Taming amp gain in single channel deluxe reverb build

[didit]

Thanks Ian --

Makes sense with your explanation. I'd asked mostly out of pure curiosity. However, few possible additions/tweaks from the Dumble recipe book might increase utility and novelty but leave that to you for further thought.

Best ..

[martin manning]

I just installed a 100K master volume pot in my single channel DR. Lets you control how much signal is sent to the PI. Works fine for me. Take a look...
https://sluckeyamps.com/tdr/tdr.pdf

Gotta say, this is a really nice little amp! Love the look, too.

[sluckey]

Thanks Martin. I really like yours too!

[imo1]

I bit on Ian's suggestion to try the Hammond OT, so waiting for that to arrive. The multiple taps open up some options for me, and I'm probably going to use a Celestion vintage 30 that I have. I love that amp for mid level amps like this. Anyway, it's a 16 ohm speaker. If I want to keep the feedback system similar, should use a 33r resistor? I know that Fender uses 100R for both 4R.

[martin manning]

This comes up all the time. You can keep the same feedback resistor on the same tap, and put the speaker on whichever one it matches, or, move the feedback resistor to the tap the speaker is on, and adjust it's value by (New Spkr Tap/Old Spkr Tap)^0.5
Given the secondary hookup for the 1620, you will want to do the latter.
Example: 16 ohm speaker and tap in place of 8 ohm, adjust the feedback by (16/8)^0.5 = 1.414
The 820 ohm series resistor becomes 1k2, or, if you have no presence cap frequency response to worry about, you could reduce the 47R to 33R as you said.
Mind the phase relationship too.

[imo1]

This comes up all the time. You can keep the same feedback resistor on the same tap, and put the speaker on whichever one it matches, or, move the feedback resistor to the tap the speaker is on, and adjust it's value by (New Spkr Tap/Old Spkr Tap)^0.5
Given the secondary hookup for the 1620, you will want to do the latter.
Example: 16 ohm speaker and tap in place of 8 ohm, adjust the feedback by (16/8)^0.5 = 1.414
The 820 ohm series resistor becomes 1k2, or, if you have no presence cap frequency response to worry about, you could reduce the 47R to 33R as you said.
Mind the phase relationship too.

Martin,

Thanks for the response. I only have the one speaker jack so unless I found a tie in for the 8R tap, it does make the most sense to change the feedback resistor.

Would i still be changing the 820R to a 1.2k or could I just change the 47R to a 33R?

What specifically do you mean by minding the phase relationship? Its pretty easy to find the primary correct windings as the amp howls with it backwards. Assuming I have that correct and follow the secondary diagram for output, I should be in phase, yes?

[martin manning]

Would i still be changing the 820R to a 1.2k or could I just change the 47R to a 33R?

Either way will work for you since there is no presence control. If there were, changing the PI tail resistor would change the frequency response of the feedback, which would require a change to the presence cap value to keep that the same.

What specifically do you mean by minding the phase relationship?

Just that it looks like the primary lead colors are reversed wrt the usual Fender convention where blue is the in-phase lead.

[imo1]

Awesome. In that case I will just change the tail, and it wouldn’t be an amp build for me without squealing leads on initial power up. Seems that no matter how closely I follow the the diagram, I always have to reverse the primary leads

[imo1]

I wanted to update everyone with the amp build. Once I get my faceplate back I will post some pics. This is the first project where I did everything. Made the cab. Tolexed it, etc. I'm really happy with the results.
For the pre PI gain, after playing with the 250k pot for a while, I settled on 82k. I am really happy with the volume expanse of the amp. It is all usable. Blown up in a cool way on 10, but not ridiculous.

I did a couple of other things that I feel like really benefited the amp:

-I doubled the capacitance of the 1st node, from 47U to 94U. This made a noticeable positive difference.
-I lowered the cathode bypass from 22U to 5u on the first 2 gain stages. Cleaned up bass, and actually seemed to shift the focus slightly where I really enjoyed cranking the mids, and it never sounded congested
-I put a dwell control in place of the 1M to ground, feeding the reverb. This is such an important control for making Fender reverbs more usable, it should be fundamental to any new builds. I love how different you can get the effect now!

In case it got lost in the thread, I now have the beefy hammond OT. It gives the amp a little more oomph.
I am using a 16R Celestion vintage 30, which sounds great. I had an 80W too and tried that, but preferred the 30 for preserving some of the softness.

I haven't played the Louis columbia electric, but I would say that this amp is definitely similar in sound. Very happy with it and can't wait to get it to me kid. He is an amazing young guitarist!

[martin manning]

Great! looking forward to seeing photos and maybe a sound clip.