1/2 of the tube for each channel?

[wavycertified]

I came across an interesting build, a simple tube buffered LM1876 amplifier. The circuit uses half of an 6922 for each channel, what is the purpose of this? To eliminate cross talk? Is it really necessary? I thought the tube already have septation plate in the middle? I know this topic have been discussed numerous time, but I cant seem find the correct answer. Can anybody tell me?

see the following schematic:

The original article:
Ipod LM1876 amp

[SY]

There's no reason to do that, even if there's no shield.

[Eli Duttman]

That sort of setup makes some sense when types like the 12A_7 group are employed. Then, channel 1 uses system 1 and channel 2 uses system 2. When the sections in use wear out, you exchange the bottles between channels. The center tap in the heater allows cross talk concerns to be dealt with, without loosing 1/2 the value in each envelope. Of course, SY rightly stated that crosstalk concerns are chasing a will o' the wisp.

[HollowState]

One crazy far-out reason is so you can select perfectly matched sections, even though that's totally unnecessary. A better reason is to make it look "cool" as well as to sell you two tubes instead of only one.

[wavycertified]

Thank you guys. I think one balanced tube will always be better than two closely matched tubes.

[SY]

You don't even need close matching- it's a cathode follower. A poorly-designed cathode follower, but nonetheless, relatively insensitive to tube matching.

[ChrisA]

Originally Posted by wavycertified

I came across an interesting build, a simple tube buffered LM1876 amplifier. The circuit uses half of an 6922 for each channel, what is the purpose of this? To eliminate cross talk? Is it really necessary?..

First off it is a tube buffered chip amp. The builder liely does not know that a unity gain buffer add almost nothing to the sound. The "tube sound" only comes with gain.

The only reason I can think of for using two tubes is the "tube rollers" who want to A/B test using a mono signal/ Likely not what the buillding had in mind.

I think He just wanted the tubes for decoration as they are not doing much else. Placebo effect mostly

[wavycertified]

Originally Posted by ChrisA

First off it is a tube buffered chip amp. The builder liely does not know that a unity gain buffer add almost nothing to the sound. The "tube sound" only comes with gain.

The only reason I can think of for using two tubes is the "tube rollers" who want to A/B test using a mono signal/ Likely not what the buillding had in mind.

I think He just wanted the tubes for decoration as they are not doing much else. Placebo effect mostly

right on...
I'm learning from all you guys lol

[Wavebourn]

Actually, tube buffers here isolate input impedances of IC that are low and non-linear from input sockets. It is the single plus that I see here, except warmness factor (look and feel).

Speaking about shields between halves of tube, they in case of cathode followers are already double-shielded by anodes.

[leadbelly]

As mentioned, a cathode follower in front of a non-inverting opamp is kind of pointless. The valve buffered gainclone started out as a CF driving an inverting opamp, which at least has a point, even though I'll bet a mediocre CF driving an LM chip is higher distortion than the bare LM chip.

If you really want something special you should try adapting Bob Cordell's work on gainclones to a tube front end (Ch 27 of his latest book).