Hi Shanx, thanks, I'm glad you think it looks good! I haven't measured the power output yet. I'm currently running it from a bench power supply which only goes up to 30V.
The clipping and distortion problems now seem to have gone entirely. I had it wired up in a pretty messy way with crocodile clips etc. I've now neatened up the wiring and have the grounds hooked up properly to a star point. This seems to have sorted it all out. I'm still getting a bit of odd behaviour on clipping into an 8ohm dummy load but I noticed that it's hitting the current limiter on the bench power supply so I suspect this is the problem. When reducing the supply voltage so the current demand is within the power supply's range, it no longer has the problem.
I'm going to order a transformer soon. I'm looking at 25-0-25 160VA toroidal. Does this sound right?
I wired up a simple preamp today with a basic diode clipping circuit, gain control and variable low-pass 'cut' control. It's not the proper pre-amp design and it's still got the Tayden Retro 55 instead of the Celestion but I think it sounds quite good. Here's a demo:
Amplifier first test - YouTube
The clipping and distortion problems now seem to have gone entirely. I had it wired up in a pretty messy way with crocodile clips etc. I've now neatened up the wiring and have the grounds hooked up properly to a star point. This seems to have sorted it all out. I'm still getting a bit of odd behaviour on clipping into an 8ohm dummy load but I noticed that it's hitting the current limiter on the bench power supply so I suspect this is the problem. When reducing the supply voltage so the current demand is within the power supply's range, it no longer has the problem.
I'm going to order a transformer soon. I'm looking at 25-0-25 160VA toroidal. Does this sound right?
I wired up a simple preamp today with a basic diode clipping circuit, gain control and variable low-pass 'cut' control. It's not the proper pre-amp design and it's still got the Tayden Retro 55 instead of the Celestion but I think it sounds quite good. Here's a demo:
Amplifier first test - YouTube
Good to hear you have that power amp clipping sorted. Had a listen to the video and indeed it sounds very good. Full sound, not tinny or fizzy at all (even playing through desktop speakers here). That's the thing about a lot of solid state amps , and even valve amps..if they don't use a high quality guitar amp speaker, the blame goes to the whole amp. That being said, the preamp is going to be doing the "heavy lifting" when it comes to the feel and tone. I like the simple type circuits for that, even if it isn't a "proper" preamp design you have on it per se, it sounds "honest".. sometimes I think that commercial amp designers focus too much on the bells and whistles features that can detract from the core sound and response. 160 VA should do, but I would double check your amp max current draw and leave some safety margin, say 25%.. Cheers!
Hi,
I've been working on the preamp for a while now and I've attached what I've got so far. It's got a normal channel and a top-boost channel. Asymmetric clipping occurs first, after the EQ on the top-boost, and pre-eq symmetrical clipping cuts in later. The normal channel is only affected by the asymmetric clipping. The inverting amplifier at the end with the 'cut' control will also serve to sum the reverb signal into the output.
I'm really pleased with the sound so far, it's very AC30-like. The normal channel is pretty muddy at low volume but sounds great when turned up a bit, especially on the strat bridge pickup. The 'treble bleed' capacitor on the normal volume control will be switchable on the final build.
I've got the Celestion gold coming in the next few days, along with the reverb tank, so I'll be able to adjust the sound more to fit the speaker.
Any suggestions would be greatly welcomed!
Thanks,
James
I've been working on the preamp for a while now and I've attached what I've got so far. It's got a normal channel and a top-boost channel. Asymmetric clipping occurs first, after the EQ on the top-boost, and pre-eq symmetrical clipping cuts in later. The normal channel is only affected by the asymmetric clipping. The inverting amplifier at the end with the 'cut' control will also serve to sum the reverb signal into the output.
I'm really pleased with the sound so far, it's very AC30-like. The normal channel is pretty muddy at low volume but sounds great when turned up a bit, especially on the strat bridge pickup. The 'treble bleed' capacitor on the normal volume control will be switchable on the final build.
I've got the Celestion gold coming in the next few days, along with the reverb tank, so I'll be able to adjust the sound more to fit the speaker.
Any suggestions would be greatly welcomed!
Thanks,
James
Attachments
Hi,
Yep, R10 should join R11, I've just connected the wire wrong on the schematic. I'll play around with the value of C11 but I think I'm going to leave the normal channel as-is. From what I've read, the normal channel on the real AC30 is pretty muddy. I suppose I could brighten it up but then it would lose the sounds you get when you turn it up and use the bridge pickup. So I think it's best to leave it as-is and have the top boost channel for bright channel.
Thanks,
James
Yep, R10 should join R11, I've just connected the wire wrong on the schematic. I'll play around with the value of C11 but I think I'm going to leave the normal channel as-is. From what I've read, the normal channel on the real AC30 is pretty muddy. I suppose I could brighten it up but then it would lose the sounds you get when you turn it up and use the bridge pickup. So I think it's best to leave it as-is and have the top boost channel for bright channel.
Thanks,
James
Hi James
Yes I have heard the Normal channel AC30 and indeed it's a darker voice at lower volumes..which may not be what most people associate to that amp..the expectation that it sounds jangly would be more the Top Boost side, or going into the Normal channel with a treble booster. So more true to it's original form leaving it as is.
Cheers!
Yes I have heard the Normal channel AC30 and indeed it's a darker voice at lower volumes..which may not be what most people associate to that amp..the expectation that it sounds jangly would be more the Top Boost side, or going into the Normal channel with a treble booster. So more true to it's original form leaving it as is.
Cheers!
I haven't had a chance to turn it up loud but it seems pretty loud. One thing I'm thinking about is the speaker's power handling. the Celestion gold can handle 50W RMS according to the spec but the amplifier on 25V rails can put out about 70W. The clipping stage limits the clean power to around 30W but when driven into distortion, it exceeds this considerably. I could attenuate the output but then I'd reduce the clean output too, which I don't want to do. I suppose I could add another hard clipping stage after the master volume to limit the power to 50W. I always hear that valve guitar amps are putting out significantly more power than their rated power when driven into distortion but I don't know how much. I also wonder if it might not be a problem as I just won't turn it up loud enough to blow the speaker.
The second problem is that, with the master on full, there's a fair bit of hiss on the output. I reduced it considerably by increasing the gain of the input stage, using LEDs to increase the clipping threshold, then reducing the gain of the post-summing clipping stage. Any ideas?
Thanks,
James
The second problem is that, with the master on full, there's a fair bit of hiss on the output. I reduced it considerably by increasing the gain of the input stage, using LEDs to increase the clipping threshold, then reducing the gain of the post-summing clipping stage. Any ideas?
Thanks,
James
Are the input jacks shorted to ground when unplugged? I assume most of the hiss will be on the Top Boost side, maybe reducing the signal before its mixed with the Normal channel will help limit the output wattage and lower the apparent noise floor of the boost circuit so it's less noticeable.
Hello, please fin an old website about a simulator of AC30. I use an archive site to access to an old snapshot of website because it doen't exist anymore.
VOX-AC30 Simulator
I have all the files in PDF in my PC so if something missing, tell me ;
VOX-AC30 Simulator
I have all the files in PDF in my PC so if something missing, tell me ;
Hi,
Thanks for the document. I remember seeing this a while ago. I've gone for a rather simpler design so perhaps not as accurate sounding as that one.
I've spent a long time fiddling with the circuit now and I'm pretty pleased with how it's sounding. I've got it all mounted on a wooden board with the PCBs, transformer and the preamp on a breadboard. I'm also using the Celestion Gold now. The updated schematic is attached. I'm still getting what I consider too much hiss on the clean sound. The master volume needs turning up a lot to get a clean sound and then there's too much hiss. I'm not sure what the best approach for solving this is. I'm also wondering if it needs a bit more bass. It's a bit thin sounding at the moment and doesn't sound as 'big' as I'd like it to.
Thanks,
James
I'm also
Thanks for the document. I remember seeing this a while ago. I've gone for a rather simpler design so perhaps not as accurate sounding as that one.
I've spent a long time fiddling with the circuit now and I'm pretty pleased with how it's sounding. I've got it all mounted on a wooden board with the PCBs, transformer and the preamp on a breadboard. I'm also using the Celestion Gold now. The updated schematic is attached. I'm still getting what I consider too much hiss on the clean sound. The master volume needs turning up a lot to get a clean sound and then there's too much hiss. I'm not sure what the best approach for solving this is. I'm also wondering if it needs a bit more bass. It's a bit thin sounding at the moment and doesn't sound as 'big' as I'd like it to.
Thanks,
James
I'm also
Attachments
That's a really a great job. Congratulations. Very interesting to see a such work. It remembers me the first effect pedals that, in my opinion, has been able to simulate Marshall, fender and Mesa Boogie amplifiers -> SansAmp GT2. Mine doesn't work anymore but I keep it carefully ... I should try to repair it one day 