Hi Peeps
I have been gathering parts for a stereo amp build and am at the construction stage. This is my second diy amp, using two LM1875 boards.
I wanted a compact unit to go with my DIY bookshelf speakers.
Can I get some advice on component layout, what do I need, what don’t I need, can it all be squeezed in?
Here is a picture of the parts in the case.
Components:
Toroidal 120VA
DC power supply board
2 x LM1875 amplifier boards
Preamp board for iPhone (if needed) and separate transformer (blue)
Speaker protection board (not yet assembled) and separate AC transformer (blue)
Anodized aluminium case with side heat sinks from Ali-express
Copper sheet to make a shielding can for the transformer if needed
It is very tight with all components used and I am not sure how to best arrange it.
Thanks
I have been gathering parts for a stereo amp build and am at the construction stage. This is my second diy amp, using two LM1875 boards.
I wanted a compact unit to go with my DIY bookshelf speakers.
Can I get some advice on component layout, what do I need, what don’t I need, can it all be squeezed in?
Here is a picture of the parts in the case.
Components:
Toroidal 120VA
DC power supply board
2 x LM1875 amplifier boards
Preamp board for iPhone (if needed) and separate transformer (blue)
Speaker protection board (not yet assembled) and separate AC transformer (blue)
Anodized aluminium case with side heat sinks from Ali-express
Copper sheet to make a shielding can for the transformer if needed
It is very tight with all components used and I am not sure how to best arrange it.
Thanks
Attachments
Can the power supply board go vertically on the right heat sink, or is it too big (wide)?
Don't bother about the copper, it won't magnetically shield the transformer.
Can you swap the RCAs with the rightmost binding posts? They're very close to the toroid.
Will the lid clear the transformer bolt? You don't want that to touch the top (shorted turn).
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Hi
Thanks for the comments.
Unfortunately the PS PCB is just too wide to go vertically.
Now you point it out, not sure why I got copper, do I need to shield the transformer?
Yea I can switch the RCA over.
I will have to trim the bolt when the toroid is installed.
Thanks for the comments.
Unfortunately the PS PCB is just too wide to go vertically.
Now you point it out, not sure why I got copper, do I need to shield the transformer?
Yea I can switch the RCA over.
I will have to trim the bolt when the toroid is installed.
It's gonna be tight in there. Forget the copper, though.
There may be no room for proper steel shield similar to this:
https://www.ebay.com/i/251787507844?chn=ps
Make certain that the bolt and large mounting washer cannot touch anything.
Alright, ditching the magnetic shielding idea
RCAs moved over.
Do I put the volume pot before or after the preamp?
Do I only use shielded cable for the wiring between the signal input and the main amplifier board input?
RCAs moved over.
Do I put the volume pot before or after the preamp?
Do I only use shielded cable for the wiring between the signal input and the main amplifier board input?
Volume control goes between the preamp and the power amp.
Twisted pairs carry the signals in/out of the volume control.
I'd run tightly twisted wire pairs straight along the RCA side of the heat sink,
and then over to the preamp. Many prefer shielded cables, though.
They'd be much more difficult to work with for this.
Thanks for the advice
The preamp is fixed 5x gain, will this help with iphone as a source, or is it not needed?
The gain these eBay amp boards is 23
The preamp is fixed 5x gain, will this help with iphone as a source, or is it not needed?
The gain these eBay amp boards is 23
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Typical LM1875 gain seems to be around x21 (26dB),
so you'd need around 0.75Vrms input to drive the amps to clipping.
Check the phone specs to see if you can ditch the preamp.
Does this information from Apple's Lightning Headphone Adapter: Analog or Digital? | InnerFidelity say that it is about 0.5v for the iphones?
Not sure how to apply 5x gain to this, is it dB or a voltage multiplier?
Not sure how to apply 5x gain to this, is it dB or a voltage multiplier?
Attachments
Looks like that's close enough to 0.75V that I'd lose the preamp.
A gain of x5 is 14dB. No units always means a factor (which has no units).
Can the protection board go vertical? If so I would move it's transformer into it's place as it's a but close to your amp board
You'll probably want it further from your inputs or you'll pick up the mains hum there. Perhaps turn the speaker protection other way so it can clear those big relays.
If it's just for you and you know not to throw it around, glue or strong double sided tape should be okay. Definitely heatshrink (double even) the connections so there's no mains voltage exposed. If you're a belt and suspenders type then you could make up a bracket or something and screw it down, or loop a cable tie around it. A PCB would be tidier of course.
If it's just for you and you know not to throw it around, glue or strong double sided tape should be okay. Definitely heatshrink (double even) the connections so there's no mains voltage exposed. If you're a belt and suspenders type then you could make up a bracket or something and screw it down, or loop a cable tie around it. A PCB would be tidier of course.
why not moving the transformers and all PS stuff front and make a shaft extension for you alps and keep all signal Stuf close to the input output?
Do you think these small amps could share one heatsink? If you kept all the power supply components in one side (the bottom in these images) you could keep AC well away from the signal path. Just a thought. something like below
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in. Amp. Amp vol
Spk. Prot. PS
Spk. PCB. PCB
Prot
Trans. Toroid. Sw
Mains
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in. Amp. Amp vol
Spk. Prot. PS
Spk. PCB. PCB
Prot
Trans. Toroid. Sw
Mains
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