Replacing a reverb tank...

[azrael]

I don't know if this really belongs here, but this is practically the only place I could think of that would know.
I have a Traynor YCV40, and I don't really like the reverb on it. It's too subtle before 12 o'clock, and after that, it suddenly gets splashy.
I noticed, the other day, that the reverb tank is hooked up via two RCA cables.
I remembered the Stage Reverb project on GG, and the tank on SBE...That's hooked up via two RCA cable, too.


So, my question:
Would buying this:
http://www.smallbearelec.com/Detail.bok?no=510
And replacing my old tank with it fix my reverb problems?
Also, would this even work? Or am I just dreaming?

[MetalGod]

when I looked into replacing the reverb tank on an Ampeg head I used to own it was way more complicated than I'd ever imagined (have a look on the accutronics website).

here's the info I needed when I got mine...

Type4   (4)
150ohm input    (B)
2250ohm output  (B)
Long delay time  (3)
Input insulated output grounded  (C)
No locking device  (1)
Horizontal open side down  (B)

[azrael]

Hmm...Did you email Ampeg about it?
If so, maybe I should email Traynor about this...

[Mark Hammer]

If I have clearly understood the technical data provided at the Yorkville Sound website (longspring Accutronics), you are unlikely to be able to get a "better" reverb pan for it, unless they used a 2-spring unit and you could get a 3-spring replacement.  It sounds to me like you are dealing with a supporting circuit issue rather than anything stemming from the pan itself.  It is certainly tweakable, but in the absence of a service manual schematic, knowing what to tweak is another matter entirely.

[cobra94]

I'll have to agree with Mark here, it's probably in the circuit (my YCV50Blue sounds similar).  The quality of the tank is not the issue since they use the same type (long two spring) as Fender.  You could try the three spring version (long) but I've seen them recommended usually for keyboard & steel guitar type applications.  If you go this route don't forget to match the input/output impedances as closely as possible or there will be "circuit issues".

Try calling the guys at Traynor they are usually very helpful (another great Canadian company).  The service manual can be found here.

http://www.traynoramps.com/default.asp?p1=7&p2=0&p_id=30

Cheers,
Peter

[axg20202]

I agree - I doubt that the tank is the problem. You mention the Stage Center reverb project at GGG. I have made this and can confirm that it works very well. You can tweak certain component values to adjust the EQ of the reverb to taste. Build it using the charge pump also at GGG.

[Mark Hammer]

Thanks for that link.


The service manual shows the reverb circuit on page 21 and also indicates the Accutronics tank used as 4EB3C1B.  The upper half of the NE5532 shown drives the audio signal into the pan, and the lower one provides the recovery gain and tone shaping.  The 100k reverb pot  performs two complementary actions.  As you move the wiper towards the pot side labelled "T", you decrease the resistance placed in series with the the 3k3 fixed resistor at the wiper, until finally the resistance in series with the recovery stage is identical to the resistance in series with the nonreverb signal (R63 - 3k3 in the upper right of this pic) at the mixing node just in front of the phase-splitter tube.  At the same time, you increase the resistance from the wiper to ground so that more of the reverb signal is preserved (i.e., not shunted to ground).

What this suggests is that an "ideal" reverb control which introduces the reverb in a manner you like probably wants a different pot taper, and likely one that is simply not commercially available.  Here, I will refer you to the Secret Life of Pots article over at www.geofex.com to explain how to adjust the taper of the pot.  You may ultimately want to replace that 100k pot with a 250k unit and suitable resistors placed between the wiper and outside lugs so that the reverb signal is blended in a smoother, more gradual manner.

The other thing the schematic shows is that there are a number of places where a cap value can be changed to provide tone-shaping and a different colour to the reverb sound.

[cobra94]

No problem Mark, I noticed that helping like that repays itself tenfold by the quality of your response. 

Now for the curious part, the YCV50 is a more marshally version of the YCV40 by way of circuit changes, output tubes, and speaker selection but I notice they change the pot value to 20K audio taper (vs the 100K linear) and use a 10K for the resistor connected to the wiper and none at the other end.  Maybe doing the same for the YCV40 will allow you to avoid the splashy point or smooth it out.

agx20202, I am also working on that project to put into a fender princeton clone I built but I'm having trouble. I am playing with the drive and recovery gains right now but suspect my cheapie reverb tank may be at fault (very low input resistance <1 ohm).   

[axg20202]

Well, one thing I can say is that the tank listed in the GGG build notes (4DB2C1D) and sold by Small Bear is not a great match for the circuit if you build it exactly as described - well at least in my experience. The critical change for me was swapping out the TL074 IC for an LM837 - it is better suited to driving a low impedence (Smallbear tank is 250 Ohm I think). If you are finding that the reverb sounds really dark and kind of like your guitar amp has been recorded in a cave, this could be the solution. When I made this change there was a dramatic improvement. It also explained why I was getting better reverb tone with the stock circuit (using a TL074) and another reverb tank I had on hand (800 Ohm). Basically its a question of matching the output impedence of the cricuit and the input impedence of the tank.

[Mark Hammer]

Appropriate advice.  In the case of this particular amp, the driver chip - NE5532 - is quite suitable for driving low-impedance loads (although some might wish to use two such op-amps in parallel for more drive current, but that's another matter).

But yes, given how low the impedance typically is on the input transducer of most reverb tanks, care must be taken to match the tank to the driver/recovery electronics so that the tank can be driven properly.  Sometimes this can be merely a question of switching one op-amp for another that handles those sorts of loads better.  Sometimes, a matching transformer (e.g., 1.5k:8r) can do it.