[Sarchi]

Thanks a lot Andrew! Yes, C5 is the B+ to ground.

Time to go scouring partsconnexion... (they're just up the road from me).

Quote:

Originally Posted by AndrewFischer /img/forum/go_quote.gif I don't know how well a 6GM8 is going to do driving 32Ω.

Broskie predicts 15dB gain for the 6GM8 line stage - my main need is for a line preamp, not a headphone amp. But I'll probably use the C1/2 switch to try both.

 

[AndrewFischer]

Quote:

Originally Posted by Sarchi /img/forum/go_quote.gif my main need is for a line preamp, not a headphone amp. But I'll probably use the C1/2 switch to try both.

A line preamp sees a higher load impedance. You could use a lower value for C2 and still get decent low frequency performance.

I don't know what your load is, but you might get away with a .33µF - 1.0µF polypropylene film cap. Switch in an Elna RFS in parallel for the headphones...

The dedicated headphone version of the Aikido uses a different output configuration. I don't know how well this is going to work. Might as well try it and see if you like the sound.

 

[Sarchi]

Quote:

Originally Posted by AndrewFischer /img/forum/go_quote.gif C8 and C9 connect the 6GM8 internal shield to ground. A film or metalized film cap somewhere between .01µF and .1µF should work. Look for low ESR at high frequency rather than just try and stick largest value that will fit. With a 6GM8 you can just use a wire for C8 and C9 and directly connect the shield to ground. Not a bad idea really. If you swap to some other tube, make sure pin 9 isn't the filament center tap.

Cool -- just want to confirm, when you say C8/C9, you meant C3 and C4, right?

 

[AndrewFischer]

Yeah C3,C4. sorry.

 

[AndrewFischer]

Quote:

Originally Posted by Sarchi /img/forum/go_quote.gif Thanks a lot Andrew! Yes, C5 is the B+ to ground. Time to go scouring partsconnexion... (they're just up the road from me).

Didn't realize you are in Canada. Ignore my brand specific suggestions -- I was going by what I can get from Digikey and Mouser.

 

[looser101]

Digikey's service to Canada is fantastic and well priced. Delivery is very fast (24-48hrs). Just use www.digikey.ca

~R~

 

[Sarchi]

Quote:

Originally Posted by looser101 /img/forum/go_quote.gif Digikey's service to Canada is fantastic and well priced. Delivery is very fast (24-48hrs). Just use www.digikey.ca ~R~

+1 on that, love Digikey.

At least some of my parts will come from digikey, since they stock the batteries. I'll order the 'lytics from them, some resistors and maybe the switch and knobs.

Finished soldering the attenuator last night; since the output impedance is 100k, I guess I'd need to bypass it for headphones.

 

[lordearl]

Hey Sarchi,

How is the build coming along?

I'm trying to do the same thing, but want a headphone amp - the idea of being able to toggle between the two would be great.

I don't know if you saw it, but Broskie did post a schematic for a 6GM8 headphone amp here:

http://www.tubecad.com/2006/06/blog0067.htm

It uses the BUF634 to drive headphones and apparently runs on the same power supply as the original design.

I can't really work out how it slots in with the original schematic (a lot of capacitors seem to have gone missing) but would sound pretty neat.

 

[Sarchi]

Hey guys,
Well I finally got everything together and finished my Aikido 24V battery linestage last night. Applied the juice...no smoke, no fire....but no sound either. Nothing, dead silence. The ECC86 tubes all glow--very faintly, V2/V4 a little more than V1/V3, which I guess makes sense.

I'll post a pic when I get home later. One thing I'm not sure about, is whether I wired the power correctly in series. I followed Broskie's instructions excplicitly; nothing on the heater pads, J4 is H+, J5 is H-, J1-2 is the only jumper. I believe the tubes are getting 6.3V but I can't seem to get a measurement on the pins...my voltmeter doesn't always work that well. (or I'm doing something stupid, more likely.)

Another REALLY dumb question - just to confirm: I'm going Source->Aikido Inputs->Aikido Outputs->Attenuator Inputs->Attenuator Outputs->Amp. This is the right way, right..?

 

[philodox]

I think the attenuator should be before the Aikido, but I don't think that would make it not work...

 

[dBel84]

Firstly, I have no personal experience with the Aikido but have been using the 6GM8's for a while running at 30V. The heaters really glow with 6.3V in these tiny tubes so it sounds like you are sucking too much current from your supply. Are you using the battery as originally planned? When you get the DMM working check the supply before and after connecting the amp. You may find that you are shorting to ground somewhere.

ps looking forward to seeing this ..dB

I agree with philodox :
Source->Attenuator Inputs->Attenuator Outputs->Aikido Inputs->Aikido Outputs->Amp.

 

[Sarchi]

Ok..

When I say 'attenuator' - I'm refering to the attenuator board which Broskie sells for use with the Aikido. I thought about this one and it seemed to me you want to attenuate the linestage output....not the source. (?)

(I did email JB asking about this, he never responded)

 

[Sarchi]

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif Firstly, I have no personal experience with the Aikido but have been using the 6GM8's for a while running at 30V. The heaters really glow with 6.3V in these tiny tubes so it sounds like you are sucking too much current from your supply. Are you using the battery as originally planned? When you get the DMM working check the supply before and after connecting the amp. You may find that you are shorting to ground somewhere.

What I'm doing...again it might be pretty dumb, is using two 12V SLA batteries as follows: couple the + leads together into J4, and the two - leads into J5. I measured the batteries and they each are reading close to 14V. But when I measure J4, I still see 14V....

Can someone explain this power hookup to me in really simple terms..

 

[dBel84]

just pulled up tubecad to get a visual of what you're talking about - sounds like you are hooking up the 12V SLA's in parallel to give you ....12V , try putting them in series : + from SLA 1 to J4, - from SLA1 to + of SLA2 and - of SLA2 to centre tab between J4 & J5. Make sure yuo are getting the 24 + V from the ends of the series batteries before hooking it up - you should be good to go..dB

as for the attenuator - makes no diff if it is the board or a simple pot, same principles apply

 

[Sarchi]

THANKS. That's a huge help.

In case anyone hasn't noticed...there's a reason I went 24V....I'm really too uneducated to handle lethal voltages. (though I have built stuff before, but always needed a guru to make sure it was safe/correct)

I'm hoping when I get home and my tubes see 6V, there will be music coming out of this thing!