Hey guys, I have had this project in mind for a while now, asked a bunch of related questions and I am finally very close to building it (got most of my parts). One of my last threads was here:
http://www.diyaudio.com/forums/instruments-amps/252690-tube-bass-preamp.html
To make a long story short, I have a working Rumble 350 chassis and I'm going to build an Alembic F2-B clone into the front end. I am 99.9% sure there won't be any problems because this is basically what Fender did with their TV series Bassmans. I'll most likely wire a jack from the PCB and house the F2-B in a separate box.
I just want to merge the two, and looking at the schematics of each, I'm not 100% sure where to do that. I see that the TV uses TL072's and the Rumble uses TL074's, which are really just dual 72's. The TV does not have the Aux. in, headphones or effects loop.
Anyway, here is my guess:
On the TV schem, the signal after R25 should connect to the Rumble schem either:
1) right before R60 or
2) right after C45/R71 (ie. the W4 pin)
Alternately, I could probably just plug the F2-B into the FX return, but then it's going through an extra buffer stage (but that may not be a bad thing).
Thanks if you can help!
http://www.diyaudio.com/forums/instruments-amps/252690-tube-bass-preamp.html
To make a long story short, I have a working Rumble 350 chassis and I'm going to build an Alembic F2-B clone into the front end. I am 99.9% sure there won't be any problems because this is basically what Fender did with their TV series Bassmans. I'll most likely wire a jack from the PCB and house the F2-B in a separate box.
I just want to merge the two, and looking at the schematics of each, I'm not 100% sure where to do that. I see that the TV uses TL072's and the Rumble uses TL074's, which are really just dual 72's. The TV does not have the Aux. in, headphones or effects loop.
Anyway, here is my guess:
On the TV schem, the signal after R25 should connect to the Rumble schem either:
1) right before R60 or
2) right after C45/R71 (ie. the W4 pin)
Alternately, I could probably just plug the F2-B into the FX return, but then it's going through an extra buffer stage (but that may not be a bad thing).
Thanks if you can help!
Oops -should have thought of that:
http://support.fender.com/schematics/bass_amplifiers/Rumble_350_2010_schematic_Rev-B.pdf
http://support.fender.com/schematics/bass_amplifiers/Bassman_TV_series_FBA_schematics_Rev-B.pdf
You can see that the front end of the TV is nearly identical to the F2-B.
I *think* that putting the F2B out right before R60 of the Rumble, I will still be able to use the FX loop but I'm not sure about impedances, etc?
http://support.fender.com/schematics/bass_amplifiers/Rumble_350_2010_schematic_Rev-B.pdf
http://support.fender.com/schematics/bass_amplifiers/Bassman_TV_series_FBA_schematics_Rev-B.pdf
You can see that the front end of the TV is nearly identical to the F2-B.
I *think* that putting the F2B out right before R60 of the Rumble, I will still be able to use the FX loop but I'm not sure about impedances, etc?
That's the place to inject if you want to use the EFX loop, since it will buffer the EFX send. Take a look at the TV schematic for cues on impedance and level matching though.
Didn't read so edited...
Yes, the 12AX7, 100k anode load, 1.5k cathode resistor has become somewhat of a standard. It does have massive gain though, not needed for most basses. You could remove the cathode bypass caps. Cheaper, simples, less space, more headroom and you don't need the gain anyway. Win-win.
Yes, the 12AX7, 100k anode load, 1.5k cathode resistor has become somewhat of a standard. It does have massive gain though, not needed for most basses. You could remove the cathode bypass caps. Cheaper, simples, less space, more headroom and you don't need the gain anyway. Win-win.
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THANK YOU for your input guys! I think this is going to be a very worthwhile mod.
Thanks Passin. I'm curious though - in my limited experience, it looks like it will buffer the tube signal even when the FX loop is not used.
To be more true to the TV circuit, I should probably bypass the FX loop (U5-D) and Line Out (U5-C) by injecting the signal right before R116, have I got that right?
...OR I could stop being lazy and just try it each way.
Thanks Passin. I'm curious though - in my limited experience, it looks like it will buffer the tube signal even when the FX loop is not used.
To be more true to the TV circuit, I should probably bypass the FX loop (U5-D) and Line Out (U5-C) by injecting the signal right before R116, have I got that right?
...OR I could stop being lazy and just try it each way.
Yep -- you could just think of it as an F1-X, not an F2-B...😎
Personally, I'd take advantage of that extra stage to tailor EFX output level to my particular needs. It's not like you're corrupting an "all-tube" signal path or anything.
BTW, have you looked at my recent build using a different ICE module?
Hey guys, I'm this close to diving in and building this sucker but I have a new question about the piezo tweeter:
Currently the Rumble 350 has an annoying hiss that I can't dial out unless I turn the tweeter off. I notice the TV Duo Ten has NO TWEETER. I can't help but wonder if this has something to do with that decision, or if my Rumble is somehow damaged. I already changed out the tweeter, so I believe the noise is coming form the circuit itself. Therefore I need to diagnose whether the hiss is coming from the preamp or power amp. It's not totally clear to me how the signal is split out to the tweeter -does it have its own "channel"?
Can anyone guide me on how to do this and/or provide a fix?
I only have a multimeter... Much appreciated!!!
Currently the Rumble 350 has an annoying hiss that I can't dial out unless I turn the tweeter off. I notice the TV Duo Ten has NO TWEETER. I can't help but wonder if this has something to do with that decision, or if my Rumble is somehow damaged. I already changed out the tweeter, so I believe the noise is coming form the circuit itself. Therefore I need to diagnose whether the hiss is coming from the preamp or power amp. It's not totally clear to me how the signal is split out to the tweeter -does it have its own "channel"?
Can anyone guide me on how to do this and/or provide a fix?
I only have a multimeter... Much appreciated!!!
According to schematic, it's just wired in parallel with other speakers but with an added 5W series resistor to limit current and power. A piezo -type driver as a load is so capacitive by itself that it can work without additional crossovers.
Anyway, it's not the tweeter horn that hisses, it's the extended high frequency response that makes hiss more easily audible.
Thanks guys,
Yes, turning up the treble control brings out the hiss more, but it's barely there when the tweeter is off.
Is there a way to locate and reduce the hiss? I'm clueless when it comes to amp diagnostics.
Yes, turning up the treble control brings out the hiss more, but it's barely there when the tweeter is off.
Is there a way to locate and reduce the hiss? I'm clueless when it comes to amp diagnostics.
If the hiss changes with the treble control, you can bet it's coming from the preamp. Bad quality, high value resistors with massive gain stages will do that. I've always been amazed by how much hiss/hum is allowed on commercial bass amps. One of the reasons I started to build my own and I always have the design goal of minimal hiss/hum.
Hey the good news is that the tube pre could help and make the tweeter usable again?
Ok, One last question:
How would I go about putting a "master" volume on the F2B like the TV Bassmans have, allowing me to run the gain up while maintaining overall control of volume? I am thinking a simple pot grounding the signal, but what value??
I ask because the volume on the TV is part of the SS circuit, and on the Rumble it's pre tone controls.
My F2B is going to be similar to Nordskov's in this thread using 2 toroids:
http://www.diyaudio.com/forums/instruments-amps/120912-alembic-f2-b-3.html
Again, many thanks!
How would I go about putting a "master" volume on the F2B like the TV Bassmans have, allowing me to run the gain up while maintaining overall control of volume? I am thinking a simple pot grounding the signal, but what value??
I ask because the volume on the TV is part of the SS circuit, and on the Rumble it's pre tone controls.
My F2B is going to be similar to Nordskov's in this thread using 2 toroids:
http://www.diyaudio.com/forums/instruments-amps/120912-alembic-f2-b-3.html
Again, many thanks!
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