Jeff Rowland

Hi Dan (Islandmandan),

I found this impedance curve for the HPD 315he, which confirms (as might be expected for a Tannoy) that its impedance characteristics are very benign. (If the link just opens at flickr.com instead of opening at the specific photo, paste the url https://www.flickr.com/photos/89700142@N03/8344329373 into the address bar of your browser). Note, btw, that in contrast to most such curves that are presented this one extends down to 1 Hz. So the somewhat low impedance magnitudes at the left end of the curve essentially represent DC resistance, and are reasonable values that can be expected to be inconsequential.

I also looked at the web pages on the amp module and the kit, and the manual.

The bottom line is that I don't doubt that the amp can drive the speaker in a reasonable manner in bridged mode, but of course how the resulting sonics would compare with stereo mode is speculative.

Another possible concern, though, is that I note that the amp module's input impedance is spec'd at a low 7K, and I suspect that in bridged mode it is likely to be around half that amount, or only 3.5K. That will be non-optimal for many preamps, especially the many tube-based preamps which employ coupling capacitors at their outputs, the capacitors typically resulting in substantial output impedance rises at deep bass frequencies.

But if you don't specifically envision an impedance incompatibility with the preamps you may use, given the very low price of this kit it would seem to be a reasonable risk. Also, perhaps it might be helpful in reaching a decision to try providing the kit you already have with a mono signal and running it in bridged mode with one speaker.

Best regards,
-- Al

P.S: Kijanki, thanks for both the input and the compliment :-)

Al, thank you. You have done your usual stellar job of research, before providing a helpful and informative answer.

It looks like the only issue will be the output impedence of my Transcendent Sound GG preamp. I used a 100 ohm Goldpoint stepped attenuator, what comes in the kit is 200 ohms.

Al, your idea of trying one speaker in bridge mode is a good one, I believe I'll try that this evening, and see how it goes.

Thanks and regards,
Dan

Ricred1, I stated 22% loudness increase, but it would be true for 2x loudness. I forgot that bridging doubles the output voltage, thus quadruples the power. In such case you can count on (substantial) 49% loudness increase. Speaker's minimum impedance remains the problem.

L=k^(1/3.5) where L=loudness, k=ratio of power.

L=4^(1/3.5)=1.49

A sincere thanks to everyone who took the time to respond. This thread is representative of how posting a question can be of value...at least to me! I asked the same question to Jeff Rowland technical support and a dealer. I'm disappointed that they didn't take the time to look up my speakers and explain why bridging the 525s may not be the best option.

Ricred1, I found them very eager to help. Perhaps it was just the particular support person. Fortunately we have this forum to learn and share