I just bought this little amp for a very good price. The first impressions are very positive. It looks nice, it has a 12" speaker, the sound is decent and it's far louder than what is acceptable at home.
However...
It has a very audible hiss. It's irrelevant while playing, but if you leave it on while you do other things it gets annoying.
The guts are a bit disappointing. SMPS and a TDA7294 circuit on the same board. And both channels go through the DSP on the front side.
I am afraid it's one of those devices that are destined to end up in a landfill after 5-6 years (unless you repurpose it or something).
The nice thing is that the chassis is roomy with lots of space for custom stuff.
So the DIY/mod plans so far are
Any other suggestions?
However...
It has a very audible hiss. It's irrelevant while playing, but if you leave it on while you do other things it gets annoying.
The guts are a bit disappointing. SMPS and a TDA7294 circuit on the same board. And both channels go through the DSP on the front side.
I am afraid it's one of those devices that are destined to end up in a landfill after 5-6 years (unless you repurpose it or something).
The nice thing is that the chassis is roomy with lots of space for custom stuff.
So the DIY/mod plans so far are
- Add a 1/4 jack/plug so that I can reuse it as a cab
- Eventually change the speaker into something nicer
- Replace the SMPS with a nice lower V chunky transformer (and glass fuses), a normal and properly filtered bridge rectifier, and nice big CRC filters.
- Replace the 7x15 regulators with nicer ones with lower impedance and less noise.
- Replace the TDA7294 circuit with an LM1875 at 20W (or even less, I will have to coordinate the PSU first) and proper beefy capacitance
- Change the crappy plastic switches/buttons with nicer metal ones
- Add a buffered FX loop
- Prepare for replacement preamps or something for when the DSP goes to the big gig in the sky
Any other suggestions?
I know what you mean. But I already have better amps and the price was right for its useful parts.
I am doing this as a project to keep me busy for a while and hopefully get some nice reusable components/pcbs in the process
Small update
The 1/4 jack and plug are in place. The existing hole is already a good size, so no need for extra drilling. Just remember to use an insulated jack, otherwise, you will get a hell of a ground loop. I had only simple cheap ones, so I used some plumber's teflon tape to insulate it.
The amp works very nicely as a cab, although the speaker could use an upgrade.
About the hiss, the problem is probably that the amp has no master volume, which means that the output of the DSP is amplified at full dB at all times.
After checking the schematic, a good solution could be to replace R409 with a voltage divider or a pot as a master volume. This will push the hiss towards the noise floor, and as a bonus, it will make the volume range of the amp more home-friendly (my current absolute max is 3.5ish)
So updated list:
The 1/4 jack and plug are in place. The existing hole is already a good size, so no need for extra drilling. Just remember to use an insulated jack, otherwise, you will get a hell of a ground loop. I had only simple cheap ones, so I used some plumber's teflon tape to insulate it.
The amp works very nicely as a cab, although the speaker could use an upgrade.
About the hiss, the problem is probably that the amp has no master volume, which means that the output of the DSP is amplified at full dB at all times.
After checking the schematic, a good solution could be to replace R409 with a voltage divider or a pot as a master volume. This will push the hiss towards the noise floor, and as a bonus, it will make the volume range of the amp more home-friendly (my current absolute max is 3.5ish)
So updated list:
- [✔] Add a 1/4 jack/plug so that I can reuse it as a cab
- [✘] Replace R409 with a voltage divider or a pot as a master volume to push the hiss down and make the volume range more home-friendly
- [✘] Eventually change the speaker into something nicer
- [✘] Replace the SMPS with a nice lower V chunky transformer (and glass fuses), a normal and properly filtered bridge rectifier, and nice big CRC filters.
- [✘] Replace the 7x15 regulators with nicer ones with lower impedance and less noise.
- [✘] Replace the TDA7294 circuit with an LM1875 at 20W (or even less, I will have to coordinate the PSU first) and proper beefy capacitance
- [✘] Change the crappy plastic switches/buttons with nicer metal ones
- [✘] Add a buffered FX loop
- [✘] Prepare for replacement preamps or something for when the DSP goes to the big gig in the sky
I finally found some time to work on the amp a bit more.
I tracked down R409 on the main PCB. But after all, the entire thing is mostly SMD parts at the bottom side. Combined with the entire high voltage SMPS stuff, this is a bit more difficult and dangerous than what the average DIYer can or should do. Please remember that SMPSs can carry lethal voltages even when disconnected from mains.
So I won't bother with this after all. The hiss and lower volume will be covered by the FX loop where I usually add an EQ pedal.
If you do not care for the FX loop, a buffered 47K pot right at the cable coming from the front-end will do the trick.
Updated list
[✔] Add a 1/4 jack/plug so that I can reuse it as a cab
[✘] (Abandoned, this will be covered by either an EQ pedal in the FX loop, or a buffered 47K pot right at the cable from the front-end) Replace R409 with a voltage divider or a pot as a master volume to push the hiss down and make the volume range more home-friendly
[ ] Eventually change the speaker into something nicer at 16 Ohms
[ ] Replace the SMPS with a nice lower V chunky transformer (and glass fuses), a normal and properly filtered bridge rectifier, and nice big CRC filters.
[ ] Replace the 7x15 regulators with nicer ones with lower impedance and less noise.
[ ] Replace the TDA7294 circuit with an LM1875 at 20W (or even less, I will have to coordinate the PSU first) and proper beefy capacitance
[ ] Change the crappy plastic switches/buttons with nicer metal ones
[ ] Add a buffered FX loop
[ ] Prepare for replacement preamps or something for when the DSP goes to the big gig in the sky
I tracked down R409 on the main PCB. But after all, the entire thing is mostly SMD parts at the bottom side. Combined with the entire high voltage SMPS stuff, this is a bit more difficult and dangerous than what the average DIYer can or should do. Please remember that SMPSs can carry lethal voltages even when disconnected from mains.
So I won't bother with this after all. The hiss and lower volume will be covered by the FX loop where I usually add an EQ pedal.
If you do not care for the FX loop, a buffered 47K pot right at the cable coming from the front-end will do the trick.
Updated list
[✔] Add a 1/4 jack/plug so that I can reuse it as a cab
[✘] (Abandoned, this will be covered by either an EQ pedal in the FX loop, or a buffered 47K pot right at the cable from the front-end) Replace R409 with a voltage divider or a pot as a master volume to push the hiss down and make the volume range more home-friendly
[ ] Eventually change the speaker into something nicer at 16 Ohms
[ ] Replace the SMPS with a nice lower V chunky transformer (and glass fuses), a normal and properly filtered bridge rectifier, and nice big CRC filters.
[ ] Replace the 7x15 regulators with nicer ones with lower impedance and less noise.
[ ] Replace the TDA7294 circuit with an LM1875 at 20W (or even less, I will have to coordinate the PSU first) and proper beefy capacitance
[ ] Change the crappy plastic switches/buttons with nicer metal ones
[ ] Add a buffered FX loop
[ ] Prepare for replacement preamps or something for when the DSP goes to the big gig in the sky
Last edited:
Hey, I Just got the Champion 40 and had planned to upgrade the speaker and possibly some amp/transformer components. just wondering if you had collected any more data?
You can change the speaker anytime. You need an 8 Ohm 12 inch speaker, capable of 65 watts or more.
I did this with an Eminence Legend 1258. However, the sound is not that much better, and the original hiss remains. The Legend was then moved to a real cab, where it excels.
@Pos1tiveContact Sorry I was busy for a while and did not have the chance to work on this any further.
This is a chipamp, so it's not very picky about the speaker. Most popular 8ohm speakers should work without an issue. Just make sure that it can handle the power that you are playing at.
I would keep the speaker change last though. The amp has bigger issues to worry about, so unless you can use the speaker on some other cab or amp, then I would wait until you are happy with the amp overall.
@OrdinaryNimda yeah you can easily find the schematic on a search engine.
My plan for now is to create a quasi effects loop right on the cable going from the DSP to the power section.
This will help me tame the power, and use my preamp, delay and reverb pedals to bypass the DSP if I want to.
This will also reveal if the PSU or the DSP is the culprit for the hiss
I will post more soon
This is a chipamp, so it's not very picky about the speaker. Most popular 8ohm speakers should work without an issue. Just make sure that it can handle the power that you are playing at.
I would keep the speaker change last though. The amp has bigger issues to worry about, so unless you can use the speaker on some other cab or amp, then I would wait until you are happy with the amp overall.
@OrdinaryNimda yeah you can easily find the schematic on a search engine.
My plan for now is to create a quasi effects loop right on the cable going from the DSP to the power section.
This will help me tame the power, and use my preamp, delay and reverb pedals to bypass the DSP if I want to.
This will also reveal if the PSU or the DSP is the culprit for the hiss
I will post more soon
Excellent! 👍
I did a small test: the HISS is always the same - even if everything is on "0" and nothing is connected to the input. So it's obviously some cheap-sh1t crappy components.
I did a small test: the HISS is always the same - even if everything is on "0" and nothing is connected to the input. So it's obviously some cheap-sh1t crappy components.
Yeah, the controls (volume, EQ, etc) are all handled digitally by the DSP, which makes debugging a bit more difficult since all the stages work at full volume all the time (hence the hiss). Hopefully the FX loop will shed some more light.
OK here is what I got
I added two switching quarter inch sockets. The right one can be used to get the signal from the DSP, and the left one to feed the signal to the power stage. Of course you can use them separately as you want. And with nothing connected, the thing defaults to feeding the DSP to the amp.
So this works like an unbuffered simple FX loop. Keep in mind that both the DSP and the power amp are connected to the ground, so you might have to fix ground loops. I only tried this with a battery powered pedal.
The main culprit for the hiss unfortunately is the DSP pcb. I do not know if it comes from the PSU or from the design itself, or from the buffer stages (yet). There is still some noise on the power stage, but it's significantly lower, and for me it was lower than the noise from my guitars.
Testing the power amp with my mojomojo in the middle like a buffered volume, I was surprised how much better the speaker was behaving. It was now ringing loudly and with much authority. Which further points that the output stages of the DSP are also probably weak.
And of course, the volume is now much more manageable for home-use.
I do not know how I will proceed. I will play a bit more with it using my preamp pedals and see how it goes. It was already working nicely as a plain cab (for example with my VOX pathfinder 10). But it's power amp is powerful and behaves nicely even at low volumes. At this point I think that its best bet is to work like a powered cab for pedals.
Here is the mod list updated and re-ordered
[✔] Add a 1/4 jack/plug so that I can reuse it as a cab
[✔] Add an unbuffered FX loop. This was huge with a pedal as a powered volume. It's surprising this way, and it might even make sense to use as a powered cabin.
[ ?? ] Prepare for replacement preamps or something for when the DSP goes to the big gig in the sky. Again, the loop gives nice options to use the amp as a final stage with some kind of preamp pedal. I will probably eventually end up doing just this.
[ ✘ ] Replace R409 with a voltage divider or a pot as a master volume to push the hiss down and make the volume range more home-friendly. I abandoned this, since this can be covered by either an EQ pedal in the FX loop, or a buffered 47K pot right at the cable from the front-end).
[ ] Eventually change the speaker into something nicer. I will eventually get a V30, but with the FX loop and a buffer in between, the speaker is much better driven and it works surprisingly nicely as it is.
[ ] Change the crappy plastic switches/buttons with nicer metal ones
The rest are currently probably abandoned. It's probably not worth it.
[ ] Replace the SMPS with a nice lower V chunky transformer (and glass fuses), a normal and properly filtered bridge rectifier, and nice big CRC filters.
[ ] Check if the DSP for noise and performance in isolation. And check if its stages can be improved.
[ ] Replace the 7x15 regulators with nicer ones with lower impedance and less noise.
[ ] Replace the TDA7294 circuit with an LM1875 at 20W (or even less, I will have to coordinate the PSU first) and proper beefy capacitance
I added two switching quarter inch sockets. The right one can be used to get the signal from the DSP, and the left one to feed the signal to the power stage. Of course you can use them separately as you want. And with nothing connected, the thing defaults to feeding the DSP to the amp.
So this works like an unbuffered simple FX loop. Keep in mind that both the DSP and the power amp are connected to the ground, so you might have to fix ground loops. I only tried this with a battery powered pedal.
The main culprit for the hiss unfortunately is the DSP pcb. I do not know if it comes from the PSU or from the design itself, or from the buffer stages (yet). There is still some noise on the power stage, but it's significantly lower, and for me it was lower than the noise from my guitars.
Testing the power amp with my mojomojo in the middle like a buffered volume, I was surprised how much better the speaker was behaving. It was now ringing loudly and with much authority. Which further points that the output stages of the DSP are also probably weak.
And of course, the volume is now much more manageable for home-use.
I do not know how I will proceed. I will play a bit more with it using my preamp pedals and see how it goes. It was already working nicely as a plain cab (for example with my VOX pathfinder 10). But it's power amp is powerful and behaves nicely even at low volumes. At this point I think that its best bet is to work like a powered cab for pedals.
Here is the mod list updated and re-ordered
[✔] Add a 1/4 jack/plug so that I can reuse it as a cab
[✔] Add an unbuffered FX loop. This was huge with a pedal as a powered volume. It's surprising this way, and it might even make sense to use as a powered cabin.
[ ?? ] Prepare for replacement preamps or something for when the DSP goes to the big gig in the sky. Again, the loop gives nice options to use the amp as a final stage with some kind of preamp pedal. I will probably eventually end up doing just this.
[ ✘ ] Replace R409 with a voltage divider or a pot as a master volume to push the hiss down and make the volume range more home-friendly. I abandoned this, since this can be covered by either an EQ pedal in the FX loop, or a buffered 47K pot right at the cable from the front-end).
[ ] Eventually change the speaker into something nicer. I will eventually get a V30, but with the FX loop and a buffer in between, the speaker is much better driven and it works surprisingly nicely as it is.
[ ] Change the crappy plastic switches/buttons with nicer metal ones
The rest are currently probably abandoned. It's probably not worth it.
[ ] Replace the SMPS with a nice lower V chunky transformer (and glass fuses), a normal and properly filtered bridge rectifier, and nice big CRC filters.
[ ] Check if the DSP for noise and performance in isolation. And check if its stages can be improved.
[ ] Replace the 7x15 regulators with nicer ones with lower impedance and less noise.
[ ] Replace the TDA7294 circuit with an LM1875 at 20W (or even less, I will have to coordinate the PSU first) and proper beefy capacitance
Last edited:
This looks really interesting. If I understand these Neutrik connector functions... the one on the LEFT can now serve as "AMP-IN", so you could use any LINE-OUT from third sources to just amplify the signal, like a PA system. (I will not bother you with ideas and suggestions, while your are studying this.)
What has to be done is pretty straight-forward - thanx for this lesson! I still have to study the "ground loop problem", and then get more Neutrik switchable connectors. I will then experiment with a BOSS GE-7 equalizer to eliminate some of that hiss (this EQ has a buffer). The Fender Champion40 has a great sound for the Tweed Deluxe and the '65 Deluxe voicing settings.
In the meantime, the picture below is of a double 1/4 socket speaker mod, with switchable Neutriks. This enables the combo to be used as a HEAD, with an AMP-OUT to an external speaker, and also to be used as a speaker CABINET. (Since I do not yet have the proper 1mm wire to connect both Neutriks, I use the short audio cable, to connect the speaker with the amp temporarily).
And when I finalize your amp mod, there will be 4 Neutriks, which means huge versatility for this amp. Education & fun for the whole family. 😀
In the meantime, the picture below is of a double 1/4 socket speaker mod, with switchable Neutriks. This enables the combo to be used as a HEAD, with an AMP-OUT to an external speaker, and also to be used as a speaker CABINET. (Since I do not yet have the proper 1mm wire to connect both Neutriks, I use the short audio cable, to connect the speaker with the amp temporarily).
And when I finalize your amp mod, there will be 4 Neutriks, which means huge versatility for this amp. Education & fun for the whole family. 😀
Last edited:
