Tandberg Solvsuper 10 - Attached Modern Devices

[Niner9]

I recently acquired A very nice condition and well working Tandberg Solvsuper 10. It is a late model with power button and AFC. produces 6-8 watts per channel, with 30 watts peak. I'm running it to RadioShack Minimus 7 pair and a Theater Solutions Sub8S with very good results in a small space. Very harmonic, well defined and imaged, full range, very pleasing music from my iPhone using a Fiio DAC, or iPod. Fine radio section, FM, AM, and SW all working well. The Minimus 7 pair is connected to the main speaker outs, and I'm using a IBLOC01 2-Channel Line Output 40W Adjustable Level Converter from the remote speaker connection to connect the Sub via line level inputs. I've set the IBLOC01 at mid-range, but I can turn it to max with no distortions in the Sub. The IBLOC01 in tandem with the Minimus 7s should be reducing the Ohm load to something below 8 Ohms per channel.
I thought I'd be clever, and attach a Monoprice 4-channel Headphone Amplifier, using a RadioShack Line Distribution Amp from the IBLOC01 to feed both the Sub and Headphone Amp. It works well, but I'm getting some left channel ground loop noise at 12 o'clock on the headphone amp control. No change with Sub on or off. If I keep it down to 10 o'clock, no noise. I can do that, and control volume from the Solvsuper with no bad effects or distortion, no complaints from the Solvsuper. The noise appears to be coming from the Solvsuper, not anything downstream from it. Same noise with Line Distribution Amp and/or Sub out of stream. I only hear the ground loop noise with headphones. I want to run the Solvsuper through the remote speaker connection only, with the Sub off, main speakers off, headphones only, with no noise. Is it safe, long-term, to do this, keeping the headphone amp at 10 o'clock, and controlling audio through the Solvsuper? Any ideas about how to resolve the ground loop noise? i'm concerned to attempt a chassis grounding to electrical grid, since Solvsuper is 220 v. What, in the Solvsuper might cause this ground loop noise? I have ordered a new IBLOC01, thinking the one I have could have a flaw, but the transformer in it is supposed to suppress ground loops. I considered using the Tape Out on the Solvsuper to feed the headphone amp, but that would give me no tone control into headphones. Schematic of the Solvsuper attached. Thanks for your consideration.

 

[gadget73]

sure its not just hum from old power supply filters? If this is all original you're pushing 60 years old on all those parts.

Grounding it shouldn't bother anything. It has a transformer that isolates it from the mains feed. I don't know that it will fix your problem though.

this is also mostly a solid state unit. The tubes are only being used in the FM tuner. The entire audio chain is transistors.

honestly it may also be a case of too many things connected to it. No need for a line level converter and a headphone amp. Would make more sense to just connect the headphones directly to the receiver. If there is no headphone jack, you can build a simple passive adapter to get that done.

https://diyaudioheaven.wordpress.com/tutorials/power-amp-adapter/

basically you can knock that together in a box and have yourself a simple interface with no electronics to cause problems. This is really all those line level adapters do in case you were curious.

 

[Niner9]

I doubt that the hum, which is only on left channel is from the PS. It can only be heard with headphones. Speakers are perfectly silent. No other dysfunction or glitch. I am very familiar with hum from bad power capacitors, which is a hum of consistent volume, regardless of volume setting. With bad power caps, the volume of the hum is dependent on the deterioration of the caps, not the amp setting. This hum is not like that. I have a collection of over 100 vintage and new radios dating from 1920s to 2019. Even modern devices can have power cap (and other) problems, Sony being famous for low spec components on some of their (even high-end) products: engineering often good, build often flawed. That kind of problem has killed many modern products.

Downstep transformer is 300 w, power draw of the Solvsuper is 42 w. Massive headroom. Downstep is brand new, used only for Solvsuper, stays perfectly cool. Solvsuper gets only warm, never hot. Thermo fuse is 234 F., it gets nowhere near that, no matter how hard it is pushed. No power distortion on the face of it.

Yes, Preamp and Power Amp are all transistors. FM receiver has two tubes, IF Amp has 2 tubes, FM Stereo Decoder has 1 tube. Hum exists left channel on headphones from any input, radio or other, so receiver sections and IF Amp are absolved.

I did ground the Solvsuper to electrical grid, and it did soften the headphone hum slightly, not in volume, but noticeably in quality; less high frequency audible in the hum with the ground. An improvement.

Thanks for the link to the homebrew power amp adapter, in above msg. I had seen that page when researching for this project, and decided against that route, more limited than my intention which includes Subwoofer to take some load off the Bass tone circuits and give the Minimus 7s more headroom. That part of this project is very successful, giving me much clarity in the tweeters, making them very impressively 3D, and some slight dynamic improvement in mid and low tones from Minimus 7 Woofers. I'm not giving up those gains.

I have a package of ferrites coming. Liberal use of them with all outboard devices may help. I may never solve this problem completely.

It is possible that for the Solvsuper part of the problem, there just may be a resistor or an array of resistors aging out of spec in the Pre Amp or Power Amp. But maybe not, because: When out of the Solvsuper, touching the input of the IBLOC01, body capacitance causes a very identical hum in headphones, on whichever channel is touched. And curiously is reduced but not eliminated when both are touched. I am now suspecting the IBLOC01 is at least part of the problem, if not the essential problem, and look forward to testing a replacement, being shipped. I may end up using one IBLOC01 for left channel, and one IBLOC01 for right channel, to prevent any crosstalk in them, which could be generated (I'm thinking) if not from circuit design, possibly from channel adjust mismatch...hard to micro-adjust the small components through the access holes, with a flexing plastic mini screwdriver. If necessary, I could use Y-cables to do the following:
Solvsuper Speaker Out L < IBLOC01 "A" L+R > Output L
Solvsuper Speaker Out R < IBLOC01 "B" L+R > Output R

Talking out these issues helps my thinking processes, thanks.

 

[peterh]

Off tread an explanation of the name "SölvSuper"
Sölv is an old scandinavian name for the noble metal silver. Sölvsuper is then very clean silver

Back to thread

 

[Niner9]

Off tread an explanation of the name "SölvSuper"
Sölv is an old scandinavian name for the noble metal silver. Sölvsuper is then very clean silver

Back to thread

That's wonderful. Thanks peterh.