Wednesday, May 24, 2006

Velleman K4700 in Quads? Ed pushes it to the limit!

Obviously the articles about building the Velleman K4700 protection-circuit in the Quad 405 were very inspiring ;-)

Hans was the first to propose an alternative location for the kit but Ed took it very seriously... He built the kit into the 303, the 405 and the 606 and he even developed a box to use the protection-circuit with any amplifier....

It is clear that Ed also will find a box of Antwerpse Handjes in the mail and he is hereby named a lifelong honorary member of Quad Spot ;-)

Do you work for Quad or Velleman, Ed?

Obviously there will be many questions on this subject, feel free to post them as a comment. To be continued....


Take a look and enjoy (click on the picture to enlarge):

In the 303

Note: in the 303 the protection-circuit is somewhat less usefull than it is in the 405. The 303 is a push-pull amp with an output capacitor, so as long as the capacitor won't fail there is no risk of having DC-current on the output, like in the 405, if one of the output-transistors breaks down. But there still is the advantage of the delayed power on/off. And with expensive speakers you never can be sure enough of course...

In the 405

Ed made a metal-adapter to fit the K4700 behind the transformer.

Note: as mentioned in earlier posts the 405 really NEEDS a better protection-circuit. I heard about several people who had their expensive speakers broken when one of the transistors gave it up. The original "clamp-circuit", even in the 405-2 does not react fast enough all the time.

In the 606

Ed even built a K4700 in the 606. This was not an obvious or easy job to do.

Update: An alternative location.

Ed mailed me some pictures of an alternative location for the Velleman in the 606. For Ed's explanations see the comments below.

In a separate box

This box can be used for any amplifier. But it should be switched on/off together with the power-amp, by a general swith or from the pre-amp.


Anonymous Anonymous said...

Dear Quad lovers,

Of course, Stefaan can not put all our prose on the page of the blog. It would be too boring. So here is some comment regarding the postings of 24 May 2006.

First about the 405. The bracket are made of 1 mm sheet aluminium. I had to drill only one hole in the 405 housing, the other screw goes through the existing hole for unscrewing the heatsink. That is why the right hand bracket (as seen from the rear) has a different shape. I put a sheet of insulation paper over the power connections.

Then regarding the 606. For those who contemplate to build a K4700 into a Quad 606, I would say: Don’t. Those who go ahead anyway, could benefit from some hard earned experience.

At first sight, a Q 606 provides ample room to facilitate a K4700. But then you find that that space is needed to service the amplifier. You have to be careful where to put the K4700 and how to fix it. Don’t do as I did (see photograph).

The space next to one of the amplifier boards would be fine, but you have to be able to remove the K4700 without removing the amplifier board. So I suggest you put the screws at position 1. I did not do this, because of tolerances. But allowing some room to slide the K4700 print backward and forward (thus avoiding mechanical strain in the board), would overcome this objection.

The reason to be able to remove the K4700 is twofold. 1) for service purposes, and 2) to be able to fasten and undo the screws of the heatsink (in my case the top front screw is hidden above – the picture is taken from the bottom – the K4700 transformer).

An alternative position might be between A and B on the picture. This is the drawing. The next time I find a reason to open the 606, I will change to this solution.

WARNING Although this Quad is much better soldered than many other ones, the wires are rather brittle near the joints. Moving the leads when working on the amplifier is unavoidable, be careful not to break them.

The black frame on top of the transformer, that holds the power supply components is made of rather soft material. Drilling holes ‘in situ’ goes easily.

Regarding the universal housing for the K4700. Please note that the K4700 requires that the loudspeaker leads are connected properly. PA (red) to the ‘live’ connector, and only one (black) lead to mass of the K4700 (the other goes straight through). To maintain this, is the drawback when not building in the K4700. A wrong connection might lead to the K4700 not working or not working properly (protecting only one channel).


8:27 PM  
Anonymous Anonymous said...

The K4700 in the 606 (continued).

In some cases, I seek perfection. So I opened my Q 606 again, to position the K4700 where I thought it would be better placed. But this time, I simulated first. (If possible, I put the picture in this comment, otherwise I hope that Stefaan will be so kind as to put it on the blog). I made a box to represent the K4700 and put this box behind the back cover. Then I found, that the available room was smaller than I first thought. I believe the K4700 can be put there (with the obvious advantage of improved serviceability), but it would require some DIY and precise measurements.

I made a more detailed picture of the current placement of the K4700 (again, I hope to incorporate it in the comment). And I made a picture to suggest an improvement, which would make the screws of the heatsink accessible.

Sorry, no pictures.


11:42 AM  
Anonymous Anonymous said...

Are any mods necessary for the Velleman K4700 for 120V. The spec sheet says 240V but I assume that it is just the mains power being delayed until powerup (or to cut out when DC comes on).


7:18 PM  
Anonymous Anonymous said...

RE: Are any mods necessary for the Velleman K4700 for 120V. The spec sheet says 240V but I assume that it is just the mains power being delayed until powerup (or to cut out when DC comes on).

Your misunderstanding how the protection kit functions. It does not delay or interrupt the AC mains power. It delays the connection of the speaker outputs at start-up and interrupts the speaker outputs if high enough DC voltage is present (such as the case when an amp typically blows up and rail voltage is dumped on the output).

The kit itself requires 220VAC to operate. Unfortunately I don't believe Velleman offers a 120VAC version.

2:09 AM  
Blogger Stefaan said...


Indeed, Velleman does not offer a 110-130V version. But DaDa will! Watch the webshop.

Joost Plugge

11:41 AM  
Anonymous Anonymous said...

Two questions:

1.I have read some comments that the standard K4700 doesn't address some of the issues that are necessary to reliably protect speakers, that it doesn't react fast enough and that the relay contacts may become welded together at high DC voltage. Does anyone have any comment on these concerns and are there any recommended modifications to the K4700 to improve its response and robustness.
2. After fitting the K4700 does the original Quad crowbar protection serve any purpose? Can it be removed/bypassed?

9:43 AM  
Blogger Stefaan said...

There are issues with the Velleman, that is why we developed our own protection unit with a better relay, but the Velleman is more economical.

Joost Plugge
DaDa Electronics

11:01 AM  
Blogger Stefaan said...

Sorry, I forgot the crowbar question. With our units or the Velleman, the crowbar can be removed.

Joost Plugge
DaDa Electronics

11:02 AM  

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