Fender Style Amp - Changing the spring reverb EQ frequency

[supersoul]

Before going to the trouble of swapping capacitors, could you plug the Princeton reverb tank into the Headstrong amp? I don't know how difficult it would be, but if it's connected with RCA jacks it might be pretty simple. It would be a way of hearing if the tanks themselves have different frequency responses.

[Question]

@Supersoul

Yes, as I mentioned in my first post that is exactly what I did as a first test.

The tanks are the same make and model and they sounded identical.

I think the reverb electronics are identical in both amps, just the Headstrong has more mids, and as a result those extra mids are also being sent to the reverb tank.

It is not an expensive or complicated experiment so when I get the parts tomorrow I will give it a try.

If anyone is interested I will post my results.

[bluenote61]

@bluenote61,

thanks for the reply. Maybe I will have my tech here in town do the soldering just to be safe.

I have done quite a lot of soldering in my studio but not on this type of point to point board.

I am interested as to why you don't think changing this cap will make much of a difference.
Do you think the mod will not change the reverb sound or that it might be due to other factors.

Another user on this thread using the same amp said he did the same mod.

I am trying to make the reverb sound like the nice reverb in my 79' Fender Princeton of which the Headstrong is a copy.

The reverb has a slight ringing resonance at about 400hz, which the Fender does not.

I know from EQ-ing my hardware studio reverbs that this is a frequency that often makes the sound a bit unclear.

I studied music and not electronics so I am very interested in what someone who has more experience with amps has to say.

Thanks!

It's my gut feeling. E.g., my Rivera-Concert has a 2.2 nF capacitor in that position and it has a great reverb sound. And you wrote in the beginning about a "muddy sound" which means to me too much low end in general. Not specific in the area between 300 and 450 Hz which will be affected by that cap switch.

Hence, just try it. And of course, I am curious about your reply.

[Question]

@bluenote61 and anyone else who is interested.

I just finished with my experiment, and to my surprise it worked!

I bought several different capacitors, even one that was larger than the original 500pf cap.
First I tried bypassing the capacitor completely, then tried each of the others in succession.

I ended up with a 271pf cap, which was much smaller than I anticipated.

At the end I hear-tested several times, alternating the 271pf with the original 500pf.

I did this with test leads so that I only soldered once.

The reverb sound is now much less resonant and the unwanted frequencies are pretty much gone.

The cheapest mod that I ever tried!

Although the design of the two amps is similar, I think the reason that the Headstrong reverb sounded different than my original Fender Princeton is the fact that the Headstrong has a much more mid-range emphasis and is much more powerful with 6L6 tubes. (somewhere around 30 Watts).
Send that signal into the reverb and it seems likely that the reverb sound will be have more mid-range and resonance.

This is my layman theory and has no basis in fact!

Thanks to everyone for taking the time to share your expertise.

[bluenote61]

Thanks for sharing the result. Does the reverb sound now like in the Princeton?

[Question]

@bluenote61

Pretty close. I think the reverb sound in each amp now reflects the tone of each amp.

The 271pf cap was the smallest that I had, but once I listened with that value cap I was satisfied.

Theoretically I could have gone smaller to get even less low end in the reverb, but it sounds really good now so I will quit while I am ahead.

[andrew]

Interesting. I'm glad you're happy with the results. The 35W 6L6 power section shouldn't have any effect on the reverb, since the reverb signal is in the preamp, well before the power tubes. I'm suspecting it could be because of the increased midrange (which is before the reverb). Just out of curiosity can you measure the midrange resistor (that's the one hanging off of the bass pot and going to ground)? In a stock Princeton Reverb circuit, it would be 6.8K. I'm guessing they might have increased that value.

[Question]

@Andrew

As I said my ideas are based on theory not on knowledge; I didn't know that the reverb signal comes from the preamp!

Sorry, I have already reassembled the amp so I can't measure anything for you.

I did have my Princeton modified with a mid-range pot on the back. I could possibly try to turn it up and see if that has a negative affect on the reverb clarity.

Anyway, I think I got lucky on this mod as I don't really know much about amps. (and it only cost me about €5!)

P.S. You can hear the Headstrong on most of the videos that I have posted, but the spring reverb is off and I am using my Bricasti hardware studio reverb.

[bluejaybill]

@Andrew

P.S. You can hear the Headstrong on most of the videos that I have posted, but the spring reverb is off and I am using my Bricasti hardware studio reverb.

Well, I"d say that's a bit of an improvement on the Fender reverb! Those things are pretty amazing.

I use either a PCM70 or more often a PCM90 for a bit of verb when recording, and leave off the amp verb as well.

[omphalopsychos]

Woah. I'd take a bricasti over a fender reverb any day. (Actually I also turn off the amp reverb and use a bricasti for my recordings).


Sorry I didn't reply sooner to other messages but it sounds like the mod was a success. I didn't realize you have the 35w version of the Headstrong. Yes I think those will produce a lot more midrange than a fender.

[Question]

Yes the Bricasti is not comparable to a Fender spring reverb, but it resides permanently in my studio so the internal spring reverb is just for live use.

[grahambop]

This thread reminds me of the time some years ago when the reverb stopped working on my Fender Twin. (I don’t have the amp now, I sold it when I couldn’t safely lift it any more!)

I opened up the tank and found that the connecting wires were incredibly thin, no surprise that one had broken. I’m no electronics expert but I can wield a soldering iron, so I soldered in a replacement wire and it all worked ok.

Anyway here’s a photo I took at the time, showing what was inside the tank. (Basically 2 big springs and not much else!)

[Herbie]

Glad to hear You succeeded!

This thread is very inspiring for me because I am not very satisfied with the reverb sound of my DIY modded Deluxe Reverb. The reason can be the same capacitor, because when I assembled another piece of the same amp to my pal, it had a perfect reverb sound.

So let’s see if there is some extra capacitors in the drawer…

[Question]

@Herbie

A few things to think about. I am pretty good with soldering, but I have never soldered in a point to point amp.

It was very easy to do; my tech friend explained where to measure the voltage to make sure that none of the caps had current remaining before doing any work. Don't mess around inside the amp unless you know how to measure voltage!

If you tend to play with a fatter Jazz sound with a fair amount of bass and mids with humbuckers, the reverb seems to have too much of these frequencies and so a low cut seems to help.

It is a cheap and easy mod that is easily reversible.

Good luck and be careful.

[Herbie]

@Herbie

A few things to think about. I am pretty good with soldering, but I have never soldered in a point to point amp.

It was very easy to do; my tech friend explained where to measure the voltage to make sure that none of the caps had current remaining before doing any work. Don't mess around inside the amp unless you know how to measure voltage!

If you tend to play with a fatter Jazz sound with a fair amount of bass and mids with humbuckers, the reverb seems to have too much of these frequencies and so a low cut seems to help.

It is a cheap and easy mod that is easily reversible.

Good luck and be careful.

Thanks for caring!

I made my first acquaintance with filter cap electricity in about age of 16 (which now means 46 years ago). I opened my "new" 50W Carlsbro head (unplugged from the wall, of course) just "to see how it works" – and got an electric shock from standby switch. I was sitting on my bed with the amp on my lap and the shock made me jump 50 cm up! Surprisingly the amp stayed on my lap, and I survived with only one burned spot on my right hand index finger.

After that I have been very very cautious about the contents of any amp. Especially when I started to build them, the first time to put the plug into the wall and flick the switch on causes a lot of nervousness.