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Old 16th December 2009, 06:45 AM   #71
mos57 is offline mos57  Italy
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But if this preamp must drive only high loads, there is no need to use follower output stage.

Why not try a single SRPP stage?

Francesco.
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Old 16th December 2009, 12:40 PM   #72
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Francesco,

I am hoping that the follower will help with overcoming my lack of funds for high quality interconnects. I also at this time have not determined the physical layout of where this equipment will reside, thus I might have a long interconnect run to the next stage.

It will primarily be used to amplify a PC sound cards output to a more useable level.

I prefer this type of layout as it is very "eligant" and "simple". I am modelling a similar cicuit with 6BX7 follower Direct Coupled to the the 27s plate output.

The less components in the signal path the better IMHO,
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Old 16th December 2009, 03:05 PM   #73
mos57 is offline mos57  Italy
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Quote:
Originally Posted by coldcathode View Post
Francesco,


The less components in the signal path the better IMHO,
That is because i suggest a single stage srpp preamp: this have also reasonable output impedance.
On the other hand, my friend tell me that the sound of 6BX7 is very very good.

Francesco.
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Old 16th December 2009, 03:51 PM   #74
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Quote:
Originally Posted by mos57 View Post
That is because i suggest a single stage srpp preamp: this have also reasonable output impedance.
On the other hand, my friend tell me that the sound of 6BX7 is very very good.

Francesco.
I have also heard that the 6BX7 is good. Attached is a schematic including the 6BX7 follower, direct coupling and Battery bias.
Attached Images
File Type: jpg 27-6BX7.JPG (40.8 KB, 180 views)
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Old 16th December 2009, 08:31 PM   #75
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Default UPDATE: Bought myself an Xmas Present!

Hello All,


I have been playing around with the idea to learn to play Bass Guitar, so i stopped into the local music shop to look at a "Beginner" bass.

Nothing caught my eye, BUT....In their used equipment section I found a Behringer FCA202 Firewire Audio "card".

Retail is $150USD I got it for $45!

The spec sheet is attached.

I wanted to "model" the pre-amp with this as the "source".
Since in Windows using ASIO drivers I have no volume control, I need a "master" volume control.

Could not find a "potentiometer" component in LTSpice so I modeled it as two resistors?

The data sheet indicates that the cards output is 2dBV (I assume 2V) since the driver control has the volume locked at about 75% I am safely assuming an output of 1.5V.

The sheet also indicated that the Output Z is about 1K so I specified the series resistance of the AC source to be 1K, is this a correct way to model it?


Any comments or suggestions are welcome as always!
Attached Images
File Type: jpg 27-6BX7.JPG (41.5 KB, 168 views)
Attached Files
File Type: pdf FCA202_P0451_S_EN.pdf (180.5 KB, 37 views)
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Old 16th December 2009, 08:37 PM   #76
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BTW - FYI,

The sound quality of the FCA202 with ASIO drivers compared to even a high quality PC sound card using WDM drivers is like NIGHT and DAY.

The firewire interface brings the Digital signal out of the PC case and to the FCA202's DA converter. The metal case and separate DC power supply cuts out ANY AND ALL Noise from the PC's Hard Drives, Power Supply, fans etc.

This is easily the BEST $50 I HAVE EVER SPENT!!

If you are looking for a quality "Sound Card" for your computer, (Kind of an Oxymoron) this is definately it!.
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Old 9th February 2010, 02:37 PM   #77
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Default Update

Well I revised again and came up with 37 - 6BX7.

9V Battery Bias on the grids of the 37.

Direct Coupling to the 6BX7 followers.

Power Supply is VR tube regulated.

Pict's to follow:

The sound is "OK" but the 37's are EXTREMELY MICROPHONIC!!
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File Type: jpg 37-6BX7.JPG (25.4 KB, 129 views)
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