Second Time Around, Anyone?

[amandarae]

I posted this on the previous thread from the hum figures I am getting on my Tubelab SSe. Pardon me for asking again.

Is there anyone who can give me the hum figure on their Tubelab Simple SE with input shorted?

Followed the wiring diagram from the site to a tee and still having a hum of about 6.3 mV at the output. I am trying to determine if the PT I have is the problem as the hum is 60 Hz. Currently using 6L6GC for output tubes and 5AR4 for recifier.

Thanks in advance!

Abe

[Ty_Bower]

I'll measure mine, but it will take a few days. Things are very busy this Easter weekend. I can put it on the oscilloscope and see what comes out. I can tell you that it is vewy, vewy quiet. I've hooked it up to 100+ dB sensitive Klipsch Chorus speakers, and you can't hear any hum if you're more than six inches away.

[tubelab.com]

There are a few variables. The biggest is choke or resistor in the power supply, and chassis layout.

I have measured the "industrial amp" seen on my web site. It is stuffed into too small a chassis and it only uses a 1 Hy choke (a bigger one wouldn't fit). I measured the total residual output with the volume knob all the way down, CD player paused. I get 3 mV on one channel and almost 4 mV on the other channel. I have measured bare boards connected up on the bench without a chassis at less than 2 mV. Most of the hum is 120 Hz in both cases.

60 Hz is not coming from the power supply. Do you see any hum at turn on before the tubes warm up? If so it's usually magnetic coupling from power transformer to the OPT.

[amandarae]

Originally Posted by Ty_Bower

I'll measure mine, but it will take a few days. Things are very busy this Easter weekend. I can put it on the oscilloscope and see what comes out. I can tell you that it is vewy, vewy quiet. I've hooked it up to 100+ dB sensitive Klipsch Chorus speakers, and you can't hear any hum if you're more than six inches away.

Thanks Ty! Same situation I have here, running 100dB speakers. That's why I am troubled by the hum. I know, from my set up that lower than 4mV of residual hum will be fine on my set up, unfortunately my amp has around 6mV.

Abe

[amandarae]

Originally Posted by tubelab.com

There are a few variables. The biggest is choke or resistor in the power supply, and chassis layout.

I have measured the "industrial amp" seen on my web site. It is stuffed into too small a chassis and it only uses a 1 Hy choke (a bigger one wouldn't fit). I measured the total residual output with the volume knob all the way down, CD player paused. I get 3 mV on one channel and almost 4 mV on the other channel. I have measured bare boards connected up on the bench without a chassis at less than 2 mV. Most of the hum is 120 Hz in both cases.

60 Hz is not coming from the power supply. Do you see any hum at turn on before the tubes warm up? If so it's usually magnetic coupling from power transformer to the OPT.

Thanks George! That is exactly what's happening on my amp. At turn ON, the usual hum is there, then it gets quiet after a few seconds as it dies down(around 1.8 to 2 mV), then it goes up again for a few second and goes back downas the tubes warms up, then it began to go up again at 6+ mV and stays there.

One thing I noticed was that on the primary side of the PT(Hammond 374BX) bottom left facing the primary(120 Vac) side which unfortunately is the corner closest to one of the OT(left side or L channel).
I can hear and feel like a motorboating sound and vibration. During turn On, the sound and the vibration were not there as the hum goes up then down as I described. Only when the tubes warmed up that it begins to have these anomalies(coincidentally, the hum increases at this point too). This is the reason why I bought a new PT to try(when it arrive) as I am more and more convince that it is the PT. I have several amps with Hammond PT and this is the only so far that has the sysmptoms I described.

I have to think how I can re-orient the PT and report back as the amp is already finish. I will also try to rotate the choke, although installed underneath and see what happens.

Thanks!

Abe

[tubelab.com]

I will also try to rotate the choke,

I have heard of chokes causing hum, but I have never seen it happen. In theory a choke input filter circuit will have big AC fields around the choke, but the SSE is cap input. The choke should not be a problem.

The Lexan TSE seen on my web site worked fine on my 87db speakers. There was a faint hum at turn on which faded away once the tubes warmed up. It went to visit some 98db speakers and HUMMMM was present. I rotated the power transformer 90 degrees and all was quiet. It has since been to see some 106db horns with silent results. All 3 transformers were lined up in a row. I rototed the power transformer before this visit. A SSE without a chassis played quietly on those speakers too. First two pictures.

In a later listening session the Industrial Amp played quietly on those same speakers. We are listening to the Uber Expensive Cary 805's at the time I took the picture. I think the cables in the room cost more than my SSE did, no maybe ONE of the cables cost more than my amp. Yes, the Cary sounded better than the SSE....but, the TSE could keep up with any amp in the room at anything less than rock concert levels on those speakers. Third picture.

[Jpeg]

I think those pictures are all the motivation I need to stop goofing off and finish my own Tubelab SE. I have seen those before, and I think it is fantastic your amps can play with the multi-thousand dollar stuff. My only question is what are those Fisher Studio Standards doing in that photo?

[tubelab.com]

My only question is what are those Fisher Studio Standards doing in that photo?

The guy with all the cool stuff is a member on this forum. He also builds and mods amps. Would you hook up a home made amp that has never been powered up to speakers that cost 10K EACH.....I didn't think so.

My test speakers say Realistic on the front! The little metal boxes not much bigger than an OPT. 30 years old and I haven't blown them yet.

My previous test speakers were home made boxes with Jensen 6X9 car speakers in them. I fed them with a SSE wired as a P-P guitar amp. There was pieces of blue foam surround all over the room.

[tomchr]

Originally Posted by tubelab.com

My test speakers say Realistic on the front! The little metal boxes not much bigger than an OPT. 30 years old and I haven't blown them yet.

Clearly you haven't tried hard enough....

Yeah... Having an old PC speaker handy for the first smoke test is rather handy. Even though I run my amps for quite a while on a dummy load with o'scope and/or audio analyzer connected and watch for misbehaving before even thinking of connecting speakers, I still try with a pair of speakers I care less about before rigging them to my "daily drivers".

~Tom

[tubelab.com]

Clearly you haven't tried hard enough....

No, the old Rat Shack speakers actually sound good enough to keep around for a while. I used them as computer speakers with a SSE for a year or so. The SSE was fully warmed up and ready long before Windows 2000 finished booting. I sold that SSE, and have gone through two computers. I now use a SPP and my Yamahas. The SPP and Vista wake up at about the same time.

I plan to make something new for the new computer I am building. It boots Windows 7 in 16 seconds. That means DHT's for every stage. I will have new high efficiency speakers too.