to the chassis with hot glue. It's not pretty but it works. After some "burn in" I'm planning to modify the PSU and make the voltage to the poweramp adjustable to get that sweet power tube distortion at low volumes.
The amp was tested in steps. First the heaters were checked. Nice glow. Then the PSU was tested with the rest of the amp NOT connected. Voltages got to about 400 volts with no load. Next the first 12ax7 was wired and plugged in. It biased correctly. Next the phase inverter. Voltages were sensible.
The poweramp and OT was then wired and the amp plugged in to a Marshall 2x12 cab. It took a little courage to turn the amp on for the first time but it was well worth it! The amp worked on the first go! Clean sounds were just great! After adding a 2.2uF capacitor to the cathode of the first pre amp stage, the available distortion range improved and the amp produced some great rock tones! Overall the amp had a bit too much top end and the distortion was a bit too bright to my taste.
Biasing
The amp biased nicely with the 270 ohm cathoder resistor. Voltage over the resistor was 17,47 volts. This with 375 volt anode gives plate dissipation of 12 watts per tube. A bit too hot maybe, but not nearly as hot as those old Vox amps. Voltage on preamp anode was 259 volts.
Some noise could be heard when the gain was at higher settings but hey, it's a tube amp it's suppose to hiss a bit. Right? I was surprised to notice that the humm from the PSU was noticable only with the master volume way past middle.
The sound
As mentioned, the clean sounds were just great! The amp had more dynamics than anything I've ever played (read: transistor amps...)! Mild overdrive was also great. Specially with signle coil neck pick-up. Nice chimey sound.
At higher gain settins the sound was maybe a bit harsh (is that a word??). Maybe too much top end. Great rock sound anyway. The bright character might actually be a feature of the EH tubes or the Hammond OT. I'll try to fix this by adding a Tranwreck style filter in paraller with the OT. We'll see...
Tweaks and mods
(18.05.2005) In order to get just a little bit more distortion and compression out of the amp I dropped the voltage of the second gain stage to about 200V. This was done with a 50k resitor in seriaes with the voltage line and a 10uF capasitor in paraller. I think this did the trick. The amp is still no "high-gain" but it wasn't even supposed to be. It gives great rock sound with good attitude. When boosted with the Särödägä the harmonics really come out and the sustain is pretty much endles. Great amp (in my opinion..)!
(01.06.2005) I dumped the idea of the output filter and added an adjustable negative feedback to the poweramp. This made lower frequencies a lot tighter and somehow the previously ineffective tone stack became much more alive. The amount of feedback can be adjusted with a potentiometer. This allows easy adjustment beetween "tight" and "loose" sounds.
(18.07.2005) The modification continues. I added a preamp tube to get a bit more gain from the amp. The preamp now looks more like the ones at www.ax84.com. This again did the trick. Smoother and more compressed lead sounds and great rock rhytm tone. The adjustable negative feeback was changed to a fixed one and master volume was moved in front of the PI.
Done, done and I'm on to the next one...
After playing a while with the amp I'm fairly convinced that it is finally ready. And actually I'm afraid to do any mods to it because it may chage the sound...
(01.11.2005) Chaged the cathode follower to an amplifier stage and removed the cathode cap from second stage. Seemed like a good move. More gain, better lead sounds.
(13.01.2005) Modified the PSU and the preamp. It's pretty close to SLO100 now. What can I say, Mr Soldano knew what he was doing when he designed the SLO. Also modified the PI a little. Changed the first tail resistor from 10k to 33k. I quess it's better now... Not really sure since I could not hear the difference at least no at low volumes.
Also notice the new clip. Some random playing with various amp settings. Recoded with SM57. No post recording EQ or effects.
(26.02.2006) After the "S0ldan0" mod I've had a lot of prblems with "buzz" and farting distortion. Nothing seemed to help so the "clipper stage" had to go and it's all "High-Octane" now. First test are convising. I hope this is it.
(17.04.2006) Seems I just cant let this go. I've done small tweking here and there and the amp is slowly taking it's shape. It now gives nice rock sounds and chrunch on it's own and when boosted with a pedal it turns into a real monster.
I also did some major simulations for the power amp with PSPICE and tuned the PI so that grid conduction is minimal. PI now breaks up at around 20Vpp. It is fed to the poweramp through 100k & 100k voltage divider. It is still enough to drive the EL84's into distortion but does not cause too much grid conduction. After a short test I noticed that it actually helped and some of the "fizzynes" in the power amp distortion had vanished.
(01.07.2006) Some major modifications were done to the power amp a couple of months back. For some reason I forgot to update this page. I quess I was too busy playing with the amp. I changed the power amp to fixed bias and did a little tuning in the preamp. Now I have bee really happy with the amp and have felt no need to tune it further. But...
...now I'm kind of longing for the bass controll I removed couple of revisions back. Actually I would like to be able to cut the bass before it even gets to the amp. My "new" Epiphone DOT has really bassy mics and the sound is not as good as it is with my Jackson Dinky HX. However using the SäröDägä in front of the amp with tone allmost maxed the DOT sound like heaven. Maybe I'll stick with this or maybe I'll buy an EQ pedal so I could tune the response to be just the way I want.
Before I didn't feel that tone controls were needed at the early preamp stages but now I must say that at least the bass controll should be right after the first stage. Or even before. Maybe I'll test with the bass controll used in the AX84 Melissa amp.
Sound samples
Finally. Samples are recorded with the following setup: Jackson Dinky HX (-> RAT) -> DD15 -> Marshall VS 2x12" -> AKG D880 mic -> Berhinger UB802 -> SB audigy 2 -> Kristal. This was the first time I've ever "really" recorded anything. Remember that when listening... And listen to the amp not the player ;) The samples were recorded when the amp had a two stage preamp instead of the current four stage preamp setup.
- Santeria - Clean
- Inside - Crunch
- RokRok - Almost full distortion
- Heavy - Boosted w/ modified RAT (and yes, harmonics were a bit rusty today...)
- Random - Painfully long and badly played clip of the latest version of the amp (13.01.2006)
- Random w/ added hights - The same clip as before but with a bit post recording treble added (13.01.2006)
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