Questions/Build Log: Soldano SLO 100 Clone

[xtian]

Finally got around to powering this amplifier up, no tubes installed. Man, this power transformer is pretty loud. In stand-by immediately after powering it up it holds a pretty steady hum. I can feel the transformer vibrating. Other amps I am used to an initial bit of PT hum when I power it on, but it will fade. This is not fading out. I left it on while I checked voltages and it stayed pretty steady. I tightened all of the screws on the PT, but that didn't seem to help as they were all pretty tight already. Any thoughts on how I might address this?

Your PT is vibrating mechanically--been there. Some PTs are born "unbalanced" and just want to hop around at 60Hz. You have two choices: tighten securely to the chassis (sometimes this makes it worse, because then the chassis serves as a sympathetic resonator and makes the noise louder), or isolate from the chassis with rubber grommets (may not be practical because the PT is too heavy). However, this mechanical vibration won't be audible at the speaker (you can actually try plugging in a speaker now, with NO tubes installed, and listen for hum). So hopefully when you button the chassis into the cabinet, the noise won't be bothersome.

[martin manning]

Maybe look into a replacement? Seems like there was some failure in the potting stage of manufacturing.

[bepone]

what is the manufacturer of the PT?
can we se better picture in laminations? i see something

anyway, there is a solution, transformer must be dismounted , removed bells and soak in transformer varnish, leave 24h to dry and test again. or returned to manufacturer like not conform compliant .

[professormudd]

This is an O-netics transformer from C3. I went ahead and emailed Rob at C3 and am awaiting a response. Per the documentation he provided with the transformer he tested and did a burn in on it before sending it to me.

[professormudd]

Despite the mechanical hum from the power transformer, I went ahead and installed some tubes and set the bias so I could finally play through this thing... MAN! The overdrive on this sounds absolutely killer! Heavy, tight, and punchy. Playing this through a 4x12 full of vintage 30s provides for some good "chugging" which is what I was after. After all, I built this in hopes it would replace my Mesa Boogie Triple Rectifier. This sounds quite a bit better, in my opinion. It is also a little less forgiving with sloppy playing than other high gain amps I have played, but I think that is a good thing. It sounds better than I had even hoped for.

The clean channel is okay, but I get the impression that this circuit isn't really meant to be clean and sparkly. I was only playing through my Les Paul Studio which has never really been my go-to for cleans anyway. I imagine it will shine a bit more when I get a chance to run my strat through it. Regardless, the clean is still better than the cleans were on the Mesa Boogie.

There is a super drastic volume difference between the clean and cruch settings for the clean channel. I reckon the crunch setting just adds a whole lot of gain.

I didn't spend too much time messing with the knobs either. I kept the EQ pretty much at 12 o'clock and was pretty content. I did turn the knobs all around just to make sure everything worked, though. I played a bit with the presence and depth as well, but again I just left them at 12 o'clock. For the overdrive, I only kicked the gain up to 2 while I played and it felt like plenty. I cranked it a bit just to see what would happen and it was so loud it was alarming. In the house I could only keep the OD master set to around 2 and it was still rather oppressive for my wife and son watching TV in the other room. I might need to get a reactive load attenuator.

Anyway, those are my initial thoughts on this amplifier. I am very happy despite the mechanical hum on the PT which is not at all noticable when playing through. Also, I could barely hear the hum over the regular noise when the guitar is plugged in. It seems to only be noticable in a silent room. Still, I am hopeful that Rob at C3 gets back to me and maybe offers me a replacement. After all, this was a very expensive set of transformers.

[bepone]

congratulations, i have built several , SLO100 has the best overdrive on the planet! i still have the chassis and boards for one, waiting for some free time
nothing beats SLO!

[roberto]

People who bought from Rob often came to sloclone asking for assistance, so I wouldn’t be so sure about a prompt and positive feedback. I hope for you to be wrong.

[professormudd]

People who bought from Rob often came to sloclone asking for assistance, so I wouldn’t be so sure about a prompt and positive feedback. I hope for you to be wrong.

Yeah, he isn't super fast on responding to my questions. It took quite a while to get these transformers shipped after I ordered them. Seems like this business is pretty low on his priority list.

I took a quick video clip to capture the humming, but it didn't seem to get picked up very clearly by my phone. I can hear it much more prominently in person, especially when the room is quiet.

https://youtu.be/rAU5jFKd7mM

[bepone]

This is a lot, not good, not acceptable, like a 10kV transformer for households on the street

If all bolts are tight (also holding the laminations) the problem is inside of transformer probably, need to be varnished.. The bobbin is vibrating on the laminations probably, and also laminations seems to be "quick" mounted to save time, E and I groups of 1 cm. I don't understand how they pass with this one on the tests.. new guy at the work?

If the manufacturer is not responding i would try to soak it in transformer varnish, leave over the night, and try to see tomorrow the situation. If the cause was bobbin, it should be fixed with varnish

[bepone]

here some short videos what to try at home

https://www.youtube.com/watch?v=YylT2lP93a0
https://www.youtube.com/watch?v=dtOwewfqucI

[professormudd]

This is a lot, not good, not acceptable, like a 10kV transformer for households on the street

If all bolts are tight (also holding the laminations) the problem is inside of transformer probably, need to be varnished.. The bobbin is vibrating on the laminations probably, and also laminations seems to be "quick" mounted to save time, E and I groups of 1 cm. I don't understand how they pass with this one on the tests.. new guy at the work?

If the manufacturer is not responding i would try to soak it in transformer varnish, leave over the night, and try to see tomorrow the situation. If the cause was bobbin, it should be fixed with varnish

Thanks for the videos.... Do you recommend any particular brand/type of varnish?

[bepone]

for power transformers which are working on kinda higher temperature it is better to go with professional transformer "insulation varnish".. ther is owen and air drying varnish.. choose air.

per example this is spray https://www.3m.com/3M/hr_HR/p/d/v000077468/ from 3M for insulation , but spray is not enough, need to soak it inside for hour or two, until all the bubbles go out..and dry it after - normal, on air.

so try to see under "insulation varnish" what is available in can..

[professormudd]

I got a reply from Rob at C3:

They do vibrate a bit and make some noise. It shouldn’t be excessive and these were normal on test here. Your video is spot on. That is the sound of an SLO at idle. These transformers are alternate vacuum and pressure impregnated with a heat cure resin that turns them into a block of concrete. The lams have to be chiseled apart

I replied indicating that I still believe it is an excessive amount of noise. I don't have a lot of hope that he will give me a return/trade-in, but that seems to me like the right thing for him to do.

O'Netics doesn't make transformers anymore, and I believe this guy bought out all of their inventory when they closed their doors. If push comes to shove, I might consider buying a PT from somewhere else. Does anyone have any recommendations for where to get a good power transformer for this amp?

[martin manning]

"That's the sound of an SLO at idle?" Really? I'm calling BS. I flipped my 100W ODS with Hammond PT on just now. The house is quiet, and I still have to put my ear 8-10" away from the head box to hear the PT hum clearly.

[bepone]

I got a reply from Rob at C3:

They do vibrate a bit and make some noise. It shouldn’t be excessive and these were normal on test here. Your video is spot on. That is the sound of an SLO at idle. These transformers are alternate vacuum and pressure impregnated with a heat cure resin that turns them into a block of concrete. The lams have to be chiseled apart

I replied indicating that I still believe it is an excessive amount of noise. I don't have a lot of hope that he will give me a return/trade-in, but that seems to me like the right thing for him to do.

O'Netics doesn't make transformers anymore, and I believe this guy bought out all of their inventory when they closed their doors. If push comes to shove, I might consider buying a PT from somewhere else. Does anyone have any recommendations for where to get a good power transformer for this amp?

ok all is clear, very high level of professionalism.
just one note, there is no any audible noise in any small power transformers (less than 1kW) usually find in guitar world..

all -random power transformers- for 100w amp should be fine..