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PostPosted: 26 Jul 2016, 09:51 
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Joined: 26 Mar 2014, 06:46
Posts: 2
Hi Bruce,
...foloving for some times now and becouse I have some bounch of 12au7 and 5814 tubes at home,I just buy some parts to build your preamp together.It will be verry interesting project.I have only one question.In my power supply after rectifier I become only 232V out,so I will use some lower value resistor in the Psu to become on the end 215-220 Volts needed for the B+.Plese tell me if I must becouse of this now used some other value for the resistor for the Heater reference voltage :confused: ??Now is there 100Kohm and 220Kohm!Plese have in mind that I will work with 5814 tubes or ecc82 and I will to have DC heaters supply but of 12,6 volts not 6,3volts like in your design,this is just becouse I have such transformer and parts at home.So plese for help about this question.


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PostPosted: 26 Jul 2016, 11:54 
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Joined: 26 Mar 2014, 06:46
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Hi Bruce,
...I folow for some time now the stuf about your preamp and I have decide to build my own.I will use ecc82 and 5814a tube for this project,becouse I have this at home.I have one question o you Bruce,becouse I become from my transformer after rectifier only 232V output,I will use smaler value of the resistor in Psu to become on the end this 215-220 volts of B+.But plese tell me if I must becouse of this use some other resistor value for the heater reference voltage.Now there is in your design 100Kohm and 220Kohm.I will to use the DC heater supply but with 12,6V of voltage end not 6,3 like in your design.
So plese for help about this,I will start asap to build the preamp becouse I have already all parts at home.
;)


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PostPosted: 30 Jul 2016, 17:48 
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Joined: 04 Jun 2008, 20:59
Posts: 4100
Location: Arizona, USA
Hi, I missed this posting. Your B+ will be OK. What I would do is use the newest variation with the LR8 regulators in the B+. Keep the first 2 sections of the filter string about the same and use 500R (or 470R) for the resistors and use the LR8 to drop what ever you get by about 25-30 volts. This will filter the hum and noise out of the B+. You will probably end up with about 180 for the B+ on the tube. I would change both cathode resistors in each SRPP to 680R (from 820R in the latest version). This will increase the current flow slightly. You can use 12 volts on the heaters as well. I would make the connection from the B+ to the heaters temporary. This way you can try both sides of the heater string to see if one is quieter than the other. It is sort of hit or miss as sometimes it makes a noticeable difference and sometimes it doesn't. My sense is that being attached to the most negative side of the heater string seems best, but I have one phono preamp that uses a similar circuit and it is quieter the other way.

Good listening
Bruce

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PostPosted: 18 Aug 2016, 22:18 
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Joined: 05 Nov 2015, 01:57
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I want to thank Bruce for sharing the plans for the Forewatt preamp. I noticed that Bruce had provided a schematic that reflected a modified preamp with a date of January 26, 2015. Can anyone share the updated schematic dated October 30, 2014.? Thanks for your assistance.

Greg E.


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PostPosted: 19 Aug 2016, 20:36 
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Hi, Sure.

Good listening
Bruce
Attachment:
Preamp PS October 30, 2014.jpg
Attachment:
Preamp main October 30 2014.jpg


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PostPosted: 25 Aug 2016, 17:39 
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Joined: 05 Nov 2015, 01:57
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Bruce,

Thanks for sharing the updated schematics. Greatly appreciated.

I noticed in one of the preamps you build you added a remote control module to the preamp. Would you recommend the manual control or remote control build. Is there any difference in sound?

Thanks again for all your help.

Greg

PS- Really enjoying my KT-120 mono blocks. Thanks again for sharing your knowledge and help.


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PostPosted: 25 Aug 2016, 20:28 
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Location: Arizona, USA
Hi, I use a remote control with my main preamp (a combination of Forewatt and Groove). It is a digital one with relay switching pairs of resistors for the volume portion and more relays for the input selection and mute functions. It works quite well. I show it as a MV-02 (might be just a V-02). It is available from a number of Asian sources for about $130. It requires a separate 12 VAC power supply. Grounding is an issue with it as the signal ground is the same as the power ground and both are tied to the chassis with a pair of reversed diodes in parallel. You need to be very careful not to create ground loops through the chassis. The actual motorized version that uses an Alps pot is nearly impossible to get hum free (below about -75 dbv). The all digital one can get to the -85 to -90 range though. The display is nice and the resistors are metal film Japanese ones. The all manual version of the preamp is about 6 db quieter than the digital one, but really the digital is quiet enough for me as I get zero noise in my system at full volume setting on line inputs. With the phono preamp mode engaged there is some hiss as that part of the circuit does add noise. The setting though is over 40 db higher than my normal listening levels so the hiss is for all intents non-existent.

Good listening
Bruce

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PostPosted: 25 Aug 2016, 20:55 
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Bruce- thanks again for the information regarding the remote control module. Appreciate the quick feedback and great help. THANKS Greg


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PostPosted: 28 Aug 2016, 19:10 
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Joined: 05 Nov 2015, 01:57
Posts: 9
I am recently retired and have always had a passion for audio equipment. One of my bucket list items is to learn the art of building my own audio equipment. A few my friends have helped me build a coupe of pieces of equipment. After their help I have gained a great appreciation for diy'ers who have the ability to make their own equipment and especially design their own equipment (like Bruce). Hats of to all you.

It is my goal now to build on my own the ForeWatt preamp. I have combined the schematics from 10/30/14 (referenced above in recent post by Bruce) and an 4/18/10 schematic (in initial introduction of the preamp in diy projects; includes a remote control). Based on this combined schematic (can be found in the below link) I have the following questions that I would be grateful if you can answer:

1- Does the combined schematic (reflected below) look OK to incorporate the MV-02 remote control?

2- I understand that the "K" symbol stands for "electro mechanical relay". Can you please recommend a relay that would go into space "K1" and "K2" in the combined schematic.

3- Should I go with option "A" or "B" (reflect in combined schematic) in respect to which output resistors to use?

4- in the original diy project write up for the preamp it indicated that the "output cap" was an important part of preamp. Can you please confirm in the schematic if I have correctly identified the referenced "output" cap.

Image

Bruce in your note above you indicate that the mv-02 remote will be around $130. Below is the link you reflected in the initial diy project for the remote. Is the remote you are still recommending?

http://diyclub.biz/catalog/product_info.php?cPath=1_248_85&products_id=195

I WANT THANK EVERYONE IN ADVANCE FOR CONSIDERING TO HELP ME WITH THE ABOVE AND TO LEARN THE ART OF BUILDING MY OWN AUDIO EQUIPMENT. THANK YOU.

Greg E.


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PostPosted: 28 Aug 2016, 20:54 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, No. That one was in an early design and has flaws. Worse 2 out of 6 were defective. The power supply and signal share a common ground and it interjects noise in high gain systems. The one below is the one I am using. It used to be everywhere now they seem a bit more scarce.

http://diyerzone.com/audio-preamp/lite- ... e-kit.html

I have considered using a variation of the IC based volume controls. There are several types. All however seem to have some limitations on input signal level. I built one about two years ago and it worked OK, but to use it with some of the higher output signals from some of my devices I had to pad down the input levels. I hate throwing away good signal level to accomodate another component then have to amplify it again. I understand that some of the newer IC based stepper controls will handle higher signal levels so I may eventually go that way. For now the Lite V02 serves my needs quite well.

Good listening
Bruce

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