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Old 10th March 2003, 09:11 PM   #1
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Default Differential to single ended...

Hi,

my output stage in my cd players uses ne5532 op amps. To pin 2 and 3 I see two 19,9k resistors...so I reckoned the op amp is in differential and the two 19,9k resistors are grid stoppers.

1.) is that the same as balanced?

I want to build a differential amp with pf86..

3.) I was thinking about 250volts 68k plate resistor..and 3mA current source for the 2 cathodes of the pf86..or should it be 6mA because there are 2 in "parallel"..
4.) How do I finally convert the differential to single ended again ..without using a transformer..can I simply join the two wires after the cap :-)...

Cheers,
Bas
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Old 11th March 2003, 06:04 AM   #2
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Hi Bas

Quote:
the two 19,9k resistors are grid stoppers
Ha, ha ,ha well said.

1. Yes. You may also wish to look at the value of the feedback resistor pin2-pin6
2. There is no 2?
3. Don't know nothing bout PF86 but they will certainly share the CC.
4. You can pick up output from a differential amp from any of the two plates through a cap - just choose your phase.


cheers

peter
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Old 11th March 2003, 09:33 AM   #3
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Default Re: Differential to single ended...

Quote:
Originally posted by Bas Horneman
my output stage in my cd players uses ne5532 op amps. To pin 2 and 3 I see two 19,9k resistors...so I reckoned the op amp is in differential and the two 19,9k resistors are grid stoppers.

1.) is that the same as balanced?
It <i>might</i> be, but without seeing the rest of the circuit I wouldn't like to say for certain.
There are no grip stoppers with opamps, because there are no grids.

Quote:
I want to build a differential amp with pf86..

3.) I was thinking about 250volts 68k plate resistor..and 3mA current source for the 2 cathodes of the pf86..or should it be 6mA because there are 2 in &quot;parallel&quot;..
If you want 3mA in eash of the PF86's then your CCS needs to be configured for 6mA.

Note with 3mA through the plate resistor, Vp = 46V. Is that what you intended?

Quote:
4.) How do I finally convert the differential to single ended again ..without using a transformer..can I simply join the two wires after the cap :-)...
My preferred method would be to use a transformer. But all you need to do is slect the phase you wish to use and connect it to the poweramp. The other phase needs to be connected to the same impedance as the poweramp input. I would run a balanced cable between the amps, and connect the "unused" side to the resistor at the amp end. that way both phases see as close to the same impedance as possible accounting for cable capacitances etc.
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Old 11th March 2003, 01:10 PM   #4
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Hi Brett

How would you describe the perceived improvements in sound quality since your system was fully balanced? I have several arms, all of which are in use and will probably get some more; does switching over to balanced mean altering the grounding arrangement of most arms? At some stage i experimented with a solid state circuit built around INA103 which is very easy to switch between balanced/non-balanced and couldn't hear any improvement but of course the output was always single ended.

thanks


peter
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Old 11th March 2003, 04:43 PM   #5
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Quote:
You can pick up output from a differential amp from any of the two plates through a cap - just choose your phase.
Thanks for the answers Peter and Brett.

Wont power taken from one of the outputs defeat the object of it being differential? If so I could always get a transformer later.



Quote:
Note with 3mA through the plate resistor, Vp = 46V. Is that what you intended?
To be honest? I really don't know..what does Vp mean? Basically I just want tubes where the opams are now...

Quote:
and connect the "unused" side to the resistor at the amp
Another resistor of 47k (like the other) and then the other end of the resistor also to ground?

TIA.
Bas.
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Old 11th March 2003, 04:56 PM   #6
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Quote:
Originally posted by Bas Horneman
Wont power taken from one of the outputs defeat the object of it being differential? If so I could always get a transformer later.
There are some advantages, but I'm not sure they'd be significant if you're only running one phase into the poweramp.
As we're not sure you DAC is diff (differential / balanced), then a balanced linestage is not worth the extra hassle.

A schematic of your DAC would be a big help in clarifying things.

Quote:
To be honest? I really don't know..what does Vp mean? Basically I just want tubes where the opams are now...
Vp = voltage at the plate. You mentioned 250V B+ with a 68k load and 3mA. Therefore the drop between the B+ and the plate is 68000 x 3mA = 204V, which leaves 46V between plate and ground.

Quote:
Another resistor of 47k (like the other) and then the other end of the resistor also to ground?
Assuming your poweramp has an input impedance of 47k, then I'd place another 47k resistor between the 'unused' phase and earth, at or in the poweramp.
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Old 11th March 2003, 05:41 PM   #7
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Unfortunately I don't have a schematic..for my cd player..it's a Sony CDP911 of around '93. I think I'll post at some other forum..say digital..maybe someone can help me.

I was using the schematic below as a blueprint or guide..I see now what you mean..they mean 250v on the plate not on the resistor!!! Thanks for the clarification..

Cheers,
Bas
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File Type: jpg no.23fig3.jpg (23.5 KB, 613 views)
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Old 11th March 2003, 06:29 PM   #8
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Just wondering: what's so great about EF86 as a line amp?
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Old 11th March 2003, 06:52 PM   #9
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Apparently the EF86 was made especially for audio applications unlike many other tubes. Not that that is a guarantee for a good sounding tube in itself.

But it has low distortion..and by many regarded as a good sounding tube...now as the pf86 is a 4,5v/300mA version as opposed to 6,3v/600mA of the ef86. Prime NOS pf86 like the "Miniwatt" version (Siemens) or philips can be had for $2 instead of $30-35 for the ef86..

I got a few of these for free from a fellow diy'er I though this would be a good application for them.

Cheers,
Bas
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Old 12th March 2003, 12:56 AM   #10
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Default EF86.

Hi Bas,

Years ago when Telefunken and Philips valves weren't as scarse as today I used to look down on the Rusky stuff.

Nowadays their EF86 is actually as good as a TFK EF806S, if not better.

If you can't find TFK PF86s I wouldn't bother and opt for the Svets..

I know, in view of our recent mail exchange you must be LOL...I'm serious though, give them a couple of weeks to settle and you'd be surprised.

Gosh...I'm starting to sound like a salesman....

Cheers,
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