| inrank |
hi,
can i make "LM3875" based power amp and a seperate pre-amp that has both phono line in and XLR inputs and outputs.
this is so i can connect a phono line out from a cd/dvd player into the pre amp then a XLR line out from the pre amp into my Tannoy TS8 subwoofer then the XLR high pass output into the power amp then that into my CSS FR125 based bookshelfs.
can this be done ?(easily and on a budget)
could i also have two sets of switchable speaker outputs ( A or B not A+B) |
|
|
| jimbo1968 |
| I can answer the last one > Yes; you'll need 2 sets of outputs and a switch. :D |
|
|
| jimbo1968 |
As for the rest, I haven't got to grips with balanced inputs yet but for the crossover you could put an active crossover in either the pre-amp or in the amp.
if the sub has built in low-pass you only need to build a high pass. Maybe this could be a line level passive filter (?).
What frequency are you going to cross?
I'm about to cross my sealed FR125s at 120Hz (I think) using the active filter board from the current group buy. |
|
|
| leadbelly |
| quote: | Originally posted by inrank
can this be done ?(easily and on a budget)
could i also have two sets of switchable speaker outputs ( A or B not A+B) |
Very easily done.
Your "preamp" will just be: phono => pot => DRV134 => XLR
Your power amp will just be: XLR => LM3875
And you need a hefty DPDT switch to switch the speaker outputs. Don't get too cheap on this or it will have poor electrical properties. |
|
|
| leadbelly |
| quote: | Originally posted by leadbelly
Your "preamp" will just be: phono => pot => DRV134 => XLR
Your power amp will just be: XLR => LM3875 |
Thought about it some more and this way is better:
phono => DRV134 => XLR
XLR => pot => LM3875
You didn't really say if you want something that will perform well or just want to do it as cheaply as possible. If the latter, you don't need a preamp at all, just make a phono => XLR cable |
|
|
| inrank |
this is the kind of thing (i think) i need.
at the moment i have a NAD L53 reciever which does not have a line out only a mono sub out.
so making a cheapish pre power for this would be good.
i want to spend as little as possible, so if there is any other way i can connect my sub to my speakers please tell me:) |
|
|
| leadbelly |
| quote: | Originally posted by inrank
at the moment i have a NAD L53 reciever which does not have a line out only a mono sub out. |
I am lost now as to what you are trying to achieve. Maybe you should step back and describe what components you have and what you are trying to make your audio chain look like. If that XLR is a mono sub-out from a receiver, you cannot use it as a signal to drive a pair of fullrange speakers. |
|
|
| inrank |
no...
the pic is what i would want the pre and power amps to look like if i made one using the LM3875 chip.
i currently have a NAD L53 Amplifier/Tuner/DVD all in one system a Tannoy TS8 sub, some Tannoy DC1000's and some FR125 based full rangers that i am making at the moment.
i want to connect either pairs of speakers to the sub so that i can play them loudly and not stress the speakers and fill in for the FR125's when using them.
sorry for the conclusion. |
|
|
| jimbo1968 |
if your receiver has bass management, all you need is the phono to xlr lead.
unless you want to build a chip amp, in which case not having line out is a problem.
what receiver functions are you hoping to retain? source selection, dolby decoding and rear amplification?
edit: just seen your previous post. Maybe all you need is a speaker switch and phono to xlr cable. |
|
|
| inrank |
well the L53 is only 2 channel and a subwoofer, it would be easy if there was a line out but there is not, but there is a VCR Line out that might work. (or a component scart out aswell)
i was looking in the summer to build a chip amp that would integrate all of these things lol.
the L53 does have LFE level but that would only effect the mono sub out i assume? |
|
|
| leadbelly |
OK, I had a look at the NAD and Tannoy manuals, and I see your predicament. The NAD does not have line out jacks, basically the only way to get a fullrange stereo signal out of it is through the speaker terminals. Even if you turned the NAD sub crossover off that would only be a mono signal through that XLR jack you mentioned.
You could rig up something to take the high level speaker outputs to line level and feed them to a LM3875. Your chain would look something like:
NAD => speaker switchbox => low level converter => Tannoy channel 2 in => channel 2 hi pass out => LM3875
Personally, I wouldn't bother. CD/DVD players are so cheap I would make a 2nd chain with a new player, especially since your sub has 2 input channels. |
|
|
| inrank |
ok, thanks.
will look out for a cheap cd player;) |
|
|
| leadbelly |
Wait, there might still be a chance :)
The NAD site doesn't show the outputs, but one of the reviews mentions a VCR tape loop. Is this true? Is there a full VCR tape loop? 6 RCA jacks, video+left+right in (play), video+left+right out (record)? If this is what there is, then yes, it is likely that the left+right out RCA jacks do have stereo line level output signal present. Maybe you can rig something up to test this. |
|
|
| jimbo1968 |
I too have had a look at the manual!
http://207.228.230.231/manual/NAD_L53_EN.pdf
Yes there is audio out (vcr).
The manual says nothing about the sub mono out.
So for correctly crossed integration we will need a 2way crossover (+sub combiner?) and amplifier. |
|
|
| inrank |
yes there is VCR tape Loop.
i connected that VCR out (red and white) into the scart on my telly, it works!
so i could connect that to a XLR connector with a bit of bodging then the XLR line out into a power amp?
well mine has a "sub pre out" |
|
|
| leadbelly |
Thanks for the link to the manual. Yes, you can likely use the VCR outputs, I've circled them in red.
So, you chain can just be:
VCR out => Tannoy in => Tannoy out => LM3875
jimbo, you keep mentioning crossover, but this is unnecessary cost, inrank can just use the crossover in the Tannoy sub. |
|
|
| jimbo1968 |
| quote: | Originally posted by inrank
well mine has a "sub pre out" |
I meant it offers no information about the sub out, other than it exists. |
|
|
| inrank |
oh ok lol
couple of things....
what is the 3rd connecter in a XLR connecter?
with the power amp (that i will make), will i need a switch to go betweent the Phono and XLR input?
what is the power rating of the LM3875 chip? |
|
|
| jimbo1968 |
| quote: | Originally posted by leadbelly
jimbo, you keep mentioning crossover, but this is unnecessary cost, inrank can just use the crossover in the Tannoy sub. |
yes, i've got crossovers on my mind at the moment.
plus I didn't get to looking up the sub yet (bloody work interruptions!) |
|
|
| inrank |
| well for the sealed enclosure i am building, the F3 point is around 80Hz |
|
|
| leadbelly |
| quote: | Originally posted by inrank
what is the 3rd connecter in a XLR connecter?
with the power amp (that i will make), will i need a switch to go betweent the Phono and XLR input?
what is the power rating of the LM3875 chip? |
XLR supports balanced signals, the 3 wires are positive phase (+), inverted phase (-), and ground. If you are trying to do things on the cheap you can just make cables that have the XLR on one end, three wires, and then at the RCA end both - and ground wires connect to the RCA body. There is more to it than this but you are unlikely to have problems.
Don't start talking about bullspit power ratings. The LM3875 will drive your FR125's loud. |
|
|
| inrank |
| quote: | Originally posted by leadbelly
XLR supports balanced signals, the 3 wires are positive phase (+), inverted phase (-), and ground. If you are trying to do things on the cheap you can just make cables that have the XLR on one end, three wires, and then at the RCA end both - and ground wires connect to the RCA body. There is more to it than this but you are unlikely to have problems.
Don't start talking about bullspit power ratings. The LM3875 will drive your FR125's loud. |
so where does the ground wire connect? to either of the two phono's?
and would it be easier to have a XLR cable from the sub to an XLR socket on the power amp or just have another bodged cable with XLR to RCA and have standard stereo phono on the back of the amp? |
|
|
| leadbelly |
| quote: | Originally posted by inrank
so where does the ground wire connect? to either of the two phono's? |
Again, the - wire and the ground wire connect to the same place on the RCA plug, for both left and right cables.
| quote: | Originally posted by inrank
and would it be easier to have a XLR cable from the sub to an XLR socket on the power amp or just have another bodged cable with XLR to RCA and have standard stereo phono on the back of the amp? |
Your preference. |
|
|
|
