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ForeWatt Tube SRPP Preamplifier - Support / Update Thread
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=2448
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Author:  Xandrell [ 09 Apr 2018, 11:35 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

My luck i got some ecc82 from Siemens. For cheap. Waiting for the rest of the parts and cant wait to begin.

Author:  gofar99 [ 10 Apr 2018, 21:01 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

Good score.

Good listening
Bruce

Author:  Diyengineer [ 19 May 2018, 14:48 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

Hello,


I have the Forewatt all together, and it sounds almost great. But I have 2 questions. I get a small amount of hum or buzz through the right channel only. The buzz seems to come mostly through the tweeter so its a fairly high frequency. It’s audible at all volumes. The left channel sounds perfect. Any ideas what might be the cause?

Second question is, should the Forewatt pass sound when turned off? With the power amps and the source on, but the Forewatt off, it still passes music that changes with the volume on the left channel only, but this is the channel that sounds great with no buzz(see above).I built it with no direct bypass also. Not sure what would be causing this.

I’ve double checked all connections. Any help would be great!

Thanks!

Author:  poty [ 19 May 2018, 17:24 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

What version of the schematics do you use?
Have you tried to change the tubes?
It is possible that some signal pass the preamp when it is off. It may be caused by different safety ground schemes in neighbours' devices. The fact that the right and left channels behave differently means that something is not equal in them: it may be a mistake in wiring, a broken part or just a schematic feature. That is why I asked for the version.

Author:  gofar99 [ 19 May 2018, 17:34 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

Hi, It seems I just lost my posting. Anyhow. I will try to recreate it. My sense is that the buzz and the signal pass through are related. I suspect a grounding issue. Think along the lines of a balanced input. Both conductors carry signal, if you ground one then the other will still get through. So if you have a high resistance to ground somewhere in your build it can act like a signal conductor and not only let signal through, but act like a pick up for EMI. I said a lot more in the other post, but this is where I would start. Compare (with the power off) the resistance from one channel to the other at every component that goes to ground in the tube area. Measure from each tube pin to ground as well. Look for differences. let us know what (if anything) you find and if need be we will go step by step after that.

Good listening
Bruce

Author:  Diyengineer [ 19 May 2018, 17:52 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

Thanks guys!!!

I’m using the latest schematics with he LR8N’s. What’s strange though is the channel that is passing sound when the amp is off is the one without the buzz and it sounds perfect at that. The channel that doesn’t pass sound when off is the one with the buzz. I’ll go through the entire circuit again tomorrow and maybe take some pictures. I tried to post some before but the file size was too large from my iPhone.

Thanks again!!

Author:  Diyengineer [ 19 May 2018, 21:35 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

How do you guys upload pictures here, I always get a error message that the file size is too large from my iPhone pictures?

Thanks

Author:  Geek [ 19 May 2018, 21:51 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

Hi,

You need to resize them before uploading.

Cheers!

Author:  Diyengineer [ 20 May 2018, 08:08 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

I was able To figure out how to compress some photos. I attached a couple so maybe someone can spot something that I missed.

Thanks

Author:  Geek [ 20 May 2018, 08:23 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

I see a lot of stray inductance with lead lengths there. I think maybe we have a parasitic oscillation....

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