Hi,
I'm thinking about making a mod to my passive preamp... I’m not an engineer and wanted to bounce my idea off of the group. My passive drives a tube amp and the problem I’m having is something I think tube amp people may have seen and can relate to so I put this question on this forum. I appreciate any time in talking on this topic all.
Background.
I have a home built passive preamp. This passive pre has a 100 K attenuator and it is routed to a pair of outputs. I built the passive so I could connect my tube amp and a sub woofer powered by a plate amp. If I have just the tube amp connected the sound is great and the unit works well. If I am running the system with just the tube amp and then connect to the passive on the 2nd set of the sub woofer the subwoofer sort of sucks the life out of the tube amp. Things sound fine but the volumn level on the tube amps drops a decent amount. I have a second tube amp that I’ve tested with.. If I connect the 2nd tube amp the issue I described with the plate amp of the sub is not happening
Issue –
I think the impedance of the tube amp and the plate amp on the subwoofer is the issue. I think the volts of the signal from the passive pre get sucked into the subwoofer where the volts can flow less restricted.
Possible cheap fix –
I found some talk on this forum that I think is related (I think)… I read some items that make me think 22k or 47k resistors on the (+) wire to the ouput RCA jacks may be the fix. I think I’d just need four resistors… Disconnect the (+) wire connected to one of the ouput RCA jacks and insert between the (+) wire and the (+) solder tab of the ouput RCA the resistor. I’d do this for the R and L of each channel. The idea here is that the resistors will isolate the two output channels from one another and the impedance bug won’t be so apparent.
I appreciate the help of the DIY group here… Again, I put this on the Tube Amp forum as I thought the tube amp folks may have experience with this given the impedance of tube amps…
I'm thinking about making a mod to my passive preamp... I’m not an engineer and wanted to bounce my idea off of the group. My passive drives a tube amp and the problem I’m having is something I think tube amp people may have seen and can relate to so I put this question on this forum. I appreciate any time in talking on this topic all.
Background.
I have a home built passive preamp. This passive pre has a 100 K attenuator and it is routed to a pair of outputs. I built the passive so I could connect my tube amp and a sub woofer powered by a plate amp. If I have just the tube amp connected the sound is great and the unit works well. If I am running the system with just the tube amp and then connect to the passive on the 2nd set of the sub woofer the subwoofer sort of sucks the life out of the tube amp. Things sound fine but the volumn level on the tube amps drops a decent amount. I have a second tube amp that I’ve tested with.. If I connect the 2nd tube amp the issue I described with the plate amp of the sub is not happening
Issue –
I think the impedance of the tube amp and the plate amp on the subwoofer is the issue. I think the volts of the signal from the passive pre get sucked into the subwoofer where the volts can flow less restricted.
Possible cheap fix –
I found some talk on this forum that I think is related (I think)… I read some items that make me think 22k or 47k resistors on the (+) wire to the ouput RCA jacks may be the fix. I think I’d just need four resistors… Disconnect the (+) wire connected to one of the ouput RCA jacks and insert between the (+) wire and the (+) solder tab of the ouput RCA the resistor. I’d do this for the R and L of each channel. The idea here is that the resistors will isolate the two output channels from one another and the impedance bug won’t be so apparent.
I appreciate the help of the DIY group here… Again, I put this on the Tube Amp forum as I thought the tube amp folks may have experience with this given the impedance of tube amps…
i think that it might help but will not solve the problem totally
the best way is to probably drive a Buffer in a way to isolate the problem of impedance...
since its for a sub almost anything will do the job .... stay with this .... a passive 100k to a source that has very high impedance is the cleanest you will ever get dont destroy it with unrelated signals or impedance
( thanks to your amplifier's impedance except clean you loose very litle of the dynamics in low power ...this is importand to keep and this is why solid state people with amplifier impedance of 22-47K cannot be happy with passives or even B1 buffers ...in low listening levels more kick is required ... )
the best way is to probably drive a Buffer in a way to isolate the problem of impedance...
since its for a sub almost anything will do the job .... stay with this .... a passive 100k to a source that has very high impedance is the cleanest you will ever get dont destroy it with unrelated signals or impedance
( thanks to your amplifier's impedance except clean you loose very litle of the dynamics in low power ...this is importand to keep and this is why solid state people with amplifier impedance of 22-47K cannot be happy with passives or even B1 buffers ...in low listening levels more kick is required ... )
Sakis, SY,
I've been doing some research on buffer stages... I agree a buffer from the passive to the Sub Woofer would be a help. Since this buffer would not be in the signal to my Tube Amp I'm thinking of a real basic PASS B1 Buffer Between the Passive and the Sub. Cheaper and I don't think I'd really hear the benefits of a tube buffer out of the sub.
???
I appreciate the advice!
I've been doing some research on buffer stages... I agree a buffer from the passive to the Sub Woofer would be a help. Since this buffer would not be in the signal to my Tube Amp I'm thinking of a real basic PASS B1 Buffer Between the Passive and the Sub. Cheaper and I don't think I'd really hear the benefits of a tube buffer out of the sub.
???
I appreciate the advice!
Hi,
So I've been doing some research and trying to learn more about input/output impedance. I agree that if I'm going to run the Passive Preamp I have that a Buffer stage is an area of need.
I've been reading about the DC coupled B1 buffer... Looks like a nice piece when built up well. I'm interested in building a tube buffer... But I'm a newbie. I've built a tube amp from kit and I've built speakers with me building crossovers from parts. Does someone have a good reference on a tube buffer project? One with some build photos and such? One with a parts list even?
Sorry for all the questions... Again, Not a designer and not much experience... Just enough to know about the risk of working high volts and having caps in the mix.
So I've been doing some research and trying to learn more about input/output impedance. I agree that if I'm going to run the Passive Preamp I have that a Buffer stage is an area of need.
I've been reading about the DC coupled B1 buffer... Looks like a nice piece when built up well. I'm interested in building a tube buffer... But I'm a newbie. I've built a tube amp from kit and I've built speakers with me building crossovers from parts. Does someone have a good reference on a tube buffer project? One with some build photos and such? One with a parts list even?
Sorry for all the questions... Again, Not a designer and not much experience... Just enough to know about the risk of working high volts and having caps in the mix.
these buffered ideas takes away from the passive model. what you need is a real autoformer volume control....and get rid of the resistive pot. Your problem is the voltage drop becuase of the pot. In the autofomer volume control model you can use the different windings to balance the levels to each input while at the same time isolating each input from the effects of the other. the autoformer approach reduces noise and distortion.
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