The (John) Koval Mod of the Original Quad turned this 3-way loudspeaker into a 2-way. John told me he did it to counteract the falling high-frequency response of the speaker, the mod adding the output of the narrow super-tweeter to the wider tweeter panel. I didn't know enough at the time (mid-90's) to ask him if that didn't cause a problem with its off-axis response (due to the increased beaming of the now-wider tweeter).
I want to modify the crossover of my quad ESL 57.
The topology remains the same, I just would like to replace the resistors and capacitors with better sounding components. It doesn't seem easy because of the high voltage environment.
1. What is the maximum voltage limit of the original 560pF cap?
2. I would like to replace the old resistors with Shinkoh tantalums. I do not have Shinkoh datasheet, but they were used in valve amplifiers up to 1000V. Fortunatelly they can be sorted in series, like the 3 x 180K resistors in the original panel. Any suggestion/solution for Shinkoh replacement?
In case of EHT, I was more radical. The original EHT was disconnected, and replaced with single high voltage valve diode (+ 1pc high voltage transfomer & 1 pc high voltage capacitor). One for the tweeter, and another one for the bass panels.
The topology remains the same, I just would like to replace the resistors and capacitors with better sounding components. It doesn't seem easy because of the high voltage environment.
1. What is the maximum voltage limit of the original 560pF cap?
2. I would like to replace the old resistors with Shinkoh tantalums. I do not have Shinkoh datasheet, but they were used in valve amplifiers up to 1000V. Fortunatelly they can be sorted in series, like the 3 x 180K resistors in the original panel. Any suggestion/solution for Shinkoh replacement?
In case of EHT, I was more radical. The original EHT was disconnected, and replaced with single high voltage valve diode (+ 1pc high voltage transfomer & 1 pc high voltage capacitor). One for the tweeter, and another one for the bass panels.
The quad treble panel will arc at around 3KV, so your caps can probably be 3kv units.
I use vishay VR68 series high voltage resistors. Here's an example:
VR68000001803JAC00 Vishay BC Components | Resistors | DigiKey
I don't know anything about those tantalum resistors you are interested in. But I always recommend people stay away from boutique audio brands as a rule of thumb. Leave component design and manufacture to the professionals.
WRT the power supply. Keep in mind that the original quads are not a good design when it comes to the polarizing circuit. The only thing keeping the panels in constant charge mode is the insanely high resistance on the diaphragms. If you mess with the power supply, you are potentially messing with the delicate balance of panel charging. And if a panel fails, the stock power supply is so wimpy that it cannot start a fire. Think that through with your new design.
Sheldon
Sheldon, thanks for your help. Unfortunately, I have no Shinkoh technical data available. The best thing I can do to ask Peter Qvortrup from Audio Note whether or not his tantalum resistors are appropriate for this project (stated sounding very similar to the original Shinkoh).
The vacuum tube EHT is a rather old story, it was made in 2004.
The vacuum tube EHT is a rather old story, it was made in 2004.
HV resistors
Hi Sheldon, I have chacked all the regular suppliers, but nary one has the HV resistors (metal film) in 150k or 180k. Mouser has the 270k, but all the others are 100k, 200k, 220k and 240k. There are a few above 1 megohm. The next best I can find are the Vishay PR01 and PR02 series which are respectively 350V and 500V rated.
Kevin
Hi Sheldon, I have chacked all the regular suppliers, but nary one has the HV resistors (metal film) in 150k or 180k. Mouser has the 270k, but all the others are 100k, 200k, 220k and 240k. There are a few above 1 megohm. The next best I can find are the Vishay PR01 and PR02 series which are respectively 350V and 500V rated.
Kevin
Hi.
Do possible to watch the schematic or the trebble panel connection photos of the first 408 mono Quad 57?
The interview of 1994:
"PW: In fact, after we made 400 of them we modified the directivity because of stereo. The directivity pattern was made for mono - not quite the same as stereo. Serial number 409 I think it was.
A: How did you change it? Driver shape?
PW: No, it was just the electrical distribution between the elements. No other modifications as far as I know."
Do possible to watch the schematic or the trebble panel connection photos of the first 408 mono Quad 57?
The interview of 1994:
"PW: In fact, after we made 400 of them we modified the directivity because of stereo. The directivity pattern was made for mono - not quite the same as stereo. Serial number 409 I think it was.
A: How did you change it? Driver shape?
PW: No, it was just the electrical distribution between the elements. No other modifications as far as I know."
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