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Old 29th March 2013, 07:25 PM   #1
coolzero is offline coolzero  Sri Lanka
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Default Suggestions Please

Can our good experts suggest some improvements to this phono/pre schematic? Not just part swapping but something theoretical.
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Old 29th March 2013, 07:51 PM   #2
DF96 is offline DF96  England
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I think that circuit cropped up in another thread a few weeks ago. It has so many weaknesses I can only assume it was designed by someone who was new to valves.
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Old 29th March 2013, 07:59 PM   #3
coolzero is offline coolzero  Sri Lanka
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Quote:
Originally Posted by DF96 View Post
I think that circuit cropped up in another thread a few weeks ago. It has so many weaknesses I can only assume it was designed by someone who was new to valves.
This is one of the commercially available product BTW .

Can you explain how to overcome these weaknesses?

Last edited by coolzero; 29th March 2013 at 08:02 PM.
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Old 29th March 2013, 09:20 PM   #4
DF96 is offline DF96  England
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Quote:
Can you explain how to overcome these weaknesses?
Redesign it.

I assume you have permission to reproduce the circuit? Perhaps you could identify it. That might make it easier for you to find other threads.
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Old 29th March 2013, 09:36 PM   #5
vinylkid58 is offline vinylkid58  Canada
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Yaqin MS-12b?

jeff
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Old 29th March 2013, 09:40 PM   #6
Eli Duttman is offline Eli Duttman  United States
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Every design has its compromises. The tweaked RCA setup I've uploaded will interact badly with a few carts. and SUTs, due to the high CMiller of the 12AX7 triode. OTOH, the tweaks fix the so/so bass extension and WRETCHED drive capability of RCA's original.

BTW, the fellow who made the original drawing (from a narrative I provided), loves "boutique" parts, but good quality, industrial, stuff is fine. Notice the changes in blue.
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Old 29th March 2013, 10:31 PM   #7
overtheairbroadcast is offline overtheairbroadcast  Canada
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For simplicity and a shorter path... Wouldn't it be easier to go with a SS based circuit for a Phono pre-amp?

(just asking...)
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Old 30th March 2013, 05:18 AM   #8
coolzero is offline coolzero  Sri Lanka
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Quote:
Originally Posted by vinylkid58 View Post
Yaqin MS-12b?

jeff
I checked the threads on this model. But nothing solid. All about just replacing parts.

Two things I noticed so far without doing anything to the internals. When using a SUT, sound changes drastically. Transformation was from OK to really nice. I think this constitutes to the fact that the input of this phono is not properly loaded for MC cartridges. I am using a DL103 so 100 ohms resistor in the input would change the sound I believe.
Replacing 12AU7 to 12XT7 changes the sound positively. Assume it is because of the difference in gain of two tubes.

I am a novice in to tube electronics so can someone guide me where to start? I am reading Morgan Jones these days to find some clues but I am an impatient person when comes to DIY

Last edited by coolzero; 30th March 2013 at 05:33 AM.
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Old 30th March 2013, 07:34 AM   #9
vinylkid58 is offline vinylkid58  Canada
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Quote:
Originally Posted by coolzero View Post
Two things I noticed so far without doing anything to the internals. When using a SUT, sound changes drastically. Transformation was from OK to really nice. I think this constitutes to the fact that the input of this phono is not properly loaded for MC cartridges. I am using a DL103 so 100 ohms resistor in the input would change the sound I believe.
It won't have enough gain without the SUT using a LOMC like a DL-103, so just leave the loading at 47k.

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Originally Posted by coolzero View Post
Replacing 12AU7 to 12AT7 changes the sound positively. Assume it is because of the difference in gain of two tubes.
There are a lot of lousy sounding 12AU7's out there. 12BH7 would be a better tube, but draws double (IIRC) the heater current, which could be an issue for the PS trans.

jeff
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Old 30th March 2013, 09:48 AM   #10
coolzero is offline coolzero  Sri Lanka
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Quote:
Originally Posted by vinylkid58 View Post
It won't have enough gain without the SUT using a LOMC like a DL-103, so just leave the loading at 47k.



There are a lot of lousy sounding 12AU7's out there. 12BH7 would be a better tube, but draws double (IIRC) the heater current, which could be an issue for the PS trans.

jeff
Thanks Jeff.
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