Hello all,
I have a rebuilt St70 with the low gain VTA driver board. Sounds so nice. I pair this up with a set of Klipsch R-51M bookshelf speakers. These speakers roll off below 70-80 Hz, so I use a powered sub to give me the lows using the high level inputs from the ST70 speaker terminals.
While evaluating the response of the system, I heard a strong peak at about 50 Hz and rapid drop after that. After various testing with my dummy 8 ohm load, I found that with the dummy load, the voltage output from the ST70 was flat down to 20 Hz. But when connected to the speaker, the voltage would drop at 60 Hz, then jump up 50% or more at 50 Hz, then fall off rapidly. The same test with a different speaker gave different results, but were not flat below 70 Hz.
So it looks like the low frequency impedance is affecting the voltage output from the transformer, which for just the bookshelf speakers is not noticeable, but once a high level sub is connected, it sounds awful.
Has anyone else observed this behavior with their ST 70? Any ideas on how to correct it so that I can still use the sub high level inputs? I also measured the voltage out of the 16 ohm terminal with the speaker connected to the 8 ohm terminal, and the 16 ohm terminal showed the same troublesome response.
I hate to buy a preamp with a sub out to solve this, I like to have minimal gear.
Thanks for any advice or input.
Steve
I have a rebuilt St70 with the low gain VTA driver board. Sounds so nice. I pair this up with a set of Klipsch R-51M bookshelf speakers. These speakers roll off below 70-80 Hz, so I use a powered sub to give me the lows using the high level inputs from the ST70 speaker terminals.
While evaluating the response of the system, I heard a strong peak at about 50 Hz and rapid drop after that. After various testing with my dummy 8 ohm load, I found that with the dummy load, the voltage output from the ST70 was flat down to 20 Hz. But when connected to the speaker, the voltage would drop at 60 Hz, then jump up 50% or more at 50 Hz, then fall off rapidly. The same test with a different speaker gave different results, but were not flat below 70 Hz.
So it looks like the low frequency impedance is affecting the voltage output from the transformer, which for just the bookshelf speakers is not noticeable, but once a high level sub is connected, it sounds awful.
Has anyone else observed this behavior with their ST 70? Any ideas on how to correct it so that I can still use the sub high level inputs? I also measured the voltage out of the 16 ohm terminal with the speaker connected to the 8 ohm terminal, and the 16 ohm terminal showed the same troublesome response.
I hate to buy a preamp with a sub out to solve this, I like to have minimal gear.
Thanks for any advice or input.
Steve
peterh
