salve 5w in classe a il frontale sono mattoni veri
I like the wall. very original. Well done!
I finished it this evening, at least all the analogue stuff. Still waiting on a couple parts for the fan controller and air filter, so that's running full speed at the moment and annoyingly loud.
When I originally visualised the layout I didn't imagine so many damn wires!
Metalwork kind of hides the ugliness:
And here's one speaker assembled:
I had a quick test of it tonight but haven't cranked it hard yet. The active crossover is an incredible improvement and far exceeds my expectations even though I've done no calibration or time alignment yet, merely set the three different gains to correct for the nominal driver sensitivities. However, my noise floor is horrifically high. Some of that is no doubt (there is a tiny hum) due to my shitty shitty cabling, but there's also much more noise coming from the DCX than I expected.
The puzzling thing is that when I tested the amp on a normal (3-way passive xover) speaker, it was NOT particularly noisy. Plug it into the ones it was designed for and you can hear the hiss from at least a foot or two away.
One thing that occurs to me is that with an active setup like this, all the gain control is way up the front of the signal chain whereas the classic arrangement is to have a volume pot right before the amp input; at low volume levels that pot eats all the noise from the earlier stages. I'm not sure how to get that kind of noise reduction at low volume back without implementing way too many (18+) attenuator boards.
When I originally visualised the layout I didn't imagine so many damn wires!
Metalwork kind of hides the ugliness:
And here's one speaker assembled:
I had a quick test of it tonight but haven't cranked it hard yet. The active crossover is an incredible improvement and far exceeds my expectations even though I've done no calibration or time alignment yet, merely set the three different gains to correct for the nominal driver sensitivities. However, my noise floor is horrifically high. Some of that is no doubt (there is a tiny hum) due to my shitty shitty cabling, but there's also much more noise coming from the DCX than I expected.
The puzzling thing is that when I tested the amp on a normal (3-way passive xover) speaker, it was NOT particularly noisy. Plug it into the ones it was designed for and you can hear the hiss from at least a foot or two away.
One thing that occurs to me is that with an active setup like this, all the gain control is way up the front of the signal chain whereas the classic arrangement is to have a volume pot right before the amp input; at low volume levels that pot eats all the noise from the earlier stages. I'm not sure how to get that kind of noise reduction at low volume back without implementing way too many (18+) attenuator boards.
That's how it always goes hehe
Are you using Behringer DCX? They have a high output level and are known to be noisy. Attenuating before the power-amps is definitely the way to go, as you have allready found out.
If your cabling is shitty you don't get noise... you get hum!
Yes, DCXs. However, there's plenty of noise even before I plug them in. I haven't tried shorting the inputs to see if that silences the output - if it doesn't then I don't think that putting attenuator last will help much.
There is a buzz more than a hum actually - 100Hz fundamental but most of the energy is up past a few kHz. I think I need to put transformer snubbers into it - in fact I'm sure I need to as the 240V cable runs around 2 sides of the box in order to reach the power switch, soft start and remote-start/thermal-shutdown relay and when it radiates rectifier noise that's been multiplied up, it'll get into everything.
Given that I'm a lazy bastard and don't want to build a Quasimodo, are there (formulae for) default RC values I can go to that will get me 90% of the way there?
Thanks, I'll have a look into those.
thanks! Just don't look too closely at the veneer, it's pretty bad on some of the cabinets, like the one pictured.
Actually on second thoughts, I think I'll just get a pile of PGA2310 chips. I have a microcontroller in each amp anyway and adding a serial port to chain them all together isn't very hard. That would also allow me to simplify the differential inputs to a single opamp each and remove the trimpot gain corrections for driver sensitivity.
The only sticking point is that I'll need Yet Another Damn Remote, and will have to mar the front face of the amps with a hole. The horror!
The only sticking point is that I'll need Yet Another Damn Remote, and will have to mar the front face of the amps with a hole. The horror!
Behringer mods
Looking at your image of your amps I see a possible reason for your hum: Your ground path!
You have put the ground star closer to the input, and not - as it should be - close to the output.
Quick fix: isolate the joint where the input ground, the input transistors and the feedback path goes to ground - keep these two/three joined and lift it from supply ground via one 100 ohm resistor.
Looking at your image of your amps I see a possible reason for your hum: Your ground path!
You have put the ground star closer to the input, and not - as it should be - close to the output.
Quick fix: isolate the joint where the input ground, the input transistors and the feedback path goes to ground - keep these two/three joined and lift it from supply ground via one 100 ohm resistor.
here is my amp..Nakamichi PA-200 re-capped, some little upgrades, and runs on class A..source was from my laptop using USB DAC 
it's a car amp but sounds pretty good!
i actually have a krell clone but since i worked out of my city, this one becomes my main system
it's a car amp but sounds pretty good!
i actually have a krell clone but since i worked out of my city, this one becomes my main system
Attachments
That's not the main earth star you refer to, it's a subsidiary star that earths the input shields and heatsinks only and therefore carries no current except for noise induced on balanced cable shields, which is why it needs to be next to the input. The power star is right above the transformers, behind the terminal strip.
I had previously set my amp input gains so that it would clip at about +0dBu in, i.e. a total power amp gain of about 27dB. I wound them down as far as I could (-12dB) which obviously helped the noise immensely. You now need to be within 1m to hear the hiss whereas previously it sounded like rain from 3m away when the DCX was powered up. Once I put in transformer snubbers, I think it might be quiet enough and if not, I'll do the PGA2310 thing to push the DCX noise down further.
Now playing in my living room
I are a happy boy.Pi-amp
This is the last "revision" of this build, I think. Totally satisfied.
Making it Better - PC Integrated Amplifier - YouTube
This is the last "revision" of this build, I think. Totally satisfied.
Making it Better - PC Integrated Amplifier - YouTube
An externally hosted image should be here but it was not working when we last tested it.
Very nice! the only thing I would "modified" is I would turn around the boards the way the inputs from chassis will be "closer" to the boards.
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