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-   -   Would a line stage/preamp be beneficial? NEWBIE question (http://www.diyaudio.com/forums/tubes-valves/109228-would-line-stage-preamp-beneficial-newbie-question.html)

awhite1159 29th September 2007 06:23 PM

Would a line stage/preamp be beneficial? NEWBIE question
 
Would a line stage be beneficial for my SimpleSE. I originally wanted to have at least the ability to switch inputs in a passive mode but now realize I may need more than that.

I don't need additional gain. Or, at least I think I don't. It seems that the output from my tuner is much lower and it sounds really great. But when I switch the cables to use my CD player, it seems to sound clipped and might even have some harmonics being produced. What's interesting is that this clipping appears even when the volume is low on the SimpleSE amp. I conclude from this that it is possible I am overdriving the 12AT7. Would a line stage control the input level to keep it consistent. Is my assumption correct?

Can someone please help with this dilemma?

Thanks.

awhite1159 30th September 2007 10:37 AM

I'm guessing that I should have searched the forum first since this question has been asked/answered a million times and that is why no one responded.

I just did a search and it looks like the Aikido line-stage would be the answer to my problem. I would be able to select multiple inputs and control the line-level. Has anyone used the combination of SimpleSE and Aikido line-stage? Before I purchase this can someone please let me know if this sounds like a good idea?

Thanks

Andy

SY 30th September 2007 12:39 PM

The Aikido would be a good choice if you need gain. If you don't, then a passive buffered preamp will be all you need and present less danger of too high an output signal. There are a few good designs floating around.

awhite1159 30th September 2007 02:03 PM

Thanks SY. I will look into this. I really love these tube based amps. I can't believe I waited this long and used solid state. I was a Novice for amateur radio when I was 16 (WN2AMH) but it was basic theory on vacuum tubes so I need to ramp up my skills. Thinking of getting back into HAM as well. Believe it or not, I used to enjoy CW.

SY 30th September 2007 02:34 PM

I was a big CW fan, too. Used to work the bottom edge of the 40 meter band (WA3KHZ).

awhite1159 30th September 2007 02:53 PM

I used to use 10 meters to try and get skip. Had alot of QSL's from all over. Wow! how did you manage to get KHz in your call sign?

Eli Duttman 30th September 2007 03:37 PM

Quote:

Wow! how did you manage to get KHz in your call sign?

Perhaps it was issued before freq. was refered to in Hz. :D

As SY mentioned, a "unity" gain line stage seems appropriate to your situation. One of the effective methods of buffering a volume control is a constant current sink (CCS) loaded cathode follower. High gm/low RP types make superior cathode followers. The current production ECC99 and 6n30p, along with the NOS 5687, have the requisite characteristics. The CCS used in "El Cheapo" and the DIY Audio PCB are candidates for this project.

A bipolar PSU is indicated for the buffer, as it eliminates a cap. in the signal path on the I/P side.

awhite1159 30th September 2007 03:47 PM

Thanks Eli. I will definitely look into that. It seems to be exactly what I am looking for.

Are you implying that SY is very old? I'm 48. I thought the real old guys were the ones who had a number as the second digit of their call sign. :D

SY 30th September 2007 03:55 PM

Actually, it was right around the time of the official changeover from kc to kHz. QST published a joke nomograph to help hams convert from one unit to the other.

The REAL old guys had 1x2 call signs (e.g., W3HT).

Eli Duttman 30th September 2007 05:46 PM

Quote:

The REAL old guys had 1x2 call signs (e.g., W3HT).

Ancient is more like it. I'm 62 and 1 of the guys I went to JHS with was issued K2RHA.

FWIW, I never could get Morse Code straight. So, I never acquired a "ticket".


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