Reverb Level too sensitive Fender Twin Reverb, Deluxe Reverb, etc

[nevetslab]

Something that has always bothered me with the traditional Fender Amps with Reverb, such as the Twin Reverb, Deluxe Reverb, Super Reverb, etc is that just barely cracking open the Reverb Level Control, it's already too much, leaving little room to turn the control level up where the pot is in it's 'sweet spot'. Has anyone come up with a simple change in the Return Level circuit to reduce the overall level and get good range on the pot in the middle area of rotation without it being in the Surf Music level of Reverb?

I'd love to go thru and knock that return level down on all of our rental inventory so there's decent range of Reverb without being stuck with too much at settings of '1' or '2'.

[The Dude]

I'll be honest. I haven't noticed that problem. What input signal are you supplying the amp and what level?

[nevetslab]

I'll be honest. I haven't noticed that problem. What input signal are you supplying the amp and what level?

10mV RMS

[glebert]

I'll be honest. I haven't noticed that problem. What input signal are you supplying the amp and what level?

I notice that on every Fender I've ever played (at least vintage or vintage-ish), I assumed everyone did and could never figure out why they never changed it. I wouldn't say "barely cracking open" though, for me usually the knob needs to be at about 2.5 to get the right sound, with a range of +/- 0.5 but never more than that unless I want to get a surf sound and rarely less except for solos.

[The Dude]

......I wouldn't say "barely cracking open" ......

Yes, that's what I meant. I got this impression from the initial post. I guess I've come to expect this from most Fender amps. And, it's not just the reverb control. IMO, volumes, gains, etc. are all similar in that they "peak" early in pot rotation on Fender amps.

[Helmholtz]

I have several Fender Reverb amps.
Typically set the knob between 2 and 3.
Never checked what the pot taper is, but if it's something like 20%, a 10% taper pot would be an improvement.

[g1]

I would agree that for most players, what you get at 3 could be up at 7 or 8 on the dial. Not sure if that would leave enough for playing 'surf' stuff though.
It makes me wonder about the original intent. Maybe more of an 'effect' as I think there was always a footswitch jack? And as an effect, you would want it very obvious?
Just speculating.

[Justin Thomas]

I modded my 75 for this exact reason - it was overwhelming on 3 & no way to get subtlety. I know it was just a couple minor parts swaps but I don't recall specifics. I don't have the amp on me currently but I can use the knob between 3 & 7 now & get it "just so."

Jusrin

[Chuck H]

I agree with Helmholtz about changing the pot taper if possible. This would be the easiest way to affect the change without reducing the overall range. I don't think reducing reverb at 3 should be done in any way that reduces reverb at 10. The whole stock reverb level needs to remain in case a player wanted get all Dick Dale like g1 mentioned. I looked at some black face and silver face schematics and the reverb pot is 100k-L in all of them. Fender indicated their pots as A for audio and L for linear. So the reverb pot is a 100k linear taper. Changing to an audio taper should fix the problem. I'd try 20% taper if you can get it. The standard Alpha audio pots are a 15% and the standard Bourns audio pots are 10%. I think CTS standard is also 10% though they do make other tapers for Fender amps. But I don't think you'll find a CTS 100k with a 20% taper. I think the Alpha at 15% will be the best off the shelf option. That would put a stock setting of 2 somewhere between 5 and 6 with the new pot.

[glebert]

One problem with changing the taper on the pots (or and change, really) is that so many people are used to using the reverb with it set between 2 and 3 that they will think something is wrong with it if they have to turn it from 4-6 (or whatever) to get the same amount of reverb sound, even if they now have the same amount of reverb available with more control.

[Tom Phillips]

One problem with changing the taper on the pots (or any change, really) is that so many people are used to using the reverb with it set between 2 and 3 that they will think something is wrong with it if they have to turn it from 4-6 (or whatever) to get the same amount of reverb sound, even if they now have the same amount of reverb available with more control.

Yep. That's an age old problem and it's frustratingly hard to explain it to owners. Some payers would worry that their friend's amp was "louder on 2.5 than their amp was on 3." One sneaky fix was to re-set the position of the knob on the shaft.

Back to the reverb...One design issue with the standard Fender circuit is that the reverb drive is dependent upon the pre-amp volume level. Therefore, a quiet player may need the higher level of reverb response at low reverb pot settings. In the end, it comes down to customized mods for a particular player. As already mentioned, that would not be appropriate for back line rental equipment.

[nevetslab]

YUP....I don't know how I had missed that in the schematics. They're using 100k Linear (100k B) taper pots. That explains it. Now, on both the Deluxe and Twin Reverbs, the Treble Pot is a 250k 30A taper, which is 30% resistance at 50% rotation, vs 250k 10A taper as used on the Bass control, which is the 'standard' Audio Taper. If we have inventory of any of the 250K 30A pots on hand, I'll try swapping that in and see if I need to make additional component changes to make these sensible. I know the Hot Rod Series amp's, their Reverb pot works just fine, like one would expect. Different circuit there. They're slugging a 25k Linear taper with a 1.5k between the top of the pot and the wiper (1.5k has a 6.8nF cap in series with it), and the output feeds the input to the LTPI mixing input thru 470k and 220k from the dry signal. Maybe scaling that for the existing 100k Linear pot (with a 6.2k resistor between top of pot and wiper) might be something to try.

Bourns_PDB18__pots_Resistive Tapers.pdf

I've attached a page from Bourns that shows the variety of tapers one can find, which shows the 10% and 30% Audio Taper curves. Perhaps using the 250k 30A pot would work just fine and not be so drastic a change from what players are used to. More to come when I get one of the amps back on the bench as soon as I've checked to see if the Guitar Dept has some 250k 30A pots on hand.

[Helmholtz]

Maybe scaling that for the existing 100k Linear pot (with a 6.2k resistor between top of pot and wiper) might be something to try.

A resistor between pot input and output should even increase reverb level at low pot settings.

[Chuck H]

The trouble with looking at "available tapers" from manufacturers is that while they are available to buyers placing orders based on minimum order quantity requirements they aren't typically readily available. I've never seen a Bourns pot with a 20% taper indicated. The only CTS pots with anythong other than a linear or 10% taper are made for Fender and only available through parts suppliers. They aren't in any catalog other than as a Fender part. But do look for sure. There are a lot of amps out there and it's always possible some manufacturer has commissioned a part. Short of that you'd need to order the MOQ yourself. Terribly inconvenient if you don't need a thousand specific pots.

[Tom Phillips]

The trouble with looking at "available tapers" from manufacturers is that while they are available to buyers placing orders based on minimum order quantity requirements they aren't typically readily available...

Exactly. You can have quite a fantasy adventure looking through the full line catalog from a specific manufacturer. You will find tables showing alpha numeric part numbers that are 10 or more characters long with each character indicating multiple options of a specific parameter. The lead time and the minimum order quantity and cost can be quite a shock as Chuck pointed out.