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PostPosted: 13 Jun 2011, 03:42 
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Pics below. Terribly disappointed with the Mordaunt Short speakers. Shrill forward treble, tons of sibilance and poorly defined bass. For a speaker with 2 bass drivers, it puts out less bass than the Goodmans single 8'', both are in sealed boxes. Ahh these will have to go back on sale. Considering the $250 price tag on the Mordaunt vs $100+ on the Goodmans, it is utterly disappointing. Bad day today!

The Goodmans deliver smooth, pleasant music, lovely silky highs and great non boomy bass.
I am starting to like sealed box bass!
Sorry for OT.


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PostPosted: 13 Jun 2011, 03:55 
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Bad speakers.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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PostPosted: 13 Jun 2011, 04:26 
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I'm having problems uploading the PS cct. Here is the amp cct.
Attachment:
SSSS.PNG

Attachment:
SSSSPS.PNG


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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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PostPosted: 13 Jun 2011, 04:40 
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mwhouston wrote:
I'm having problems uploading the PS cct. Here is the amp cct...


And the attachment you have at this time is non-clickable :(

Maybe Gio needs to give the forum a swift kick in the backend? ;)

Cheers!

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PostPosted: 13 Jun 2011, 08:28 
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Geek wrote:
Maybe Gio needs to give the forum a swift kick in the backend?

When the image is non-clickable, that means that the image you are viewing is already being displayed at the full size.

Mark, the circuit schematic you sent was the same size as that posted. Please send me the full size drawing and I will add it. I have added in the power supplly you send me.

Cheers.

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PostPosted: 13 Jun 2011, 11:12 
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mwhouston wrote:
What about the output cap? Is 470nf OK? I got to listen for 6 hours straight and all is good. The preamp appears to be flat across the whole spectrum of frequencies. BoZ seems to emphasise the mids a little more, not that I dislike it. I didn't tube roll but when it is in a case I will. Unfortunately I have a buzzy wall wart. I might by another to see if this is just a bad one. If not I will have to make my own wart.

Don't forget the input impedance of what you are driving is parallel to your output. So a .47 uF cap won't cut it if he's using less than 100K on the amp he's driving. SS gear typically use 10-20K, so 2.2uF would be sized for something in that range.


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PostPosted: 13 Jun 2011, 11:52 
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Hi.
mwhouston wrote:
In the cct. I am using (slighly different to the one I have posted) there was no cathode bypass cap. The preamp was really down on gain. So I have added a 220uf 16V low ESR bypass cap. The gain has lifted.

Questions:
(1) What player you use to drive this linestage? If it is a CD player, or a MP3, why you want to lift back up the gain with the cathode resistor bypass cap?
(2) What cathode bias voltage is this amp?
(3) Why you installed the NFB resistor AFTER the O/P coupling cap?

c-J

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PostPosted: 13 Jun 2011, 16:56 
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cheap-Jack wrote:
Questions:
(1) What player you use to drive this linestage? If it is a CD player, or a MP3, why you want to lift back up the gain with the cathode resistor bypass cap?
(2) What cathode bias voltage is this amp?
(3) Why you installed the NFB resistor AFTER the O/P coupling cap?

I agree it is more of a line stage than preamp. The guy I'm buiding it for needs some gain so by bypassing the cathode R it should have lifted it a little. Currently I'm using an Oppo CD player. Plenty loud.

I'm not sure of the bias voltage, if I get a chance I measure it. The NFB is after the cap because I'm following the original schematic and that's how it was there.

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PostPosted: 13 Jun 2011, 17:01 
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mwhouston wrote:
What about the output cap? Is 470nf OK? I got to listen for 6 hours straight and all is good. The preamp appears to be flat across the whole spectrum of frequencies. BoZ seems to emphasise the mids a little more, not that I dislike it. I didn't tube roll but when it is in a case I will. Unfortunately I have a buzzy wall wart. I might by another to see if this is just a bad one. If not I will have to make my own wart.

rock4016 wrote:
Don't forget the input impedance of what you are driving is parallel to your output. So a .47 uF cap won't cut it if he's using less than 100K on the amp he's driving. SS gear typically use 10-20K, so 2.2uF would be sized for something in that range.

That explains the large output cap. I can find the input R of the amp it is to drive. This preamp is to be used as a center channel preamp with a 120W SS amp. So it may not need huge bass extension.

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PostPosted: 14 Jun 2011, 08:59 
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Hi.
mwhouston wrote:
I'm not sure of the bias voltage, if I get a chance I measure it. The NFB is after the cap because I'm following the original schematic and that's how it was there.

Once you tell me what cathode bias voltage you measure, I'll decide if I can suggest you how to make this "super simple" linestage more super simple & sound even better.

c-J

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