Ryan & Erwin's SSS #002 Madness

[martin manning]

While installing my chassis in a cabinet i noticed that reversing the polarity of the reverb drive signal results in lower noise on the reverb return.
Maybe this is usefull to some. My cabinet is lower than original and i had some hum with the return pot on full. Reverse polarity of the drive signal fixes this.
I had wondered why the polarity of the drive signal was reversed on the japanese schematic, and now i know...

So the only change made was you swapped the reverb transformer secondary leads, green instead of black to ground? Do you have any theory as to why this would reduce hum at the return? I would think the more important thing there is the phase of the feedback signal going the input stage.

[Richard1001]

Yes i swapped the wires. Not on the transformer (the RCA plugs are located under the board and can't be reached once the board is in place) but on the reverb tank. I switched the coil wires.

My only theory is that the powertransformer induces a magnetic field in the iron of the driver coil (this coil is close to the transformer) and this results in a little vibration of the springs that causes a hum on the secondary (return coil) side.

There is no hum induced on the return side itself. This i tested. Moving the driver side away from the transformer (turning the tank 90 degrees outside of the amp) also results in eliminating the hum while the returncoil is still in the same place.

I think the 2k2 /100 ohm feedback network on the reverb input / driver preamp counteracts the induced hum in the driver coil. A little signal feedback to the coil would create a magnetic field in the iron with a reversed polarity Counteracting the induced magnetic field, would reduce vibrations in the springs and less hum on the return side.

It's all theory, i did not measure anything.

[hermannbjorgvin]

Yes i swapped the wires. Not on the transformer (the RCA plugs are located under the board and can't be reached once the board is in place) but on the reverb tank. I switched the coil wires.

My only theory is that the powertransformer induces a magnetic field in the iron of the driver coil (this coil is close to the transformer) and this results in a little vibration of the springs that causes a hum on the secondary (return coil) side.

There is no hum induced on the return side itself. This i tested. Moving the driver side away from the transformer (turning the tank 90 degrees outside of the amp) also results in eliminating the hum while the returncoil is still in the same place.

I think the 2k2 /100 ohm feedback network on the reverb input / driver preamp counteracts the induced hum in the driver coil. A little signal feedback to the coil would create a magnetic field in the iron with a reversed polarity Counteracting the induced magnetic field, would reduce vibrations in the springs and less hum on the return side.

It's all theory, i did not measure anything.

I took mine to an amp repair guy to help me start it up and he mentioned to me the reverb tanks have a high/low impedance side, so you measure the resistance across both RCA inputs and put the high or low resistance further away from the transformers, that reduces hum. I don't remember whether it was the high or low impedance side that should be furthest from the transformers, should have been taking notes, someone here definitely knows.

[M Fowler]

Place the tank farther away from the PT and yes it makes a difference on tank orientation like you noted.

[timrobertson100]

Hey folks, I'll shortly start ordering up parts to assemble my PCB and chassis (thanks Erwin!) over winter. I'll do a build thread with photos, and share the experience.

Can I please ask for collective advice?
I have a mercury vibrolux transformer set I plan to use (two 6L6 / 35W). My thoughts were to stick to the same circuit Ryan posted, adjusting the bias voltage as needed for the 6L6s, but then tweak the dropping resistors on the power supply to get the same voltage on the PI and preamp stages as the standard schematic. I'd keep the filtering caps and all else the same.

Does this seem a reasonable approach, please?

[rccolgan]

I think I found a good solution to the chassis mounting annoyance that some folks are having aligning loose nuts. I picked up a rivet nut gun and rivet nuts and drilled out 17/64" holes to accomodate. I used 8-32 size nuts and didn't press in super tight or "bottom out" the hand tool. I really like the results and was a lot quicker mounting the SSS. The only issue is first aligning the screw into the nut however I believe that problem exists no matter what the solution is. I also will be using this tool a lot more in my builds and around the house!

Note: I chose less expensive ones from Amazon. There are some really high end ones out there but for less than a price of a NOS RCA 7025 tube, this is a good choice in my opinion
Rivet nut gun: https://amzn.to/2W8t1NG
Zinc plated steel rivet nut 205pc pack: https://amzn.to/2LvKtth

[Richard1001]

Great idea! A cagenut works very well to, but involves cuting a square hole. No aligning issues though because the screw drops in the hole.

[Vertigo]

I think I found a good solution to the chassis mounting annoyance that some folks are having aligning loose nuts. I picked up a rivet nut gun and rivet nuts and drilled out 17/64" holes to accomodate. I used 8-32 size nuts and didn't press in super tight or "bottom out" the hand tool. I really like the results and was a lot quicker mounting the SSS. The only issue is first aligning the screw into the nut however I believe that problem exists no matter what the solution is. I also will be using this tool a lot more in my builds and around the house!

Note: I chose less expensive ones from Amazon. There are some really high end ones out there but for less than a price of a NOS RCA 7025 tube, this is a good choice in my opinion
Rivet nut gun: https://amzn.to/2W8t1NG
Zinc plated steel rivet nut 205pc pack: https://amzn.to/2LvKtth

If folks want to try this without purchasing the setting tool, you can sometimes set them with a bolt and a pair of pliers; especially in situations like this where you have access to the barrel. Just don’t use a stainless bolt and be aware that if you don’t fully set them, you’re much more likely to end up in a situation where it spins when you’re trying to remove the bolt in the future, though I assume there is some interference with the side wall of the chassis in this specific situation. Rivnuts usually rely on clamping pressure between the flange and the compressed barrel to stay tight.

[Richard1001]

This week i did some experimenting and took my amp to a local farm to test it at full power. At home i noticed that the switch next to the level pot (the one that says 'mid') didn't have any usefull purpose. It is a 1000pF brightcap on the level pot and all it does is accentuate a ton of high's and highmid that makes amp the sound very ... well like talking through a megaphone. I thought that on full power the effect would be less, but this was not realy the case. I can't think of any use for this sound, but if anyone uses it for something, i would sure like to know. Maybe i am doing something wrong.

I also noticed that the amp can be bright. Clean there is no problem and using overdrive pedals neither, but when i overdrive the preamp using the PAB it was to much at high volume levels. With the Fet it was ok, but still i was thinking that it would be nice to have some control over the high frequency's like a presense pot. I know mesa boogie uses just a high cut as presense in some amps. So i decided to experiment and instead of using the mid switch as a treble boost, connect it as a hf cut.
I did not even have to open the amp to try this, i just soldered a 1nF cap on a jack and put it in the preamp out so the cap is connected from the wiper of the level pot to ground. The result was very good. At low levels, the cap doen't do much, but the higher you set the level pot, the more effect it has cutting the very high frequency's making the amp sound very nice when overdriving the preamp at high volume levels. I tested it using a load resistor and redbox speaker simulator since i can't crank the amp on full at home.

Since it it so easy to try (you don't have to open the amp, just solder a 1nF cap on a jack and plug it in the preamp out) I would like to know what others think of this and hear what you think.

[erwin_ve]

This week i did some experimenting and took my amp to a local farm to test it at full power. At home i noticed that the switch next to the level pot (the one that says 'mid') didn't have any usefull purpose. It is a 1000pF brightcap on the level pot and all it does is accentuate a ton of high's and highmid that makes amp the sound very ... well like talking through a megaphone. I thought that on full power the effect would be less, but this was not realy the case. I can't think of any use for this sound, but if anyone uses it for something, i would sure like to know. Maybe i am doing something wrong.

I also noticed that the amp can be bright. Clean there is no problem and using overdrive pedals neither, but when i overdrive the preamp using the PAB it was to much at high volume levels. With the Fet it was ok, but still i was thinking that it would be nice to have some control over the high frequency's like a presense pot. I know mesa boogie uses just a high cut as presense in some amps. So i decided to experiment and instead of using the mid switch as a treble boost, connect it as a hf cut.
I did not even have to open the amp to try this, i just soldered a 1nF cap on a jack and put it in the preamp out so the cap is connected from the wiper of the level pot to ground. The result was very good. At low levels, the cap doen't do much, but the higher you set the level pot, the more effect it has cutting the very high frequency's making the amp sound very nice when overdriving the preamp at high volume levels. I tested it using a load resistor and redbox speaker simulator since i can't crank the amp on full at home.

Since it it so easy to try (you don't have to open the amp, just solder a 1nF cap on a jack and plug it in the preamp out) I would like to know what others think of this and hear what you think.

Hi Richard, the 1nF across the lvl pot is way too much. I think it is there in case using the passive fx loop, to compensate the high impedance cable losses.
Although the 1nF should work a 68pF or even lower would be more realistic for the passive loop.

I cant comment on the pab overdrive you are experiencing, this feature is not in my amp. The sss002 and my trusty 80-ies ts9 is heaven, so I set it as a pedal platform in case I want more drive. Your 1nF cap on the jack seems like a great tweaking idea.

No fireworks in the Netherlands this year, you still manage to upset the cattle with a blasting sss002!
Happy New year!

Erwin

[Vertigo]

I too have been wondering about the usefulness of the Mid switch for the past few weeks and feel similar to you that it sounds more like it's accentuating the highs. I have managed to fool my ears into accepting it if I don't play for a few days and leave the mid switch on when I power up and start playing.

Is anyone else getting overdrive sounds out of theirs? If I push the preamp volume past 1 o'clock it'll clip without the FET, and with the FET on, it'll clip sooner. Same thing for the Level pot, anything past noon clips and none of it sounds good. This is all through a Boss WAZA TAE as with my entire family being home, I can't run it at that volume through a speaker.

[Richard1001]

My volume pot has a audio taper and with low output fender single coils without any boost engaged it starts clipping at 7-8 on the dail.
With the fet boost on, it sounds like SRV 'clean'. The high filter makes a lot of diffrence in the sound and amount of overdrive. I use the 2400pF the most when overdriving the amp itself. Low filter up two or 3 steps.

I changed the fet preamp somewhat, mostly to get low noise floor. I added a resistor and small cap to block rf (i have lot of amateur radio geeks nearby) and lowered the voltage using the stock 220K/8k2 voltage divider. I found that the lower voltage resuls in lower noise. The Fet i use is the Tochiba 2SK30ATM. It gives a 12db boost and set it to 10db with the trimmer.

I just realized and tryed the 3nF to ground setting with the mid switch on. If you do this it sounds pretty mid heavy but still ok. The highs are kind of back to, and i can see how this would make a fuzz or harsh distortion pedal sound more decent. I don't know if this would be the intended use though.

I think i will be going for a hf cut switch.

And if you don't have PAB Erwin, you can try it by setting the rock/jazz switch in the 'middle' position I have to do that on my ODS clone in wich i did not include any relays.

Happy newyear to you all!

[Vertigo]

My volume pot has a audio taper and with low output fender single coils without any boost engaged it starts clipping at 7-8 on the dail.
With the fet boost on, it sounds like SRV 'clean'. The high filter makes a lot of diffrence in the sound and amount of overdrive. I use the 2400pF the most when overdriving the amp itself. Low filter up two or 3 steps.

Thanks for clarifying that. I've had this impression that this SSS didn't really break up. It clearly does, and at least to my ears, it's not a good sound.

[Richard1001]

Thanks for clarifying that. I've had this impression that this SSS didn't really break up. It clearly does, and at least to my ears, it's not a good sound.

Well i did some comparing of schematics, gutshots and layouts of sss1, 2 and 4 and the ceriatone clone and i found that the sss-002 is missing a gridstopper after the filtersection where all the other sss have one.

The sss-001 has a 68k gridstopper on the board, next to the 100k to ground.
The gutshot of the sss-004 shows what looks like a gridstopper on the shielded wire comming from the filtersection.
The ceriatone shows a 220k gridstopper, the 100k resistor to ground is on the filter.

The sss-002 has no gridstopper in the schematic and on Ryan's board has only the 100k to ground resistor. On the gutshot of the sss-002 there is clearly ony one resistor visable, so either this is the 100k to ground or it could be the gridstopper if the 100k to ground is wired on the filter itself.
Looking at the gutshot of the 002 (wich is a bad quality photo) i could not detect a yellow band on this resistor. On all the other resistors that are either 100k, 220k, or 470k i can see one or two yellow bands. It would seem that this is not a 100k resistor but another value without bright yellow.

One other thing i noticed is the first local feedback resistor. On the schematic it says 1M, but looking at the guthot i can see a yellow band on this resistor and the value sure looks like 100k to me. I saw that the sss-001 has a 100k in this position. I will try this and see how this sounds.

[martin manning]

Interesting observations, thanks for posting and sharing the results of your experiments when you get there. A grid stopper on the filter recovery stage would roll off some high frequency, and then the 3n to ground being isolated to a single switch position would make a bit more sense. First LNFB level did seem extremely low with 1M/100Ω.