PS-2A Clipping/Unnatural Distortion Issue with Fender '68 Custom Twin Reverb

Stage & Studio Power Station PS-2
1

Hi Everyone,

I’m experiencing an issue with my PS-2A that I hope someone can help me with. I am a novice when it comes to load/reactive boxes, though I’ve tried researching to the best of my ability. I’ve included an audio sample.

Here’s my setup:

Amp: Fender '68 Custom Twin Reverb

Speaker Load: Internal 2x12" (4 ohms total)

Connections:

I’ve disconnected the internal speaker jack and connected it to the Fryette SPKR OUT via a Pro Co Power Plus female to male speaker cable since the Twin’s speaker cable is not long enough to reach by itself (INT. SPKR Cable to Fryette SPKR OUT).

I’ve connected the twin to the Fryette AMP IN via a 12 gauge GLS Audio speaker cable from the Twin’s INT. SPKR (INT. SPEAKER to Fryette AMP IN).

Please note that I was hesitant, but tried mixing and matching the connections, including attempts with the EXT SPKR in the in the Twin. Currently, the Fryette is not connected to the twin in any way.

PS-2A impedance: Set to 4 ohms

Volume settings: Twin around 2–3; Fryette volume at ~8-9 to 12 o’clock

LINE IN LEVEL switch: Tried both HI and LO positions

The Twin sounds perfectly normal when run directly into its internal speakers and its tubes are in great condition. It also sounds normal and low and loud volume when the Fryette is in bypass mode. But, when connected through the PS-2A in operating mode, the tone sounds clipped and unnatural—even at very moderate and low levels. The Fryette is handling all cabling (including the high-quality speaker extension) and the connections are solid as far as I can tell. I have also tried consulting the manual, forums, and diagrams, etc. and I’m just not able to understand what the issue is. I also haven’t seen much concerning a Fender '68 Custon Twin Reverb, which is a beast in and of itself, though I’m hoping the issue isn’t that it’s too much of a beast for the Fryette.

I would also like to be able to run a line out to my IK Media AXE I/O interface → MacBook Pro using Logic as my DAW.

My goals here are to be able to live record and silently record while keeping that fender tone present all while running my guitar through my pedalboard into the Twin, etc., as well.

But, firstly, I’d like to get it running by just plugging my guitar straight in to the amp and connected to the Fryette for live, clean sound with no issues.

I would love to be able to troubleshoot with someone over the phone, but wanted to post this first in case I’m missing something and to have it down on paper to refer to. Everything I had researched suggested that this product was best to handle the power of the twin, so I’m hoping I’m just missing something.

Thanks for reading this and thanks for your time and support!

-Tabin

2

Hi Eric, Welcome to the Fryette Forum! Please tell me the control settings that you used on your Fender Twin when recording this audio clip. Also please provide the date and place of purchase, serial number, and a clear picture of the inside of the PS-2A’s chassis taken from about 12" above the unit. You’ll need to remove the top cover for this, see attached video for details. Then we’ll go from there. Thanks! Gil

3

Hi Eric,

Welcome to the forum!

There are a couple of things going on here that likely bear on the behavior of this amp under load.

First of all, the original design of this amp is not exactly the same as the reissue. They even tell us that in the marketing literature:

“Fender even reduced the negative feedback, which gives you exceptional touch sensitivity.”

Secondly, they state:

“Inside, you’ll find custom-made Schumacher transformers, just like they used on the originals.”

Schumacher’s main business these days is making battery chargers. The transformers they made in the 60s were produced in Illinois with a particular grade of American grain oriented steel. Up into the early 2000s they migrated their production to Mexico.

We know this because we used to buy transformers from Shumacher until around 2005. Our experience with those parts was that they did not sound the same as the earlier production and it was difficult to get confirmation of the exact steel they were using. When our main engineering contact and sales manager there retired, we stopped using them. We later discovered that they were in fact NOT using the original steel we specified.

So, what does that have to do with your experience?

  1. The feedback network in an amplifier is a critical element in the behavior of the power amp stage of the amp.
  2. The brand name on the transformer in no way guarantees its performance since certain elements of the actual design and assembly of that part can vary slightly, which would have a very noticeable impact on its behavior.
  3. The speaker. This new model uses a Celestion. The original Twin is famous for its clean headroom at a very respectable volume. It was also famous for blowing even the most rugged speakers available including Altecs and JBLs. Those speakers had very large magnets - at minimum 60 oz. The “V-Type” speaker used in your amp is sonically aimed at Fender type amps, so it makes sense that they are using here. However, it has 30oz magnets, which has deeper implications as you will see.

Your audio clip exhibits an obvious case of parasitic oscillation. This is a type of oscillation that rides on the top of (thus parasitic) the output signal. That is a byproduct of the amplifier output not liking the load it is driving once you get to a certain amplitude.

Reducing the internal feedback, will make the amp sound more “alive” as Fender advertises. The reality is that it makes the power amp stage potentially more unstable and sensitive to different loads. It will also help compensate for the smaller magnet structure of the current speakers. And since they claim that there are additional modifications likely aimed at achieving a smoother transition into distortion, something the original Twin is famously terrible at, it is no surprise that if you mess with that formula in any way, you are likely to hear where the limitations are in this design.

If the output transformer does in fact differ from the original design, that could be aggravating the new feedback specs as well.

What do we do about this?

The reactive load in the PS2A is pretty versatile and maybe you can dial it in to avoid the oscillation.

Have you tried different setting of the Voicing switches? If not, try that. If the different settings don’t help, try the 8 ohm setting and let me know what happens.

If no luck there, it may be that the amps feedback reduction is too excessive and could stand to be dialed back closer to the original spec. But that’s just speculation on my part.

Please try the above suggestions. Also try a different speaker cab and see what happens.

Dave

4

Thanks for getting back to me!

The settings on my Twin when powered on are only that the Custom and Vintage channels are set on “Bright” and Volume at 3, max.

The S/N for the Fryette is PS2A258765. It was purchased through Musician’s Friend on April 6, 2025.

Fryette_Inside_TopDown
Fryette_Inside_TopDown1920×1446 267 KB

Hope the pic is what you need. Thanks, again.

Eric

5

Thank you so much for the information, very interesting. I just took off the top to reply to the other person helping me. I’ve tried the different voicing options and dialing it in, but have not tried the 8 ohm impedance. Once I get this back together, I will try that and get back to you. Unfortunately, I don’t have another speaker option. Again, that’s a wealth of information for me, so thank you for explaining all of that.

Eric

6

Hey Dave,

Just tried the 8 ohm option and unfortunately I’ve garnered the same result.

Eric

7

OK, try pressing the ground lift switch on the back of the PS-2.

And just for my info, please confirm that both the Amp In and Speaker Out impedances on the PS-2 are set to 4 ohm.

BTW, I mention the differences in the reissue amp because this is the first time we’ve heard of any issue with any era of Fender amps, including most of the reissues.

8

I can confirm pressing the ground/lift switch and that the impedance for both speaker and amplifier are set to 4 ohms. I’ve also not read a single thing suggesting that this wouldn’t work with the twin!

Eric

9

Alright, the last thing I can think of, which probably should have been the first thing that came to mind is as follows:

Close proximity between the guitar pickups and the PS-2 can cause feedback, which normally causes a squeal. But this is something decidedly different. That said, I just want to confirm that the guitar is connected directly to the amp input and there are no other connections to the amp or power station (pedals, etc).

Then I would just want to confirm that the amp and PS-2 are connected to the same AC outlet.

Finally, is the PS-2 sitting on top of the amp? If so, remove it. In the Twin, the open side of the chassis is facing upwards, making magnetic coupling between the PS-2 and the internal electronics of the Twin a possibility that could potentially cause this issue.

If that doesn’t do it. I’m out of ideas. I can tell you that I am very familiar with the sound in your clip and the various aspects of amplifier design and behavior that can cause it. The only thing I don’t know is what the amp looks like inside and what are the values of the components in negative feedback loop in the amp.

Dave

10

Dave,

Guitar is connected directly to the amp, nothing in between and connected directly to the Fryette. Both the Fryette and amp are connected to the same outlet (no surge protector, etc.)

However, I’ve had the Fryette on top of the twin. Since it’s a bit late now, I will separate them first thing in the morning and will post back here. It cannot be said enough of how much I appreciate your time and patience with me on this! We shall see tomorrow!

Thank you,

Eric

11

Hmmm…I think we’re getting somewhere!

Dave

12

Hey Dave,

This morning I tried separating them and still got the same result. However, though I routinely tested the amp by itself at high and low volumes with no issues, today I’m experiencing that same sound, by itself at normal and loud levels and completely disconnected from the Fryette. It seems clear that for some reason the amp is the issue.

I’m guessing the tubes need to be replaced (which I did almost exactly one year ago) or the sockets might be dirty? It’s gotten usage, but not heavy usage, so while we seem to have narrowed down the issue, I’ve got bigger fish to fry apparently. I’ll most likely be returning the Fryette and putting that money towards whatever is going on inside the amp and hopefully down the road here, I can reacquire one of these PS-2A’s.

I’d love to hear your thoughts on the potential tube issues, though I understand that’s not what the forum is for, so no worries if you cannot provide any information or context I’m lacking. What a morning! As always, thank you for your time and I appreciate all the information and help you’ve given me.

Cheers,

Eric

13

Thanks for the update.

I’m actually not surprised to hear that. Relieved actually, because that kind of oscillation is usually endemic to a design.

I wouldn’t suspect tubes unless perhaps you inadvertently swapped out a preamp tube with the wrong type at some point.

Is it possible you never turned the amp up loud enough to expose this sound before using the PS but pushed it harder now without the PS to see if it’s still there?

14

I definitely turned her up higher than 3 prior to all of this and when connected to the Fryette I wouldn’t/couldn’t get past 3 on the vol. I had no issues even when connected to the PS in bypass mode, so this is all pretty frustrating. I’m sure I used and installed the right tubes, as well, since I haven’t had issues until this morning. It all feels too weird with a side of Murphy’s Law. I don’t know much more than replacing tubes, though, so I have no idea what the issue could be. I could take her in to a local shop and see what they say, I guess! I’m all ears for any other suggestions!

Eric

15

Just FYI…

16

Well, would you look at that. What a headache!! Relieved, but even more confused now! Thank you for this!

Eric

17

Mona Lisa Vito says: “Wait! There’s moah!”

image
image299×168 16 KB

https://www.diyaudio.com/community/attachments/fender-68-cs-twin-pdf.762366/

We often say that most amp companies seem to know frightfully little about power amp and transformer design. This is hard evidence to back that up.

None of the “armchair engineers” on that thread are even in the ballpark on the probable cause, so you can ignore the highlighted section of the schematic. Apparently some big brain at Fender is just as adept at poking a stick in a hornets nest as the commenters.

The real issue is as described in my first response. Looking at the schematic is like there’s a little character wearing red mittens jumping up and down waving and screaming “Over here! Over here!”

Anyway, that’s not a big money fix for anyone with a clue. Where are you located?

Dave

18

Well, that’s a relief to read! And an even better movie reference! I am located on Long Island, NY, Nassau County, Long Beach area.

19

Well, if you have a local shop you trust, that could be helpful. If they are a Fender authorized outlet, they may have a more recent schematic or can obtain one. And if they can provide me a copy of that, I can give him a couple of things to try.

Meanwhile we have friends at Fender. I’ll see what I can dig up because now I’m really curious.

Cheers,

Dave

20

Thank you so much! I have a local shop but I wouldn’t say they’ve earned my trust just yet as I just recently moved back here. But, I’ll poke around for a Fender authorized outlet, too. I appreciate all of this greatly!

Eric