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Integrated tube amp used as power amp only

S

singzh

Active Member
Hi Folks,

Another newbie question...

I am using the Line Magnetic LM-210ia as a power amp only (There is a pre-in on this amp). In this casee, do the small preamp tubes (a pair of 12AX7s) have any impact on the sound quality?

I have some nice telefunken 12AX7s not sure if I should put them in.

Thanks,
Singzh
 
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You really need to see where the power amp input sits in the circuit to see what effect the small signal tubes will have. The phase inverter tube will likely be in play, so you could do some tube rolling and see what impact it has on the sound. There could be others, but without a schematic I can't say.
 
Thanks!

Yes. I am getting confusing results... Some were saying the Line Magnetic pre-in does not really bypass the preamp section.
 
My question is why. Why do you want to use it as power amp only? Is the way the amp sounds not good enough? The Line Magnetics equipment seems to be well designed and built, so I am surprised that you feel you need to use a separate preamp, or is there more to the story?

I looked but could not find a schematic in my quick search. I was going to suggest to hook up you preamp, simply pull out the 12ax7 tubes and see what happens. If you get sound then you know the 12ax7 are not in the amplification chain when pre-in is selected. HOWEVER, I don’t know if the 12ax7 is involved in the way the 310a is biased so don’t try it without first checking the schematic.

The circuit is most like minimalist, so it might be easy for you to trace out the schematic if you can’t find one.

Good luck.
 
JohnT123 said:
You really need to see where the power amp input sits in the circuit to see what effect the small signal tubes will have. The phase inverter tube will likely be in play, so you could do some tube rolling and see what impact it has on the sound. There could be others, but without a schematic I can't say.
Click to expand...
Line Magnetic LM-210ia is an 300B SE integrated amp, so probably no phase inverter involved.
 
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OK. I think I got the answer...

The 12ax7's are indeed bypassed. The LM210IA has the same configuration as the LM219IA (the top of the line models)

The LM508IA etc are different, the preamp stage are not really bypassed for those models

Thanks for the help,
Singzh
 
spantou01 said:
Why do you want to use it as power amp only? Is the way the amp sounds not good enough?
Click to expand...
If the OP feeds from a DAC that has a volume control, he may want to compare the sound with and without the preamp section in the signal path. I made a similar comparison - with the integrated volume control almost at maximum and the DAC volume control cautiously raised up from 0 to desired level. Different sound.
 
eiraved said:
I was wondering the same thing. Are you using it to bi-amp your speakers?
Click to expand...
Well. There are many situations where you want to use it as a power amp only. And that’s why the amp offers a pre-in in the first place I guess.
1. I am indeed using the 210ia to power the top end and mid-range only. There’s a 500w ss amp to take care of anything below 53hz (a pair of JBL 18” 2245Hs). There is an active crossover between preamp and the two power amps.
2. My dedicated preamp has phono and many other features that I need.

I am glad to learn the 210ia is actually really bypassing the preamp sections like the 219ia does. I can save the Telefunkens for good
 
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