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Post by Chuck Elliot on Oct 11, 2010 19:53:28 GMT -5
I am intending to add a high quality bypass to my pre using the XDA-1 (pre-ordered).
I need the HT bypass and crossover features of either the USP or XSP, but not all the other input selection nor the volume control.
One other feature I need is output attenuation. My subs need 10dB more than my mains. 89dB vs 99dB.
It seems that this is a very simple product and would create a complete HQ bypass system:
Inputs:
L/R/Sub1/Sub2* from Pre
L/R from XDA-1
Outputs:
L/R/Sub1/Sub2* to Power Amp
Rear Panel Controls:
Crossover Levels
Attenuation Levels
*1 or 2 Sub Mix Switch
When not powered on the input is taken from the pre otherwise the XDA-1. Remote is just a On/Off.
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Post by Chuck Elliot on Oct 12, 2010 10:39:59 GMT -5
I offered the above as a general product idea. Emotiva has lots of bigger fish to fry at the current time which I fully understand.  The issue at hand is that the need for the combo of a XDA-1 and the USP-1 or XSP-1 is somewhat redundant for those of us that don’t intend to use anything but a digital input in a HQ bypass system. The XDA-1 has a volume control and multiple digital inputs. The HT bypass feature and the analog crossover feature are all that is needed. I am sold on using subs with my mains for 2 channel listening. When I first added subs to my system I was still running my Klipsch Cornwalls as my mains. These guys have 15” woofers, but the detail added to the low end with the subs was remarkable. Anyhow, I’m off to do this as a DIY project. Elliott Sound Products makes a great little crossover PCB that will be perfect for this. sound.westhost.com/project09.htm All I need to add is a relay system to switch between the HT and the XDA-1 inputs. I can't wait to get the XDA-1. I bet it’s gonna be a killer! |
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Post by Chuck Elliot on Oct 16, 2010 9:48:04 GMT -5
I've started ordering parts so this will be ready when the XDA-1 ships. You can select what op amps are used in the crossover so I've ordered some Burr Brown OPA-2134s which are what the XDA-1 uses.  |
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Post by Chuck Elliot on Oct 21, 2010 22:20:50 GMT -5
Well, I have the chassis out for quote at Par-Metal www.par-metal.comThe front is just a power switch with soft blue light built it. On the rear the larger circles are XLR connectors to connect to the XDA-1. The smaller ones are the ones for the pre and power amp connections. Plus a power plus.  |
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Post by UT-Driven on Oct 22, 2010 0:51:32 GMT -5
Very cool project. I look forward to seeing how it works out.
Doug
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Post by ramundo on Oct 22, 2010 11:25:14 GMT -5
This is interesting.
I have the USP-1 with home theater by-pass and I was considering making up a similar add on with just the relays. With the USP-1 you need to have the USP-1 power on to have the signals pass through for TV/Movies.
Let me know if you come up with good quality signal relay for this application. I would be concerned with frequency response and crosstalk between channels with general purpose relays.
Ray
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Post by Chuck Elliot on Oct 22, 2010 12:02:43 GMT -5
I just got the chassis quote and placed the order.
$79 for a 16x12x3 black chassis
$50 to do my cutouts.
I also got all the rear and front connectors jacks and switches on order from Parts Express. Plus the crossover PCB.
Yes, the unit will be in HT bypass when the power is off. I am researching relays today and I need to design a delay on power-up circuit to drive them to block the op-amp power-up noise.
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Post by Topend on Oct 22, 2010 14:31:35 GMT -5
Looks like a great idea. You should sell these. Can it be powered on 240v and 115v?
Dave.
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Lonnie
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Post by Lonnie on Oct 22, 2010 15:52:52 GMT -5
I've started ordering parts so this will be ready when the XDA-1 ships. You can select what op amps are used in the crossover so I've ordered some Burr Brown OPA-2134s which are what the XDA-1 uses. The basic concept is sound and should be a fun project. The only thing I would suggest is to change the opamps being used. The TL072 is a good general purpose opamp, but it is a little slow and the noisy in my opinion. Everyone has there favorites but is you want a very smooth response I would recommend the LM833. If you want to very detailed and open sound then chose a good j-fet input with a high slew rate preferrable around 50V/uS and this will really open things up and be able to keep up with the discrete output stage in the XDA. In all cases whatever you choose be sure they are unity gain stable. Have fun and let us know how it turns out. |
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Pauly
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Post by Pauly on Oct 22, 2010 16:44:12 GMT -5
"The basic concept is sound and should be a fun project. The only thing I would suggest is to change the opamps being used. The TL072 is a good general purpose opamp, but it is a little slow and the noisy in my opinion. Everyone has there favorites but is you want a very smooth response I would recommend the LM833. If you want to very detailed and open sound then chose a good j-fet input with a high slew rate preferrable around 50V/uS and this will really open things up and be able to keep up with the discrete output stage in the XDA. In all cases whatever you choose be sure they are unity gain stable."
What language is this? lol This kind of stuff is way over my head. I give you guys props for knowing this kind of stuff. I hope the project works out well for ya cfelliot.
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Post by Chuck Elliot on Oct 22, 2010 21:36:14 GMT -5
I've started ordering parts so this will be ready when the XDA-1 ships. You can select what op amps are used in the crossover so I've ordered some Burr Brown OPA-2134s which are what the XDA-1 uses. The basic concept is sound and should be a fun project. The only thing I would suggest is to change the opamps being used. The TL072 is a good general purpose opamp, but it is a little slow and the noisy in my opinion. Everyone has there favorites but is you want a very smooth response I would recommend the LM833. If you want to very detailed and open sound then chose a good j-fet input with a high slew rate preferrable around 50V/uS and this will really open things up and be able to keep up with the discrete output stage in the XDA. In all cases whatever you choose be sure they are unity gain stable. Have fun and let us know how it turns out. Lonnie, I guess you missed it I've already switched to the Burr Brown OPA-2134s! I did miss one thing in my planning: a trigger input to let the XDA-1 turn it on!!! |
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Post by Lonnie on Oct 22, 2010 21:55:11 GMT -5
The basic concept is sound and should be a fun project. The only thing I would suggest is to change the opamps being used. The TL072 is a good general purpose opamp, but it is a little slow and the noisy in my opinion. Everyone has there favorites but is you want a very smooth response I would recommend the LM833. If you want to very detailed and open sound then chose a good j-fet input with a high slew rate preferrable around 50V/uS and this will really open things up and be able to keep up with the discrete output stage in the XDA. In all cases whatever you choose be sure they are unity gain stable. Have fun and let us know how it turns out. Lonnie, I guess you missed it I've already switched to the Burr Brown OPA-2134s! I did miss one thing in my planning: a trigger input to let the XDA-1 turn it on!!! That is a good choice for the opamps. Well if you want to add a trigger, then just add a DPST relay between the power supply and the output relay. To trigger it just use an Opto. Relay power from the PS would go through the Opto to the gate of a Mosfet. Power would go to the crossover and other relay board. The grounds from those boards would go to the source on the fet. Drain goes to ground. Then the XDA will turn it on. |
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Post by rixtergonzo on Oct 23, 2010 19:34:05 GMT -5
Lonnie, I guess you missed it I've already switched to the Burr Brown OPA-2134s! I did miss one thing in my planning: a trigger input to let the XDA-1 turn it on!!! That is a good choice for the opamps. Well if you want to add a trigger, then just add a DPST relay between the power supply and the output relay. To trigger it just use an Opto. Relay power from the PS would go through the Opto to the gate of a Mosfet. Power would go to the crossover and other relay board. The grounds from those boards would go to the source on the fet. Drain goes to ground. Then the XDA will turn it on. Very nice serious thread. I like it.  |
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Post by Chuck Elliot on Oct 24, 2010 13:20:09 GMT -5
Thanks for the idea Lonnie. I decided to let the trigger just control the relays. The power switch contols relay and crossover power. Now I'm going to call in a favor from a friend and see if I can get this built on a PCB - After I breadboard it just to be sure!  |
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Lonnie
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Post by Lonnie on Oct 24, 2010 14:28:47 GMT -5
Thanks for the idea Lonnie. I decided to let the trigger just control the relays. The power switch contols relay and crossover power. Now I'm going to call in a favor from a friend and see if I can get this built on a PCB - After I breadboard it just to be sure! I like it! Simple, clean, elegant, that's the way to do it. Looking over the schematic I just have one quick question. Will you be able to pull enough current through the LEDs to pull down the coil and not over heat the diode junction in the LED? If so, then you have a winner on your hands. |
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Post by Chuck Elliot on Oct 24, 2010 14:56:50 GMT -5
Lonnie,
The relays are rated at 9.1mA draw at 12V.
The LEDs primary use is just to dump the 15V supply down to 12V with their 3V Vf rating. The LEDs are actually rated at 20mA constant. Their illumination, which from prior experience I know they will do with 9-10mA, is just a side benefit.
Chuck
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Post by Lonnie on Oct 24, 2010 17:30:54 GMT -5
Lonnie, The relays are rated at 9.1mA draw at 12V. The LEDs primary use is just to dump the 15V supply down to 12V with their 3V Vf rating. The LEDs are actually rated at 20mA constant. Their illumination, which from prior experience I know they will do with 9-10mA, is just a side benefit. Chuck Cool, take pics when you get it done and post them. I would like to see it. |
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MikeWI
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Post by MikeWI on Oct 25, 2010 8:24:11 GMT -5
Lonnie, The relays are rated at 9.1mA draw at 12V. The LEDs primary use is just to dump the 15V supply down to 12V with their 3V Vf rating. The LEDs are actually rated at 20mA constant. Their illumination, which from prior experience I know they will do with 9-10mA, is just a side benefit. Chuck Cool, take pics when you get it done and post them. I would like to see it. I imagine a cost / supplier list for DIY'ers would be handy. Likely people will ask about paying him to build one for them. Mike |
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Post by Chuck Elliot on Oct 25, 2010 9:26:51 GMT -5
I've tried to post my sources for stuff as I go along. I will continue to do so. The only "custom" piece is going to be the relay PCB. It's not my intention to get into the business of building these. I would assume that if this project gathers enough interest Emotiva might consider offering something similar as an add-on to the XDA-1. As it stands, I'm getting close to the cost of a USP-1, but that wouldn't be half the fun that doing this is! |
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Post by stuofsci02 on Oct 25, 2010 14:29:33 GMT -5
I am not sure if you have implemented your time delay circuit for muting the relays while the op amps power up, but a simple RC circuit could be used to delay the relay reaching its pull in voltage..
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