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Old 15th November 2006, 09:08 PM   #1
SteveA is offline SteveA  United States
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Default Aikido question

I have the Aikido pcbs designed by John Broskie. I installed both C1 and C2 and intend to switch between them as described in the construction notes. The notes suggest using two rotary switches. Since I will also install the stepped attenuator also from Mr Broskie(three knobs) I want to reduce the number of knobs on the preamp. SinceI have a few DPDT toggle switches laying around, is there any reason not to use one to accomplish the switching?

Thanks,
SteveA
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Old 15th November 2006, 09:36 PM   #2
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Hi Steve,

Without going to Broskie's pages to see just where these capacitors are, I would assume that a make-before-break switch is probably desirable to avoid switching transients and loud noises.

A rotory switch comes in both make-before-break (shorting) and break-before-make (non-shorting) A toggle switch is only non-shorting and would almost surely make loud pops when switched.

Victor
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Old 16th November 2006, 12:43 AM   #3
jayme is offline jayme  United States
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Agreed. You would definately want to use a make-before-break switch if you wanted to flip between caps while playing music...

Even then, it would be best if the cap that was NOT in the signal path was then shorted to ground.

You could use a normal toggle, but you should power down before switching, or at least install a mute switch which shorted the outputs to ground.

If you aren't comfortable with a switch in the output signal path, you could have two sets of RCA outs, one for each cap....just switch your interconnects (powered down, of course).
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Old 16th November 2006, 01:22 AM   #4
SteveA is offline SteveA  United States
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Thanks guys!! I have power supply question (or two) also. First question is:
The power supply, PS8, on the Welborne site could be used for the Aikido, yes?

Second question:
Broskie said (IIRC) to reference filament supply to 1/4 B+ and provides a circuit to accomplish that. Assuming PS8 can be used for Aikido, I would presume that circuit could be added to PS8. Is that correct?

Thanks again,
SteveA

PS, I was not thinking of switching during play. I would select the C1-in or C2-in prior to playing while powered down. I would think a toggle would work in that situation.
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Old 16th November 2006, 02:11 AM   #5
jayme is offline jayme  United States
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The welborne PS8 should work fine, especially for the B+...but you may want to try the heaters straight up with AC before trying the regulated DC. I found AC heaters on my Aikido sounded awesome, and I had no issues with noise or hum.

The filiment reference is easy...just run the full B+ into a 300k 2watt resistor and then split the output...one wire to the filament center tap and another wire to a combo 100k resistor bypassed with a .1uF cap....both connected to ground (The cap provides a straight-wire shunt for any AC on the line). It is a simple voltage divider.

Plus, it provides a shunt to ground for the PSU when you turn off the amp.
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Old 16th November 2006, 02:25 AM   #6
SteveA is offline SteveA  United States
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jayme,
Thanks again
Steve
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Old 19th November 2006, 01:15 AM   #7
jal4172 is offline jal4172  United States
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Default C1 and C2

Yes, you can use a toggle swith. I put mine in the back of the unit
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Old 19th November 2006, 02:07 AM   #8
jal4172 is offline jal4172  United States
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In reply to the make before break, I belive it does not make any difference. Since the both the capacitors are charged through their resistors there should not be any noise. I can swith on the fly with absolutly no noise. BTW - Oil cap sounds better that the film in mine.
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Old 20th November 2006, 08:01 PM   #9
SteveA is offline SteveA  United States
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Quote:
Originally posted by jayme

The filiment reference is easy...just run the full B+ into a 300k 2watt resistor and then split the output...one wire to the filament center tap and another wire to a combo 100k resistor bypassed with a .1uF cap....both connected to ground (The cap provides a straight-wire shunt for any AC on the line). It is a simple voltage divider.


Sorry, bit of a newbie, but by "one wire to the filament center tap" you refer to the center tap of the filament transformer, correct? or no?

Thanks,
Steve

PS Thanks jal4172
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Old 20th November 2006, 08:25 PM   #10
jayme is offline jayme  United States
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Quote:
Originally posted by SteveA



Sorry, bit of a newbie, but by "one wire to the filament center tap" you refer to the center tap of the filament transformer, correct? or no?

If your transformer has a center tap for the filaments, then yes.

Mine didn't, so I created one with two 47R resistors. Wire each resistor to a leg of the filament transformer and then wire the other ends of each resistor together. This "mid point" serves as a pseudo center tap, and you can connect the B+ reference here.
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