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Old 12th October 2010, 10:27 AM   #1
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Default Benny's new ForeWatt SRPP pre amplifier

Hi everybody,

here I want to share some pics of my pre amp, the ForeWatt, also designed from my very dear friend Bruce Heran. By this occasion, I want to thank him for making this possible for all of us. If anybody is interested in any of my projects, I am very happy to assist.
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File Type: jpg ForeWatt.jpg (50.5 KB, 1057 views)
File Type: jpg Under The Hood Final (600 x 450).jpg (83.0 KB, 1025 views)
File Type: jpg PSU side.jpg (42.6 KB, 1008 views)

Last edited by Bennybuis; 12th October 2010 at 10:30 AM. Reason: forgot something, haha
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Old 12th October 2010, 11:01 AM   #2
Brit01 is offline Brit01  United Kingdom
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Very nice wiring and layout. Congrats.

Hope my current OTL project will end up as meticulous as your example.
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Old 12th October 2010, 11:36 AM   #3
Brit01 is offline Brit01  United Kingdom
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btw - what are you driving with this SRPP design?

I've used SRPP for headphone uses with excellent results.
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Old 12th October 2010, 03:25 PM   #4
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Hi everybody,

sorry for not being more clear about it, this is just my regular pre amp, I am driving my OddBlock with it. The OddWatt is just not loud enough to be operated without a pre amp, well almost, since it has so much power, but the pre amp really does the trick, it sounds warm and rich and doesn't color the sound (much). One input of the pre amp is bypassed, only the poti is in the signal path, this way I can operate my RIAA pre amp for the record player stand alone without having to mess with wires, each time I want to listen to a record.

This pre amplifier goes very well with my premium amp and is very much advisable. SRPP has some noise rejection from nature and gives you real low distortion, otherwise almost not to reach with tubes, this is why I love SRPP as a pre stage or pre amp. If anybody is interested in one of my amplifiers, I am very happy to assist building one.


Kind regards from Holland





Ben
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Old 15th October 2010, 03:41 PM   #5
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I am extremely interested in this design. I am just finishing Pete's Engineer's Amplifier which I intend to use as my primary listening amp. And so I will be in need of a well designed pre-amp through which I can run (and attenuate) my CD, MP3, and into which I can run the output of my RIAA phono pre.

How do I go about getting full schematics? With some trial and error I could handle the layout, but of course a layout diagram (or advice specific to this project) would be helpful.
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Old 15th October 2010, 04:33 PM   #6
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DIY ECC802S (12AU7 / ECC82) Vacuum Tube SRPP Preamplifier


What i dont get is ive been tought (by tubecad no less) that the srpp needs to be matched to the destination.

AKA you make one to drive a 10k load, its not going to sound good driving a 100k load.

On the bright side its only a gain of 10, most cd sources need a gain of 2 tops.
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Old 15th October 2010, 04:47 PM   #7
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by nightanole View Post
DIY ECC802S (12AU7 / ECC82) Vacuum Tube SRPP Preamplifier


What i dont get is ive been tought (by tubecad no less) that the srpp needs to be matched to the destination.

AKA you make one to drive a 10k load, its not going to sound good driving a 100k load.

On the bright side its only a gain of 10, most cd sources need a gain of 2 tops.
For line level applications I have never found matching to be in any sense critical with an SRPP based line stage. You can measure a few dB difference in the distortion spectra, but it is generally low enough that you cannot hear it at all IMSLE.

Personally I do like the 6SN7 a lot in SRPP, the ECC82/12AU7A much less so - arguably in many cases this circuit is little more than an audio fashion statement. (That doesn't stop me from liking fashion.. ) You will get significantly lower output impedance with a straight CF in most instances.. I like transformer coupled line even stages better..

I generally find line stages with 10dB or less gain to be preferable to high gain versions. (My current line stage has 4dB of gain) When using a phono stage I place the additional gain required for this source in the phono stage as it is better from a noise performance standpoint.
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Old 16th October 2010, 07:40 AM   #8
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Hi Kevin,

thanks for the reply. The Russian 6SN7's I used made me lots of trouble, they are real noise antenna's, I had to do some rather unorthodox things to make it work at all. For my next ForeWatt I will try the 6N1P for once. I like the sound of those tubes and quality is also rather good. I love SRPP for it's low distortion and it's simplicity. I use SRPP also as the pre stage in ALL my projects, if find a nice schematic, I usually disregard whatever pre stage they are using and I use a SRPP instead. Depending ob how much voltage swing I need, I use the 5751 or 12AX7 or EEC82 (12AU7 and it's derivations).

All the best.


Benny
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Old 10th November 2010, 11:37 AM   #9
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I've found some (8, actually) 200V 1.0uF 1uf K40Y-9 PIO caps that I would like to use, but the schematic calls for 400V caps. Is there some arrangement of these that I can use to create a 400V 1.0uF capacitance? Would a series + parallel arrangement suffice or do I need to create a voltage divider ahead of these? Or do I need to look for other caps?
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Old 10th November 2010, 12:30 PM   #10
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I see you have a beautiful wooden box. But how do you keep all the rf noise out of the signal??

Is there a fuse in the power section? I can't see one.
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