NewYorkDave 2 bottle- output attenuator?
- Thread starter Freddy G
- Start date
Help Support GroupDIY Audio Forum:
NewYorkDave
Well-known member
You could use a 1K audio-taper pot after the output transformer. A constant-impedance stepped attenuator would be better, but the pot will work OK. Just make sure the load that follows the pot is not less than 1.5kOhms.
Thanks Dave,
I've got a bunch of different styles of attenuators I could use (24 position Goldpoint Elma switches). There is a shunt, a ladder and a mini V. Would one of these work as a constant impedance stepped attenuator?
(every time I write the word "impedance" now I think about my "re-amp" box that I silk screened "Impedence"!)
Freddy :sam:
I've got a bunch of different styles of attenuators I could use (24 position Goldpoint Elma switches). There is a shunt, a ladder and a mini V. Would one of these work as a constant impedance stepped attenuator?
(every time I write the word "impedance" now I think about my "re-amp" box that I silk screened "Impedence"!)
Freddy :sam:
Kingston
Well-known member
On my two-bottle, I did the unbalanced (floating) bridged-T 600-ohm attenuator newyorkdave posted on the original one-bottle thread.
There were only 6-step dual switches available here on short notice so I recalculated some values and did a version that does 5dB attenuation steps to -25dB and the off position.
Simple and works like a charm.
There are some calculators for just this purpose to work out your own stepping somewhere on the net. I seem to have misplaced the links that I used.
There were only 6-step dual switches available here on short notice so I recalculated some values and did a version that does 5dB attenuation steps to -25dB and the off position.
Simple and works like a charm.
There are some calculators for just this purpose to work out your own stepping somewhere on the net. I seem to have misplaced the links that I used.
kiira
Well-known member
Are you guys adding the output attenuator in order to be able to vary the output and still drive the the input? That seems pretty worthwhile - I've been having a lot of fun using my 2 bottle as a preamp for my guitar. I wouldn't mind having some tone controls. :razz:
Kiira
Kiira
Kingston
Well-known member
[quote author="kiira"]Are you guys adding the output attenuator in order to be able to vary the output and still drive the the input?[/quote]
Yeah. Admittedly, due to the pre-amp design the gain is very linear and driving it is rather subtle. I accidentally usually saturate the output transformers before noticing much impact on sound.
In fact, I asked about similar no-frills designs that can be abused as well. Collins 6q1 was suggested with interstage gain added, but newyorkdave's response was this:
http://www.groupdiy.com/index.php?topic=16727&highlight=
.. a no-feedback mod of the one-bottle, capable of a tubey driven sound as well. :thumb: Certainly on my to-do list.
Yeah. Admittedly, due to the pre-amp design the gain is very linear and driving it is rather subtle. I accidentally usually saturate the output transformers before noticing much impact on sound.
In fact, I asked about similar no-frills designs that can be abused as well. Collins 6q1 was suggested with interstage gain added, but newyorkdave's response was this:
http://www.groupdiy.com/index.php?topic=16727&highlight=
.. a no-feedback mod of the one-bottle, capable of a tubey driven sound as well. :thumb: Certainly on my to-do list.
Marik
Well-known member
And don't forget an old trick for an attenuator--insert a pot between + and - of the output transformer secondaries --simple and elegant.
NewYorkDave
Well-known member
rlaury
Well-known member
Hi Group:
There's a little problem with figure #1.
It's actually not an attenuator at all.
It's a sort of a phase rotator really.
At center rotation the signal cancels.
I just thought I'd bring it up before
someone builds it.
RonL
http://www.nashaudio.com
There's a little problem with figure #1.
It's actually not an attenuator at all.
It's a sort of a phase rotator really.
At center rotation the signal cancels.
I just thought I'd bring it up before
someone builds it.
RonL
http://www.nashaudio.com
clintrubber
Well-known member
[quote author="rlaury"]Hi Group:
There's a little problem with figure #1.
It's actually not an attenuator at all.
It's a sort of a phase rotator really.
At center rotation the signal cancels.
I just thought I'd bring it up before
someone builds it.[/quote]
You sure ? The sim might be fooling us for not showing a completely floating secondary.
I've never tried this kind of att myself but have seen it being mentioned & used, so can't imagine it won't work.
(This is another of those posts that I wouldn't have replied to if it was April 1st since I'm not sure if it's.... :wink: )
Regards,
Peter
There's a little problem with figure #1.
It's actually not an attenuator at all.
It's a sort of a phase rotator really.
At center rotation the signal cancels.
I just thought I'd bring it up before
someone builds it.[/quote]
You sure ? The sim might be fooling us for not showing a completely floating secondary.
I've never tried this kind of att myself but have seen it being mentioned & used, so can't imagine it won't work.
(This is another of those posts that I wouldn't have replied to if it was April 1st since I'm not sure if it's.... :wink: )
Regards,
Peter
martthie_08
Well-known member
Dave, thanks for the drawings, what are the resistor and pot values for figure 2 - 300 Ohms and 1K log?
kiira
Well-known member
[quote author="Kingston"]
Yeah. Admittedly, due to the pre-amp design the gain is very linear and driving it is rather subtle. I accidentally usually saturate the output transformers before noticing much impact on sound.
In fact, I asked about similar no-frills designs that can be abused as well. Collins 6q1 was suggested with interstage gain added, but newyorkdave's response was this:
http://www.groupdiy.com/index.php?topic=16727&highlight=
.. a no-feedback mod of the one-bottle, capable of a tubey driven sound as well. :thumb: Certainly on my to-do list.[/quote]
Oh thanks Kingston I had not seen that one from Dave. I'd be interested in that as well, I need a pre to put into the pre-comp-eq I've started and a one bottle would be nice.
So you made a 6 step bridged T attenuator from the design Dave provided a while back? I had to take my atten. out because it was causing big trouble, but with all the gain this has I'll need one and a multi value one would be really nice. Maybe I'll bug you shortly about wiring it up.... I have this major inability to translate switch schematics into the 3D world of the switch. urk :?
I've already used mine briefly to do a little demonstration tracking for some friends' band. They use stuff like the 1216M (I think?) for pres and they were just blown away by the clear full sound of the NYD-2b. I think their idea of what toobs sound like was based on the starved plate designs that are around... not a real tube design.
later,
Kiira
Yeah. Admittedly, due to the pre-amp design the gain is very linear and driving it is rather subtle. I accidentally usually saturate the output transformers before noticing much impact on sound.
In fact, I asked about similar no-frills designs that can be abused as well. Collins 6q1 was suggested with interstage gain added, but newyorkdave's response was this:
http://www.groupdiy.com/index.php?topic=16727&highlight=
.. a no-feedback mod of the one-bottle, capable of a tubey driven sound as well. :thumb: Certainly on my to-do list.[/quote]
Oh thanks Kingston I had not seen that one from Dave. I'd be interested in that as well, I need a pre to put into the pre-comp-eq I've started and a one bottle would be nice.
So you made a 6 step bridged T attenuator from the design Dave provided a while back? I had to take my atten. out because it was causing big trouble, but with all the gain this has I'll need one and a multi value one would be really nice. Maybe I'll bug you shortly about wiring it up.... I have this major inability to translate switch schematics into the 3D world of the switch. urk :?
I've already used mine briefly to do a little demonstration tracking for some friends' band. They use stuff like the 1216M (I think?) for pres and they were just blown away by the clear full sound of the NYD-2b. I think their idea of what toobs sound like was based on the starved plate designs that are around... not a real tube design.
later,
Kiira
NewYorkDave
Well-known member
The simulator will only show you signal amplitudes relative to ground. Sometimes you need to define "ground" in a simulated circuit in a manner that's different from how it's wired in real life--or else you'll get misleading results.
You need to look at the relative amplitude between pins 2 and 3 of the XLR. So, to get the simulator to display correctly, ground the low side of the attenuator.
In real life, the low side can be grounded or ungrounded, at the user's option, depending on what yields the best results. It's just a simple voltage divider circuit.
It's a bridged-T attenuator. The two fixed resistors are 600 ohms. The dual "pot" is an unequal value with a special taper; it's not a pot you can buy commercially, at least not nowadays. The usual way of implementing this now would be as a stepped attenuator, using a two-pole switch. Here's an example:
Schematic
You need to look at the relative amplitude between pins 2 and 3 of the XLR. So, to get the simulator to display correctly, ground the low side of the attenuator.
In real life, the low side can be grounded or ungrounded, at the user's option, depending on what yields the best results. It's just a simple voltage divider circuit.
It's a bridged-T attenuator. The two fixed resistors are 600 ohms. The dual "pot" is an unequal value with a special taper; it's not a pot you can buy commercially, at least not nowadays. The usual way of implementing this now would be as a stepped attenuator, using a two-pole switch. Here's an example:
Schematic
rlaury
Well-known member
RE: Fig1
Your ok if you ground one side. But not ok floating.
Build and try it. Look at it with a scope. When the upper arm
of the voltage divider is equal R to the lower arm, the signal
cancels. When upper arm is larger R than the lower, the phase is
flipped. I don't see any benefit of having the transformer if
you have to ground one side. The other fig's are correct though.
The fig below is workable version of fig1. Maybe this is what you
were thinking about.
RonL
http://www.nashaudio.com
Your ok if you ground one side. But not ok floating.
Build and try it. Look at it with a scope. When the upper arm
of the voltage divider is equal R to the lower arm, the signal
cancels. When upper arm is larger R than the lower, the phase is
flipped. I don't see any benefit of having the transformer if
you have to ground one side. The other fig's are correct though.
The fig below is workable version of fig1. Maybe this is what you
were thinking about.
RonL
http://www.nashaudio.com
NewYorkDave
Well-known member
Dude, you're not getting it. I didn't say you have to ground one side in real life--you can if you want, but you don't have to. But you DO have to ground one side in the simulator if you want the simulation to run correctly. Simulations are not reality!
People get so wrapped up in the idea of "ground"... The destination device (whatever it is) hooked up to the XLR jack cares about the amplitude difference between pins 2 and 3 and doesn't give two shits if one of them is "ground" or not. But the simulator does care--it will only show you the amplitude relative to ground, not some arbitrary point, so you have to play along and ground one of those pins to see the voltage difference between them.
Another trick: set up another transformer, 1:1, to represent your balanced receiver. Inject the output of the pot into its primary, ground the low side of the secondary (to give your simulator that reference it needs to keep it happy) and look at the signal voltage at the high side of the secondary as you run the pot up and down.
Indeed. It works, and takes about as much time to wire up as it does to simulate.
People get so wrapped up in the idea of "ground"... The destination device (whatever it is) hooked up to the XLR jack cares about the amplitude difference between pins 2 and 3 and doesn't give two shits if one of them is "ground" or not. But the simulator does care--it will only show you the amplitude relative to ground, not some arbitrary point, so you have to play along and ground one of those pins to see the voltage difference between them.
Another trick: set up another transformer, 1:1, to represent your balanced receiver. Inject the output of the pot into its primary, ground the low side of the secondary (to give your simulator that reference it needs to keep it happy) and look at the signal voltage at the high side of the secondary as you run the pot up and down.
Indeed. It works, and takes about as much time to wire up as it does to simulate.
Kev
Well-known member
[quote author="NewYorkDave"]Dude, you're not getting it. .... But you DO have to ground one side in the simulator if you want the simulation to run correctly. Simulations are not reality![/quote]
that's why they call them sim.... :shock: nevermind Dave
it does actually take some time to write a good model in software
and then check the device in reality
and then go back to the model to make adjustments
and around and around you go
then when you have good data you can inject the results in to the more complicated Simulator that carries even more data and more models
and around and around you go
:grin:
yes when done right it call all be worth it
and
yes for the simple stuff
it's just easier to build and test the real thing
that's why they call them sim.... :shock: nevermind Dave
it does actually take some time to write a good model in software
and then check the device in reality
and then go back to the model to make adjustments
and around and around you go
then when you have good data you can inject the results in to the more complicated Simulator that carries even more data and more models
and around and around you go
:grin:
yes when done right it call all be worth it
and
yes for the simple stuff
it's just easier to build and test the real thing
skipwave
Well-known member
Hmmmmmm, haven't we talked about this before. :wink:
http://www.groupdiy.com/index.php?topic=2229
http://www.groupdiy.com/index.php?topic=5779
http://www.groupdiy.com/index.php?topic=2192
http://www.groupdiy.com/index.php?topic=1860
http://www.groupdiy.com/index.php?topic=2229
http://www.groupdiy.com/index.php?topic=5779
http://www.groupdiy.com/index.php?topic=2192
http://www.groupdiy.com/index.php?topic=1860
Kev
Well-known member
yep
and we probably will again
you get that
and we probably will again
you get that
