I’ve been helping another member upgrade his Quest audio step-up transformers via a series of PM’s (since we both speak French, much of the conversation is in that language). But I figured it’s worth sharing with everyone and if there are corrections or enhancements other members contribute on this thread, then we can all benefit.
So the goal of the exercise is to update the (very old) transformers in a Quest ML. Many of the older ML’s had sub-optimal transformers by today’s standards. The newest transformers improve upon their performance a good bit.
Now, there are some theories that the less than accurate (in the high-frequencies) transformers were used to essentially cause a high-frequency rise in system response as a side-effect of their ringing at >10Khz. And that using the newer transformers might actually decrease overall system HF response. So be forewarned.
My take is that even if the response is a bit lower in the high-end, it will be cleaner overall. Actual measurements show a bit smother response as a result.
OK, so which transformers to use?
The common consensus over on DIYAudio is that the Amplimo’s from Holland are the best choice for a ML.
The 1:75 transformer should do fine on most panels, although the 1:50 would also work and give an even greater HF headroom.
So, how to connect it into a ML?
First, carefully document the existing transformers hookup and create a plan for which old wires will go to which new wires before disconnecting anything.
Also, it’s important to understand the basic layout of an ESL.
So to recap, the basic topology is to take the audio input signal (after crossovers) and feed the input side of a step-up transformer. The outputs of which will drive the stators of the ESL.
Note that the Center tap output on the transformer is used to provide a ground reference signal to the diaphragm high voltage energizer circuit (EHT) . (although I have SL3’s that do NOT do that, instead using the Neg signal to provide this).
So the goal of the exercise is to update the (very old) transformers in a Quest ML. Many of the older ML’s had sub-optimal transformers by today’s standards. The newest transformers improve upon their performance a good bit.
Now, there are some theories that the less than accurate (in the high-frequencies) transformers were used to essentially cause a high-frequency rise in system response as a side-effect of their ringing at >10Khz. And that using the newer transformers might actually decrease overall system HF response. So be forewarned.
My take is that even if the response is a bit lower in the high-end, it will be cleaner overall. Actual measurements show a bit smother response as a result.
OK, so which transformers to use?
The common consensus over on DIYAudio is that the Amplimo’s from Holland are the best choice for a ML.
The 1:75 transformer should do fine on most panels, although the 1:50 would also work and give an even greater HF headroom.
So, how to connect it into a ML?
First, carefully document the existing transformers hookup and create a plan for which old wires will go to which new wires before disconnecting anything.
Also, it’s important to understand the basic layout of an ESL.
So to recap, the basic topology is to take the audio input signal (after crossovers) and feed the input side of a step-up transformer. The outputs of which will drive the stators of the ESL.
Note that the Center tap output on the transformer is used to provide a ground reference signal to the diaphragm high voltage energizer circuit (EHT) . (although I have SL3’s that do NOT do that, instead using the Neg signal to provide this).
We should work on something....
