6 channel pre amp?

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lbstyling

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Joined 2008
#1
hello all,

Im looking to buy or build a 6 (or 8) channel pre-amp for use with analogue outs from a bluray player.

The idea is to avoid the whole processor stage.

The pre will need a single master vol control that controls all 6 channels at a balanced level and possibly trim levels for each channel.

so far Ive found a kit from selextronic thats designed for use with the behringer dcx2496

Multi channel volume control DCX2496

there is also the passive option-

Passive Vorstufe mit High-End Leitplastikpoti


I would prefer the active option, but is the selectronic pre a realy good design? what other options are there? any easy diy options?

is there a cheap way i could try it with a second hand mixer or somthing- just to try?

thanks people.
 
#2
Building your own is cool, but one has to ask - why? What is the "processor stage" you are trying to avoid? In the HT receiver?

The Bluray player has to have some sort of processor in it to supply you with analog outputs. Is it worse than one built into an HT receiver?
 
#3
hi panomaniac, how are you?

home cinema recivers are poor quality generally and focus on features over porformance, and due to having the amp section (and me wanting to use my own power amp) they dont have very good sound to my ears at all.

so this means that a processor would be the best option .....except there is only 1 hdmi processor available for reasonable money new (the emotiva umc-1) and it has many issues.

besides this, many of us over on avforums have come to the conclusion that the legacy processors of the past are still vastly superior when used via the multi channel in, with the dac stage and speaker distances etc done in the player.
This is possibly down to the huge amount of jitter the hdmi interface inherently has (often 8000ps or more)- its been argued that bitstreaming stops this happening- but many have now separately confirmed a big difference between even very expensive hdmi bitstreaming processors and old legacy units in foavor of the legacy units.

The value of legacy processors with multi-channel inputs AND a pure analogue bypass mode (lexicon mc12 etc) has been rising very quickly because of this, and are now very expensive considering that when used for this perpose, most of the unit wont be in use.

so whats needed is a good 6 or 8 channel preamp preferably active and top quality, for reasonable money.
 
#4
OK, gotcha.
Finding a good 6 channel pot or attenuator is the real problem. I've played with the Alps 4 and 6 channel pots, but they tend to come in 100K, which I'm not crazy about. Having the motor and remote is nice, tho.

After that it's just a 6 channel buffer. What were you thinking, opamp, buffer IC, transistor or tube? Once you know, you just have to build.
 
#5
I've been thinking the same type of multichannel preamp based on either the Cirrus Logic
or TI PGA chips, It could possibly be designed to have a master volume and individual
channel trimming. The idea of a LCD display and even being able to use the controlling
processor to provide input selection also is attractive. Volume control could be adjusted
by remote, FP pushbuttons, or optical rotary encoder.
I'm not a programmer though and haven't been able to find controller chips pre-programmed.
 
#6
coloradosounds ideas seams good- but I assume this would be a big job to build/design.

I like the idea of valves, the only thing is that I get the impression It could be expensive for this option and how well is it going to drive 20hz bass notes?

not sure what buffer ic is- is that a chip baised design?

transistor design seams likely, as long as the sound isnt too hard.

would this be a good pot?-
DACT audio attenuators

they sell all the components to do what i want- I think this will be expensive though.

Multi-channel active preamp using CT101
 
#8
lbstyling said:
coloradosounds ideas seams good- but I assume this would be a big job to build/design.

I like the idea of valves, the only thing is that I get the impression It could be expensive for this option and how well is it going to drive 20hz bass notes?

not sure what buffer ic is- is that a chip baised design?

transistor design seams likely, as long as the sound isnt too hard.
Click to expand...

I don't see any reason why it couldn't drive 20Hz unless attempting to drive
very low impedence. It is only used as preamp - line level.
The chips have capability of driving loads down to about 600 ohms so just about
any power amp isn't going to limit the output and no excessively small caps in signal
path. The only case where I would see needing buffers is if the source has abnormally
high output impedence.

lbstyling said:
would this be a good pot?-
DACT audio attenuators

they sell all the components to do what i want- I think this will be expensive though.

Multi-channel active preamp using CT101
Click to expand...

The CT2 attenuators by themselves won't offer capability to trim channels,
but I like that concept in the second link of using the 6 deck control and the 3
CT101 boards beneath it and then wiring in some smaller trimmers.
 
#9
coloradosound said:
I've been thinking the same type of multichannel preamp based on either the Cirrus Logic
or TI PGA chips, It could possibly be designed to have a master volume and individual
channel trimming. The idea of a LCD display and even being able to use the controlling
processor to provide input selection also is attractive. Volume control could be adjusted
by remote, FP pushbuttons, or optical rotary encoder.
I'm not a programmer though and haven't been able to find controller chips pre-programmed.
Click to expand...

About 7 years ago, when the DCX2496 first came out, there was a lot of interest in 6-channel preamps...so I made one. It used the TI PGA chips, and had all the trimmings: optical rotary encoders, graphical LCD display, IR remote control, etc. However, the design ended up being expensive..one day I added up the costs and found it was between $500-$600. A bit out of the DIY'er price range.

I never actually used it as a preamp--ended up using it as a fancy A/B speaker switch that provides volume level compensation. It could be made a lot cheaper by using a single PC board, mechanical encoders, cheaper knobs, a simpler display and so on, but I never revisited the design. Someday I may get around to coming up with a low-cost version. Every once in a while I see posts about wanting a 6/8-channel preamp or a volume-compensated speaker switch box, but I've never seen enough interest to justify the design time.

An externally hosted image should be here but it was not working when we last tested it.
 
#10
Cool Neil. I remember you talking about that. At one point you had found a nice volume chip for me that had no built in opamp. Searched our emails but could not find it. Not to worry, Maxim has a few, as well as Toshiba. There is even one that does not need a micro, just a rotary encoder. Has opamps, tho.

It would make a good project for the forum. Group buy, may even.
 
#13
coloradosound said:
Did you use the Atmel or the Microchip interface?
Click to expand...

I'm an old Motorola guy--I use the Freescale 68S08 series of micros. You are obviously confusing me with someone much younger 🙂

I'm not opposed to using the newer PIC chips, but Freescale has some great development tools that are very cheap, and they have a good selection of features and packages in the 'S08 series. So does PIC, but I've got the instruction set and architecture of the 6800 memorized, so I'm sticking with them until I really *have* to change.
 
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