No work surfaces make me cranky. I'm still on the Intersound Mini-Six. My work surface for this particular project up to this point has been, I shit you not, a Hallicrafters S-53 sitting on top of the Lafayette U-50 standing on its side.


Here's an overlay of the circuit components I pulled out of the malfunctioning negative side of the +/- 12 volt power supply.


Here's a pulled trace from extracting the master volume control, not really an impediment, just annoying.

In plotting my approach to repair this unit, I've opted for simple regulation in the power supply. A regulator, instead of a discrete circuit. I'm going to learn what I can from the original circuit, but as a matter of course I'm taking the easy way out for now.


Turns out I didn't have TO-92 regulators on hand either, so the legs of a TO-220 are trimmed to fit.


Next step should be obvious..

So, I slapped a voltage regulator in and fired it up.

Lo and behold, there is now a negative voltage! However, it is less than 12 volts; and establishing a negative rail has pulled the positive rail down by several volts as well.

It was at this point that the ludicrousness of sitting on a box on top of a milk crate while working on a "table" that essentially boils down to a balancing act really sunk in. All tinkering is in stand-by while I sort out space issues.

Take care of your work-bench.

So, I made the offhand comment of planning to trim my set-up down to a single rack for a casual show tomorrow evening. Such statement was met with a bit of derision, to which I'll let my actions speak for me... instead of peppering my conversation with the satisfyingly juvenile "I'll show you!" and making an ass of myself.

Well, more of an ass than usual anyway.


My as yet unresolved mixer problem ceases to be a concern within the criteria I have set: nothing more than 16u of rack space leaving enough room for cables I'll need under the lid.

Enter the Intersound Mini Six 1u monophonic six input line mixer. My plan is to piggyback this unit with another line mixer in order to establish a wider swath of routing.


Not a whole lot going on here, the 1/4" output is in parallel with the XLR, allowing a feedback weave with the other mixer.


There's a bit of elbow room in here; no time to ponder the possibilities though, as this unit originated in the bad amp room and as such should be considered non-functional.

Visual reveals no burn marks, olfactory reveals no foul odors. The plunger power switch is sticky and favors a firm hand, which cultivates my optimism in regards to operability. See, the bad amp room was a dumping ground for stuff based on saleability, so, as has been confirmed already, originating there does not always equate to being broken.

I plug it in, push the switch, no pilot light.

Measure AC at switch and confirm operation, so the neon is shot, no worries. AC at secondary of power transformer, so far so good. DC at ICs evident at positive rail, but nonexistent at negative rail.


Perhaps it is running these 4558s on just +12 VDC?

Sidelong glance reveals open positions for additional ICs, currently it sits at two inputs per 4558. I'll file the observation of elbow room on circuit alongside the elbow room in the case and get back to the power supply, which is what I need to address prior to tomorrow evening.


I conclude that no, this unit is not supposed to be supplying a single +12 volt feed to the opamps, as the axial electrolytic cap at lower right is sitting on top of a negative voltage, which must be deadheading into an open circuit somewhere.

Time to connect the dots on the negative rail.