Has anyone ever set two ST70s up as mono blocks, how did or would it work?
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Bugs wrote:Thanks Bob,
I do have one set of 4 ohm speakers I can biamp. Would anything be gained by building a pasive filter set at the woofer XO frequency to send the high frequencies to one amp and the bass to the other amp? I know there are electric XOs for doing this, but they are a bit spendy.
GP49 wrote:"In a case like this you can run an 8 ohm non inductive resistor across the tweeter terminals to present the proper impedance for the amp."
BUT: If the 1Ω tweeter is run with an 8Ω resistor across its terminals, i.e. in parallel, the overall impedance will be LESS than 1Ω.
Bob Latino wrote:Over the years and listening to a number of ST-70's in a biamp mode as well as in mono > IMHO the best way to implement two ST-70's in one stereo system is to VERTICALLY biamp with one ST-70 on each stereo channel. If the speakers have their own crossovers and dual inputs I see no reason to build another crossover. There are two advantages to vertically biamping as opposed to HORIZONTALLY biamping (one amp on the two woofers and one amp on the two tweeters) at least with Dynaco ST-70 amps.
1. Vertical biamping allows greater signal isolation between the two amps. You may (as one customer noted to me) a greater sense of stereo separation and/or a larger sound stage.
2. Vertical biamping allows TWO quad caps (B+ DC power storage) to deal with the power hungry bass notes. If you horizontally biamp only one quad cap now has to deal with the bass from BOTH stereo channels.
Bob Latino wrote:Bugs,
If you have the stereo/mono switch bypassed and your preamp has TWO outputs per channel you could run two cables to each amp OR just get TWO "Y" connectors - one for each ST-70 with two male connectors on one end and one female on the other. Plug one Y connector with the two males into each ST-70 and then your interconnect from the preamp into the female of the Y connector.
Bob Latino wrote:There is one caveat here if you run any biamping without an active crossover. Usually the crossover in most speakers is set up so that the woofer section creates a larger impedance than the tweeter section but the TOTAL inpedance is 8 ohms (or 4 ohms if your speakers are 4 ohm speakers). When you separate them, the woofer ALONE may have 7 ohms and the tweeter 1 ohm. In a case like this you can run an 8 ohm non inductive resistor across the tweeter terminals to present the proper impedance for the amp. If you don't, and run one channel of the amp (the one driving the tweeter) hard into a 1 ohm impedance, you could take out an output tube or worse yet an output transformer. Output transformers do not like being driven into a virtual dead short (an impedance of 1 ohm or less).Bob
Bugs wrote:Hi Bob,
I'm being overly cautious, I just want to make sure I'm not causing any problems down the line.
Is it safe to assume that if I use two ST70s and two biampable 4 ohm speakers (using the passive crossovers) and one ST70 drives the right channel and the other the left channel and on each ST70 one output drives the bass and the other output drives the mid and high I should be okay?
Can the output transformer driving the mid and high on each ST70 potentially see a short?
Bugs wrote:Well, that's enlightening. Across the bass speaker wire terminal I get 4.7 ohms and across the mid/tweet terminal I get 0 ohms. Can't tell if my meter reads in fractions of an ohm?
Sounds like a straight short to me.