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Old 30th December 2002, 05:27 AM   #1
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Question bridge mono tube amp

bridge mono st-70 do it ?.help me
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Old 30th December 2002, 11:05 AM   #2
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Default BUILDING BRIDGES

Hi,

You will require a phase inverter for one channel.

You then send the signal to both channels and hook up the speaker to the + terminals of the amplifier.

If you need to drive an 8 Ohm speaker the 4 Ohm taps of the OPT should be used.

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Old 30th December 2002, 11:58 AM   #3
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Default Transformer Polarity Inversion......

Car audio retailers (and wholesalers) sell line level transformer coupled DC isolation boxes.
These can be modified to provide polarity inversion of one channel WRT the other.
This will cause the two amplifiers to run in anti-phase, and with the 4 ohm tap arrangements that Frank mentions, you have a cheap and easy means of bridging.

Eric.
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Old 30th December 2002, 12:02 PM   #4
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Default Q

Hi Eric San,

Quote:
Car audio retailers (and wholesalers) sell line level transformer coupled DC isolation boxes.
These do not have an insertion loss?

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Old 30th December 2002, 12:08 PM   #5
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Does anyone happen to have a inverter/tube circuit? Anyone can make a bridging circuit out of op amps. How about a real burn your fingers circuit for this application? In a brigded situation with tubes how much is to be gained by bridging? With solid state amps the power is multiplied by a factor of 3 or 4 times depending on the power supply and the circuit makeup.

Joe
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Old 30th December 2002, 12:09 PM   #6
dhaen is offline dhaen  Europe
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Quote:
These do not have an insertion loss?
You mean voltage? They need not have... depends on the turns.
Actually, if it did, you could get over it by using 2.
I think the biggest drawback might be source loading.

Bye,
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Old 30th December 2002, 12:15 PM   #7
dhaen is offline dhaen  Europe
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Quote:
with tubes how much is to be gained by bridging?
I don't think it's a good route for HiFI. The distortion will be complex, the load undefined.
With SS, bridging brings 2 benefits that are absent from tubes:
1) Increased power for the same supply rail.
2) Ability to use half value smoothing caps on a common supply rail.
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Old 30th December 2002, 12:16 PM   #8
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I think that Frank is correct about the insertion loss here.

I think that another consideration here might be performance/frequency loss.
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Old 30th December 2002, 12:17 PM   #9
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Hello,

Quote:
Actually, if it did, you could get over it by using 2.
Exactly that I had in mind.

Quote:
Does anyone happen to have a inverter/tube circuit?
I do have a Counterpoint SA Pi phase inverter...never got around to drawing the circuit diagram.

Actually it uses one ECC88/6DJ8 as an anode follower with almost no gain.
There is a little trimpot on the frontplate to adjust gain setting but I can't hear any difference any way I turn it.

You can easily build your own with just a dual triode,all you need to know is that any single amplifying stage will invert absolute polarity.

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Old 30th December 2002, 12:19 PM   #10
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Default Cheap, Easy And Good Phase Inverter....

On my workshop system, I have one with reversing switches that I fitted on the primaries, and it works just fine for AUS$12.00 plus switches.
The secondaries need to be resistively loaded to avoid peaking in HF, but distortion is not noticeable, and I find the system is long term nicer with the transformer coupling.

Eric.
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