Tremolo TMB Questions

[Rvaughan68]

Finally got this done. I had to take a break while moving to another city but everything checks out and sounds great. Thanks for everyone's input during the process. The cab just arrived and I'm ready to drill for the mounting screws but I had 1 final question for Josh. What size screws do I need for do I need for the chassis. I have some M6 X 30mm screws and they thread into the top of the cage nut but will not go all the way through. Finished chassis pics below.

[JMPGuitars]

Looks nice! You need 1/4-20 machine screws. I look forward to hearing your demo.

Thanks,
Josh

[Rvaughan68]

Awesome. Will post some sounds when I button it up. Thanks again.

[Rvaughan68]

The only issue I’m having with the amp is the reverb circuit has serious hum which increases as I turn up the pot. It also has the reverb “impact” sound you get if moving the amp and set it down hard. Only this happens if you barely touch the amp. Does it matter which cable you plug in from the tank at the chassis? Just thought of that.

[JMPGuitars]

Yes, the cable connections matter. The orientation of the reverb tank, and its placement, also matter.

[Rvaughan68]

Thanks. A couple more questions. Volume pot goes from 10 loud as crap in a 1/4 turn or less. Its an Alpha 500K audio pot. Is this normal. Looking at voltages I have some swings. See results below. Any concerns or steps I need to take to adjust.

[JMPGuitars]

Your plate voltages are too high, and your reverb plate voltages that high will probably cause some trouble.

You left the most important row of voltages off the chart. The bottom row tells us where your B+ is. ABCD are all marked on the docs.

Thanks,
Josh

[Bieworm]

Looks like you’re going the zener route to lower your B+ voltage. You will need a variety of 5W zener diodes to tweak that.

[JMPGuitars]

Looks like you’re going the zener route to lower your B+ voltage. You will need a variety of 5W zener diodes to tweak that.

Well, not a big variety. If we could see his B+, we would know how much voltage actually needs to be dropped. I would guess 20 or 30V, but knowing is better than guessing.

[Rvaughan68]

Here are the rest of the voltages. High.

[JMPGuitars]

I would get some 5W Zener diodes. Use either two 20V Zeners, or three 15V Zeners (I would do the latter). Review the thread in my signature for reducing B+ if you need to.

Thanks,
Josh

[Rvaughan68]

I’ll do that. Thanks for the info. Do you think the higher voltages are affecting the volume sensitivity.

[JMPGuitars]

Yup. If the voltages are way off like that, you can expect odd behavior. Especially with sensitive parts like the reverb.

[Rvaughan68]

Installed 2 - 5W 20V diodes between the filter caps per Josh’s layout. Attached are the revised voltages on the second row. Original voltages on the top row before the diode install. The original b+ voltages were overwritten. These are the readings after the diode install. Does anything still look off?

[JMPGuitars]

The voltages look much better, but I'm guess A is wrong. You should write the dropped voltage after the Zeners for A, not the first filter cap before the Zeners.

How does the amp sound/behave now?

Thanks,
Josh

[Rvaughan68]

Amp sounds great. Extremely happy with the tone and responsiveness. I’ll record and post some samples. Couple of minor things. Volume still goes from 0 to 10 in the first 1/3 turn. Not sure what to de about it. The pot is correct type and wiring checks out. Reverb has some feed back and noise as you turn it up but I need to get a bag and isolate the tank better. I think it will be fine.

[JMPGuitars]

Amp sounds great. Extremely happy with the tone and responsiveness. I’ll record and post some samples. Couple of minor things. Volume still goes from 0 to 10 in the first 1/3 turn. Not sure what to de about it. The pot is correct type and wiring checks out. Reverb has some feed back and noise as you turn it up but I need to get a bag and isolate the tank better. I think it will be fine.

Awesome!

The volume thing sounds normal. With 18W amps, you usually get to max headroom by 3 or 4, and the rest of the sweep is how much dirt you want. You have to mess around a bit with pick attack to really experience it and see what levels you like the most.

Positioning of the reverb tank is important too. The red pot (out) on the tank needs to be away from the OT.

[Rvaughan68]

Couple of pics of finished product

[JMPGuitars]

That looks great!

[Bieworm]

Nice! Makes me want to build another one of my Ironside versions. I will have to though, for I just sold my spare one to a guy who runs a recording studio. I only have my prototype left ( which I’ll never sell! It’s the very first incarnation of the Tremolo TMB)

The studio guy is great! He bought 3 amps built by me since last august