Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Foreplay III => Topic started by: John Roman on September 25, 2012, 07:06:37 AM
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I installed some 20K Goldpoint attenuators along with a 4 pole 3 position selector switch from Goldpoint in my EFP3. Now I have no volume control. I can't attenuate either channel no matter what output I use. When I switch to that output I get max volume. I've checked the attenuators and selector out of the circuit and they appear to be working normally.
John
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yep - sounds like the attenuator is out of the circuit. That happend to me once. Fortunately the song didnt start out real loud! The song started with a dog barking. I was really faked out. It sounded so real!. Those are the kind of story we will tell our grand kids or great grand kids! Naah.. probably not!
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Not meaning to Hi-jack here but have a question related to attenuators. My memory was that these attenuators (sweetest whispers, right?) were really well received when Bottlehead released them way back when. Lots of chatter for how good they sounded, outright let alone bang for the buck. Im sure there are many who feel there are better sounding stepped attens. for more money, there always are. But my question is, and this is highly subjective, how much is gained, sonically, by upgrading the attenuators to something "affordable", like Goldpoints for example? Are we talking about the barely audible IF one is golden eared, maybe 2 or 3% improvement? Are we talking about clearly audible changes that definitely change the sonics but whether it is "better" or not is a personal opinion? Or are we talking a definite improvement that most would agree upon? I have read that some (many) did not find the smd resistor Goldpoints to be better at all, they felt they were downgrades. That makes me wonder how much improvement, if any, can really be expected from something like Goldpoints with leaded resistors.
My selector switch has no stops, it operates fine in the 3 positions, but it rotates beyond those 3 active positions is both directions. There is too much wiring involved to bother with just replacing the switch for missing stops. But I would replace it with a different Selector if I were to also "upgrade" the attenuators. I have no real hankering to do so because of my memory of how well the stock attenuators were received by the diy community back when. And, I am very happy with the FPIII and the system. Im not one to always be looking for improvements. As long as it sounds good (and is quiet, that's my biggest peeve really) Im content to just enjoy the music. So, I ask for subjective opinions on the above questions, probably more out of curiosity.
Basically, I guess Im asking ... how good are the stock attenuators considered to be these days?
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Hello John,
It would help to know how you have these wired. The Goldpoints have an input, output, and ground, if you could let us know where each of those terminals is connected, that should help.
-Paul
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High Desmond - I dont think you are going to find much of a 'review base' on attenuators. IMO, its not a BIG issue. There are plenty of really smart designers/engineers of current excellent sounding high value gear that still use the Japanese go-to pots, the Alps Blue Velvet (Burson, Schiit, Peachtree etc). The current agreement is that the stepped pot using discrete resistors for each step sound 'the best'. You could probably debate about what brand or type of resistor sounds better than another. Another rage is the opto-potentiomiter. - Probably worth buying a few different types and experimenting.
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I've used Sweetest Whispers, Radio Shack pots, PEC pots, and have heard in other equipment various forms of stepped attenuators. They all make an audible difference. My one problem with some of the cheaper stepped attenuators was that the switch would get noisy over time and required cleaning which can be a real pain. I haven't heard Goldpoint or Dact attenuators but have read many mixed reviews of both. I've also read about the optocouplers and while they seem promising they are quite a bit more expensive.
I prefer the mono PEC pots which are relatively cheap (~$11ea) and sound really good.
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Hey Desmond,
In the FWIW column having listened to both the SW and GP (with SMD) attenuators and selectors I believe the difference is subtle. The quality of the GP switches are better, but then they should be at $80 a pop.
I do think the SW set up competes very well sonically with the GP (with SMD resistors). In fact I think it exceeds the GP's. I made a judgement mistake in not getting the GP custom mini V pots but have chosen to live with it until the new Pre comes out.
HTH,
John
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Hello Paul,
Here is how the Goldpoint 20K pots are wired:
left channel: in to 17U, ground (blk) to 16U and common on pole 3 of selector switch and out to common on pole 4 of selector switch.
right channel: in to 37U, ground (blk) to 40U and common on pole 2 of selector switch and out to common on pole 1 of selector switch
Thanks for helping,
John
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From what I can tell, that is correct. What's coming to mind immediately is that if you removed all the series resistors at the input, you would end up with the volume control acting as a variable load instead of an attenuator, and this would present the symptoms you have. If you'd like to remove all those resistors at the input, you can do this if you rewire the Goldpoints "as directed" on the PCB of the switch body.
If I'm totally off here, feel free to post a close-up pic of one of the switches as-wired and we can take a peek.
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hello Paul,
Here's some pix. LMK what you think.
John
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Thanks for the input everyone. And again John, sorry to Hi-jack your thread.
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from selector switch-red to in of vc -black to out of vc-from out of vc-- to terminals 40 and 16---ground from vc to 37 and 17
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No worries D, how you doin?
J
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Having done a similar swap recently with the GP parts, it seems that the GP 'C' at the selector switch should go to the INPUT of the GP volume control, and not the OUTPUT. This would give you a reversed volume control the way it is now. The rest of the connections I can't remember the order that they go in or to.
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Odd, this actually looks to be hooked up correctly, though as others have mentioned, you can go from the selector switch to "In" and then wire the output to the preamp circuit, but it should work as-wired.
It would be good to verify that the attenuator is working, can you place a probe on "GND" and a probe on "OUT", then measure the resistance as you turn the knob (with the preamp unplugged of course), then report back. I also didn't see it in your origninal post, but I'd assume that the preamp was working without the Goldpoints?
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http://www.goldpt.com/schm_ser.html
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I had to double check, even though I 'knew' that I was right. Simply put, the in and out of your volume controls are wired in reverse. That means what would normally be 0 volume is now FULL volume. As you turn the control clockwise, the volume would Decrease, instead of Increase, because of the wiring of the volume controls.
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No worries D, how you doin?
J
Im doing pretty well, no complaints. Thanks for asking. Hope the same holds true for you. Although, Im sure you'll be doing even better when you get those attenuators working ;D
If you think about it, please post some impressions of the Goldpoints when you get some listening mileage in. Thanks.
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Why does the wire from the selector switch enter the "Out" of the attenuator? Wouldn't the wiper be the normal "out"?
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With the series input resistance, wiring the output of the selector switch to the "out" of the volme control will still yield a variable resistor underneath the input series resistance. Assuming the control is 15k, having the volume control right in the middle would set up 30K (or more) as the series input resistor and a 7.5k resistance to ground. Moving the control all the way up would give you a 15k/15k, and all the way down would short the incoming signal.
Using the input terminal on the attenuator as the output just adds some series resistance between the attenauator and the grid of the 12AU7, but this resistance does not attenuate the signal.
The OP could try switching the input and output connections, I'd imagine that the problem would persist.
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Why does the wire from the selector switch enter the "Out" of the attenuator? Wouldn't the wiper be the normal "out"?
The Foreplay III is not wired as a normal attenuator. It's a shunt-more attenuator, and it's not a normal one of those either. This particular wiring sets it up so that a momentary failure of the switch contact removes the source; in a normal shunt mode connection such a failure acts as a momentary full-volume setting.
Actually, this is a variant of a classic "ladder" attenuator, which is (I'm sorry, it's not my fault!) NOT what is called a ladder attenuator today. You have to go back to the fifties to fine the classic ladder, which is a series of pi attenuators. It used to be the standard of quiet attenuators, used especially in live broadcast situations.
As you can see, there really are many attenuator wirings that are not "normal" but are still used in many situations.
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Hello Paul,
Indeed the pre was working correctly prior to these changes. Prior to the GP install I modified the pre for use with 6SN7 output tubes. Paul J. posted:
"All the pins are different between the tubes. You have to wire the triodes as in the circuit diagram, which means you have to choose which triode is the voltage amplifier and which is the cathode follower. Once you have done that, you will know which grid takes its input from the level control." How do I determine that?
John
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Right, the FP III is the different kind of volume control. The usual output is the input, the usual input is the output and ground is still ground.
I just refreshed my memory by looking at the schematic.
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Right, the FP III is the different kind of volume control. The usual output is the input, the usual input is the output and ground is still ground.
I just refreshed my memory by looking at the schematic.
Hmmmm.... I built the following diagram with some help:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.co-bw.com%2FImages_Audio_DIY%2FGold_Pt_Attent_Switch.jpg&hash=818f0c5e24bae580723f15bcccd63992bc1d5b91)
It also seems to follow DebK's images of her GP mods. But when I sat down and traced where the wires went, the attenuators connect to the "A" and "B" tubes which feed the RCA output jacks. So, in support of what Grainger says, the correct diagram should be (please correct me if I am wrong):
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.co-bw.com%2FImages_Audio_DIY%2FGold_Pt_Attent_Switch_New.jpg&hash=36c92d6c090bbcf95fd599df8e9e2ac062d087bd)
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The top diagram is consistent with the schematic, but in actuality both diagrams will function in the preamp, with the bottom diagram providing constant input impedance, with the top schematic having better range (IMO).
The OP should check to be sure these controls have a variable resistance between GND and Out and Out and In through the rotation of the control.
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Thanks Yoder,
The new diagram was helpful.
John
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John: does it work now as it should? I have not tested mine yet. I am finishing up the Eros and then will start all of the testing of the Para's, FP III, and Eros...then the truth shall be revealed!
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Hello Yoder,
Just got the pre working this morning. I had it wired using the upper diagram and had no volume control. I re-wired it using the lower diagram and volume control is normal for both channels. It seems fine now except I've picked some emi. I think the unshielded wiring between the selector and attenuators is a possible cause? It was shielded in stock form so..... any ideas for just shielding it? piece of foil with a drain wire wrapped around it?
Thanks for the help,
John