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What is the input impedance of the Sugden A21aP power amp?

I have a wonderfully sounding class A power amp, essentially the power section from the revered Sugden A21a (the 90's version). 

But I have been searching wide and far for specs on the input impedance as well as the power output rating on a 4 ohm load (it's 25 wpc into 8 ohm).

Can anyone help? I don't have access to measuring tools.

The reason I want to know is that I would like to match it with my Audio Note M1 tube preamp, which has a high output impedance of between 2,5 and 5 kiloOhms. This translates to a weak bass performance/bass rolloff when playing into the Sugden. With my cheaper transistor preamp, I don't have this issue. 

If I know the specs of the Sugden, I can have my Audio Note dealer modify the M1 with a feedback loop to lower its output impedance to match. 
9radua1
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georgehifi's avatar
georgehifi
10,312 posts
 
If I know the specs of the Sugden, I can have my Audio Note dealer modify the M1 with a feedback loop to lower its output impedance to match.
That's the wrong way to do it, better off getting the Sugden input impedance changed from 24kohm to 68kohm so long as it doesn't effect the output dc offset too much.

Cheers George
9radua1 OP
2 posts
 
Thank you for the advice. 

@kosst, Stereophiles measurements were for the integrated, whereas mine is the poweramp only version. They would have different input impendances, no?

@george, thanks, I will look into that. 
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