#30 - Billy fixes the Sunn Spectrum 1 (Part 4 of 5)

Moving along we complete the refurbishment and now were on to the modifications. Time to do some permanent modification to this otherwise pristine Spectrum 1.
References: www.bustedjunks...

[@orehorst]

Bill, that's a great video production and sharing of information. Thanks.

[@BustedJunkStudio]

Much appreciated!

[@TonePriest]

I decided to play a game and take a shot every time I heard the popping bubble sound. I'm typing this comment from the ICU. Great video - love the episode recap!

[@totallyunmemorable]

I'm really enjoying this series.
I have a Sunn Sceptre that I've modified fairly extensively. I haven't looked at all the schematics from this era but several that I have looked at are all the same circuit (with only the difference of the addition or lack of reverb and tremolo, maybe different output tubes). They're all bass amps . . . basically. They can be made into great guitar amps with mainly just some cap changes. Did you make any circuit changes? I was wondering about that big, white 250uF cap in the preamp. I changed that to a 2uF for a huge improvement.
One really easy thing that greatly improves the touch sensitivity is to disconnect the yellow negative feedback wire from the output jack.
But a question if I may: Sunns, I read somewhere, are particularly bad about ground loop noise. Do you think it would be feasible/practical/advisable to convert it to a star ground or - what is it called, satellite - ground?

[@BustedJunkStudio]

Sunn's of this era are a ground loop minefield for sure, I talk about this a bit in these videos. It is kind of star looped to begin with but that's kind of negated when all the hardwire grounds are doubled up with chassis grounding. Maybe a lot of ground runs can be eliminated making things less loopy but that's a lot of work.

[@BustedJunkStudio]

The preamp cathode bypass capacitor is the key to the tone of this amp and for most other amps as well. changing this value greatly changes the tonal characteristics of the amp, it's the most critical part in the whole amp. Depending on the intended use, a larger or smaller value really aids in achieving optimal tone for the application. If 2uF does it for you then that's what you should use. I left mine at 250uF because I was not trying to mod the amp too much, only bring it back to factory specs.