ODS 124 PCB Build

[professormudd]

I built one with the same PCB. Came out great!

I see you opted to use a separate JFET board. Mind if I ask why?

Where did you get your chassis and head cabinet?

[professormudd]

I got my iron yesterday. I had to file the PT cutout a bit because it was too big for the hole (that's what she said).

I'm also going to have to drill holes for the choke and the output transformer.

Question, does the orientation I mocked up look appropriate?

[xtian]

Orientation of PT vs OT--you can't really tell without listening (especially with the choke between). Do the headphone trick.

[erwin_ve]

Standard Dumble orientation is like below. The bell of the PT facing down I not causing much trouble. If the bell of the the Pt is facing the bell of the ot it would be a very different story...

[xtian]

Yeah, but the position of the choke is important too. I learned this by listening. If you set up the PT and OT as shown, energize the PT and listen to the output of the OT with headphones, you can hear more or less hum as you move the choke around in between the two. You're actually bending or deflecting the magnetic "envelope" generated by the PT.

This is critical to minimize the hum heard at idle (even in standby mode), even with no tubes installed. I'm picky with this, because most of my builds get played at bedroom levels, and the hum bothers me. If you were only ever going to play in a band on stage, you'd never notice.

[erwin_ve]

Yeah, but the position of the choke is important too. I learned this by listening. If you set up the PT and OT as shown, energize the PT and listen to the output of the OT with headphones, you can hear more or less hum as you move the choke around in between the two. You're actually bending or deflecting the magnetic "envelope" generated by the PT.

This is critical to minimize the hum heard at idle (even in standby mode), even with no tubes installed. I'm picky with this, because most of my builds get played at bedroom levels, and the hum bothers me. If you were only ever going to play in a band on stage, you'd never notice.

Thanks for your explanation xtian.
I never encountered what you described on my Ods builds, (I did when building a Trainwreck), however it may be of relevance to the topic starter using a steel chassis?

Erwin

[professormudd]

Yeah, but the position of the choke is important too. I learned this by listening. If you set up the PT and OT as shown, energize the PT and listen to the output of the OT with headphones, you can hear more or less hum as you move the choke around in between the two. You're actually bending or deflecting the magnetic "envelope" generated by the PT.

This is critical to minimize the hum heard at idle (even in standby mode), even with no tubes installed. I'm picky with this, because most of my builds get played at bedroom levels, and the hum bothers me. If you were only ever going to play in a band on stage, you'd never notice.

Thanks for that insight. I also tend to play at bedroom levels 80% of the time, so the hum would not be okay with me. Also, I want to do this as well as I am able to.

I finally tried the headphone test and I could hear differences almost like pointing your guitar pickups at a fluorescent lamp (different tone, but the positional variances are what I am comparing to). Not from the choke moving around in there, but just moving the PT around. The choke position did not seem to matter.

I will be orienting my choke as erwin_ve showed. I was not sure if it was "okay" for the choke leads to share a grommet with the output transformer leads, so I had placed it where it could use its own discrete hole. I have abandoned that and will be mounting it the "standard" way.

[professormudd]

Question: The layout for 124 proper as well as the layout provided with this board seem to indicate that shielded wire is NOT prescribed for the master volume. Is this correct? I just want to make sure before I commit to soldering.

[martin manning]

Correct.

[professormudd]

Correct.

Thanks. Would you mind helping me understand why it is not necessary here, but it is necessary for the other areas where the signal passes from one side of the chassis to the other?

[martin manning]

Correct.

Thanks. Would you mind helping me understand why it is not necessary here, but it is necessary for the other areas where the signal passes from one side of the chassis to the other?

It's all about the signal to noise ratio. Both signal and noise will be amplified, but by the time you get the the MV the signal is much higher than the noise and it's no longer necessary.

[professormudd]

I get it now. Thank you for making it simple!

[professormudd]

I mounted the iron, set wire on the pcb, and did the majority of the tube socket wiring.

I have a question regarding the diode for the 1/2 power switch. I have a few options. Which is more appropriate? Or something different entirely?

1. LED
2. I have a few labeled as uf5408-6-0635g
3. 1n400x 1amp

[martin manning]

I have a question regarding the diode for the 1/2 power switch. I have a few options. Which is more appropriate? Or something different entirely?

1. LED
2. I have a few labeled as uf5408-6-0635g
3. 1n400x 1amp

LED. It's supposed to be a visual indication that half-power is selected.

[professormudd]

I have a question regarding the diode for the 1/2 power switch. I have a few options. Which is more appropriate? Or something different entirely?

1. LED
2. I have a few labeled as uf5408-6-0635g
3. 1n400x 1amp

LED. It's supposed to be a visual indication that half-power is selected.

Thank you. I am sure my questions might seem to have pretty obvious answers, but I would rather double-check.

Follow-up: I do not want/need a light indicator for this function. Can I just run the resistors directly to ground?