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Groovewatt - tube RIAA phono preamp
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Author:  StEeLz [ 27 Nov 2017, 23:07 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Forgot to specify the Phono stage has 2 pairs of Nuvistors inside (Circled part of the picture)!

Author:  gofar99 [ 28 Nov 2017, 08:39 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi , Nuvistors work fine. I tried some a while back. The biggest issue was that the gain was lower. They really didn't seem any quieter than a number of off the shelf ECC803Ss/ECC83Ss.

Good listening
Bruce

Author:  Geek [ 28 Nov 2017, 13:34 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

gofar99 wrote:
The biggest issue was that the gain was lower. They really didn't seem any quieter than a number of off the shelf ECC803Ss/ECC83Ss.


Was reviewing the datasheets for them little nuvistor things. Most aren't all that high on the micromhos side of things. That's probably the problem :|

Author:  gofar99 [ 30 Nov 2017, 15:30 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

The ones I tried had leads and would be a bummer to replace (or even test in my tube tester). The USA NOS ones were much too costly to consider. Another reason to not use them. I attached a photo of the main circuit board of one of the versions that used nuvistors.

Good listening
Bruce
Attachment:
IMG_1356.jpg

Author:  Geek [ 01 Dec 2017, 14:07 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

From your pic Bruce, I just realized why I think they looks so cool.... they remind me of TO-5 cased germaniums! :D

Author:  tdmoreno [ 30 Dec 2017, 00:29 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi Bruce - first of all, thanks for putting out a great schematic and project forum. I’ve had my eye on building it for some time and the forum has been great resource throughout my build.

I’ve completed building schematic (finalizing case to come) and feeding into my antique Curtis Mathes cabinet. Preamp sounds great and is high gain as advertised. The only minor issue is that it’s almost too much gain as usable volume control on antique cabinet is really small (i.e. – volume control incredibly sensitive). I’d like to keep antique cabinet volume control original to prevent effecting the use of radio.

Thus, wanting to know if trim pots can be used to adjust gain of preamp? If so, what values and location in schematic?

Or any other suggestions?

Thanks in advance.

Author:  gofar99 [ 30 Dec 2017, 16:03 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, I would probably put trim pots on the output side. Depending on how much excess gain you have you could use something like a 20-100K pot. Fixed resistors would also work and be a better long term solution (less noise etc). Put a pot there temporarily and when you get the level you want take it out of the circuit and measure the resistance between the center tap and each end, then use those values for fixed resistors.

Good listening
Bruce

Author:  tdmoreno [ 17 Jan 2018, 22:11 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Thanks Bruce. I ended up using a 100K resister on the output as you described.

Finally finished the case and put everything back in. Still sounding great.

One thing I would like to add for future builders. When first built, I was experiencing a lot of noise after about a minute of being turned on. Finally realized that the LT1085CT voltage regulator was overheating. Audio would still play thru but noise was terrible. Installed heat sink and no more issues.

Todd

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Author:  gofar99 [ 18 Jan 2018, 22:01 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, Good show. Nice build. It looks a lot like some of mine. Wood with metal and the mesh top. I see you followed the layout for the active board as well. It is what I have found best for low noise. Yes a regulator that is getting too hot will introduce noise.

Good listening
Bruce

Author:  coaltrain [ 31 Jan 2018, 23:29 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

I finished my Groovewatt and sounds great. Very minimal noise with Groovewatt connected to Forewatt then Oddblocks, only audible with forewatt turned to 70-100% which is wayyyy too loud anyway. When I connect my Rega P2 player, there is a hum, seems 60Hz to me but could be wrong. It is not audible at normal low listening levels but bugs me that I can here it when a record is not being played. The hum is there when the Rega is connected whether it is on, off, unplugged from mains. Does not change when one RCA id disconnected vs the other, might be a little less with left disconnected. When I looked up "Rega P2 player hum" I came up with a whole bunch stuff. Any suggestions, I am thinking it must be a grounding issue with Rega going to my Groovewatt since without the Rega system is quiet.
If the answer is take the Rega back I can live with that since I only have had it 6 weeks.
Thanks

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