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Old 6th November 2004, 08:30 AM   #1
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Default Multi-Channel Contol Unit

Hi Guys,

Not sure where to post this, but here goes:

I wish to connect 5 or 6 separate valve (tube!) amplifiers to a DVD player, using the Surround Sound outputs of the DVD player. The valve amplifiers do not have any means, passive or active, of controlling the amplitude levels fed into them. The amplifiers will be mounted in an equipment rack beside the TV, and I am desiring to connect them to the DVD player via some sort of multi-channel
control unit. The control unit should feature remote control of volume levels by preferably cordless means. I have done a Google search for something in this vein, and just ran away when I saw the US $ prices, which seemed to resemble Serial Numbers rather than pricing of such a unit.

Does anybody here have any ideas for such a unit? I would prefer a simple unit without gizmos; all I require to control is simply volume levels and maybe remote power On/Off, but no other fancy gimmicks. I would prefer building my own unit if suitable components are available.

The need for a *remote* controller is for ease and convenience of adjusting volume levels from my listening position. Manually adjusting the amplifiers at their location is not an ideal option.

-Eric
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Old 6th November 2004, 03:11 PM   #2
mcs is offline mcs  Denmark
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That shouldn't be a big problem.

The options you have (as I see them) are either:

1. A motorized volume pot
2. A relay attenuator
3. Attenuator chips

Option one is a bit difficult. I have never seen 6-gang motorized pots, and getting three or more pots to rotate at the same speed is not easy.

A relay attenuator would be easier, but it does take up a bit of space. I recently made a 64-step stereo attenuator, and the board size was about 7*9cm. That used standard DIL-relays, but you could make the board smaller by using miniature relays. For your 6-channel setup you could just use three stereo boards.

The attenuator chips are available in many different versions. The widely used TI chips (PGA2310), are not very tube friendly. They need to be driven by a low-impedance buffer (meaning op. amp.), and they also include op. amps. themselves. The National LM1972 may be better. It needs a high impedance buffer on the output, which could be a tube instead of the FET op. amp. recommended by the datasheet. But I have no idea how the National chips "sound".

You could also combine the relays and chips. Use relays for the "important" channels and chips for the less important ones.

Then there's the control part. The relay attenuators and chips can be controlled the same way, so the control section can be made the same way for both. What features do you need? You need a volume control, obviously. How about a rotary encoder on the box, combined with IR remote? Do you want to be able to adjust the relative levels of the different channels combined with a "master" volume control? Do you need some sort of display to show the volume setting? The "control section" for the stereo attenuator I described is just a 20-pin IC, so if doesn't have to be too complicated (or expensive).

Best regards,

Mikkel C. Simonsen
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Old 6th November 2004, 03:34 PM   #3
Sherman is offline Sherman  United States
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Default Re: Multi-Channel Contol Unit

Quote:
Originally posted by Family_Dog
[B...I wish to connect 5 or 6 separate valve (tube!) amplifiers to a DVD player, using the Surround Sound outputs of the DVD player. The valve amplifiers do not have any means, passive or active, of controlling the amplitude levels fed into them...

-Eric [/B]
Eric,
Not exactly DIY and maybe not what you are looking for but the JVC RX-8030VBK (among others) is a HT receiver that also happens to have preamp outputs for 5.1 surround. I've seen it for under $250 US.

You can connect your tube amps to the preamp outputs. You would then connect your DVD to it and be able to control both the receiver and DVD from the remote. Of course you still have to turn the tube amps on and off manually.
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Old 6th November 2004, 05:10 PM   #4
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Hi Mikkel & Sherman,

Thanks for your thoughts on this subject. From the start, I imagined that a 6-gang motorized pot would be pretty impossible to find, or horrifically expensive if it was available. One of the prime considerations would also be a master volume control.

Sherman's idea makes good sense, I'm not sure whether this particular model of JVC is available locally, but there will be other amplifiers locally available which could offer a separate pre-amp output. I guess this might be the easiest and possibly cheapest way to go. I doubt I would be able to construct anything with as many features as a ready-made HT amp for anywhere near the price that I would be able to buy one for.

-Eric
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Old 6th November 2004, 11:27 PM   #5
Sherman is offline Sherman  United States
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Quote:
Originally posted by Family_Dog
...I'm not sure whether this particular model of JVC is available locally...
-Eric

It seems to be the rule rather than the exception that the name or model number of identical units are different in different parts of the world.

The next JVC model up 8040 has the same outputs also. I'm sure you are right about other models having the same or similar features but it is sometimes hard to get the information. For instance you probably won't see the fact that the JVCs have preamp out listed on the websites that sell them. I found out about it here (search for "5.1 decoder").
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Old 8th November 2004, 10:46 AM   #6
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Default LM1972

Quote:
The attenuator chips are available in many different versions. The widely used TI chips (PGA2310), are not very tube friendly. They need to be driven by a low-impedance buffer (meaning op. amp.), and they also include op. amps. themselves. The National LM1972 may be better. It needs a high impedance buffer on the output, which could be a tube instead of the FET op. amp. recommended by the datasheet. But I have no idea how the National chips "sound".
Very nice !
For me - much better then CS3310, even that 3310 has more beautiful "objective parameters"!
Try to use LM1972 with "all tube" amplifier (6L6) and with my "hybride" -tube SRPP input stage + mosfet SE (Pass Zen3).
No sound degradation after placing the LM1972 between the CD and the amplifier.
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Old 8th November 2004, 07:34 PM   #7
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Guys,

I was fortunate today in finding a 2nd-hand Denon AVR2802 Receiver which has pre-amp outputs available on the rear panel. Cost about $500 which is not too bad a price for this unit here in South Africa. Beauty of this is that it solves my problem for a good FM tuner as well

-Eric
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Old 8th November 2004, 10:10 PM   #8
Sherman is offline Sherman  United States
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Quote:
Originally posted by Family_Dog
Guys,

I was fortunate today in finding a 2nd-hand Denon AVR2802 Receiver which has pre-amp outputs available on the rear panel. Cost about $500 which is not too bad a price for this unit here in South Africa. Beauty of this is that it solves my problem for a good FM tuner as well

-Eric
Good job finding a suitable unit. After a lot of searching this forum and the web in general it really does seem that at least for now some type of HT receiver is the least expensive way to drive a 5.1 DIY system. Plus one generally gets a universal remote and sometimes (as you did) a decent FM tuner.
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Old 9th November 2004, 06:14 PM   #9
Nisbeth is offline Nisbeth  Denmark
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Quote:
Originally posted by mcs
TThe options you have (as I see them) are either:

1. A motorized volume pot
2. A relay attenuator
3. Attenuator chips

Option one is a bit difficult. I have never seen 6-gang motorized pots, and getting three or more pots to rotate at the same speed is not easy.
Hello Mikkel, have a look at these: http://cgi.ebay.de/ws/eBayISAPI.dll?...730904068&rd=1
I have bought two of them and they look and feel like they are good quality parts. I plan to use them for a 6-channel preamp but unfortunately I will not be able to finish the design for a foreseeable future (due to work and studies )


/U.
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Old 9th November 2004, 06:40 PM   #10
mcs is offline mcs  Denmark
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Thanks. I have never seen the 6-gang pots for sale (and I haven't fealt like buying a box of 150).

But I still have to expand my own system from 1 to 2 channels before thinking of 6 channels... I also have a time problem

Best regards,

Mikkel C. Simonsen
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