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  #21 (permalink)  
Old June 29, 2011, 09:03 AM
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Turns out the volume from the line out from my receiver needs to be controlled by the amp it is connected too. I guess I'd need an integrated amp for that purpose. Or can I add a volume knob to the DIY amp?

Can't seem to find a quote for shipping to Canada from Emotiva. Was looking at getting their preamp and making my amp perhaps.
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Old June 29, 2011, 08:07 PM
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Depending on impedances you might be able to use just a ganged potentiometer, but I highly doubt it would work out. You would have to buffer the output from the pot with an op amp. I don't know if it's standard or not but my transformer came with 12V and 18V auxiliary windings which is very convenient for this sort of thing. Add probably $10 or so in various componts and a small protoboard and you're set. You would also have the ability to change the gain too.

For example if (I don't know the exact numbers off hand so I'll improvise) say the ClassD amp needs a 2V signal to reach maximum out put but your receiver only has a 1V line level, you can make that op-amp buffering the pot have a gain of 2 and then you will be able to get max output of your system before clipping occurs. Or if it's the other way around, making the op-amp buffer have a gain of 0.5 will allow you to use maximum signal strength from your receiver and both will reach max at the same point. Probably sounds more complicated than what it is. As a side note - once you're to this point you can add on a lot of bells & whistles relatively easily if you like... fancy led bargraph VU meters, clipping indicators, subsonic filters, etc.

And yes you can put it in any case you like. Being a class D amp (refering to the topology not the brand) they are stupid efficient. That little aluminum bar on the PCB is all the heatsink req'd so ventilation requirements are minimal but you will still need some as I'm sure the transformer could get quite warm. I've seen some real nice wooden boxes people have made to match their speakers, looks classy.

This DIY thing really snowballs, doesn't it?
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  #23 (permalink)  
Old June 29, 2011, 08:36 PM
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Been reading around, and these do get awesome reviews! Saw some pretty neat cases made for them also. I think there is a kit that comes with a knob to control the gain.

But again, since I'm just getting my feet wet in this whole DIY audio thing (thank god I haven't had an urge to upgrade my PC recently!) maybe I'll start small, buy a class D amp that you suggested and find myself a nice mid level pre-amp with a couple connections and only run my setup in stereo for now and forget about 5.1 for now.

I'm just not 100% sure how it fully works. If I want a 5.1 setup, can I only go the receiver way or ... I've seen 5 channel amps. But for now a good pre-amp with spdif would be awesome to play all my FLAC from my computer.
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Old June 29, 2011, 09:49 PM
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Quote:
Originally Posted by ADay2Long View Post
I think there is a kit that comes with a knob to control the gain.
They're the same but different. The adjustable gain is intended to adjust for the difference in line level I mentioned and not to be used as a volume control. Amplifiers typically need to work within certain ranges of gain in order to remain stable but I don't know if this is the case with class D amplifiers as I've never looked into them enough to design one. But i'm sure the gain range would be too limited to be used as a volume control - besides wouldn't you want the volume adjustable by a remote?

Sorry to get your speaker build OT, but since you're the OP I'm assuming you don't mind? And sorry if this gets long.

Hopefully there is some useful information here but my plan is this; I have two requirements music (highest priority) and HT and I use an HTPC for both. I'm going to get a high end sound card - I was planing on a upper ASUS card like the D2X but all their upper cards are NLA or require an add on board to go from 2ch stereo to 7.1 that is out of stock everywhere for a while so I'm going to get a DX in the interim. But apparently the DACs in these rival high end receivers any way. I also have an HK AVR235 that has alot more output than the 65W on the spec sheet would suggest. My plan is to run 5.1 analog from the soundcard to the receiver.

For music I will set the reciever in 2ch mode with no processing but the receiver still maintains volume control and the analog shows up on the analog outs. From there the bypassed analog goes to the ClassD amp so I get the cleanest signal while still being able to switch modes and use my remote (a Harmony) to control volume.

For HT I'll enable the other outputs on the reciever to drive the center channel and surrounds but the analog will still go straight through to the ClassD amp for the mains. Again the receiver won't be doing any processing as that will all be done by the sound card and I won't be using it's (probably mediocre) DAC but I still get volume control of all the channels. These HK receivers are not much above $200 on the used market since people are ditching them for HDMI capable receivers but what a deal for use of a few of it's amps and signal steering capability that is all remote driven. FWIW in my experience (although others will probably argue otherwise) SQ matters less for HT (referring to the surrounds) that the last few % gained in using ultra high end DACs and super clean amps would be lost so I can justify relying on the receiver to handle those duties. Though I may grab another ClassD board and run it off the power supply on my amp to run the center channel.

For watching TV I'll feed spdif from the STB to the receiver and use it's DAC, but it's TV so is ultimate SQ really that important? then internal amps for the center and surrounds and analog out to the ClassD amp. There may be a better way to do what I'm planning but I've given it a lot of thought and research and haven't found any better solutions. So if anyone has a better plan, that would be your queue to jump in.

Again sorry to clog up your thread!
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  #25 (permalink)  
Old June 30, 2011, 10:02 AM
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That's fine!

I've been looking around and found an HK AVR 635 for $225, has pre-outs for all 7.1. Sounds like a good deal to me, what do you think?

It's a lot more powerful than what I have now and a lot cheaper also! People are giving these HDMI-less receivers away.
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Old June 30, 2011, 12:28 PM
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That sounds like an awesome deal.
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Old June 30, 2011, 03:46 PM
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Alright, so the design is decided and we've finally had a sunny day here so I was able to purchase my MDF from Home Depot. As always it was a good excuse to purchase M0aR clamps.

Yes honey, that will only make 2 speakers!


And our postal service has been on strike for the last 2 weeks and they finally went back to work Monday so a nice surprise was waiting for me when I got home!


I will start cutting tomorrow since it's Canada Day and I'm off work! Wee.
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Old June 30, 2011, 03:48 PM
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Duuuuuuuuuuude your making ME envious of this.. but for now I'm pretty happy with my old skool Nuance speakers I paid $80 for :P
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Old July 1, 2011, 09:17 PM
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So this morning I decided to attack the XO. Took a lot more time than I thought but I wanted to get it right.







And tested each speaker to make sure everything worked. Only managed to complete 1 XO, the forecast was rain for tomorrow so I wanted to get the cutting out of the way.

A $25 well invested in a Freud blade. One of those things that you hesitate to buy and once you use it, you're like OMGosh why didn't I do this waaay before?!?! It cuts really well.



You do what you can when your table saw is the size of your hand...



Now I had a problem ... my poor man's fence (metal) was too short ... so I came up with a poorest man's fence (MDF). Made sure it was straight and square and worked surprisingly well. Although all the time spent to make sure it was straight ... next time I'll drive to Home Depot and buy a longer fence.



And the obligatory shot of the pile of cut wood (sides, fronts and backs). Pieces for the tunnels were also cut.



Aiming to finish cutting tomorrow (I really hate cutting when I don't have the proper tools), and glue the 1/2 to 3/4 baffle, and glue the tunnels.
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Old July 2, 2011, 06:31 AM
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It's funny as I was going to suggest an Emotiva amp. I bought the UPA7 (now discontinued) a while back that just kicks all sorts of ass. They ship to Canada so you don't have to worry about that. Feel free to give them a call or email, they are really responsive and friendly. If I remember correctly my UPA7 cost around $80 to ship but it's also an 80 pound amp
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