Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Topic started by: manfred99 on January 09, 2010, 09:11:24 AM
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I searched other areas for this topic and couldn't find anything, if I am posting in the wrong area, please point me in the right direction.
I recently purchased a very clean, well built example of a Foreplay II preamp with C4S upgrade, works very well, better sonics than my ASL preamp. But it does have a slight upper frequency buzz in both channels that comes through the speakers. I have viewed many posts in the archived Bottlehead forum about this problem and need some help in installing the snubbers which may(or may not)help alleviate the problem. I have changed tubes with several different sets, turned off all electrical devices on the circuit, ran a ground between the Foreplay and the amps(Dodd Audio mono blocks), removed the cable TV line. The hum remains. The hum does go away when preamp is turned off. The hum was not present with the ASL preamp.
Can anyone explain where the HV snubbers go in the preamp, and what parts do I need to at least try this. I do have soldering skills, though I would be better off looking at pics of the installed snubbers rather than try and decipher schematics.
An e-mail with pics would be of great help.
Tom
Portland, Oregon
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Before diving into this, are you certain that the problem arises in the preamp? If it is a power supply induced noise you can turn the preamp off and before the capacitors discharge the buzz will stop. That is, as soon as the switch is off the buzz will be gone. Maybe it will be more apparent if you play some music and hear the buzz go away before the music fades out.
VoltSecond has a site with a lot of information on Legacy products. This page has the HV Snubber on it, but the page also says filament snubber:
http://www.siteswithstyle.com/VoltSecond/foreplay_filament_snubber/Foreplay_filament_snubber.html
There is not a picture of the snubber on that page. IIRC, it takes 2 - 5 terminal, terminal strips to construct the circuit. These are still sold at RS.
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When I turn the preamp off, the buzz immediately stops. So where do I find "RS".
Tom
Portland, Oregon
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I expect he is referring to "Radio Shack". If you look at the underside of your FP Chassis plate, you will see that the parts are connected to 5 position terminal strips. They have these very same strips at Radio Shack, or something remarkably like them, that they sell in a package of 3 or 4, IIRC. In the '274-xxxx' series of parts, I believe. Useful for mounting snubber parts.
If the sound you are hearing is a "buzzy" sound with a fundamental of 120 Hertz, the snubber will put a big dent in it. If it is more like a hum at 60 Hertz, that will require something else.
Sorry, I don't have a picture for you, but surely someone else does; there had to have been quite a large number of snubbers installed in Foreplay 2's back in the day. If all else fails, ping forum member Wardsweb; he takes excellent pictures of his work, and I would have to think he made and FP 2 with snubber at some point!
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You might consider just replacing the UF4007 rectifier diodes with a pair of Cree Schottky diodes; the 600v ones should be sufficient. Schottkys don't have a reverse recovery spike, not even an ultra-fast one...
The virtue of this is that there is no modification of the circuit or layout to make.
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Thanks very much, I'll see if I can find where these diodes are and take it from there.
Tom
Portland, Or.
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Anybody have a source in the USA for UF4007 Schottky 600v diodes?
Thanks,Tom
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Not sure about the US, though I think I saw them at Mouser.
In Canada, partsconnexion has them in different flavors.
http://www.partsconnexion.com/rectifier_diode_cree.html
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Thanks so much, I hate to be a pest but what amperage should I use, or does it matter?
Tom
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The UF4007 is a 1 Amp diode, with a reverse Voltage of 1000 Vdc. As Paul noted, 600 Vdc should be adequate. Truth be told, you could probably get by with less current, too.
I'm pretty sure the Schottkys will have a different designation.
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Since JC says it replaces a 1 amp diode, the cheaper 1 amp Cree should be fine.
Check with others on this forum whether you need a heatsink. I always heatsink mine, so I never checked the ratings for when a sink is required.
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Thanks very much for the help, hopefully this will get rid of the buzz.
Tom
Portland, Or.
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Cree CSD01060 is what we use in the Paramount and Eros. 600v, 1A, no heatsink. Less than $1 at DigiKey among others.
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The 4 diodes in my Foreplay II have 3 legs, all the Cree diodes I see at the 3 online sources I've found have 2 legs, including the CSD 01060. I may learn to live with this buzz, I may be in over my head on this one.
Tom
Portland, Or.
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I don't have a Foreplay, but by definition a diode should only have an input and an output.
A transistor would have 3 legs. Are you perhaps confusing them?
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Sounds like you got a kit preamp without the manual. Never a good idea. Ping Eileen next week when they are back from CES and see about getting a manual so you know the terminal designations and have some pictures of the parts - it will help a lot. Make sure you ask for the C4S upgrade manual as well.
The 3-legged TO-126 black flat-pack transistors are on the four C4S boards. Somewhere further back there is a power supply, with some large round electrolytic capacitors. Scrunched down among the terminal strips are two diodes - black cylinders about 1/2 inch long and 3/32 in diameter, with a wire out each end. Those are the rectifier diodes; they have a white band around one end to indicate the cathode. The Cree diodes are TO-220 flat packs, quite a bit larger; and one of the leads has a wide chunk near the plastic body, indicating the cathode end.
Do be aware that buzz can have many sources, so nothing is a guarantee that it will kill the buzz. Just thought I ought to say that. Very many hum and buzz problems have been siolved on this forum over the years, sometimes on the first try and sometimes only after many experiments and exchanges. It can be frustrating while it happens, but it's a real thrill when you succeed!
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The only components that look remotely like the Cree diodes are on these 4 small boards, pic enclosed. I also have enclosed another pic of 4 small components that are connected to a cap. While I was in the preamp, I checked for any cold solder joints, redid any questionable joints and it still has the buzz.
Where in the preamp are these 4 diodes located?
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi146.photobucket.com%2Falbums%2Fr271%2Fmanfred8%2Fforeplay3.jpg&hash=10c32a0fe08f0fca5cf236de0f16d4f0229f0049)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi146.photobucket.com%2Falbums%2Fr271%2Fmanfred8%2Fforeplay2.jpg&hash=49ccc2d57d69d8256feec724701e21a0c5e838ec)
Thanks, Tom
Portland, Or.
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Tom,
The four diodes are the black cylindrical black components with silver bands around them in the first picture. (red wires coming in and blue wires going out) The ones you think are Cree diodes are on the constant current source (C4S) circuit boards. Those are transistors. The C4S boards have two transistors, one with black plastic on the outside one with a metal can for the outside. Both can be seen in your second picture.
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Got it. When I put in the new diodes, do they need to go in a specific orientation, i.e.( +)(-), and is the silver band on the current diodes positive or negative?
Thanks for all this help, I do have a lot to learn. Next week I'm replacing the driver boards in my Dynaco Mark III's.
Tom
Portland, Or.
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The silver band on the UF4007 indicates that that end is the Cathode of the diode. The un-marked end is the Anode.
I'm not sure how this is designated on the Cree package, but you do indeed need to pay careful attention to which lead goes where.
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In looking at a likely Cree suspect, I would say you will find that pin 1 on the Cree package is the cathode, same as the banded end of the UF4007.
http://www.cree.com/products/pdf/CSD01060.pdf (http://www.cree.com/products/pdf/CSD01060.pdf)
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The diodes conduct from the unbanded end to the banded end. That is how they rectify. Banded diodes like the UF4007s that Bottlehead now uses go in the same way that the current diodes are put in. Be certain that you remove only one diode at a time replacing it with the new diode.
You will notice in your picture that two of the diodes have a banded end toward the blue (DC) wires and two have the banded end away from the blue wires.
There should be an electronics supply house in Portland that sells UF4007 diodes.
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Hey there Grainger.
I think what he wants to do is replace the UF's with Crees. That way he can dispense with the whole snubber nonsense (well, not nonsense, but a pain in the butt if you can just replace some rectifiers with 5 dollars worth of schottkys).
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Hey there Grainger.
I think what he wants to do is replace the UF's with Crees. That way he can dispense with the whole snubber nonsense (well, not nonsense, but a pain in the butt if you can just replace some rectifiers with 5 dollars worth of schottkys).
Yup. As I remember a poster once mentioned that after the UF4007s you could put a Cree or other soft recovery diode and eliminate the reverse recovery spike. Since a Cree won't pass it and has a minimal forward drop. I don't remember if it takes 2 or 1 in series.
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I'm missing something. Why after? Why not instead of?
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Before the bridge you have AC, and four legs, after the bridge you have a positive buss and negative buss. The noise is supposed to be riding on the high voltage so you just put a soft recovery, Cree diode in the direction of the current (cathode to the capacitor) on the positive leg. I still can't remember if there is any need on the negative leg. It is already grounded so it may not need it.
I think VoltSecond is who suggested this.
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OK, so my memory is shot!
First, there were two different power transformers used with the early Foreplays; one had a center-tapped high voltage section (which needs two diodes) and the other had a single winding and needs four diodes. You have the latter.
Second, the earliest Cree silicon-carbide high voltage Schottky diodes had a fat section of the cathode pin, but the current versions don't - you now have to identify pin 1.
It looks like the pins on the Cree diodes are not long enough to reach the full length of the terminal strip, which as you can see in the picture is the current setup.
So, whether you use the Cree diodes in place of the UF4007, or add the RRSF (reverse recovery spike filter), you will need to come up with a replacement mounting and wiring scheme.
I don't recall in this thread any mention of grounding the chassis plate by connecting terminal 14 to terminal 13 - that has helped many an old Foreplay. In the pictures the chassis plate does not look like an aluminum color - I hope that's just the computer's color rendition!
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Chassis plate is aluminum, but painted a gold color. I ordered the diodes from PartsConnexion. I'll post again after the install. I'll also get a manual from Bottlehead. Plus try and see if I can ground the terminal 14 to 13. or maybe it already is.
Thanks again,
Tom
Portland, Or.
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Tom, you should make sure that the circuit common terminal, terminal 12 is wired to the safety ground (where the incoming power wire grounds). Try it first with a jumper. But I think it is a good idea regardless for safety sake.
Just about everyone who put in the jumper lowered the noise. A very few rare instances the noise increased. That is the reason for trying the jumper first.
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So I tried connecting terminal 12 to the ground leg of the power, very loud hum. Terminal 14 is connected to terminal 13, as suggested in one of the previous posts. I tried one of the Cree diodes( I have 4), connected after one of the existing diodes(being careful to connect the cathode end correctly). The buzz is a little quieter, but not much. I tried connecting a second Cree to the other diode that is oriented in the same direction, a lot more buzz. Removed it, of course. So I have only one Cree diode installed.
One issue that may be related is a grounding noise when ever I touch the volume. It does have a stepped attenuator. I appreciate all the help so far. I feel that I am getting somewhere, slowly but surely. Just that last bit of buzz....
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Tom,
I'm going to look and see which terminal I should have suggested be connected to T13. (I'll post here to verify whether T12 was right or wrong.)
Looking at your quote in Red, this makes some sense, depending on which diode you connected the Cree after. That is, it should be after the diode that is connected to the positive on the first capacitor in the power supply filter.
Looking at your quote in Green, I'm not sure what was done. If it is connected between the power supply common and the anodes of the two diodes that are connected to the power supply common then that is where it should be inserted.
Cree diodes negate the need to install the RRSF since they have no reverse recovery spike. I'm pretty sure one between the + of the bridge to the first filter capacitor should block all the reverse recovery spikes that the stock filter could pass. So if the red text is correct the bridge is not your source of buzz.
So I tried connecting terminal 12 to the ground leg of the power, very loud hum. Terminal 14 is connected to terminal 13, as suggested in one of the previous posts.
I tried one of the Cree diodes (I have 4), connected after one of the existing diodes (being careful to connect the cathode end correctly). The buzz is a little quieter, but not much. I tried connecting a second Cree to the other diode that is oriented in the same direction, a lot more buzz. Removed it, of course. So I have only one Cree diode installed.
One issue that may be related is a grounding noise when ever I touch the volume. It does have a stepped attenuator. I appreciate all the help so far. I feel that I am getting somewhere, slowly but surely. Just that last bit of buzz....
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I put the first diode after the diode that is pictured here on the right, the second diode I installed was to the diode next to it. Both diodes have the banded(cathode) end going toward the cap. I will take another pic this afternoon of what I did.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi146.photobucket.com%2Falbums%2Fr271%2Fmanfred8%2Fforeplay3.jpg&hash=10c32a0fe08f0fca5cf236de0f16d4f0229f0049)
Tom
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Tom,
This sounds like you put a Cree diode from a diode cathode to the terminal strip. Is that right?
Looking at your picture it seems the terminals are numbered from top (1) to bottom (5). What should help is putting a Cree diode from (anode) terminal 2 to (cathode) the blue wire. I.E. in series with the blue wire. This should guard against reverse recovery spikes.
This all assumes that your problem is caused by reverse recovery spikes.
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Well, this is what I did. So it should have gone from the blue wire, cathode end,to the second diode, anode end? I have a pic with a line drawn as to wear the diode should connect.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi146.photobucket.com%2Falbums%2Fr271%2Fmanfred8%2Fcree1.jpg&hash=eff43dd8c4e3e7d40905de87aadd5e704b00f915)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi146.photobucket.com%2Falbums%2Fr271%2Fmanfred8%2Fcree2.jpg&hash=c20f1e9fee38b8d452a1512ac3505741a1b35329)
Tom
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Tom,
The simplest way to do it is in series with the blue wire. I would try to swap the UF4007/Cree combination on the left with the diode that is second from the right. Be careful to keep the directions right, that is, both have to be swapped to give you a full wave bridge.
I wouldn't try to mess with the other diodes, just swap 1 and 3 (numbering from left to right).
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I put the Cree diode as per your previous message, Cree diode from (anode) terminal 2 to (cathode) the blue wire. I.E. in series with the blue wire, the buzz didn't change.
So I have enclosed another pic with the wires numbered 1-4, please explain again, I didn't quite understand which left and right.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi146.photobucket.com%2Falbums%2Fr271%2Fmanfred8%2Fcree3.jpg&hash=3dcce9ce939b67fa3c9e9a69961dcdddf03d1e67)
Tom
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Tom,
The Cree diode is not really where I suggested. For the Cree diode to be as I suggested it would have the anode on terminal 2 and cathode soldered to the blue wire.
However, I saw something completely different in your previous picture. I don't know why.
What you did is put the Cree diode in series with one of the two diodes that feeds terminal 2. That would eliminate 1/2 of the RRS noise. Another Cree diode with its cathode on Terminal 2 and in series with diode 3 (last picture) would eliminate the last half of the RRS noise.
I'm still wondering why I didn't see the Cree diode correctly in the picture. Age maybe?
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Sorry, that was a previous pic, just to get the numbers on. Here's how I have it. Cathode on the blue wire, anode to terminal 2. Still have the buzz. I'm pretty sure at this point that the buzz is coming from somewhere else.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi146.photobucket.com%2Falbums%2Fr271%2Fmanfred8%2Fcree4-1.jpg&hash=069c8e143fb69ce8e0de07323e7ed37d281f295f)
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That is just as it should be. If there is buzz the diodes are not at fault. No RRSF will help.
What is your situation now?
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Buzz remains. I have a spare preamp to use. I may take it to a local tube audio repairman. Not sure what else to try. Filament snubbers? I'll make a copy of Voltseconds web page when I take it in. I never learned to read schematics.
Thanks for your time and effort.