First Lm3886

Status
Not open for further replies.
Jump to Latest
#141
Hi PJPro

I would say stick with what you have for this one. You can use the pricey stuff on the next, and compare between the two. You will know if it sounds worth the extra to you!

I use cat 5 for signal wires, largely because I get offcuts from a mate for free and other than it being awkward to strip it's nice to work with.

John
 
#142
I don't mind spending a bit of money. After all, my binding posts and rca sockets were hardly cheap.....it'd be a pity to skimp on cable if a small outlay would improve things.

3684712885_1e8026dabc.jpg


3684712691_bb893732ca.jpg
 
#143
all that cool stuff you are buying 🙂

Could you please post pics of the cases you bought? I would like to see the inside mounting provisions.

You are using voltage regulators to feed the LM3886s I am not sure if that's a good idea.

Basically you're adding at least one more transistor in the path from the PSU filter capacitors into the speakers. That transistor and whatever else is connected at its base, is not an audio grade transistor - and even if it were its job is to try to react to changes on both ends, on its collector and on its emitter (I am assuming a series regulator), which means when its collector voltage changes because the transformer regulates for example, or when its load decreases because your LM3886's audio transistors open some more, it will react to those changes trying to keep the emitter voltage constant, but it is not an audio grade transistor so its hfe chart can be anything, and as it reacts to changes that have already happened one would need to ask how quickly it does so and so on. Plus how much noise it and whatever is at its base generate and inject into your LM3886s. Plus other things I have not thought about.

Unless you are driving a 4R speaker and your transformer/PSU gives out too high voltage ? Is that why you're doing it ?
 
#145
It is the LM3886 that cannot handle more than about 60 volts on a 4 ohm speaker and a total of about 83 volts regardless. Other chips, or other amplifiers might scale differently, better or worse. The choice of the transformer therefore is imposed by the chip not by the speakers. Well more accurately by the combination.
 
#146
Are you saying that I can use my 25v tranformers with 4 ohm speakers? I thought this was on the high side......with 18v recommended and 22v as a maximum.

It is for this reason I wanted to consider the option of regulators....so allow me to use 25v transformers with 4 ohm speakers.

My work around (for now) is to use 8 ohm speakers 🙂
 
#148
OK. I received the new power modules today and, hurrah, they look like they're the right ones.

3772264039_f8308cbf9d.jpg

Schurter DD12.9121.111 Power Inlet Module with Schurter 4301.1413 Fingergrip Fuse Drawer (shorting bar in the neutral side).

3773072576_5bc8b103e7.jpg

Aluminium Shielding
 
#149
I was bored on the train home and answered from the bbry, so I did not justify : I clicked on your link to check the cases, and noticed a message where you said something like "the choice of transformer determines the speakers", and wanted to let you know it is the chip that imposes the limits not the speakers.

In your case you have bought the 25V ones (like I did, only I bought a single 300VA) and that should give you 39.48 VDC on each rail (offload), which is very very near the max the LM3886 can take, and definitely well above the recommended max for 4 R, so you need to stay with 8 R speakers (which I had thought was the norm anyway).

OK I can see the case you got now, it seems it does not have a double bottom. How are you meant to mount transformers and other bits and pieces on to it?
 
#151
PJPro said:
Are you saying that I can use my 25v tranformers with 4 ohm speakers? I thought this was on the high side......with 18v recommended and 22v as a maximum.

It is for this reason I wanted to consider the option of regulators....so allow me to use 25v transformers with 4 ohm speakers.

My work around (for now) is to use 8 ohm speakers 🙂
Click to expand...
me would at least try the 2x25V transformer. It is not a black or white decision, these things are grey...
regards
 
#156
Funny you had me scratching my head for a bit. Looks like it might be on the line side.
I could estimate it for you Andrew, but probably not that significant compared to the ferrite core leakage on the other side.
besides anything else it provides is a bonus
 
#158
Also check ground to IEC shield continuity. I think there might be none, so you must make it anyway at the chassis for best effect ie chassis hole fit tight with paint filed off on outside edges. This is a detail hassle I know.
In addition IEC ground to chassis at secure chassis bolt for safety and star ground point, so only use those 2 places for chassis grounds period full stop.
 
#160
infinia said:
Also check ground to IEC shield continuity. I think there might be none, so you must make it anyway at the chassis for best effect ie chassis hole fit tight with paint filed off on outside edges. This is a detail hassle I know.
In addition IEC ground to chassis at secure chassis bolt for safety and star ground point, so only use those 2 places for chassis grounds period full stop.
Click to expand...
OK. I'll measure continuity from the shield to earth....and take the precautions you specifiy. I'm keen to make sure the amps are safe. Again, thanks.
 
Status
Not open for further replies.
Top Bottom