First of all, I would like to say hello to the diyaudio community seeing this is my first post, and thread.
Hello!
For a while now i have been gathering parts to build myself a amp, because the old one that i am currently using doesnt sound as nice as it used to or compared to other ones.
I am building two PA150 board for a stereo system. I am planing on using the amp to drive two 8ohm speakers. I know that this amp is abit overkill for my speakers, but i want to have the option to use multiple speakers at the same time on the same channel (ie 3x8 ohm,2*6ohm etc.) and also when i use the amp just for two 8 ohm speakers it will not get as hot.
PA150 - 3x LM3886 PCB assembly guide
I have a few problems in building this amp, more like questions actualy:
I am using a 600va with 2x24v sec, a 50amp bridge, and a total of ~20k uF. Those are quite big numbers for me, and frankly i am quite scared of a falieure, so i am using a esp soft start board to limit the inrush current, but the board seems rather small for the job. What do you think guys, is it enough to keep everything in check?
Regarding the amplifier, i am using a 15 uF cap on the input just as in the article on Shine7. I'v read some different oppinions regarding the value of the input cap and I would like some light shed on this topic. Mainly whats the difference btwin a lower value vs a bigger one, and also a ballpark ideea of what a small value is xD
I also want to integrate some form of attenuation and or buffer on the input.
Attenuation, as in a volume pot or stepped attenuator(ladder type maybe? Its cheaper and found a promising one on ebay, eizz by the name). A buffer to drive some vumeters and the amp, some tips are highly welcome.
As much as i tried i couldnt figure what the input impedance of the amp is for sure. I keep getting 3.something using some formulae i found on mr Nuuk's website and others.
One more thing, can i use some thermal tape ( the one that you use on the video card vram for instance ) to isolate electrically and thermal-couple the chips to the heatsink? Im asking because i cant find mica washers in to-220-11 format anywhere.
I will come back with a edit or another post if I forgot something or have something new
!
Thank you guys for your patience, I hope this is the right place to post (to me it seems like it) and please excuse any grammar misshaps, im writing this off my phone.
-Vld
Hello!
For a while now i have been gathering parts to build myself a amp, because the old one that i am currently using doesnt sound as nice as it used to or compared to other ones.
I am building two PA150 board for a stereo system. I am planing on using the amp to drive two 8ohm speakers. I know that this amp is abit overkill for my speakers, but i want to have the option to use multiple speakers at the same time on the same channel (ie 3x8 ohm,2*6ohm etc.) and also when i use the amp just for two 8 ohm speakers it will not get as hot.
PA150 - 3x LM3886 PCB assembly guide
I have a few problems in building this amp, more like questions actualy:
I am using a 600va with 2x24v sec, a 50amp bridge, and a total of ~20k uF. Those are quite big numbers for me, and frankly i am quite scared of a falieure, so i am using a esp soft start board to limit the inrush current, but the board seems rather small for the job. What do you think guys, is it enough to keep everything in check?
Regarding the amplifier, i am using a 15 uF cap on the input just as in the article on Shine7. I'v read some different oppinions regarding the value of the input cap and I would like some light shed on this topic. Mainly whats the difference btwin a lower value vs a bigger one, and also a ballpark ideea of what a small value is xD
I also want to integrate some form of attenuation and or buffer on the input.
Attenuation, as in a volume pot or stepped attenuator(ladder type maybe? Its cheaper and found a promising one on ebay, eizz by the name). A buffer to drive some vumeters and the amp, some tips are highly welcome.
As much as i tried i couldnt figure what the input impedance of the amp is for sure. I keep getting 3.something using some formulae i found on mr Nuuk's website and others.
One more thing, can i use some thermal tape ( the one that you use on the video card vram for instance ) to isolate electrically and thermal-couple the chips to the heatsink? Im asking because i cant find mica washers in to-220-11 format anywhere.
I will come back with a edit or another post if I forgot something or have something new
!Thank you guys for your patience, I hope this is the right place to post (to me it seems like it) and please excuse any grammar misshaps, im writing this off my phone.
-Vld
I use a soft start for nearly all my builds. That starts the transformer with a current limiter in the primary for a couple of hundred milliseconds.
I hear the transformer grumble a bit charging up the mains smoothing bank.
I often use ±20mF for each amplifier, that's 80mF to be charged up to ~50V in a stereo amplifier and I don't bother with a slow charge circuit.
I have never blown a 25A/35A bridge rectifier.
@AndrewT I understand how a soft start works My concern is if the soft start board from Rod Elliott is too small or not. He says in his article that the board is perfectly capable of starting a 500VA transformer, but it looks abit small to me. Maybe I'm just a bit paranoid.
I dont quite understand what you are trying to tell me about +-20mf, are you trying to tell me you are using 20 000 uF per rail per amp? 80 000 in total?
My concern is if the soft start board from Rod Elliott is too small or not. He says in his article that the board is perfectly capable of starting a 500VA transformer, but it looks abit small to me. Maybe I'm just a bit paranoid.I dont quite understand what you are trying to tell me about +-20mf, are you trying to tell me you are using 20 000 uF per rail per amp? 80 000 in total?
Yes, you are reading my comments correctly.
The soft start is just a resistance in the primary circuit that gets bypassed by a relay after a short delay. It does not need to be big, not even for a 1kVA transformer.
I have used much bigger capacitor banks than your 20mF and have never used a slow charge circuit.
The Krell Klone I built up had ±75mF in the monoblock fed via a 25A bridge rectifier. But I only used this during extended testing. I don't have long term reliability data for this.
Most of my stereo amplifiers have ±40mF or ±45mF again charged via a 25A, or 35A bridge rectifier.
I have never blown a bridge rectifier.
The soft start is just a resistance in the primary circuit that gets bypassed by a relay after a short delay. It does not need to be big, not even for a 1kVA transformer.
I have used much bigger capacitor banks than your 20mF and have never used a slow charge circuit.
The Krell Klone I built up had ±75mF in the monoblock fed via a 25A bridge rectifier. But I only used this during extended testing. I don't have long term reliability data for this.
Most of my stereo amplifiers have ±40mF or ±45mF again charged via a 25A, or 35A bridge rectifier.
I have never blown a bridge rectifier.
I'd much rather research as much as I can beforehand, this is the reason I started this thread actually.
Yes, people learn from mistakes, but people also learn from research. In the diy audio section of learning, I think it's actualy safer and cheaper to learn from reasearch.
Any input regarding the other questions is welcome
Yes, people learn from mistakes, but people also learn from research. In the diy audio section of learning, I think it's actualy safer and cheaper to learn from reasearch.
Any input regarding the other questions is welcome
well, one thing is sure, you can never go wrong by sticking to AndrewTs answers and suggestions. Danielwritesback (i hope i managed to spell it correctly..) is allso a guy to keep an eye on. and tomchr too.
i wrtie this meanwhile i don't allways 100% agree with them. even so if i would get stuck with something, i would blind trust them.
i wrtie this meanwhile i don't allways 100% agree with them. even so if i would get stuck with something, i would blind trust them.
An inrush-prevention doesn't actually need a relay in many cases either. A resistor that decreases in resistance as it heats up is actually fully capable of driving a medium load device. Electronics doesn't have to be hard at all
ntc inrush current limiters are certainly the simplest solution - but during operation they provide a hot spot of 80..120C - that does not suit everybodys taste.
An inrush-prevention doesn't actually need a relay in many cases either. A resistor that decreases in resistance as it heats up is actually fully capable of driving a medium load device. Electronics doesn't have to be hard at all
Yes, I do not want a ~100C hotspot in the chassis and that is the (only) reason I chose the soft start with relays option, even if it adds complexity to the design
.not really belongs here but its loosely connected.
i had the chanse to see some interesting russian DIY amplifiers where the inrush limiting methood was a lightbulb in series with the xformer, a verry crude solution that acted as a means to indicate the thing is running. verry crude devices from an era where actually owning equipment suitable to do public address stuff (aka do sound reinforcment for a political speech) was awarded with a one way ticket to a siberian work camp.
and guess what, i specificly remember this amplifier as it was driving a speaker made out of the neck of a vodka bottle and a huge coil around it.
i had the chanse to see some interesting russian DIY amplifiers where the inrush limiting methood was a lightbulb in series with the xformer, a verry crude solution that acted as a means to indicate the thing is running. verry crude devices from an era where actually owning equipment suitable to do public address stuff (aka do sound reinforcment for a political speech) was awarded with a one way ticket to a siberian work camp.
and guess what, i specificly remember this amplifier as it was driving a speaker made out of the neck of a vodka bottle and a huge coil around it.
@Arty
I saw once something like that whenI visited a guitar teacher at a arts highschool. He had a small room PACKED full of random bits and bobs, anything from diy amps to some weird stuff I dont even know what they did. One thing i remember stuck out was a weird amp with some huge heatsinks that had 2 lightbulbs. At the time i belived they were a form of integrated "lamp" so he could read better in the dark, somehow i doubt that now.
Anymore thoughts on the original questions guys?
I saw once something like that whenI visited a guitar teacher at a arts highschool. He had a small room PACKED full of random bits and bobs, anything from diy amps to some weird stuff I dont even know what they did. One thing i remember stuck out was a weird amp with some huge heatsinks that had 2 lightbulbs. At the time i belived they were a form of integrated "lamp" so he could read better in the dark, somehow i doubt that now.
Anymore thoughts on the original questions guys?
A bit of a update:
I reciced most of the parts i need to get the amp running and test it for dc offset callibration. I will be posting again with the results. As a sidenote if anyone will be doing some smd soldering, please get some kind of a clamp to hold the pieces down, it took me almost a hour of fiddling to fit a binch of them :lol:.
I reciced most of the parts i need to get the amp running and test it for dc offset callibration. I will be posting again with the results. As a sidenote if anyone will be doing some smd soldering, please get some kind of a clamp to hold the pieces down, it took me almost a hour of fiddling to fit a binch of them :lol:.
Another update:
I finaly finished the electrical work somewhat, the amp runs great with a small exeption, but i'll get to that in a bit
Today i finished what you can see in the photo, and tested the board prior to hooking it to my speakers, i measured a small dc offset, but nothing to worry (about 10 mV) the amp fortunately didnt blow up or go up in flames/smoke, so that was nice feeling for the first power on. After some more testing i hooked my speakers to it and started listening to it but i noticed a slight hum to it, about 100-150 hz , it was barely audible on a pair of 89db/8ohm speakers, but it is there. I suspect it's the ground wiring but i'll have to get back to it.
All in all i am pleased with how it sounds, apart from that hum when nothing is playing, and as a plus it gets just a tad warm when listening at above normal levels.
Some advice, tips, or just thoughts are always welcome.
I finaly finished the electrical work somewhat, the amp runs great with a small exeption, but i'll get to that in a bit
Today i finished what you can see in the photo, and tested the board prior to hooking it to my speakers, i measured a small dc offset, but nothing to worry (about 10 mV) the amp fortunately didnt blow up or go up in flames/smoke, so that was nice feeling for the first power on. After some more testing i hooked my speakers to it and started listening to it but i noticed a slight hum to it, about 100-150 hz , it was barely audible on a pair of 89db/8ohm speakers, but it is there. I suspect it's the ground wiring but i'll have to get back to it.
All in all i am pleased with how it sounds, apart from that hum when nothing is playing, and as a plus it gets just a tad warm when listening at above normal levels.
Some advice, tips, or just thoughts are always welcome.
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I've seen at least one design that used a light bulb to bias the single ended output stage. This is very unconventional design, but it works. I think it would be cool to build as a learning experience.
And if I lived somewhere that I wasn't allowed to have anything bigger than a table radio, then I could see building it and using it, if that's all I could get my hands on.
120 Hz hum is power supply. There is something in your circuit that needs isolation from the power supply. Or maybe your grounds are not arranged properly. If that's the case, and you sort it out, then your amplifier will sound better than it does now regardless of the hum. Been there, done that; and you will be amazed at how much better your equipment sounds when you get the grounding right!
Start with Andrew's advice.
After reading some other threads on this subject, i feel like i have a ground loop at the inputs because i hooked a couple of rcs's with some light duty cable and the grounds connected to the amp boards, using a ipod as a source, but until i test it i can't say for sure. I'll follow Andrew's advice as soon as possible.
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