Bottlehead Forum
Bottlehead Kits => S.E.X. Kit => Topic started by: Jet on June 26, 2022, 01:55:36 PM
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Previously I had posted about having no sound in my right headphone driver while using the S.E.X. 3.0 Kit and I got a recommendation to just touch up joints T6 and T7 of the right channel output transformer. This seems to have given me sound in right driver but upon further listening it's significantly quieter than the left.
Things I've tried:
Swapping the tubes again yet the channel imbalance doesn't follow the tubes.
Hooked up the S.E.X. 3.0 amp to a digital source and played a test tone, it made it very clear that the right driver had quite a bit more volume.
Using different RCA cables.
Different pairs of headphones.
Everything has passed resistance and voltage checks.
Thank you for the help on my previous post yet I still need some assistance.
Attached is a current picture of the wiring in my kit.
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Here's a joint that doesn't look soldered.
I see lots and lots of untrimmed leads. I would get a set of side cutters (something like the CHP-170) and trim all those random leads back.
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I've cleaned up those untrimmed leads and took a look at that joint, it feels solid but I'll be sure to touch it up. While checking it out I discovered the terminal next to it (36U) looks really off up close and actually feels quite loose! I'm gonna redo everything on that terminal tomorrow.
Thanks so much for leading me in the right direction, I'll give an update once it's done. :)
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I touched up those joints yet when I use the amplifier the left driver is still louder than the right.
Any other suggestions?
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You might go back and redo your voltage measurements. Note any differences between channels now that you have the circuit working.
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You appear to be missing the resistor at A10.
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The resistor is at A10, it's just that you can't see it in the angle of the picture.
I did voltage checks again, everything is within the recommended values.
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Can you post the make and model of your DVM? We can help you send a 60Hz tone into your amp and measure it with your meter if it's sufficiently sensitive.
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Sure, I'm using a Klein Tools MM320 Digital Multi-Meter.
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That won't quite get the job done. You'll need a meter with a 2V AC scale (yours only goes down to 200V, which is totally perfect for residential electrical work).
This one is generally pretty easy to find close by, but if you're not in the US let me know where you are and I'm sure I can find something appropriate that's close by.
https://www.harborfreight.com/11-function-digital-multimeter-with-audible-continuity-61593.html (https://www.harborfreight.com/11-function-digital-multimeter-with-audible-continuity-61593.html)
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I should be able to get that exact multi-meter in the next few days, I'll give an update when I do.
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If A9 and A8 are allowed to touch, you would get really low output, though I would expect some deviations in some of the voltages under those circumstances.
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Got the exact meter!
What's the next step?
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You can download a 60Hz test tone or use a signal generator app on a phone/tablet with a headphone output, then feed that 60Hz tone into the amp with the source device turned all the way up.
You will want to set the meter to the 2V scale and measure the AC voltage between ground and each center pin of each RCA jack, then ground and each outer (non-ground) lug of the volume pot, then each middle lug with the pot about half way up.
You should see about 0.3V going into the RCA jacks, and some attenuation of that voltage appearing at the output of the volume pot.
None of these tests (so far) require the amp to be on, so you can get a feel for doing this without the amp on.
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Finally got the chance to do the test, everything is around your recommended value of 0.3 AC voltage only being off by around 0.015.
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You now need to repeat the test with the amp on but measure the AC voltage available at terminals 4 and 18 with the volume pot turned all the way up. This voltage will be substantial enough that you'll want to be on the 20V scale.
If those are equal, then check 3 vs. 17.
If those are equal, then check each of the positive binding posts.
At least one of those checks with yield and imbalance. I have them listed in order so that once you find the imbalance, you can stop and we can debug, as all of the following steps will continue to show an imbalance.
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Before trying the next test you recommended I decided to repeat the previous one with the 60Hz tone and without voltage, I'm now getting 0.575-ish volts AC with a small fluctuation in the thousandths decimal place. Would this indicate the issue with my amp? What's causing this?
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What AC signal voltages do you see at the terminals listed?
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Terminals 4 and 18 were around 8.30 AC with some variation around 0.01 and 0.04 AC volts on the 20 volt scale.
Terminal 3 was about 16.6 AC with some variation around 0.01 and 0.09 volts AC on the 20 volt scale. At terminal 17 I had to switch to the 200 volt scale to get a reading and it was around 157 volts AC with some variation of about 0.1 to 0.6.
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This narrows things down a bit. Seeing the same voltage coming out of 4 and 18 tells us that the first amplification stages are working properly on each channel.
The 10x lower voltage is a bit puzzling on the second stage. You could get a pretty big difference if the 1000uF cap on that side wasn't well connected, but not that much of a difference. I think the next test I would do is to temporarily remove the white wire attached to terminal 10 on the output transformer of that side, then recheck the voltage at terminal 3. We would generally expect this voltage to rise a bit with that wire disconnected, but if it pops up to 150+ volts AC, that would be helpful information. If the voltage at terminal 3 doesn't change with that wire disconnected, then there's a bad solder joint around that socket or an untrimmed lead possibly touching the chassis or a neighboring terminal that is not allowing the signal to reach the output transformer.
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Terminal 3's voltage didn't change with the white wire at terminal 10 of the corresponding output transformer being disconnected and terminal 17 is still reading 150+ volts AC.
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If you reconnect that wire, what AC voltage do you see at terminal 11 vs. 25?
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Well I soldered the wire back at terminal 10 of the output transformer and I began testing terminals 11 and 25, I wasn't get much voltage out of either one and when I was testing 25 something in the amp suddenly started to make a slight popping sound and then there was smoke so I unplugged everything and turned it off. This doesn't seem like a good sign.
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I now notice that the white wire going to the output transform that I just soldered again was in contact with the underside of the capacitor attached to terminals 35 and 36, could that have had anything to do with it?
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You'll probably want to go back and do a DC voltage check to be sure all the DC voltages are still correct.
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I checked the DC voltages, they all seem to be correct and within the recommended values.
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Now with signal playing through the amp I would check the AC voltages present at 11 and 25.
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When playing a 60hz tone through the amp with the source and potentiometer turned all the way up I got an initial reading of about 0.017 volts AC on terminal 11 but it then went down to about 0.03 and sometimes even 0 volts AC. Terminal 25 reads stable around 0.016 volts AC.
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Is the lead of the cap attached to terminal 3 touching the bare shield wire under it? That will suck out all your signal.
What you need to be looking for is metal bits on components touching each other when those components don't go to the same terminal. This could also be leads poking through a terminal strip and touching things they aren't supposed to.
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The cap attached to terminal 3 and the bare shield wire under it don't appear to be touching.
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It might help to see some more photos of the build on the A side of the circuit.
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Here are some pictures of side A.
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5L needs more heat and more solder.
9L had leads that should be trimmed off.
10L needs more heat so the solder flows out.
11L needs more heat so the solder flows out.
10L had leads that need to be trimmed back.
The STP wiring that goes to the 12 pin socket needs to be as close to the chassis plate as possible. I see one piece of it and it looks like the foil from the STP is touching the lead of the black Solen cap it's next to. Both of these wires are also installed over the 680 ohm resistor, which is incorrect.
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I've now made all of those changes to my wiring and I rearranged the STP wires, both of them now go under the 680 ohm resistor. The foil from the STP wiring wasn't making any contact with the black Solen cap.
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Is there any change to the performance of the amp?
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The left headphone driver is still much louder than the right although I do hear a significant hum in the right driver now which I think is new.
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Are the DC voltages still correct?
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All the voltages are normal except for terminal 18 which is reading about 0.023 volts DC when I should be getting 0.
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This is likely to be a solder joint issue or a component touching something it shouldn't be. If you'd like to send it in for repair, you can contact Eileen at queen(at)bottlehead(dot)com regarding getting a repair box.
Otherwise reflowing all the solder joints on the A side of the amp, moving the Solen cap up a bit so the body of the cap isn't touching anything, and ensuring that all your component leads are trimmed should get your amp into working order.
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Thank you for your assistance, I've sent Eileen an email about a repair box.
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I sent an email to Eileen about a repair box on Sunday but I haven't gotten a response?
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Hi Jet, I don't seem to have an email from you requesting a repair box. Do you mind sending it again to [email protected]? Thanks so much, Eileen
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The request should've come from Geoff Spear
I've received the box and I just packed up the amplifier, it should be ready to ship out tomorrow. :)
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Today I got this SEX amp on my bench. The 220 ohm resistor between A10 and A8 was poorly soldered and creating a major part of the channel imbalance (about 20dB). Two of the jumper wires on the output transformer got hot enough during soldering to melt together and short out, which effectively reduced the output of that channel to nothing.
Either problem on its own wouldn't be that difficult to track down, but the intermittent nature of the loose 220 ohm resistor made sorting all of this out rather difficult.
Once these two issues were dealt with, I discovered that one of the 6FJ7s was not super happy about operating with these issues, but I have a loose replacement that's a match for the remaining good tube.
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Thanks so much for the update and letting me know exactly what was wrong with the amp, it's nice to know that the issues are being taken care of. :)