Amp Deal of the Century!

gdpeck

madmax wrote: »

I've been here at work all evening listening to these bookshelves and I just don't believe what they sound like!

http://www.radioshack.com/sm-homeplug-digital-receiver-speaker--pi-2104193.html

They have a cheapy 5" woofer and a cheapy soft dome tweeter but they just sound so darn good. I could listen for hours. They reproduce an acoustic bass really nice and the treble is very sweet. I've been listening to BR5-4-9 (modern bluegrass) and Michael Bloomfield (blues) and cannot get over the pleasantness and pureness of the sound. I think a lot of it has to do with the crossover. It is a simple cap crossed over at 10K with the woofer running full range. These are keepers for sure!
madmax

Would these be good for a cheapy near field office system? They would be replacing some cheap cambridge soundworks 2.1 computer speakers.

madmax

Absolutely excellent if you could find them.
madmax

gdpeck

madmax wrote: »

Absolutely excellent if you could find them.
madmax

OK got'em, but I'm totally confused by how to wire a line in into them. Which board is the amplifier, and where do I wire the line in?

gdpeck

gdpeck wrote: »

OK got'em, but I'm totally confused by how to wire a line in into them. Which board is the amplifier, and where do I wire the line in?

OK, things look a little clearer now. I got the amp and the speakers and I can see a little better what is going on by looking at the amp board. On question though. Am I going to end up not usering the multi-speaker switch on the back of the speaker, because it looks like it is wired to the receiver board only.

madmax

You don't have to use it but can. It just switches left input to both channels OR right input to both channels or combined (mono) input to both. (If I recall correctly).

ben62670

fredv wrote: »

I was bored, and I took mine apart last night for the sake of "see what exactly this thing is".

I think the tranny is good for what it does, replace the output transistors tip42c/tip41c pairs will probably improve the reliability (won't burn out as easy if you accidentally crank up the volume with a low impedance speakers) won't won't give you more output power. I will say, don't touch it until it is bead

Given the power supply is only a capacitor (6800uF, one per rail) after a single bridge rectifier, I am pleasantly surprised the low ripple noise!! Maybe there is some noise rejection circuit downstream, need to look at it further.

Has anyone replaced the output transistors. I feel the best cheap upgrade would be the transistors. I have already bypassed the whole front panel with no issues of noise, DC offset, and an improvement of SQ (lower noise). There is no hiss at all with the volume bypassed:) My only complaint is the bass seems a little thin.

ben62670

What is the limitation of power with these. Is the weak link the PS, or the output transistors?

ben62670

T amp is about the same output, and does not use a toroidal type PS. I have completely removed the tone controls, and the op amps just leaving the volume, and balance. The sound improvement was well worth the trouble. I get about 103 DB c weighted on my RS SPL meter which is plenty. I just want to tighten it up a bit. SNR is good:)

fredv

Ben, the power supply really doesn't have enough juice, IMHO. Don't bother to replace the output transistors, not worth it. If you're itching for a new project, spend the money and time somewhere else, and that's what I am doing :-)

ben62670

fredv wrote: »

Ben, the power supply really doesn't have enough juice, IMHO. Don't bother to replace the output transistors, not worth it. If you're itching for a new project, spend the money and time somewhere else, and that's what I am doing :-)

I have been watching some of your notes here, and at DIY:)
OK that being mentioned I was also contemplating running 2 amps. One per channel (Bi-Amping) with an active XO reserving more juice for bass. What are your thoughts? These are just computer speakers (monitor 4.6 clones) so they are only 3 feet from me.
Thanks Ben

Edit
Is the 15v DC rail good for 1 amp?

fredv

ben62670 wrote: »

I have been watching some of your notes here, and at DIY:)
OK that being mentioned I was also contemplating running 2 amps. One per channel (Bi-Amping) with an active XO reserving more juice for bass. What are your thoughts? These are just computer speakers (monitor 4.6 clones) so they are only 3 feet from me.
Thanks Ben

Edit
Is the 15v DC rail good for 1 amp?

2 amp + active XO to drive a 4.6 from 3 feet away, that will be more than enough for how they are intended to use :-)
I am running only one against the M5 underneath the computer desk. The "under the desk" gain gives it a 3 dB boost for free Regarding to the 15V rails, it is not even close to the 1A that you want. Look at the 2 x 1.8K dropping resistors that connects to the +/- rails, you can pretty much estimate the original preamp draws approx 14ma (drops 25V). Are you planning to replace the preamp with a XO board? If so, you may want to consider to build it externally with it's own PS. It will be resusable that way as well

Cheers,

ben62670

fredv wrote: »

2 amp + active XO to drive a 4.6 from 3 feet away, that will be more than enough for how they are intended to use :-)
I am running only one against the M5 underneath the computer desk. The "under the desk" gain gives it a 3 dB boost for free Regarding to the 15V rails, it is not even close to the 1A that you want. Look at the 2 x 1.8K dropping resistors that connects to the +/- rails, you can pretty much estimate the original preamp draws approx 14ma (drops 25V). Are you planning to replace the preamp with a XO board? If so, you may want to consider to build it externally with it's own PS. It will be resusable that way as well

Cheers,

You read my mind:) They are computer speakers so... I shall steal 12v from the puter for the XO. Can't get much cleaner than that. I think?

Thanks Fred

ben62670

Well I found some Accurian powered speakers. Of coarse I could not leave them alone. I luckily had an Accurian amp handy. I traced the circuits on the amps board, and did the same on the powered speaker's amp. Found what I was looking for. Bypassed all the crap. Op amp, tone controls, volume, and balance. Sounds better, but not as good as my Polk monitor 4.6 clones. I am very tempted to make an SDA type powered speaker. A 2 channel amp in each cabinet, 2 MW's, one tweeter, and a 12" PR. Am I retarded? Would a 12" PR on each side of a monitor look really stupid? I would have to make the cabs kinda deep. I am thinking this could be used as my Puter/bedroom system. I have the parts mostly. I think I just typed myself into it. I think I will copy and paste this in the puter speaker thread. Yes I will.

nms

ben62670 wrote: »

Well I found some Accurian powered speakers. Of coarse I could not leave them alone. I luckily had an Accurian amp handy. I traced the circuits on the amps board, and did the same on the powered speaker's amp. Found what I was looking for. Bypassed all the crap. Op amp, tone controls, volume, and balance. Sounds better, but not as good as my Polk monitor 4.6 clones. I am very tempted to make an SDA type powered speaker. A 2 channel amp in each cabinet, 2 MW's, one tweeter, and a 12" PR. Am I retarded? Would a 12" PR on each side of a monitor look really stupid? I would have to make the cabs kinda deep. I am thinking this could be used as my Puter/bedroom system. I have the parts mostly. I think I just typed myself into it. I think I will copy and paste this in the puter speaker thread. Yes I will.

That was really funny reading that and watching your thought progression!! Go for it - the world can always use more Frankenpolks!

ben62670

I should not be encouraged
http://www.polkaudio.com/forums/showthread.php?t=53273
The voices are telling me to build again:eek:

Edit
My Shrink told to get a hobby.
Now I can't afford to see him:D

fredv

FWIW, Steve (polk65) built a pair from the monitor 4.6 (?) cabinet, the SDA CRS XO, and the CRS's drivers, but no 10" PR and SDA crosstalk link. I had the chance to do a home try. One Accurian was obviously under power to drive them. Also, keep in mind, SDA needs common ground, if you have each cabinet uses one amp, it may not work and can't be called SDA :-) But if you have all the parts around, then what the , I will say, go for it !!! Now here is the second voice, LOL.

ben62670

The speaker wiring would be a funny thing. These amps are common ground, but I would have to do some funny speaker wiring. I am thinking the Speakcon connectors. That way no matter what once wired properly it can't be screwed up. I think I would use the electronic XO, 3 amps, and for the SDA a 9.6mh between the ground, and the 200uf caps for the bass blocking duties. A little head scratching. Nothing major.

madmax

Just thought I would mention my amp has been powered up for use with my computer since 4-20-07 without a problem. I wonder if its burned in yet?
madmax

michael_w

I listened to one of these at the Richmond Polkfest on a pair of mini voigt pipes / tapered quarter wave lines and it was a little harsh but I'm sure with a less bright and forward speaker it would make a great combo. Awesome for $15

cmy330go

madmax wrote: »

Just thought I would mention my amp has been powered up for use with my computer since 4-20-07 without a problem. I wonder if its burned in yet?
madmax

Funny you should mention that. I just discovered the other day that the one I have on my garage system has been on for months and I hadn't even noticed. Still working great!

Now if I could just figure out what to do with the 5 I still have in boxes. Oh and the speakers.:rolleyes:

apc

Were there 'matched' speakers or do you just have some stored in the garage? I'm still looking for a set to go with my amp.

madmax

michael_w wrote: »

I listened to one of these at the Richmond Polkfest on a pair of mini voigt pipes / tapered quarter wave lines and it was a little harsh but I'm sure with a less bright and forward speaker it would make a great combo. Awesome for $15

It may have still had the preamp board hooked up. Once I wired around that the harshness I heard went away. Not the perfect amp that will replace a mega-dollar one but if I had to use it all the time I wouldn't mind terribly. It does a respectable job with high eff speakers.
madmax

madmax

Is there a way to bridge these amps?
madmax

michael_w

Yes, the preamp section was still in the amp and we were running it off of USB dac going to a laptop, which in itself is a bright enough combo. Throw my Channel Islands passive in the mix and it'd probably sound great.

Danny Tse

Back in stock....

http://www.radioshack.com/product/index.jsp?productId=2049804

MillerLiteScott

I am going to pull mine off the storage shelf tomorrow and try it with a pair of RTA 8TL's that I picked up the other day.

Scott

ben62670

Danny Tse wrote: »

Back in stock....

http://www.radioshack.com/product/index.jsp?productId=2049804

sweet!

madmax

Awesome little amp. I wonder why they are back, especially at that price with no transmitter available? I bet they found a bunch of them in a warehouse somewhere.
madmax

billbillw

What the eff...I ordered a couple of these cheap things to play with. Probably use one for my computer instead of the T-amp that I was planning on getting. The other one will probably be used to power a set of zone-2 speakers on my screened in porch.

madmax

At the original price I would not have bought one but for $15 its a no brainer. They sound good.