Addin a second set of outputs to a pre amp,?'s
strider
Posts: 2,568
Hey guys,
I'm interested in adding a second set of outputs to my Tim Rawson built Pass B1 pre amp. When I purchased it, I had spoken to Tim about adding a second set of outputs and he indicated that it wouldn't be that big of a deal to do sometime down the road. First, if I could tell you what I believe to be true, please let me know if I'm off base. Then, assuming that I understand correctly, I've got a couple of procedural questions.
My understanding(s): Pretty simple process, just need to add RCA jacks to the back of the enclosure, grab the signal in the same place the original output jacks get them, ground the new RCAs in the same manner that the original ones are. No need to add any electrical components, as far as I can tell there will be no change to output impedance or level.
Questions:
- Rather then soldering another wire into the PCB for the signal to the new RCAs, can I solder a jumper wire from the original RCA jack to the new RCA jack for each channel?
- Not sure what to do with the ground for the new jacks, would there be a downside (added noise?) if I ran a jumper wire as I plan on doing for the signal to the new RCAs?
- I've got some 24 ga(?) chassis wire, just simple stranded copper stuff, is that ok? Also have shielded wires of various configs, but that stuff's such a PITA to work with....Depending on how I end up wiring up the new jacks, should I try to twist the signal and ground wires for each channel together?
Attached is the Nelson Pass article on the B1, the schematic is at the bottom of page 2.
Thanks in advance,
Ben
I'm interested in adding a second set of outputs to my Tim Rawson built Pass B1 pre amp. When I purchased it, I had spoken to Tim about adding a second set of outputs and he indicated that it wouldn't be that big of a deal to do sometime down the road. First, if I could tell you what I believe to be true, please let me know if I'm off base. Then, assuming that I understand correctly, I've got a couple of procedural questions.
My understanding(s): Pretty simple process, just need to add RCA jacks to the back of the enclosure, grab the signal in the same place the original output jacks get them, ground the new RCAs in the same manner that the original ones are. No need to add any electrical components, as far as I can tell there will be no change to output impedance or level.
Questions:
- Rather then soldering another wire into the PCB for the signal to the new RCAs, can I solder a jumper wire from the original RCA jack to the new RCA jack for each channel?
- Not sure what to do with the ground for the new jacks, would there be a downside (added noise?) if I ran a jumper wire as I plan on doing for the signal to the new RCAs?
- I've got some 24 ga(?) chassis wire, just simple stranded copper stuff, is that ok? Also have shielded wires of various configs, but that stuff's such a PITA to work with....Depending on how I end up wiring up the new jacks, should I try to twist the signal and ground wires for each channel together?
Attached is the Nelson Pass article on the B1, the schematic is at the bottom of page 2.
Thanks in advance,
Ben
Wristwatch--->Crisco
Post edited by strider on
Comments
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Yes.
Questions:
can I solder a jumper wire from the original RCA jack to the new RCA jack for each channel?
That will be fine .Assuming a metal chassis be sure the body of the new connectors are isolated from the chassis to avoid ground loops.- Not sure what to do with the ground for the new jacks, would there be a downside (added noise?) if I ran a jumper wire as I plan on doing for the signal to the new RCAs?
Your 24awg will be fine.If they will be more than a couple of inches I would twist them together.- I've got some 24 ga(?) chassis wire, just simple stranded copper stuff, is that ok? Also have shielded wires of various configs, but that stuff's such a PITA to work with....Depending on how I end up wiring up the new jacks, should I try to twist the signal and ground wires for each channel together?Testing
Testing
Testing -
Thanks GV, already had the holes for the new jacks drilled so it didn't take any time to get it wired up last night. Works great, the pre's much more versatile now.
Thanks again,
BenWristwatch--->Crisco -
That's what I like to hear and Fred's a good guy. Now let's see some pictures of the B1...
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That's what I like to hear and Fred's a good guy. Now let's see some pictures of the B1...
I'll try to sneak some up tonight. Gotta forewarn you, though, it's pretty damn ugly.
Sounds good, though!Wristwatch--->Crisco -
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Hey guys,
I'm interested in adding a second set of outputs to my Tim Rawson built Pass B1 pre amp. When I purchased it, I had spoken to Tim about adding a second set of outputs and he indicated that it wouldn't be that big of a deal to do sometime down the road. First, if I could tell you what I believe to be true, please let me know if I'm off base. Then, assuming that I understand correctly, I've got a couple of procedural questions.
My understanding(s): Pretty simple process, just need to add RCA jacks to the back of the enclosure, grab the signal in the same place the original output jacks get them, ground the new RCAs in the same manner that the original ones are. No need to add any electrical components, as far as I can tell there will be no change to output impedance or level.
Ben
Ben,
That's a very simple and functional preamp design from looking at the schematic. Since it's so simple, I think the ultimate mod for getting a second preamp output is just to clone the entire gain stage after the pot. The input impedance of the FET stage after the pot is really set by the gate impedance and is very high so that adding a parallel FET stage should not be a problem.
The only reason I mention this possibility at all is because the output impedance is basically set by the series resistors R204 and R104 (1kohm). You didn't mention what load your amplifier/equalizer or whatever is, but if the combined driven impedance is anything less than say 25kohm, you may start to see some measureable power loss in the interface.
But if everything is 50kohm or more (more typical), don't sweat it and just add a second pair of jacks like what was suggested! No reason to go overboard. But some people like myself might do it anyways...
:o
