Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: denteom on January 27, 2023, 07:16:24 AM
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I finally finished the upgrade but ran into some problem. I noticed immediately the D tube is dim compared to the C tube. Do I need to plug the D tube deeper and not getting enough contact? (It's a daunting task plugging these small (6CM7), feels like it might break. The 300B glow looks equal. When I measured the voltages at terminal 45 I get 6.5 vdc. But terminal 60 voltage went up to 7.8 vdc. The LED on the output upgrade PCB all lighted up bright and equal intensity.
Also not sure how to measure kREG voltage. Is the black lead still connected to 4u and use the red lead to measure kREG? positive or negative terminal. Or do I remove the black lead at terminal 4U then measure kREG (-) with black terminal and kREG (+) with red terminal? Not to sure about this.
The voltage at Terminal 46 is 175 vdc while terminal 51 showed 225 vdc.
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To measure Kreg you use the red probe just like all the rest of the measurements.
I would list the OA, OB, KregA, and KregB voltages on the new boards. The glow intensity of the 6CM7 can change substantially from tube to tube, so that's not necessarily indicative of a problem.
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Thanks, what about the voltage imbalance between the two halves? it's kinda wide difference, need to troubleshoot anything?
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It would be good to know the IA, IB, OA, OB, KregA, and KregB voltages on that upgrade board before being concerned about the other voltage difference.
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Found the problem it is the Kreg B. But what should I do?
Measuring voltage at
Terminal 45- 6.4 VDC
Terminal 60 - 7.2 VDC
Terminal 46 - 175
Terminal 51- 210 VDC
IA 220 VDC
IB 230 VDC
OA 175 VDC
OB 220 VDC
KregA 8.2 VDC
KregB 200 VDC
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The KregB tells me that the 431 regulator on that side is deceased. You also either have a massive miswire on that side of the PC board, or possibly that the resistor on pin 8 on that 6CM7 socket isn't well connected to ground.
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Finally I got it right it was just the black solid wire connecting -reg to bB one end went loose
The new measurement are now spot on:
voltage at
Terminal 45- 6.4 VDC
Terminal 60 - 6.4 VDC
Terminal 46 - 175 VDC
Terminal 51- 175 VDC
IA 215 VDC
IB 215 VDC
OA 175 VDC
OB 175 VDC
KregA 8.2 VDC
KregB 8.2 VDC
I'll give it a listen in a while
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Having problem with sound. The volume became very soft and muffled with either using RCA or XLR. Before I was already okay with the third coarse notch. There is also an audible crackling sound. It is the same using a power amp to speakers, or to a headphone amp. I thought my problems are over. How do I trouble shoot this?
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The left channel sounds slightly softer. It sounds like a bad sounding radio. kinda lost it's life,
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Did your voltages change when you discovered this problem?
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I did listening after the voltages were already correct. If you mean to check it again I have not taken it out from the audio chain. I will check it again later after work. Just the voltage checks found on the output upgrade manual? No need for additional voltage checks?
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I would still measure OA and OB on the large C4S board installed with the attenuator upgrade.
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I got almost the same values
Terminal 45- 6.2
Terminal 60- 6
Terminal 46 175
Terminal 51- 175
IA- 215
IB- 215
OA- 175
OB- 175
KregA- 8.2
KregB- 8
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Could you check OA and OB on the large C4S board with the heatsinks?
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The from the C4A board (BeeTwo Quiet)
OA 115
OB 115
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Well all your tubes are working properly. When I have run into issues like this, usually it ends up being input/output wiring issues that are causing the problems.
It may help to post some build photos and we could look at what you have built.
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Nice to know the voltages are fine. I don't think it is the input. Have checked that before during the initial build and the upgrade one, have already fixed the problem, already re-enforced, added additional solder to the inputs and was listening to the unit prior to the second upgrade and it was fine. I think it is the output since we de-solder and resolder again with added xlr. Hope these photos can tell what the problem is.
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With the preamp running, play a 60 Hz tone into it using an 1/8" TRS to RCA adapter and an old phone or a computer as a source with the volume control turned all the way up. Turn the level controls to maximum, then set your meter for AC volts and measure the AC voltage at:
1. Pin 3 on each 4 pin socket
2. The center post of each 9 pin socket
3. The center post of each output RCA jack
That will give a good idea of where the signal isn't getting through.
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Does the trs in one end headphone and the other end in stereo that is 2 RCA or the more common, 2 ends in TRS which commonly used in battery powered portable speakers? Then I plug it in the inputs? Will the small TRS be easily be plugged to the line in (no need for adapters)? If it ends in a single TRS where do I plug it on the red side or on the (white or black side of the line-in?)
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Also can can the problem be also due to poor contact on the nine pin tubes? Not sure how hard should I push. The pins are so tiny unlike the one on the 300B which is easier to push through the socket. They should build sockets like the ones on PC computer, with zero insertion force. hahahah...
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Plug something like this into a computer or old phone (the 1/8†trs side) and run RCA cables from this adapter to you BeePre2 input.
ANDTOBO 3.5 mm TRS to Dual RCA F (2-Pack), 3.5mm Stereo Male to Dual RCA Female Audio Breakout Adapter https://a.co/d/2NiSSZ8
Please unplug all outputs from the BeePre. Max out the volume on both the computer/phone and BeePre2, play this, and take the measurements that PB has indicated.
https://youtu.be/TULW_-zRjgo
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I got 0 ACV on all the pins that you told me to check using the red as test lead and the black one clipped on number 4 terminal. That's weird, what could be the problem? I plugged the pre amp yesterday to my speakers with switching of the 6CM7 tubes location. Still same problem very soft volume and sounding like mono (not stereo) despite everything on the pre amp is maxed out.
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Could you post a picture of your meter or the make and model? If it is one that only has a 200V and 700V scale for AC, then you may need a different meter.
Another test you can try is playing the tone through the cable with the volume on your electronic device maxed out, then just use your meter across the AC plugs to check the AC voltage there.
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This is antique multi-meter from dad, still working fine. How low AC volt do I have to turn it down to? BTW it is now switch to DC cause I rechecked again the DCV so far they are still within the parameters. I did placed it on 1000, 250, 50 ACV (I think I tried 10 also). Below the photo is the TRS adapter with the RCA. I plugged it to my phone, then tried it on the headphone out of the Macbook air as well.
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Yeah that analog meter is really good for certain things, but not for chasing signals that start out at less than 1V.
If you're in the US, I would grab one of these:
https://www.harborfreight.com/electrical/electrician-s-tools/multimeters-testers/11-function-digital-multimeter-with-audible-continuity-61593.html (https://www.harborfreight.com/electrical/electrician-s-tools/multimeters-testers/11-function-digital-multimeter-with-audible-continuity-61593.html)
On the 2V AC scale, you can resolve these signal voltages pretty easily.
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Ok I'll try it again at 10. If still can't get a signal, I have a friend who has an oscilloscope. Not sure if he has a less than 2VAC. What should I expect from the voltage test?
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If you measure the AC voltage on the RCA plugs before plugging them into the BeePre, that would be your starting signal (probably around 0.3V-0.5V). That same voltage should appear on pin 3 of each 4 pin socket (you can leave the preamp off for that test).
With the preamp running and the volume controls turned all the way up, you would expect somewhere around 1.5V or so on the center post of each 9 pin socket, and you would expect to see nearly that same voltage at each RCA output jack.
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Finally found the problem. It was the 220 ohm 1/4 watt resistor connected to C7 and the center pin of socket C. I forgot to trim off the excess wire after soldering it to C7.
My last problem is the fine volume control 0 db. it looses contact on the left channel, I have to tap it, press on it or wiggle it. The other fine channels are ok. I've sprayed contact cleaner to the switch and switch it several times but the performance is kinda erratic. Not sure if this problem is also causing the ever so slight softer sound on the left channel. How do I resolve that problem?
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The fine switch doesn't really work that way. The input/output are connected by wire, not the switch, so what you're more than likely dealing with is one of the empty terminals on that switch making contact with the metal hardware on the switch itself.
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So how do I resolve that problem on the 0 db? Switching from -1.5 to 0 db, yes there is sometimes a slight loss in sound in between. Which does not happen when I switch between the other fine channel switch, transitioning on the other fine channels is ok. It's only between the -1.5 to 0. The -1.5 db and lower all work fine.
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Is the channel dropping or not getting louder?
A channel dropping means you lose the signal completely.
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Yes I lose the signal completely on the left channel. But I regain it by pressing on the knob, at times tapping or wiggling it helps. Also it really sounds a bit softer on the left. If I switch it to -1.5 db and lower db knobs it is balanced.
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This means that the 0dB position is in close contact with metal on the switch body and needs to be spaced out. This does not mean that the switch is not making contact on the 0dB fine position.
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Do I need to try to bend with pliers, sandpaper it to have better contact or add solder?
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Maybe you could post some photos of that switch in your build.
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hope these photos help.
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With the fine switch not on -0dB, can you check the DC resistance between the chassis and each empty lug on the fine switch?
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Where will I put the Black lead? Is the black lead the chassis? Or do I clip the black lead to the chassis?
Does that mean checking the lug without the a resistor attached to it?
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One probe on one lug of the fine switch not connected to anything, one probe to the chassis with your meter set on DC resistance.
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Switched at -4.5 db fine knob
At -1.5 db 85 k Ohm
At -3.0 db 36 k Ohm
(not sure of the decimal point. get confused by the analog meter)
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I'm talking about the DC resistance between each of these two terminals and ground. Your readings don't make a whole ton of sense. In a properly functional BeePre, these should be OL, in your BeePre one may be close to 0.
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Sorry about that, didn't get instructions right. When I measured again I got the same reading on both the empty lugs, it showed infinity result.
There were time when I got 0 ohm, but upon checking the lead was touching the nut beside it, so I think that was an error on my part.
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You want to be sure that the nuts that hold the switch together aren't allowed to touch the metal on that switch position. That is about the only mechanism for losing a channel only on that switch setting.
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Ok so you mean, I should tighten it and try again?
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No, I mean you need to physically inspect the switch to be sure the nuts and hardware on the switch itself are not contacting the empty lugs I point to with the arrows.
If those lugs touch the metal switch hardware, that will short a channel to ground when the switch is on the -0dB setting. That is how you lose a channel with the way the fine switch is wired.
Again this is undesired metal-to-metal contact on the switch itself that needs to be addressed.
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OK, thanks for the tip. I'll try to check on it during daytime, so I can have more light. Hope that will be my last issue. Give you a feedback in a day or two.
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Thanks got everything sorted out, My Beepre2 is singing so beautifully. On to the next Bottlehead kit!
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Just a last minor problem, I still sometimes get a loss of signal on the left speaker. But this time just doing light tapping on the fine knob at 0 db will already do the trick (no need for wiggling the knob). It sometimes occurs after playing music for awhile like 5-10 minutes. Hope that goes away through time.
From our last exchange of text, I really did not find something shorting it. What I did last time was just loosened and re-tightened (but not too tight) the screws holding the assembly of attenuators to the chassis. Somehow things improved with that maneuver.
But still randomly I run into that problem. Once I get back the sound the left channel, sounds really balanced and no distortion.
Overall the Beepre 2 sounding really fantastic!