Fender Tone Master FR-10 and FR-12 "FRFR" cabs

[Rickboot]

My tubes amps are noisy. This will be more amp in the room.

 

[Stone]

AC power ground loops are normally related to hum. Internal ground loops can cause noise; the other common source is a poorly regulated power supply (voltage and/or current noise), or thermal noise which gets amplified.

I'll give it a stab sometime tomorrow. There're some odd things on those teardown images @jellodog shared which immediately caught my eye - f.ex. the back panel has two big grounding point posts, but only the preamp PSU and the AC connector are wired to them; everything else seems to be daisy-chained. I have a vague hope that proper star grounding may improve the amp's noise floor.

Star grounding is the best way for sure, but this hissing can be a a host of other issues
SNR (signal to noise ratio) can also be due to improper shielding , poor wiring, dampening factor of the amp can also be a factor and perhaps even a low quality tweeter which is probably where the hiss is more predominant (tweeter swap should be vey easy to do if you'd like to troubleshoot)
I would be curious to see the tweeter in the TM is it a cheap $5,00 Goldwood tweeter or more expensive one like the Eminence APT80?

 

[Stratzrus]

AC power ground loops are normally related to hum. Internal ground loops can cause noise; the other common source is a poorly regulated power supply (voltage and/or current noise), or thermal noise which gets amplified.

I'll give it a stab sometime tomorrow. There're some odd things on those teardown images @jellodog shared which immediately caught my eye - f.ex. the back panel has two big grounding point posts, but only the preamp PSU and the AC connector are wired to them; everything else seems to be daisy-chained. I have a vague hope that proper star grounding may improve the amp's noise floor.

Star grounding is the best way for sure, but this hissing can be a a host of other issues
SNR (signal to noise ratio) can also be due to improper shielding , poor wiring, dampening factor of the amp can also be a factor and perhaps even a low quality tweeter which is probably where the hiss is more predominant (tweeter swap should be vey easy to do if you'd like to troubleshoot)
I would be curious to see the tweeter in the TM is it a cheap $5,00 Goldwood tweeter or more expensive one like the Eminence APT80?

You guys know a whole lot more about this stuff than I do. Clearly it's a common problem so I hope that those with the knowledge can figure out what the best fixes are and will post them if any can be identified.

Given the number of units likely to be sold and the pervasiveness of the noise issue, largely hiss as I understand it, perhaps once some fixes are identified they will be worthy of their own thread.

Legions of us will be eternally thankful for anyone who can come up with some workable solutions to this issue.

 

[Stone]

Yeah i get that this issue is frustrating for the owners seeing that its highly regarded besides this issue
and it offers what we can say as good price performance ratio
Based on the Pictures show by our good friend @jellodog I'm pretty sure its not a shielding problem the ClassD amp seems to be isolated in what appears to be a Faraday cage.
Not having one I cant troubleshoot but for those who do have one can have a go at it if they so please

 

[aflynt]

Star grounding is the best way for sure, but this hissing can be a a host of other issues
SNR (signal to noise ratio) can also be due to improper shielding , poor wiring, dampening factor of the amp can also be a factor and perhaps even a low quality tweeter which is probably where the hiss is more predominant (tweeter swap should be vey easy to do if you'd like to troubleshoot)
I would be curious to see the tweeter in the TM is it a cheap $5,00 Goldwood tweeter or more expensive one like the Eminence APT80?

That's interesting. What is it about low quality tweeters that make the hiss louder? In the case of my FR-12, the hiss is MUCH louder coming from the tweeter than from the woofer. Measuring the SPL right off the grill cloth, over the woofer the noise floor is 45db and over the tweeter it's 64db. I just figured that the level the hiss itself was higher in the frequency range above the crossover point, but you're saying that it's possible that the tweeter is the issue?

-Aaron

 

[Stone]

That's interesting. What is it about low quality tweeters that make the hiss louder? In the case of my FR-12, the hiss is MUCH louder coming from the tweeter than from the woofer. Measuring the SPL right off the grill cloth, over the woofer the noise floor is 45db and over the tweeter it's 64db. I just figured that the level the hiss itself was higher in the frequency range above the crossover point, but you're saying that it's possible that the tweeter is the issue?

-Aaron

Not sure, could be the Culprit due to certain Tweeters with different sensitivity may react differently based on the amp, so cant say for sure 100% that it would be the case, I merely suggested it as a possible first step in troubleshooting to eliminate that the Tweeter might be the culprit
But i suspect its most probably the ClassD Amp
@jellodog did you notice where the crossover electronics are located ?

 

[Stone]

Crossover can also be the culprit there are cheap X-overs and better quality X-overs

 

[jellodog]

@jellodog did you notice where the crossover electronics are located ?

I didn't, no; sorry. Probably under that inscrutible cage somewhere.

 

[TSJMajesty]

Any thoughts on the 10 vs. the 12?

 

[la szum]

Any thoughts on the 10 vs. the 12?

Apparently, they're both noisy-ish. So I am going to call it a draw.

 

[Lysander]

Ok, the culprit is definitely the preamp. If you unplug it from the power/patchboard which goes to the power amp block (HornOut), the amp is dead quiet - you basically have to put your ear right next to the grill to pick the faintest hiss.

I was fearing this Hanser Class-D power section had something to do with it but, no, it seems to be very good quality.

So, there's hope. More work ensues.

EDIT: Also, this thing is built as well as any Fender cab i've seen. Every wood joint is caulked, and all cabling between the control plate and the inner cab goes through a single small, covered hole.

 

[paisleywookiee]

Soon to come: Lysander FR12/10 Mod Services.

 

[Stone]

Ok, the culprit is definitely the preamp. If you unplug it from the power/patchboard which goes to the power amp block (HornOut), the amp is dead quiet - you basically have to put your ear right next to the grill to pick the faintest hiss.

I was fearing this Hansen Class-D power section had something to do with it but, no, it seems to be very good quality.

View attachment 11959

So, there's hope. More work ensues.

EDIT: Also, this thing is built as well as any Fender cab i've seen. Every wood joint is caulked, and all cabling between the control plate and the inner cab goes through a single small, covered hole.

Awesome !! were you able to Verify the X-over ?

 

[paisleywookiee]

So do you think the preamp is replaceable?

 

[holoholo]

Soon to come: Lysander FR12/10 Mod Services.

Sir is this an exclusive Official TM FR Facebook only service?

 

[paisleywookiee]

Sir is this an exclusive Official TM FR Facebook only service?

I’ll see what I can do for ya.

 

[jellodog]

So do you think the preamp is replaceable?

It's got clip on connectors, so if Fender send out a board revision to dealers (or even direct), it should be easy to replace; no soldering.

 

[Lysander]

Awesome !! were you able to Verify the X-over ?

Nah, not yet, i'm only going through the preamp/control boards right now. As noted, the amp barely makes a noise without preamp input, so i have no doubt the power amp section and speakers are doing their job just fine.

So do you think the preamp is replaceable?

By Fender, you mean? Yeah, the board is pretty much plug-and-play - it's not even directly connected to the I/O, so the most annoying part would be removing the pot knobs in the process.

 

[Stone]

Nah, not yet, i'm only going through the preamp/control boards right now. As noted, the amp barely makes a noise without preamp input, so i have no doubt the power amp section and speakers are doing their job just fine.



By Fender, you mean? Yeah, the board is pretty much plug-and-play - it's not even directly connected to the I/O, so the most annoying part would be removing the pot knobs in the process.

No, you have determined the issue, I was just curios to see it

 

[Lysander]

Trying to "fix" grounding only introduced hum to the equation. I think the problem is that the power for the preamp is actually generated by the power amp section and feed back through a long cable, which doesn't appear to have any significant filtering on the preamp board end.

The power amp provides +/- 12 VDC, which feed the "Power sense" circuitry and the preamp itself.

This is where where the power goes to the preamp board. The rest is AC power filtering, and sensing circuit to mute the output (via a relay) until power stabilizes, to prevent turn-on thumps - which wouldn't be fun on a super-loud "FRFR".

As noted, neither the "PowerSense" nor preamp boards have any significant power filtering. The preamp itself is surprisingly old-school analog, so i'd expect power noise to dramatically affect the sound. I need to try adding some filtering caps, but i don't know if i have any available right now

EDIT: Nope, there're two 100uF decoupling caps for power in the preamp board. That should be more than enough.