Blackface Bandmaster more "vibrato" intensity

[Quatro]

I am working on a bandmaster -

http://www.thevintagesound.com/ffg/schem/bandmaster_ab763_schem.gif

I've looked around and can't seem to find answer to this question (maybe because there isn't one). Is there a way to increase the intensity of the tremolo with this circuit?

Thanks

[sluckey]

If you suspect the trem is weaker than a new bandmaster should be, replace the tube, roach, caps, resistors in the trem osc and driver circuit.

If you think the trem is doing all it can and all the components are good, there's not much you can do.

[HotBluePlates]

If the roach is working as it should, you should be going from nearly-no-volume to a volume limited by the 50k Intensity pot.

But slack heat-shrink around the roach could allow light in to reduce the range of the optoisolator resistance change. And I wonder if opto's sometimes have a age-related failure where they don't exhibit the full range of resistance change.

If the 25uF cathode bypass cap on the 2nd half of the vibrato 12AX7 has dried up, the plate voltage may not swing as wide and reduce the apparent effect.

So, if this is a vintage Bandmaster and the 25uF cap is original, try replacing it and seeing if intensity improves.

If not, or if that cap was already replaced, look at the opto heat-shrink and see if it seems slack. You could probably just wrap the part in electrical tap or new heatshrink to try to effect a cure.

If all else fails, you might try a new optoisolator.

I have honestly never tinkered with this vibrato circuit, so I don't know if raising the value of the 50k pot (to maybe 100k) will help. The VERY big problem is the pot's taper is Reverse-Audio, so you will be hard-pressed to find alternate values.

[jojokeo]

Check that the three caps there in the values shown on the schem. ie  2 - .01uf's and a .02uf are correct.

Gerald Weber speaks to changing one of the .01s to a .02 which slows down the oscillation further but, going to far with this and you'll start to lose your tremolo intensity also.

[SoundmasterG]

Assuming the trem is functioning correctly, the only way that I know of to increase the intensity of it is to move it to an earlier point in the preamp as far as to where it injects. The Silvertone 1484 is a roach trem but it injects after 1 stage and it is known for having a nicely intense trem effect. The Blackface and Silverface Fenders inject the trem after two stages where the reverb effect also injects into the preamp, and it has much less effect there.

Greg

[Quatro]

What's the downside to injecting earlier?

[HotBluePlates]

What's the downside to injecting earlier?

You inject to a single-ended stage.

Most of the advancements in tremolo circuit design sought to eliminate the pumping effect when the trem is on but you're not playing. While you could argue this is an issue of background noise, there is some lower limit below which it is impossible to reduce the noise.

So the idea that designers came up with was to inject the tremolo in a balanced stage. Notice that Fender created the Tremolux which injected the trem at the shared cathode resistor of the paraphase inverter. Doing this, the trem causes both push- and pull-sides to increase and decrease volume at the same time. But the output transformer only responds to a signal that's the difference of these two sides (hence push-pull); the common tremolo signal itself does not pass through the OT.

So if everything is perfect, there is no tremolo pumping with no guitar signal, but when you play, your guitar sound has its volume raised and lowered by the trem.

Same approach with output tube bias-vary, just a different injection point.

A single-ended stage can't do this. So the effort to inject late in the amp is all about reducing the pumping noise when you're not playing. The tradeoff is you typically need a much larger trem signal to overcome/impact the guitar signal at a later stage in the amp.

[sluckey]

I don't think there is a downside or upside to injecting the trem earlier in the signal chain when using a LDR based optocoupler such as used in the Bandmaster. The typical Fender roach doesn't vary any bias. It simply places a shunt resistance across the signal path. There is no pumping effect with this type of trem. You can hear the background noise (hiss) vary as the signal amplitude is varied, same as you would hear just by turning the volume control. I suppose if you used the LDR to actually change the bias on an amp stage you would have to deal with pumping.

[HotBluePlates]

And hence why Fender last tremolo improvement was to switch to an optoisolator, even if the bias-vary stuff is more fashionable now.

Course, all the amps I've had with a bias-vary trem sounded more appealing to me than a big blackface Fender trem. I haven't tried the new vactrols in an amp though, and my Fulltone Supa Trem (with vactrols) sounds quite nice.

[SoundmasterG]

The Silvertone 1484 trem uses a roach and is probably the best sounding roach trem I've heard or played. To my ears it compares very well with the bias modulating trems. The only significant difference that I can see when compared to a Fender BF/SF roach trem setup is that the roach is something they cobbled together from parts and encased in tape at Danelectro where the amps were made instead of using a standard part like Fender did, and they injected the signal earlier in the circuit. On my brother's 1484 that I modded, I even found a way to make it work with both channels with the earlier injection and not affect the stock Fender reverb circuit that I added, though at the moment I don't remember what I did and would have to look at the schematic I drew up for the mods.

Greg