bluesboy Posted June 18, 2021 Share Posted June 18, 2021 Over the past year and a half I've assembled 4 Transcendent Sound kits. I built the Mini Beast power amp, the Grounded Grid preamp, phono pre amp and most recently the new Slider pre amp with a phono section. The sound of these OTL amps is nothing short of amazing. My speakers are hybrid Khorns using Altec Altec 511Bs and 902 drivers for the mids and Beyma tweeters that I built about 15 years ago. One problem though. With both the Grounded Grid/phono pre combo and the phono section of the Slider I'm hearing what seems to be a ground loop hum. I swapped power amps ( 2A3 amp) and the hum goes away. Same result when I tried an old Yamaha ss receiver. You can't hear the hum with music playing just slightly between tracks. The hum increases with volume. These amps are otherwise dead quiet through the other line inputs even with the volume turned all the way up. I've tried cheater plugs on all components and installed an isolation transformer that cost me 200 bucks in between the amp and preamps with no results. Any ideas? Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted June 18, 2021 Share Posted June 18, 2021 The plugs you use to troubleshoot are 10 or 20 bucks for the set. Worth every penny. This is a step by step process to identify the source of your hum. https://www.jensen-transformers.com/wp-content/uploads/2014/08/ts_guide.pdf 1 Quote Link to comment Share on other sites More sharing options...
bluesboy Posted June 18, 2021 Author Share Posted June 18, 2021 Thanks for the help. I already have a Jenson C1-2RR isolation transformer. I'm wondering what would happen if I installed the transformer between the output of the turntable and the input of the preamp. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted June 18, 2021 Share Posted June 18, 2021 11 minutes ago, bluesboy said: Thanks for the help. I already have a Jenson C1-2RR isolation transformer. I'm wondering what would happen if I installed the transformer between the output of the turntable and the input of the preamp. Look at page 6 of the link. The plugs show you where to actually put the transformer. You can guess and guess or you can get a couple of their dummy plugs and figure out exactly where to put it. Quote Link to comment Share on other sites More sharing options...
bluesboy Posted June 18, 2021 Author Share Posted June 18, 2021 I just ordered 2 of the test plugs from Jenson. Quote Link to comment Share on other sites More sharing options...
Bubo Posted June 19, 2021 Share Posted June 19, 2021 18 hours ago, bluesboy said: One problem though. With both the Grounded Grid/phono pre combo and the phono section of the Slider I'm hearing what seems to be a ground loop hum. I swapped power amps ( 2A3 amp) and the hum goes away. Same result when I tried an old Yamaha ss receiver. You can't hear the hum with music playing just slightly between tracks. The hum increases with volume. These amps are otherwise dead quiet through the other line inputs even with the volume turned all the way up. I've tried cheater plugs on all components and installed an isolation transformer that cost me 200 bucks in between the amp and preamps with no results. Any ideas? Get a tester, and test every electric outlet in the house to see if they are installed correctly. Listen to determine if the hum is 60Hz or a different freq. Use test tones on your phone to compare. Can you post a drawing of your components and their connections to each other and to the power ? Are all of the components plugged into the same power strip ? What else is connected to the same circuit breaker ? Are there any other electrical devices of any kind inc lights on the same circuit and close to the equipment or on top of a speaker ? Do you have a PC connected to the system ? Does your phono have a ground wire installed ? Disconnect the phono and other components leaving just the amp, is there hum ? Add one component at a time and see when the hum starts with no music playing Photos are always helpful Quote Link to comment Share on other sites More sharing options...
KT88 Posted June 19, 2021 Share Posted June 19, 2021 A very good list, Bubo. I would just like to add if there are light dimmers installed in the house. 1 Quote Link to comment Share on other sites More sharing options...
billybob Posted June 19, 2021 Share Posted June 19, 2021 This pinned link may be of some assist: Quote Link to comment Share on other sites More sharing options...
bluesboy Posted June 19, 2021 Author Share Posted June 19, 2021 The problem is not with the wall outlets as the phono hum goes away another power amp is used. I've tried a Jenson isolation transformer between preamp and the amp and between the TT and the preamp with no affect. I took pictures and sketched the layout. I can't find a way to attach. 1 Quote Link to comment Share on other sites More sharing options...
bluesboy Posted June 23, 2021 Author Share Posted June 23, 2021 I finally figured out how to attach photos. I had exceeded the attachment capacity. 3 Quote Link to comment Share on other sites More sharing options...
babadono Posted June 23, 2021 Share Posted June 23, 2021 On 6/18/2021 at 1:13 PM, CECAA850 said: The plugs you use to troubleshoot are 10 or 20 bucks for the set. Worth every penny. This is a step by step process to identify the source of your hum. https://www.jensen-transformers.com/wp-content/uploads/2014/08/ts_guide.pdf Could be CIC not a ground loop at all aye CECAA850 Quote Link to comment Share on other sites More sharing options...
bluesboy Posted June 23, 2021 Author Share Posted June 23, 2021 What is CIC? Quote Link to comment Share on other sites More sharing options...
babadono Posted June 23, 2021 Share Posted June 23, 2021 An IsoMax between the preamp and the offending power amp did not fix your hum? Hmmmmmm... or should I say Hummmmmmmm Are either or both 2 prong or 3 prong AC plugs? So......everything is perfect(well at least acceptable to your ears) when one amp is in your system. And then ALL you do is change to another amp and the hum appears? Quote Link to comment Share on other sites More sharing options...
babadono Posted June 23, 2021 Share Posted June 23, 2021 Common Impedance Coupling. It is when chassis ground currents and signal ground currents are using the same wire as it always does in unbalanced equipment. It is always present in unbalanced equipment, it is just a question of whether its magnitude is objectionable or not. If you have "dummy plugs" coming you are well on your way to the solution. Quote Link to comment Share on other sites More sharing options...
bluesboy Posted June 23, 2021 Author Share Posted June 23, 2021 I tried the IsoMax between the amp and preamp and between the TT and the preamp. The hum is still there with the power amp shown. But when I hook up the 2A3 amp (on top of the corner horn) the phono section in the preamp is dead silent. Quote Link to comment Share on other sites More sharing options...
babadono Posted June 23, 2021 Share Posted June 23, 2021 @CECAA850 is the GG preamp the same one you had trouble with? Quote Link to comment Share on other sites More sharing options...
babadono Posted June 23, 2021 Share Posted June 23, 2021 @bluesboy you installed the IsoMax at the power amp? I mean with short cables to the power amp. Quote Link to comment Share on other sites More sharing options...
bluesboy Posted June 23, 2021 Author Share Posted June 23, 2021 12 minutes ago, babadono said: @CECAA850 is the GG preamp the same one you had trouble with? Yes the GG pre with the Transcendent phono pre behaved the same way. Quote Link to comment Share on other sites More sharing options...
bluesboy Posted June 23, 2021 Author Share Posted June 23, 2021 9 minutes ago, babadono said: @bluesboy you installed the IsoMax at the power amp? I mean with short cables to the power amp. Yes Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted June 23, 2021 Share Posted June 23, 2021 1 hour ago, babadono said: @CECAA850 is the GG preamp the same one you had trouble with? It was in the system but I think it was cabling or the amp. Whatever it was, its gone now. Quote Link to comment Share on other sites More sharing options...
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