Now I am hooked :'( I couldn't get enough after Marsha so I decided to make another one. What is it?
This is a preamp modeled after the famous Vox AC-30 top boost. In addition to the 12ax7 input, second stage and cathode follower I have included a switch to bypass all of that and switch in an EF86 pentode input stage. These both go into a phase inverter "approximation" which is the same as the Marsha pre-amp; it is simply a Fender triode gain stage with 22nf coupling caps. The style of wiring is tagboard and PTP. This uses a Weber cap can for filtering and I went with bridge rectifiers to save a little space. This runs off of a Weber 12VAC to 260VAC step up transformer and ends up with about 380VDC under load. Unfortunately I had to run two regulators to run the EF86 and 12ax7 filaments (I was a little close to the max current of a single and the EF86 runs on 6.3 volts only anyways). This is all wired into an anodized red Hammond 1590DD.
How does it sound? Well the top boost stage has a bad connection somewhere so it is a little fizzy and needs one more run through. Easy fix. But the EF86 stage is awesome. Just crazy cool sounding. I never realized how much the EF86 would be so compressed in a good way. It gets squishy and fuzzy gritty sounding with enough drive. Just on the edge of breakup is the best sound. It makes my roland cube test amp sound incredible. Demos this weekend when I get the TB stage fixed. The PI approx. is running a JJ ecc803 which I never really liked that much so it may change to an ecc83 later.
Between this and the Marsha I am set for awesome pre-amps. These will both eventually run into my 5F2A Princeton clone to bypass the Fender preamp and go directly into the 6V6 stage. I can't wait!
(http://i693.photobucket.com/albums/vv299/pnordeen/20120926_205049.jpg)
(http://i693.photobucket.com/albums/vv299/pnordeen/20120926_205020.jpg)
That's bitchin! :o ;D
Duuuuuddde. Unbelievable. I want to hear it!!!
very sweet build.
what are you using the regulators for exactly?
This is sick! Awesome job ;)
OMG. (I said 'F yeah' out loud...) Scuse me but thats friggin awesome! Nice PTP action Paul... love a demo when you're done tweakerising... Boom! 8)
Thanks guys. Demos this weekend when I get a chance. I went through the TB channel with a fine tooth comb and can't find anything totally obvious ??? Ill have to start doing component checks.
Misha, the regulators are for the tube filaments. I could probably run the 12ax7 filaments on 12VAC without the center tap but I don't want tons of high current AC lines running all over the place. The other regulator is tuned under load (LM317) to 6.3 volts to run the EF86. Those suckers get hot too, I hope they last...
Oh and thanks to Timbo BTW for suggesting this project. You were dead on about the EF86 sounding killer!
Nice build! I love all those big caps and resistors.
C
:o
Really cool dude.
I am super impressed that it is all point-to-point/tagboard as well!
Nice build! I love all those big caps and resistors.
Agreed; especially because they are actually necessary, and aren't just shoehorned in to add to the 'mojo' factor ;).
Oh man I want to hear this. That's a LOT of stuff crammed into such a small "head." Hope the top boost circuit gets better. :)
Thanks! I actually did a layout before hand, rather than just wing it like I did the Marsha. It turned out a little nicer this time around.
The top boost works up to about halfway on the gain knob then something weird happens and it gets kind of fizzed out. What I have hear of it though it is super bright; I thought that 500pf cap was a little small and holy smokes it is ear piercing! I may swap the 500 out for 22nf if I can't hang with the shrill. Anyone have a real AC-30 to confirm I am not crazy?
That looks terrific!! Love it! Great fawking job Sir!! :o 8)
And his that a 1590DD(Tall)? if yes, where did you source it? Would be perfect for my Firefly project! ;D
Quote from: GrindCustoms on September 27, 2012, 02:57:52 PM
That looks terrific!! Love it! Great fawking job Sir!! :o 8)
And his that a 1590DD(Tall)? if yes, where did you source it? Would be perfect for my Firefly project! ;D
It is the tall 1590DD. I got this one from pedal parts plus. It was 17 bucks before powder :o but Ive seen it elsewhere for more. Is the firefly the one that uses a single ended 12AU7 as a power tube?
I haven't heard it yet and I already want it.
Quote from: JakeFuzz on September 27, 2012, 03:02:32 PM
Quote from: GrindCustoms on September 27, 2012, 02:57:52 PM
That looks terrific!! Love it! Great fawking job Sir!! :o 8)
And his that a 1590DD(Tall)? if yes, where did you source it? Would be perfect for my Firefly project! ;D
It is the tall 1590DD. I got this one from pedal parts plus. It was 17 bucks before powder :o but Ive seen it elsewhere for more. Is the firefly the one that uses a single ended 12AU7 as a power tube?
Thanks for the info! I may choose a fancy color it makes a really long time that i did'nt bought a painted enclosure.
Yup, it's that amp, my first amp project :)
Dude this is sick!
Did you consider running it off a SMPS (nixie-style) power supply to avoid the transformer?
Or is there an advantage to the transformer?
Very impressive job! ;D
Quote from: GrindCustoms on September 28, 2012, 04:03:06 AM
Thanks for the info! I may choose a fancy color it makes a really long time that i did'nt bought a painted enclosure.
Yup, it's that amp, my first amp project :)
Yeah I've seen that amp kit. It actually uses one 12au7 as a self split kind of deal so it does run in push pull. That has about 1 watt output right? Man that is cool, let us know how it sounds. I think one of the miniature vox night train heads was like that. I am also slowly putting together a deacy amp with an 8"; that should be an interesting one.
Quote from: MattOcaster on September 28, 2012, 11:42:27 AM
Did you consider running it off a SMPS (nixie-style) power supply to avoid the transformer?
Or is there an advantage to the transformer?
I've never seen those type of power supplies before. Is that MOSFET and 555 acting like a high voltage charge pump? That is a wild idea. I wonder if it can get up to around 350 volts. It can deliver enough current too. Ill have to look into this in the future. Thanks!
Yep, it'll get up to 350V - and without a bulky transformer!
Im actually working on a Bassman preamp with a SMPS psu.
All on breadboard at the moment but it works!
There have been other DIY designs using the SMPS, like the Frequency Central "Superfly" amp and the Analog Sound "GTFO" overdrive. I used the GTFO power section for my project.
Check it out :)
Quote from: MattOcaster on September 28, 2012, 05:17:37 PM
Yep, it'll get up to 350V - and without a bulky transformer!
Im actually working on a Bassman preamp with a SMPS psu.
All on breadboard at the moment but it works!
There have been other DIY designs using the SMPS, like the Frequency Central "Superfly" amp and the Analog Sound "GTFO" overdrive. I used the GTFO power section for my project.
Check it out :)
That is ridiculously cool. I see how it works now, very much like a high voltage charge pump. The Weber tranny isn't too bad as far as cost ($20) but I agree it is a pain to lug all that weight around.
Quote from: MattOcaster on September 28, 2012, 05:17:37 PM
Yep, it'll get up to 350V - and without a bulky transformer!
Im actually working on a Bassman preamp with a SMPS psu.
All on breadboard at the moment but it works!
There have been other DIY designs using the SMPS, like the Frequency Central "Superfly" amp and the Analog Sound "GTFO" overdrive. I used the GTFO power section for my project.
Check it out :)
I've actually wanted to build an amp using the nixie SMPS, but I heard it may cause hum, so I rejected the idea. I may try it myself to see if I have any issues.. But please, keep us posted on your project! ;)
SMPS is generally not recommended for amplification... particularly high gain. A world of transients and ripple awaits you... which translates to whistles, whines and other intermittent weirdness. Linear transformer based is the way to go.
Quote from: JakeFuzz on September 28, 2012, 12:50:19 PM
Quote from: GrindCustoms on September 28, 2012, 04:03:06 AM
Thanks for the info! I may choose a fancy color it makes a really long time that i did'nt bought a painted enclosure.
Yup, it's that amp, my first amp project :)
Yeah I've seen that amp kit. It actually uses one 12au7 as a self split kind of deal so it does run in push pull. That has about 1 watt output right? Man that is cool, let us know how it sounds. I think one of the miniature vox night train heads was like that. I am also slowly putting together a deacy amp with an 8"; that should be an interesting one.
I was on PPP site yesterday night and none of the DD sized enclosure listed where in the «Tall» sizing.......i may be stupid or just not getting it..........
And yes it's a 1watt amp, also have a 8inch speaker on his way for a little cab for this amp, really excited about this project.
Quote from: JakeFuzz on September 27, 2012, 06:14:41 AM
Thanks guys. Demos this weekend when I get a chance. I went through the TB channel with a fine tooth comb and can't find anything totally obvious ??? Ill have to start doing component checks.
Misha, the regulators are for the tube filaments. I could probably run the 12ax7 filaments on 12VAC without the center tap but I don't want tons of high current AC lines running all over the place. The other regulator is tuned under load (LM317) to 6.3 volts to run the EF86. Those suckers get hot too, I hope they last...
Oh and thanks to Timbo BTW for suggesting this project. You were dead on about the EF86 sounding killer!
Man Paul, sheesh. You get the credit for this one, it is SO STINKING NEAT! Really good work here.
Quote from: nzCdog on September 28, 2012, 09:36:41 PM
SMPS is generally not recommended for amplification... particularly high gain. A world of transients and ripple awaits you... which translates to whistles, whines and other intermittent weirdness. Linear transformer based is the way to go.
off topic but...
peavey actually released a 300 watt bass amp with a switching power supply called the VB-3. it runs 8 x el34's and 5 preamp tubes. http://www.peavey.com/products/index.cfm/series/813/Pro%E2%84%A2%20Series (http://www.peavey.com/products/index.cfm/series/813/Pro%E2%84%A2%20Series)
SMPS are possible for audio, but they need to be purpose built, primarily the switching frequency needs to be well above the audio range, and they need to be well regulated.
I'm fairly certain this is a switched power supply.
http://milbert.com/gaga
Quote from: stecykmi on September 30, 2012, 03:32:20 PM
off topic but...
peavey actually released a 300 watt bass amp with a switching power supply called the VB-3. it runs 8 x el34's and 5 preamp tubes. http://www.peavey.com/products/index.cfm/series/813/Pro%E2%84%A2%20Series (http://www.peavey.com/products/index.cfm/series/813/Pro%E2%84%A2%20Series)
That looks pretty cool :)
QuoteSMPS are possible for audio, but they need to be purpose built, primarily the switching frequency needs to be well above the audio range, and they need to be well regulated.]SMPS are possible for audio, but they need to be purpose built, primarily the switching frequency needs to be well above the audio range, and they need to be well regulated.
Fair comment Misha... In theory its got to be possible, its just my experience in the lab at school with switched mode means I wouldn't recommend it at all... even my TC Nova Delay SMPS wall wart gives intermittent noises... :(
I love this build.
The outside looks great, but the wiring is particularly cool.
Thanks!
Just a little update. I finally got some time to do some basic checks on the TB channel and I still cannot find whats wrong. All voltages and current draws are normal. Component values have been triple checked. The issue is that as I turn the gain knob past about 12 it goes into a fizzy crackling mode, where the fizz sits in the back of a low volume clean signal all the way up to maximum on the gain. Audio probing tells me that directly off of the plate of the first tube I am getting this issue which means it can only be from a weird ground connection with the V1 cathode and the gain pot or there is some kind of strange output impedance problem with V1 as I turn up the gain. I have disconnected V1 from the circuit and will probe it like this next. Could it be that I used a 1.5K cathode resistor instead of around 3K because the real Vox is a shared cathode/twin triode setup? It sure doesn't seem like it but it is the only thing I can see that is different at this point. ???, another strange thing I was seeing is that as I increase the gain up to maximum the current draw into the cathode follower increases and the plate current into V1B decreases...
Is it possible that the problem is with V1 and not with the circuitry Paul?
Jacob
Quote from: jkokura on October 01, 2012, 01:35:06 AM
Is it possible that the problem is with V1 and not with the circuitry Paul?
Jacob
Yep I thought that too. I swapped V1 with a few different tubes and I still get the same results.
Mind. Blown. Amazing work. Just amazing.
I see in my crystal ball a rack of hot-pluggable preamps with a microcontroller switching scheme. It's only a matter of time ... ;)
I don't know if you've been there, but the Hoffman amp forum (http://www.el34world.com/Forum/index.php) is loaded with tube gurus. I have no doubt they'd be able to help you out.
Quote from: JakeFuzz on October 01, 2012, 01:40:38 AM
Quote from: jkokura on October 01, 2012, 01:35:06 AM
Is it possible that the problem is with V1 and not with the circuitry Paul?
Jacob
Yep I thought that too. I swapped V1 with a few different tubes and I still get the same results.
Worth a try suggesting. Hmm... I'm not an amp guru, but my gut says that your though about the wrong plate resistor might hold true. Is it also possible you're using a bad resistor in there somewhere, one that's introducing the noise?
Jacob
^sounds likely to me as well, when I was messing with the preamp on my Supro V1 and V2 have a shared cathode and it did not like my experimenting there at all! V1 is preamp, and V2 is Tremolo in that amp. I'd try to see if increasing the 1k5 cathode resistor helps. You have a schematic I can look at?
Thanks guys! I think I will try a 2.7K in there tomorrow if I get a chance. It has got to be something simple like this. That is definitely a possibility Jacob about the noisy resistor, Ive gone through and checked almost all of the values that would be suspect. Man it would be tough to find if it were an intermittent thing. I've pumped myself up watching AC-30 videos on youtube! I've rewired the ground for the first stage and increased the plate voltages into most of the pre-amp (V1s were sitting around 120 at the plate which is a little low but it is 220K so...). We'll see if one of these works over the next few days, then demos I promise :D
Paul, it is probably well worth chopsticking all around in there if you haven't yet. Intermittent stuff usually reacts fairly noticeably to the chopstick tap-tap-push-push-tap. Did I mention how neat this project is yet? Serious.
Looks really cool!!!! I hope you get this figured out soon.
-Dan
Okay I think I've got this figured out. What I was hearing from the TB channel was a very low volume clean signal with some interference riding along. I adding grid stoppers on V1B (56K) and a large one on the PI approximation (100K); this killed all weird fizziness I was getting. I still had extremely low volume though and barely any drive at full tilt. Checking out single channel schematics, most people omit the 220K ground reference which acts as a voltage divider right before the PI. This 220K/220K divider acts as a blend between the bright and normal channels. I typically don't omit these because they reference ground when the opposite channel volume is all the way down. I am positive this will allow me to drive the last triode stage much harder if I remove it; Ill try it when I get home. It is also a little concerning that the pre-amp was producing such little drive up to this point though. I've been seeing mixed schematics on the web whether or not people put a 25uF cathode bypass cap on the second stage triode. This will definitely increase the gain and I think it is worth a shot.
I am also going to re-design the PI approximation. I have been able to match the frequency response of a real PI by going through some basic calcs. It is really just changing the values of the coupling caps around to get the same bass cut response in and out of that last stage. I can't match the gain of the real PI though without adding a huge voltage divider between the tonestack and this last stage. I think we go down by about 6-8dB from a standard triode stage to a LTPI! I am going to test values of the grid resistor feeding into that last triode stage with a pot to see what sounds best.
[soundcloud]http://soundcloud.com/jakefuzz/ac30[/soundcloud]
I've still got issues with the TB channel. To me it doesn't sound like it is saturating anywhere near the amount it should be. EF86 channel still sounds great. A little bit of the fizzies that will probably come out will slightly larger input grid stoppers. Another demo when the TB channel is working properly.
Played with a strat with CS'69 pickups into a clean TRRI with no reverb on. The rangemaster is a CV7112 Ge version.