IF you have a preamp with an output impedance that is below 100, it will serve the same function as the buffer in providing a low source impedance for the transformer. You will have the additional effect of whatever cable you are using, but it should be minimal. Another way to look at it is this, one less part in the signal path.
I have a DIY B-1 with volume knobs as pre amp, which should not present an output impedance problem "softening" the highs, but F-6 has no more gain basically than F-5, which is a small problem with some speakers, gain wise.
If the BA-3 FE preamp's output impedance is as high as is said it would soften the highs, right? Assuming more gain is needed with a particular pair of speakers would it work (I understand somewhat more circuitry and somewhat of a waste of it) to run the BA-3 FE into the B-1?
If so, would it be advantageous to either:
Run a BA-3 FE without volume control into B-1?
Or, Run BA-3 FE with volume control into B-1 without volume control?
Budweiser's build is where I got this idea, I believe he had BA-3 FE ( no volume control, just FE) going into B-1 with volume control, feeding F-4, IIRC. Or was it B-1 into BA-3? May have been!
I think it was that way...but I would need buffer next to amp...
I know I could use a more efficent set of speakers, or different power amp, but that isnt my inquiry.
Thanks for any input,
Russellc
If the BA-3 FE preamp's output impedance is as high as is said it would soften the highs, right? Assuming more gain is needed with a particular pair of speakers would it work (I understand somewhat more circuitry and somewhat of a waste of it) to run the BA-3 FE into the B-1?
If so, would it be advantageous to either:
Run a BA-3 FE without volume control into B-1?
Or, Run BA-3 FE with volume control into B-1 without volume control?
Budweiser's build is where I got this idea, I believe he had BA-3 FE ( no volume control, just FE) going into B-1 with volume control, feeding F-4, IIRC. Or was it B-1 into BA-3? May have been!
I think it was that way...but I would need buffer next to amp...I know I could use a more efficent set of speakers, or different power amp, but that isnt my inquiry.
Thanks for any input,
Russellc
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I will just have to rethink my plans. I can remember in my tube days, I had (and still have a AVA Super Pass II. Being a tube preamp without a cathode follower arrangement, it had a higher output impedance. Their "cure" for this was an option to install a solid state buffer on the output. I didnt do this, but that's what got me thinking about this with the B-1. Many said it changed the nature of the preamps sound.
I can only imagine doing it here, plus altering the BA-3 FE feedback wise would likely change it as well. I think I will first, just try it and see if it is disagreeable, and if so either rethink which system/speakers this F-6 will go in, or devise a different preamp. I suppose the BA-2 as preamp would have the same problem? I've got the board for it...
Russellc
I can only imagine doing it here, plus altering the BA-3 FE feedback wise would likely change it as well. I think I will first, just try it and see if it is disagreeable, and if so either rethink which system/speakers this F-6 will go in, or devise a different preamp. I suppose the BA-2 as preamp would have the same problem? I've got the board for it...
Russellc
Good news, I will let you know how it works out. Still waiting for store to get boxes, all else is ready to go, boards, power supply, transformer all waiting.
Same deal with Aleph J....but F-6 is first, going to use 4U Deluxe, I will step up size to 5U Deluxe for Aleph J, may repurpose it later for something that would require it.
Russellc
Whoops, just noticed you mentioned "output stage" you are talking about the BA-3 power amp, right? Not the BA-3 FE...
I will still let you know how BA-3 FE works with F-6 It works great with F-5, a completely different amp than F-6.
Russellc
To follow up, Russell, if you look at the distortion figures for the B1, you can see that the circuit is best suited for small signal use. As you begin to ask for more voltage swing, you see that performance is dignificantly affected. It does incredibly well for what it was designed for, buffering a signal in the 0-2V range.
Attachments
If you decide to forego the buffer, just remember that the source should be
DC coupled or you will experience motor-boating.
You are talking about not using the Jfets and going straight into the transformer right? This isnt a comment in regard to my fore going the B-1 and trying the high output impedance of the BA-3 FE right? Just paranoid!
Russellc
Jensen says the leaded equivalent is the current part # JT-123-FLCF, which is formerly part # JT-112-LCF.
The leaded version has several advantages over the pcb version for the F6, so I'm using it in my amps.
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The pcb can be made relatively small and compact when the Jensen is not mounted on it.
Even if you mount some of the large power supply capacitors on the pcb, it will still be of reasonable size.
The Jensen can be mounted as far as possible from the power transformer, with the four twisted pairs run to the pcb.
Also, the Jensen's physical orientation can be optimized wrt the power transformer, for minimum hum pickup.
A mu metal shield could be installed around the chassis-mounted Jensen in difficult situations.