TTSH, spring reverb mods
Alritey let’s continue details of my TTSH with two spring reverb modifications. If you’re looking for other build / modification posts on the project, please visit the main page right here.
Opamp Upgrade
This modification is done to improve the noise floor of spring reverb, by upgrading the opamp in the output amplifier circuit (recovery amp). The mod was suggested by user Nordcore at Muffwiggler forum and looks like this:
TTSH reverb driver mod schematic by Nordcore.
I sort of failed with adding this mod in that I didn’t bother taking before and after audio recordings: So it’s rather impossible to say how much the noise floor was effectively reduced. On my TTSH the circuit was noisy before and is noisy after.. Yet I’d still say it’s better.
On to the build..:
The reverb driver circuit in its stock config
All unnecessary parts removed..
100nF cap installed on reverse (front) side..
.. followed by 2n2 cap.
Jumper wire to connect tank output and install 6K8 to position R288 (2M2).
Add 22uF cap and 68R resistor..
..and the opamp upgrade is good to go!
One side effect of this mod is that it will reverse the opamp configuration (from inverting to non-inverting). So the dry and wet signals will have 180 degree phase difference. Now depending on taste you may or may not like the weird fake stereo / cancellation effect this creates, but I’m definitely with the “NO NO NO!!1” camp. The easiest way to fix the cancellation effect would be to install one additional opamp to either input or output side of NE5534 to flip the phase difference back to zero. However since the spring reverb tank I have in my TTSH (Belton BL2AB3C1B) cost about 23 euros I thought I’d splash out for the project just a little bit more, and go for the way more epic…
Stereo Reverb Modification
!! .. This one is quite simple to pull off too: You just need to build a second identical recovery amp of which ever type your TTSH has (stock or modified) and route their outputs to Left / Right output channel faders (by unlinking them). You could also install a dual opamp buffer to flip both recovery amp outputs to same phase as the input, but simply going stereo removes most annoying phase cancellation effect.
I didn’t bother taking build snaps, but you’ll get the idea:
The additional (extra) recovery amp built on veroboard & installed over main board
Input signal for the new recovery amp is taken from junction of C90-R72-R276-R281-R282 via a 100R resistor. I chose to connect the output to right channel fader as it’s trace (from main board recovery amp) was easier to cut (see photo above). New board can be powered using one of the many pin header locations on the main board, so feel free to pick the most difficult-to-install location if you like. I went for the header sitting right next to main board recovery amp.
Note that on the output side I left GND unconnected on the main board. It does connect to GND on the new board though, so that the twisted cable will turn out sort of a ‘shielded’ cable. You could use a proper shielded cable of course, but I just had a some bits of twisted pair cable left over from wiring the TTSH loudspeakers and opted to use them here. Anyway when shielding interconnects, hooking up only one end of the shield to GND is kind of ‘playing it safe’ to steer well clear of ground loops.
As for the tanks, I thanked myself a dozen times for building a case with enough depth to fit both tanks on top of one another, without risking the topmost tank short-circuiting anything on the TTSH main board. It’s like as if I’d have some mad precognition skills! ;).
Alternatively, the new tank would’ve of course fit below the existing tank but then the former would’ve been quite close to the PSU. So it’s better off this way, keeping both tanks as far away from the PSU as possible.
Tanks stacked on top of one another using standoffs..
..and the bundle installed to the case.
And that’s it for the spring reverb mods. Check out these sound demos of what my TTSH sounded before and after the stereo mod:
NE5534 upgraded recovery amp (mono)
NE5534 upgraded recovery amp (stereo)
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