We've all been using solderless 1/4” audio cables on our pedalboards for years.
So when Greg was building a new pedalboard for himself (for once) last year and was making some custom DC power cables, it dawned on him that if he could use solderless DC plugs, his board would go together faster and be neater at the same time.
So here it is, our 2.1mm DC solderless plug, which can be used as a straight plug or right angle (90º) along with our small diameter solderless cable. True freedom from the currently bundled, cheap plastic DC plugs and cable.
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The amp has been completed and has now been under testing for a few days… It has surpassed my expectations.
Finished specs :
2x 5881 output tubes
3x ECC83 preamp tubes
5F6A circuit with a few tweaks
Celestion Creamback Alnico 12" speaker
Standard 3 Monkeys 1-12 ORG combo cab
Presence, Middle, Bass, Treble, Vol 1, Vol 2 , 2 inputs per channel, 2 channels
Black levant covering
White Acoustone grillcloth
I am pleased.
When we last saw the amplifier the board was just dropped in. Before wiring it all up I like to get the input jacks in. These are plastic insulated jacks as found on most British amps. They are plastic to insulate them from the chassis and allow for any point in the chassis to be used for grounding the input. I am going to tie them to the quietest point which just happens to be located directly under them.
Here we see the progress made on the Rogers Stevens amp. This post is more photo heavy as I feel I have said quite a bit already today.
This collage shows the order in which I build EVERY amp. It's a layered procedure. I start with wiring the octal sockets and then move on to the power supply. The leads from the power transformer are all carefully located per my design philosophy.
The switches, indicator lamp, IEC inlet and fuse holder are now in place and wired up. Zip ties keep the harness from shifting and provide reinforcement for each wire.
The output transformer is wired into the chassis. The leads are twisted on the primary and zip tied on the secondary side both are routed to avoid unwanted coupling.
Potentiometers are then bolted to the chassis and wired to one another…
Next the brain (main circuit board) is dropped in. I am very close now to the finish line, although this is by no means a race.
More to come…
Before going on to todays progress reports I thought I would take a minute to say a few words about lead dress and circuit design. For some this is repetitive and for others it will be eye opening… But I really think everyone can benefit from these truths.
We have seen how component placement and lead dress can effect performance in anything but a subtle way. A well executed design will be synergistic. A circuit designed without regard to these principals WILL exhibit all kinds of unwanted loops and injection points for noise that will impede the performance you want in an amplifier.
Here is the main thrust--------> Most if not all mass produced printed circuit card amplifiers are designed by software. A schematic of the circuit is loaded into a program and the program spits out a layout. This layout determines the actual component placement as well as the placements for interconnections between all these parts (the traces).
Problem-----> The software has no regard for lead dress and it simply cannot do what a skilled engineer can.
Solution????----> An engineer must modify the circuit spat out by the software to make things work. This is usually what ends up happening. The software designed circuit never works exactly right and must be debugged as best as can be done. Progress can be made but the engineer will be hampered and ultimately frustrated by the fundamental weaknesses in the design. :(
Long story short, compromises will be necessary to allow for a moderate level of functionality and stability… always at the expense of "tone".
Hope you found this useful... Rogers update to follow… -Ossie
This is the chassis just after attaching the xformers, sockets, and ground plane points. Lots a wiring to follow. Take special note of these ground plane points, they are located in many different parts of the chassis.
The reason for the multiple locations of ground lugs is simple- all grounds are not created equal.
These points all have different paths and impedances to the "real" ground. These paths are like rivers of current carrying ac and dc signal out of the amplifier, some are further upstream than others.
Its important to note that some points carry more "dirty" signal that are the byproduct of dc filtering. Placing a sensitive ground point in the path of these dirty grounds can inject noise into the circuit... Hummmmmmmmmmmmmmmm
We want to keep the most sensitive stages of the amp as far upstream as possible. The most sensitive stage of the amp is the input. Keeping all this in mind and utilizing your brain gives you the best chance for eliminating noisy loops and gives you the best chance for a nice quiet amplifier.
The lugs closest to the power inlet are the closest impedance to real ground, the one that is on your house or studio structure. This is the end of the ground plane for our purposes…
A nice solid 24k gold spike inserted into the earth would be an ideal final ground point, but it probably would get stolen. -Ossie
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