dave slagle pre build

[oceanobsession]

Building a dave slagle pre , using a seiden 2 pole 23 step attenuator , I understand the wiring from the autoformers but its wiring the switch that has me thinking this
is from his site ,

Thats all there is to it! Pay close attention to the switch rotation. When the switch is rotated all the way counterclockwise (off) this is where the ground connection goes, then as you rotate the switch clockwise you simply connect the taps in order (-42, -39 etc.). If you reach full volume (the signal in lead) and still have remaining taps on your switch, simply connect them all together or insert a stop to prevent any contacts from being left open. Further questions about hookup can be asked in the forum.



its the ground connection that has me confused , if you connect the first pin of the switch to earth it then joins with the output which would give you a short , or am i missing something , any clues phil.

[Ali Tait]

Yes, that’s what you want with the volume fully counter clockwise, means there will be zero output, which is what you want.

[awkwardbydesign]

The input connects to one end of the AVC winding. The ground to the other end, as he says. The output (wiper on a pot) connects to the moving contact on the switch. The input to the power amp will indeed be grounded at full attenuation (just like a pot), but the output from the pre will not, as the signal has to pass though the whole of the winding to get there.
Does that help? I'd be interested in the results, as I use a TVC on the output of my 01A pre, but considered a Slagle AVC.

[Ali Tait]

They are very good indeed, I built one a good while ago. Sold it on when I got hold of some Tribute autoformers, not sure they are much better if at all though.

[oceanobsession]

So basically the 42db attenuation would still allow some sound from the speakers , so the first segment OFF position joins ground and output , this
would be like the 2 wires touching in a pair of interconnects . isnt this a short . phil.

[Ali Tait]

Yes, but that's fine, won't do any harm.

[oceanobsession]

Hi dick , when i get the soldering sorted ill let you know how it sounds , i think i understand now about grounding the output , cheers for your help phil.

[oceanobsession]

Yes, but that's fine, won't do any harm.

cheers for your help , phil.

[awkwardbydesign]

So basically the 42db attenuation would still allow some sound from the speakers , so the first segment OFF position joins ground and output , this
would be like the 2 wires touching in a pair of interconnects . isnt this a short . phil.

Ah, no. There are three wires here, and the important one, the output from the pre, is never shorted. Input to power amp is. Whenever I test a power amp for faults, I generally start with the inputs shorted to minimise spurious noise.

[awkwardbydesign]

They are very good indeed, I built one a good while ago. Sold it on when I got hold of some Tribute autoformers, not sure they are much better if at all though.

I have a Glasshouse TVC upgraded with Sowter transformers, used as a stand-alone unit or at the output of the 01A DHT pre (input pot turned to max) as the volume control. If I was closer (to practically anywhere, I live in Plymouth!) it would be interesting to compare the two.

[oceanobsession]

well folks , due to having more time on my hands ive managed to finish the slagle build phil.

[walpurgis]

How's it sounding Phil?

[Made in 1968]

Nice job phil with the Heat shrinks on the solder joints..

[oceanobsession]

It has replaced a tisbury pre , and sounds very annalogue with improved bass , also sound quality at low volume has improved also , seems to have removed any digital edge/brightness , i used cmc phono sockets which was a mistake , to tight on most interconnects , also you have to use to much heat on the earth connection which can melt them internally , should have gone for the audionote silver , i may replace these at some point , you need
some patience for all the soldering , volume level seems to have improved on the tisbury . phil.

[walpurgis]

It has replaced a tisbury pre , and sounds very annalogue with improved bass , also sound quality at low volume has improved also , seems to have removed any digital edge/brightness , i used cmc phono sockets which was a mistake , to tight on most interconnects , also you have to use to much heat on the earth connection which can melt them internally , should have gone for the audionote silver , i may replace these at some point , you need
some patience for all the soldering , volume level seems to have improved on the tisbury . phil.

When soldering sockets, put a spare plug into them. It helps absorb excess heat and keeps the plastic parts straight.

TVC's and AVC's tend to have a bit of gain, hance the higher volume.

[oceanobsession]

Hi geoff , good idea with the plug , but ive heard other people complaining about the diameter of the plug , it seems to pick up mains hum if positioned to close to other equipment , i think you are supposed to use shielded interconnects , it dont like to be anywhere near the valab phono , i didnt take the earth from the plugs to the case that may help who knows , phil.