Speaker load options

[patrick620]

Just got the kit to build for a former client whom I built the Moreplay for. Very happy. I have not dug into this build deep just yet. Why no extra jacks with a common ground or a selector switch for different speaker loads? 8 and 16 is all my customer is concerned with. I do not need him calling me in the middle of the night to resolder the OT taps as he rolls speakers. Anyone have any thoughts on this? Thanks. BTW, the speakers are a set of Stephens TruSonics and a pair of Goodmans 15" Triaxial and pair of 8 ohm Voice of Theater.

 

[Paul Birkeland]

When you see an output transformer that has a four wire secondary setup with 0, 4, 8, and 16 ohm connections, you end up with half of that winding unused when using the 4 ohm connection.  This is not particularly optimal, and in a zero global feedback amp, it's possible to design the transformer secondaries so that either all of the copper or nearly all of the copper is in use regardless of the speaker impedance configuration.  For this reason, our iron is a little more cumbersome to wire on the secondary side, but that extra effort is rewarded sonically. 

From my personal experience, I have yet to run into a 16 ohm speaker that could really make use of the extra juice.  I would just leave the amp on 8 ohms and not worry about it.  We did at one point offer a PC board that mounted above the OT-2 and offered impedance switching capabilities, but the switches used were frequently out of stock and have since been discontinued.  I seem to also remember that at some point PJ drew up a switching configuration using a 4P3T switch as well.

 

[Paul Joppa]

To clarify, the 4-pole 3-throw switch was for the Paramount OT-1 transformer. You need a 4P4T to handle all four impedances on the OT-2.

You can get away with a 2P2T switch for 8 or 16 ohms on a Paramour. One switch per channel.

 

[patrick620]

There are several ways to mod this. I guess I just wondered why I needed to mod it if the OT already has those options and why this was not included in the original design. My client has a nice set of vintage 16 ohm speakers, but as we all know, most speakers are 8 ohm. I also know that dropping the speaker load is ok with tubes, to an extent, as opposed to solid state, but I would rather have the speaker load match the correct winding on the OT.

 

[Doc B]

We weigh how many customers would really use a given option vs. how much it would add to the cost. If only a few ask for this it's probably not effective to spend the design time or adding costs to the BOM considering the price increase it would require. The few who want a switch can come here and ask how to install one if they don't know how. We offered those impedance switching kits for the S.E.X. kit years and only sold a handful each year.

Regarding your client calling you in the middle of the night - our kits have always been designed to be built by the buyer and used buy the buyer. Once one of our customers has built a kit themself it usually seems pretty trivial to them to go back in and reconnect a wire or two to change impedance. We're quite committed to creating a rewarding, creative experience that is empowering for the end user as well as delivering a product that we feel sounds pretty good. So a customer who hires someone to avoid that part of the experience is perhaps not at the center of our design focus.

 

[Paul Birkeland]

My client has a nice set of vintage 16 ohm speakers

If these are super sensitive vintage altecs, your client sure might be happier with the output transformers set to 8 ohms!

 

[patrick620]

Thank you for the replies. My client is a dear friend who has suffered a stroke and can hardly use his left hand. That is why I am helping him build the kit. He is very involved but he no longer has the motor skills to solder. So far we are both very happy with our current and previous dealings with Bottlehead in every way. Thank you, Doc B and your staff.  btw, the speakers are Stephens TruSonic CX120 and a pair of Goodman 15" triaxiom. I forgot the make of the 8 ohm speakers. I wanna say they are vintage JBL