ampex 351 pcb

[bluesbaz]

I am in love with the Ampex 351 but not its size. I would like to sell mine off and make some smaller clones.
Here is my design. Thoughts?

 

[bluesbaz]

And the Schematic which should be easy enough to find but here's mine.

 

[buildafriend]

now you do this, after I sold some ampex 351 transformers I had laying around.

I think it's a good idea and I agree.

 

[bluesbaz]

Mea Culpa!

 

[shmuu102]

I wouldnt mind a stereo 3 space rack unit......    I have 3 old 351's waiting for my attention still

someone source some knobs and a VU that resemble the original, and ill draw up the front panel, and fire up the CNC machine.

 

[mitsos]

Is there an aftermarket output transformer for this? It needs a feedback winding...

 

[Brian Roth]

Sowter 9084.

Bri

 

[abbey road d enfer]

I am in love with the Ampex 351 but not its size. I would like to sell mine off and make some smaller clones.
Here is my design. Thoughts?

I would use thinner traces in order to decrease parasitic capacitance and increase clearance.
Now there are many kinks that are not consequencial but still don't have the look of a professional design.
For example, from pin 6 of V1 to R10/C1, it should be a straight line, R49 & 37 should be rotated 90° CCW in order to reduce the length of the trace to pins 2 & 3 of V4, and so on.
And then, C2A goes to ground via a convoluted way. As a result the ground currents pollute the input signal ground.
C2A should be physically and electrically as close a spossible to the binding post AND to the output stage ground.

 

[rlaury]

I'd do away with the ground plane all together. Nothing but trouble. Use an individual  ground per stage
and tie those grounds to "0" volts at a single point. Use 40 mil traces for signal, 62 mil for power .125 for ground.
Just say'n.

 

[abbey road d enfer]

I'd do away with the ground plane all together. Nothing but trouble.

I don't agree. A ground plane is trouble only if it allows ground currents from output stages or unregulated supply currents to interfere with low level currents. A static shield ground pour, connected to the reference ground is good design practice for tube stuff. Some care must be exerted in order to minimize parasitic capacitance in very hi-Z areas, though.

Use an individual  ground per stage and tie those grounds to "0" volts at a single point.

No. Definitely wrong. That's the unfamous abuse of the star ground concept. Proceeding that way makes each stage have a different reference. Proper arrangement is hierarchical ground or "ground-follows-signal". Indeed, in valve equipment, this is often invisible because the currents are typically much lower than SS circuits. Still, the principle is identical. there should not be different rules for tubes and SS.

 

[Chris_V]

The main point here is that the layout is far from optimal.
When using a ground pour like that,  you want to have has little as possible "semi-islands".
The solution is a good placement of components, choice of routing and thin traces.

Look at the ground connection of the gain pot, it can be almost direct if you route the wiper on the right of the pot.
R1, R44, R46 can be slightly moved to prevent cutting the ground pour.
Thiner signal traces will solve almost all other problems.

 

[craigmorris74]

Don't know if this is helpful, but thought I'd share it anyway:
http://recordingwithgas.com/GAS_351_PCBs.html

 

[Whoops]

Don't know if this is helpful, but thought I'd share it anyway:
http://recordingwithgas.com/GAS_351_PCBs.html

Those PCB's are replacements for the original boards in the 351 unit.

What the op wants to accomplish is doing one pcb of the bare and simple Mic preamp circuit.

By the way Bluesbaz, hows your project going?
I will do the same thing in the next weeks, just not sure yet it I try to design a pcb or if I will do it with a turret layout.
I really like turret layouts for tube stuff, easier to follow the circuit, easiar to troubleshoot/repair and replace components, and its also huge fun

Thanks

 

[Ritchie Paris]

I would to share my works on this Ampex 351...