My MOSFET amplifier designed for music. - Page 22 - diyAudio
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Old 26th July 2008, 09:39 AM   #211
Mooly is offline Mooly  United Kingdom
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Hello Francis,
Yes- the second Op-Amp was just to preserve phase. Whether it makes any audible difference I don't know. Perhaps ommiting it and swapping the speaker leads would be better, but that never "feels right" somehow -- bit silly really.
If you have a signal generator why not rig up the FET's as I showed and try them, there must be many J-FET's that are suitable. I didn't match them at all as they are simply used either fully on or fully off. Any small difference in on resistance, say 35 ohms intead of 25 is totally swamped by the series input resistance. The first OpAmp operates as a mixer of course and to get the performance from the FET switching you have to use the virtual earth configuration, don't be tempted to use the non inverting configuration instead. As a bonus for some reason the inverting mode always seems audibly better to me. Maybe because there is no common mode error voltage.
I am just re reading your post "100 % listening to CD no source selection required"
Do you mean you don't need remote control over input selection or no input selection at all (just the CD input) in which case you don't need any FET's Just an OpAmp and the ALPS volume control.

The sound does grow on you-- try some CD's you don't play much for whatever reason.
The "other project" is just a bit of fun at the moment, this amp with the Lateral FET's is still as valid as ever -- and every time I listen I know how "right" it sounds.
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Old 26th July 2008, 02:19 PM   #212
rellum is offline rellum  France
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Hi Karl

I have built a preamp based on a PGA2311. Input selection is made of relays and I have only two inputs for my two cd players. Usually, I only power on one player and everything is fine. While testing, I discovered a nasty crosstalk with both playing. I controled my board wich is hand wired but found no default. You seemed so happy with your fet switches that I thought of building one but without manual selection. The pic will monitor the inputs and select the one wich is playing music. The soft will manage everything's needed . Less current consumption, perhaps softer switching and the pleasure of building something unusual. I learned all those things by myself and its always a challenge for me to succeed.

I thank helpfull people like you and Lineup and many others, that give guys like me the opportunity to progress in audio diy.


Best regards,
Francis
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Old 26th July 2008, 02:35 PM   #213
Mooly is offline Mooly  United Kingdom
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Hi,
O.K. The FET's as I use them give as near total isolation as is possible. With the volume of the amp on full and audio applied to all (3 in my case Aux, Mini Disc and tuner) unselected inputs there is no audible breakthrough at all. Even with 10 volts squarewave shoved up one of the inputs there is zero breakthrough even with ears right up to tweeter. None - nothing - - zilch

Try those FET's you have.
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Old 26th July 2008, 03:01 PM   #214
Mooly is offline Mooly  United Kingdom
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Your crosstalk problem ? Sounds like something has gone astray a bit. Relays aren't that "bad" and the crosstalk should be minimal, even just with a single pole contact. If you have a circuit for it post it up. Could it be capacitive crosstalk at all ? perhaps if you are using high impedances anywhere. That's one reason I run the FETs' into a virtual ground configuration. The coupling between adjacent print is minimised as there is no "voltage" present. You would have to see the board layout to see what I mean, but work it does, it really is total isolation.
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Old 26th July 2008, 03:47 PM   #215
lineup is offline lineup  Sweden
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Quote:
Originally posted by rellum
Hi Karl
---------
I thank helpfull people like you and Lineup and many others, that give guys like me the opportunity to progress in audio diy.
Best regards,
Francis
Well, I always want to take care of those trying diy audio.
I do not know why .. just that I care for others!

rellum, Francis
if you knew what good things I have discovered from questions and 'stupid' newbies suggestions,
you would be really surprised.
Beginners have a FRESH MIND and they so have new and other ideas.
That those Electronics Engineers never even can dream up.


Thanks Francis.
For joining our gang of DiyAudio gangsters.
You soon be an audio guru, almost ... like me
Let's see what you construct in 2009, 2010 and 2011.
When YOU teach those beginners ..

Lineup, sincerely
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Old 27th July 2008, 08:54 AM   #216
rellum is offline rellum  France
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Hi Lineup

Guru, I'm affraid when I see this word somewhere. There are generally many hidden things behind it.
There are so many things out of my control in audio that I will stay a monkey, monkey see - monkey do.

Thanks for the kind words.

Francis
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Old 30th August 2008, 07:41 AM   #217
lineup is offline lineup  Sweden
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Default Re: My MOSFET amplifier designed for music.

Quote:
Originally posted by Mooly
Hi, Well after having seen all the amazing projects and designs you guys have come up with I thought I would share my design on these pages. First and foremost this was designed for music reproduction in a domestic setting and without wanting to "hijack" another current thread, YES amplifiers do sound different, that is why I spent so much time in the development of this one. This amp is without doubt "musical" in all the best sense of that term, it's ability to recreate a believable soundstage is absolutely compelling. If anyone is interested in what it looks like and further details there are some piccys in the "Post your solid state pics here" forum. (About post 283) The thinking behind this project draws on the work of the late John Linsley Hood whose designs and thinking I much admired.
Regards Karl

Are you sure Mooly
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Old 30th August 2008, 10:54 AM   #218
Mooly is offline Mooly  United Kingdom
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I used to be indescisive, but now I am not so sure
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Old 6th September 2008, 07:06 AM   #219
lineup is offline lineup  Sweden
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Mooly,
You posted one schematic in
Post #288 in 'Post your Solid State pictures'
along with images of your amplifier + your sound system.

Question:
How far from the 'final/latest version' is your schematic, 2 February 2008

Guess there has been a few improvements .....

Regards
Lineup
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Old 6th September 2008, 07:16 AM   #220
Mooly is offline Mooly  United Kingdom
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Hi Lineup,
The only change has been removing the 150pf cap on the input transistor. Nothing else. Totally 100% stable. Musically, out of this world. Oh and that 0.22 ohm series output resistor, which has always been present, just me, I kept missing it of the circuit
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