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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:  Diyengineer [ 12 Oct 2018, 21:43 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

Hi Bruce, thanks a lot,

Yes, I do have a scope. And to note, my power amps do not have input blocking caps and 1M resistors. Also, I have had this motorboat problem on both the left and right channels at different times so I’m inclined to think there’s not a problem stemming from either monoblock.

I will replace the diodes and try it tomorrow, I have some UF4007’s that I can replace them with.

If that doesn’t fix it, I’ll try the 2.2 cap. Also note, the 4.7 caps in there are the second set. I have replaced them the last time this happened. Would a bad ground possibly ruin them?

On my last go around with this, I ended up re-flowing all ground joints and pretty much all joints relating to this part of the circuit. I use 63/37 leaded solder.

I attached a picture of that portion of the circuit. The pic is a little older, the 4.7 caps are different now, but that part of the circuit has the same layout still. The black wire off of the bottom 4.7cap is the single ground wire for the main PS board that goes to the input jack. I can take a current pic tomorrow also.

Thanks again!

Author:  Diyengineer [ 13 Oct 2018, 09:27 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

The Verdict,

After replacing all the components in the regulator circuit one by one, the faulty component was the 470k resistor. I’m sure this was probably the part that fixed it the previous two times. I ended up just replacing all the components those times as well.

This means that I have had 3 different resistors fail in those positions 3 times so far. Any ideal as why? I’m using 1W resistors in those positions, maybe they need to be a higher wattage?

Thanks

Author:  gofar99 [ 14 Oct 2018, 16:36 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

I use 1/2 watters just fine. The current in that part of the circuit is really low and they ought not have issues. It could be a bad batch of resistors. I got an assortment of carbon film ones a while back and they were supposed to 5%. 1/2 watt. About 1 in 20 was within spec and some failed in use. If the cause of the problems was the resistors then I would try another brand. Most have voltage limitations, but in my experience it seldom matters. Perhaps you have that exception.

BTW, that is a nice looking layout.

Good listening
Bruce

Author:  Diyengineer [ 14 Oct 2018, 18:18 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

Ya, I’ll try a different brand.

I used PRP brand in those positions each time which I believe are supposed to be a fairly decent brand while being inexpensive. I use PRP for pretty much all of my amps with good luck. Must have just been a bad batch of 470k’s perhaps.

Thanks for the comment on the layout. I’m pretty happy with how the project came out all in all. Sound is beautiful except for when the resistors went bad.

Thanks!

Author:  Larry49 [ 21 Nov 2018, 11:36 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

HISS
Hello everyone,
I have a problem with white noise too high "HISS" with volume zero or in any position and I do not understand what can be generated
If I use Groovewatt and a self-built transistor amplifier, it's okay, but if I connect the Forewatt with ECC802S I have hiss even with shorted inputs
The schemes are the last ones
sorry for my English
thank you

Author:  poty [ 23 Nov 2018, 08:55 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

There is a discussion starting here: viewtopic.php?f=9&t=43&start=1890#p54825
Several hints have been already mentioned. Just not to repeat them in this thread.

Author:  Larry49 [ 26 Nov 2018, 16:33 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

Fixed the problem, it was the fault of the LR8K4 that oscillated
thank you all

Author:  stwh [ 22 Mar 2019, 09:49 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

Hi all.
I am a newbee at this. I have previously built a tube amp using a PCB and the ForeWatt will be my first using a schematic.
My question is where does the 0v lines from the power go? Do they go to the ground?
Sorry if this is a silly question.

Great site by the way

Thanks
Steven

Author:  ILoveHiFi [ 22 Mar 2019, 14:46 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

So if you have a high voltage supply with +2xx Volts and 0v wire, you connect the "black" 0v wire to ground of amplifier.

If the transformer is 250ac -0- 250ac you connect the 0v wire of transformer to ground.

Author:  stwh [ 22 Mar 2019, 15:55 ]
Post subject:  Re: ForeWatt Tube SRPP Preamplifier - Support / Update Threa

ILoveHiFi wrote:
So if you have a high voltage supply with +2xx Volts and 0v wire, you connect the "black" 0v wire to ground of amplifier.

If the transformer is 250ac -0- 250ac you connect the 0v wire of transformer to ground.



Thanks for the reply. Just wanted to be sure. Much appreciated.

Steven

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