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2-channel preamp in HT system?


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10 replies to this topic

#1 of 11 Bill Curran

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Posted February 14 2007 - 02:28 AM

Hi All,
I'm looking to upgrade the 2-channel sound in my HT system. Does anyone know of a way to incorporate a 2-channel preamp into my existing set-up?

Pioneer Elite DV 45A Universal player
Outlaw 950 surround pre / pro
Proceed Amp 5
I want to add an Adcom GFP 565 preamp into the system.
Any advice would be greatly appreciated.
Thanks,
Bill

#2 of 11 Dan Driscoll

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Posted February 14 2007 - 03:50 AM

Quote:
Originally Posted by Bill Curran
Hi All,
I'm looking to upgrade the 2-channel sound in my HT system. Does anyone know of a way to incorporate a 2-channel preamp into my existing set-up?

I've done this with several different stereo preamps and been very happy with the results. Unfortunately, the GFP 565 doesn't have an HT Bypass, so you'll have to do this the slightly harder way.

1. Turn off and unplug the power for all components
2. Connect your 2 channel sources to the GFP 565, including the L/R stereo outputs from the 45A, for CD playback.
3. Connect the main L/R pre-outs from the Outlaw 950 to the GFP 565
4. Connect the left and right outputs of the GFP 565 to the Amp 5

When listening to 2 channel sources, don't turn on the 950, only the GFP 565, and operate as a normal stereo system.

For multi-channel sources, you will need to set the volume control on the GFP 565 to unity gain. This is usually the 12 o'clock position or the middle of the adjustment range, but you will need to experiment to find it. What you are trying to do is have the main left and right signals from the 950 pass through the GFP 565 without being attenuated or amplified. It doesn't have to be perfect, but you do want it to be close. Once you have found the unity gain position for the GFP 565 volume control, mark it, so you will be able to go directly to it next time. Now re-calibrate the speaker settings on the 950, or the DV-45A, if you are using its analog outputs.

For MC playback, turn on the 950 and the GFP 565. On the 950 select the appropriate input. On the GFP 565 select the input that the main L/R pre-outs from the 950 are connected to and set the GFP 565 volume control to the unity gain position you previously marked. The 950 will be the master volume control.

As a precaution, you should always set all volume controls to minimum before powering up the system.

There are also ways to hook-up the main L/R hi-rez outputs from the DV-45A to the GFP 565, but it can get complex and uses a lot of cables.

I hope this helps.
Dan

"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."
--Benjamin Franklin

#3 of 11 Alon Goldberg

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Posted February 14 2007 - 05:51 AM

Dan, excellent post

#4 of 11 Mark Russ

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Posted February 14 2007 - 07:05 AM

To expand on that further, the GFP-565 does have a processor loop.

#5 of 11 Bill Curran

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Posted February 14 2007 - 07:29 AM

Hi Mark,
What is the significance of the Adcom having a processor loop?
Thanks,
Bill

#6 of 11 Dan Driscoll

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Posted February 15 2007 - 04:05 AM

Quote:
Originally Posted by Mark Russ
To expand on that further, the GFP-565 does have a processor loop.

Hi Mark,

I found the Owner Manual for the GFP 565 on the Adcom website and glanced through it. After reading it, I don't think the processor loop of the GFP-565 is the same as an HT bypass. It appears the the processor loop routes the output of the GFP 565 to an outboard device (reverb, EQ, etc.) for processing, and then accepts the output of that device back. This sort of processor loop was common in 2 channel preamps designed in the '70's thru the early '90's, before 5.1 receivers and processors became common.

An HT bypass on a modern 2 channel preamp accepts the main L/R pre-outs from an HT receiver or processor and routes them directly to the outputs of the preamp, completely bypassing the volume and tone controls of the preamp. It basically takes the 2 channel preamp out of the circuit between the HT processor and the power amplifier.
Dan

"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."
--Benjamin Franklin

#7 of 11 Mark Russ

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Posted February 15 2007 - 04:20 AM

Hello Dan & Bill. No, the loop is not a true bypass. It is basically sort of a lot like a tape monitor loop.

However, it is another option for what Bill was trying to do. Some of the same things Dan said would still apply, such as the 12:00 volume position of the 565 for "unity gain".

Dan's method would also work as well just as he stated it too, however, the simplest thing of all to do might be to just get a "Y" splitter for the main L/R inputs to the power amp.

I have a system with a B&K Reference 5 S2 2 channel pre-amp and a B&K Reference 125.2 S2 power amp for 2 channel music listening, and a Cambridge Audio Azur 540R AVR, and I have both the B&K 2 channel pre-amp and the CA AVR's main L/R pre-outs going into the B&K 125.2 S2 power amp's inputs via a Y splitter. Just to be on the safe side, I never have the power to the B&K pre-amp and the CA AVR on at the same time.

To further complicate it, there is also a NHT X1 active crossover hooked up to both the B&K pre-amp and CA AVR too.

On a side note, it's amazing to me that Adcom still has the owner's manual available for a product discontinued well over 10 years ago. That's too their credit.

#8 of 11 Dan Driscoll

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Posted February 16 2007 - 03:46 AM

Quote:
Originally Posted by Mark Russ
Dan's method would also work as well just as he stated it too, however, the simplest thing of all to do might be to just get a "Y" splitter for the main L/R inputs to the power amp.

Hi Mark,

I have generally advise against this type of hoop-up, because it creates impedance issues. The first is that a Y cable itself is not an impedance matched device. This isn't a problem when the Y ends are hooked up to something where the input impedance is the same on both legs, such as the L/R inputs of a subwoofer amp, and it works very well in that type of application.

But it can be a real problem when there is a significant impedance mismatch between the legs, such as between the input of the power amp (typ. >10K ohms) and the relatively low impedance of the preamp and processor outputs (typ. <100 ohms). This is true even if the preamp or processor is turned off, it still presents a low impedance to anything connected to the output port. That means that the active device will be driving mismatched loads, a classic recipe for distortion, reflections and standing waves.

If you want to do a combiner type hook-up, the best solution is to use a real combiner. A real combiner will isolate the source devices (the preamp and processor) from the input of the power amp. One designed for audio use will even have the appropriate impedances (high for the inputs, low for the output). I don't recall seeing them in the consumer market, but I know they do exist in the pro audio market and they are very common devices in the analog, RF and microwave electronics industries.

Quote:
On a side note, it's amazing to me that Adcom still has the owner's manual available for a product discontinued well over 10 years ago. That's too their credit.

Adcom is a quality company. Their sound isn't to my taste, but their equipment has excellent build quality, it lasts forever and, from what I've heard, their customer service is also very good.
Dan

"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."
--Benjamin Franklin

#9 of 11 Mark Russ

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Posted February 17 2007 - 04:18 AM

Thanks Dan, I'll look into those real combiners.

I'll have to use the connection method you described in post #2 of this thread with no other choice if I ever actually hook up these Jolida hybrid integrated amps that I picked up two of relatively cheap (about $200 each shipped) about a year and a half or so ago, at the same time, one on ebay and one on Audiogon:

http://www.jolida.co...ls/jd1703.shtml

with the intentions of eventually setting up a 6.1 surround system with them by simply adding an AVR with pre-outs to use as the pre-pro for them, but I just have never got around to it. The Jolidas have just been sitting in my garage since I got them. I need to get to it! In fact, the same CA AVR I previously mentioned that is now with the B&K separates was what I was planning on using as the pre-pro for the Jolidas. First, I guess I need to get matching tubes for both units though since the ones that came in them are different from each other.

Regarding Adcom, yes, they are a quality company that I have nothing but respect for.

#10 of 11 Bill Curran

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Posted February 20 2007 - 01:17 AM

Thanks for the advice, Dan & Mark,
I followed the Dan's instructions and everything sounds great.
Bill

#11 of 11 Dan Driscoll

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Posted February 20 2007 - 06:19 AM

Hi Bill,

I'm glad I could help out. Enjoy the music. Posted Image
Dan

"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."
--Benjamin Franklin


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