If any one can help me with this it would be appeciated.
Outputs are wired as per tubelabs diagram (below) for CFB & UL, on my Hammonds in order to get negative cathode feedback I had to wire my black (common) to the speaker terminal and the yellow (8ohm) to the screw terminal on the board.
I have bought 6 binding posts so that I can connect a post to 4 and 8 ohm taps on each channel. (In case I use 4 ohm drivers at some point).
Am I ok to do this still? If so will I still be ok to use CFB when speakers are connected to the 4ohm taps too. Or should I just use four binding posts rather than 6 and if I change speakers open the amp and switch the secondary wires so that the speakers are connected to the 4 ohm tap.
Any clarification appreciated.
Thanks
Matt
Outputs are wired as per tubelabs diagram (below) for CFB & UL, on my Hammonds in order to get negative cathode feedback I had to wire my black (common) to the speaker terminal and the yellow (8ohm) to the screw terminal on the board.
I have bought 6 binding posts so that I can connect a post to 4 and 8 ohm taps on each channel. (In case I use 4 ohm drivers at some point).
Am I ok to do this still? If so will I still be ok to use CFB when speakers are connected to the 4ohm taps too. Or should I just use four binding posts rather than 6 and if I change speakers open the amp and switch the secondary wires so that the speakers are connected to the 4 ohm tap.
Any clarification appreciated.
Thanks
Matt
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Hello. Thanks for the reply. I have taken feedback fromvthe 8 ohm tap but want to connect both the four ohm and 8 ohm taps to binding posts so that if I ever need to connect 4 ohm speakers I can. In other words I would have 6 binding posts on the back of the amp, 3 on each channel , 1 x common, 1 x 8 ohm,, 1 x 4 ohm. I thought i read somewhere a post from George (tubelab) saying that you can only do this if your transformer secondries are of a certain direction. Unfortunately i cant seem to find this post now.
Matt
Matt
Hi Matt,
I wonder if you are conflating a couple of different things.
Phase of the NFB is linked to the secondary winding direction, so you just need to confirm that it works OK. You will get a lot of howling if it is the wrong phase, so then you swap the order of the OPT secondary leads when you connect.
There are different schools of thought about how to handle NFB with different impedance loudspeakers. I have seen just one connection from the secondary being used, regardless of the speaker connection, and switchable 4/8ohm solutions, where different NFB components are connected depending on the speaker load impedance.
I think the purist solution is to have a tuned solution for both 4 and 8 ohm, and that complicates the wiring a bit. Probably has to be a switched in some way to do it properly.
I wonder if you are conflating a couple of different things.
Phase of the NFB is linked to the secondary winding direction, so you just need to confirm that it works OK. You will get a lot of howling if it is the wrong phase, so then you swap the order of the OPT secondary leads when you connect.
There are different schools of thought about how to handle NFB with different impedance loudspeakers. I have seen just one connection from the secondary being used, regardless of the speaker connection, and switchable 4/8ohm solutions, where different NFB components are connected depending on the speaker load impedance.
I think the purist solution is to have a tuned solution for both 4 and 8 ohm, and that complicates the wiring a bit. Probably has to be a switched in some way to do it properly.
Firstly thanks for your help. I have the transformer in the right phase now, but to do this the yellow wire (Labelled 8 ohm by Hammond) is connected to the pheonix connecter on the board and the Black wire (Labelled Common by Hammond) is connected to the speaker. I think that I see what you are saying now though about switching between the Green & Yellow wires into the board in order to achieve connection to 4 or 8 ohm taps. I am not going to go down this route as the wiring is going to be way to complicated with too many wires and switches if I do. If I ever need to use the 4ohm speakers (unlikely) I will need to re-wire the amp to the 4ohm tap and that wouldn't be too hard to achieve. It means I have two sets of CMC binding posts spare too.
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