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
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
Hi Bas
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
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
Bas Horneman said:
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.
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?
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.
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
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
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.
To be honest? I really don't know..what does Vp mean? Basically I just want tubes where the opams are now...
Another resistor of 47k (like the other) and then the other end of the resistor also to ground?
TIA.
Bas.
Bas Horneman said:
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.
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.
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.
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
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
Attachments
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
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
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,
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,
Is the a 1meg grid resistor a problem for the preceding stage?
I am assuming that the differential op-amp stage is the first...and maybe only stage after the dacs...
So I guess I should ask if a 1meg impedance is a problem for the dac?
I saw the posts on the other dac thread here at tubes...saw figures like 6ohm...or are they talking about other things here?
Cheers,
Bas
I am assuming that the differential op-amp stage is the first...and maybe only stage after the dacs...
So I guess I should ask if a 1meg impedance is a problem for the dac?
I saw the posts on the other dac thread here at tubes...saw figures like 6ohm...or are they talking about other things here?
Cheers,
Bas
EF86
Hi,
If the EF86 is the input of an amplifier I would lower it to 100K.
OTOH, if a stage is directly preceding it and wiring can be kept to a minimum, I would go for the 1Meg.
What are you feeding the EF86, you don't use a xformer?
The 6 Ohm R does the I/V conversion at the input of the xformer.
Cheers,
Hi,
If the EF86 is the input of an amplifier I would lower it to 100K.
OTOH, if a stage is directly preceding it and wiring can be kept to a minimum, I would go for the 1Meg.
What are you feeding the EF86, you don't use a xformer?
The 6 Ohm R does the I/V conversion at the input of the xformer.
Cheers,
Hi Frank,
Thanks for helping.
I am thinking that what I am feeding the EF86 is the same signal that goes to the differential op-amps..NE5532. So I guess the I/V conversion..(If any) has allready taken place.
Essentially I am replacing the NE5532 with an EF86 differential stage.
Unfortunately I don't have a schematic of my cd player.
Cheers,
Bas
Thanks for helping.
I am thinking that what I am feeding the EF86 is the same signal that goes to the differential op-amps..NE5532. So I guess the I/V conversion..(If any) has allready taken place.
Essentially I am replacing the NE5532 with an EF86 differential stage.
Unfortunately I don't have a schematic of my cd player.
Cheers,
Bas
Eureka...It works..
Last night I fired up my CD player with the PF86 differential output stage.
To my complete amazement it worked!!!!
Will borrow a digital camara next week and post pictures..
Sound improvement was not the day and night difference I was expecting. Instruments sound more like real instruments...was about the only improvement I heard...Bass seemed a little less
Still have some noise issues...I suspect the toroïdal power transformer...it's the same one I used for a preamp that made the same noise
Filament supply is DC...star earthing is being used.
Anyway...am a happy camper...
Cheers,
Bas
Last night I fired up my CD player with the PF86 differential output stage.
To my complete amazement it worked!!!!
Will borrow a digital camara next week and post pictures..
Sound improvement was not the day and night difference I was expecting. Instruments sound more like real instruments...was about the only improvement I heard...Bass seemed a little less
Still have some noise issues...I suspect the toroïdal power transformer...it's the same one I used for a preamp that made the same noise
Filament supply is DC...star earthing is being used.
Anyway...am a happy camper...
Cheers,
Bas
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