Yes. I built the kit according to the instructions first. With the exception of using a grounded IEC connector with a grounded power cord. The amp has always been quiet.
In this case I am not sure why I am getting low level 60hz on the output. If anyone has any ideas your help will be greatly appreciated.
If you want to know why you have low level hum, you can ship your amp to Sun Valley . They will give you a full report to explain to you why you have low level hum. There are multi reasons getting low level hum.... building skill, components layout, grounding. and dirty power source... etc.. As it is a Point to Point amp, it is not a big deal to de-assemble the amp and to re-assemble agian.. YOU will be succeeded on your second attempt.
Is the hum present on both channels or just a single side? Are you using a 5AR4 rectifier tube or the SS unit provided with the kit? Is your IEC earth grounding point making good contact with the chassis? (i.e. paint scraped off and star washer between lug and chassis) The DC filament supplies could cause hum, but those are channel independent, so doubtful both supplies would have the same defect if hum is present on both channels. Do you happen to have a high res photo of the completed underside you could share with us?
-Chris
Ron,
Knowing the hum is in both channels is helpful to the analysis. Thanks for sharing the photo. I'll take a closer look after work tonight. However, for now, I have a suggestion that is quick and easy. It may not solve the issue, but it is nevertheless best practice. You have the input coax cables tied together with and running parallel with the 300B filament supply wiring for a couple of inches (left side of your photo). In all my years of car audio installs, I have always made sure to separate signal runs and power runs as much as possible, and when they have to be close, always try to have them perpendicular. You should try removing that cable tie and pulling the blue/green wires away from the coax cables, and situate the blue/green wires so they are not parallel with the coax cables. You could be coupling the residual 60 Hz component in the DC filament supply into the audio input signal lines. The hum pots will address this at the output tubes, but it cannot affect noise imposed onto the preamp input stage.
-Chris
Ron,
Maybe I'm not seeing enough detail in your photo, but it looks like you have grounded the positive terminal of your right channel speaker output. I think the grey wire should be by itself on the positive post and the two black wires should be on the negative post. You may want to take a closer look at this.
-Chris
Maybe I'm not seeing enough detail in your photo, but it looks like you have grounded the positive terminal of your right channel speaker output. I think the grey wire should be by itself on the positive post and the two black wires should be on the negative post. You may want to take a closer look at this.
-Chris
Hi Chris,
Yes, that was a bit of carelessness on my end when I took the filament supply out to check the output transformer connections. The problem was quickly identified and fixed when I got no sound from that channel. I also seperated the input coax wiring from the blue and green filament supply.
I am still getting ~0.125mv of AC on the output with no input connected so the hum problem is still there.
I appreciate your help thus far and if you have any other ideas, it would be great.
Ron
Yes, that was a bit of carelessness on my end when I took the filament supply out to check the output transformer connections. The problem was quickly identified and fixed when I got no sound from that channel. I also seperated the input coax wiring from the blue and green filament supply.
I am still getting ~0.125mv of AC on the output with no input connected so the hum problem is still there.
I appreciate your help thus far and if you have any other ideas, it would be great.
Ron
Hi Ron,
I read in an earlier post that you still had the hum even when you removed the rectifier and disabled B+. Is that still the case now?
How are you measuring the hum on the output? Do you have an oscilloscope?
Did you really intend 125 mV? Since 0.125 mV is actually 125 microvolts, that would only drive about 16 microamps through an 8 ohm VC. I am surprised if that level would be audible in the speakers.
Are you using the 4, 8, or 16 ohm tap on the OPTs for your speaker connections? You probably stated previously, but what speakers are you using?
Your photo confirms you selected 3 dB for the negative feedback gain, which is what the manual recommends for the triode configuration. Regardless of which OPT tap you are using for the speaker output, double check that your negative feedback is using the 16 ohm tap. Also make sure you have jumpered the 0 terminal and the E terminal on the OPT, it is easy to miss that step in the manual. Note that the manual includes 2 schematics, and one is specific for the Hashimoto OPT option, so make sure you are using the correct one for tracing and testing.
Did you use the WBT 805 silver solder with the kit for all the joints? That solder is lead free and can be fussy. I have found that the the flux core in lead-free solder is not always sufficient and it is necessary to use additional liquid rosin flux to get good flow and adhesion. Actually, I am old school and still prefer some lead in the solder. There is a lot of controversy over ROHS vs non-ROHS soldering, but that is off topic for this thread. It certainly could not hurt to re-inspect all the solder joints with some sort of high magnification and re-flow anything that looks questionable.
I am still looking at your photo for additional clues. I will wait for you to answer these questions and then think about what to check next.
-Chris
Hi Chris,
That is 125mv, typo on my side. I am using the 8 ohm tap and the feedback is indeed connected to the 16 ohm tap. I have also made sure that the 0 terminal is connected to the E, did not miss that part.
I have checked all solder joints and they all have good connection from what i can tell. I also checked the resistance between the negative output terminals, the star ground point, the chassis and volume pot. looks like the resistance is 0 for all these connections and it all connects to the ground terminal on the IEC socket.
My speakers are full range Lii Song F18's, single driver, no crossover. Should be a simple load on the amp.
-Ronen
That is 125mv, typo on my side. I am using the 8 ohm tap and the feedback is indeed connected to the 16 ohm tap. I have also made sure that the 0 terminal is connected to the E, did not miss that part.
I have checked all solder joints and they all have good connection from what i can tell. I also checked the resistance between the negative output terminals, the star ground point, the chassis and volume pot. looks like the resistance is 0 for all these connections and it all connects to the ground terminal on the IEC socket.
My speakers are full range Lii Song F18's, single driver, no crossover. Should be a simple load on the amp.
-Ronen
Forgot to mention that there is no hum at this point with the rectifier removed.
Ron,
Thanks for the info.
You did not mention whether you have an oscilloscope or not.
I was also asking, is the hum still present with the B+ disabled (rectifier tube removed)?
[Oh, I see you just posted the answer to this.]
If that is the case, without plate voltages present, about the only plausible explanation I can think of is that the power transformer is electromagnetically coupling with the output transformers to produce the hum. I notice in your photo that you did not twist the two sets of power transformer wires going to the the filament supply plate. Those wires run in close proximity to the output transformers and it is certainly possible they could induce current in them. The photo of the SV built product shows all of the wire groups of the power transformer twisted, even the main AC input. You might want to try desoldering the two 3-wire groups from the filament supply plate lugs, twisting them, and reconnecting them.
[It still would not hurt anything to try this. Maybe twist the main AC input wires also.]
-Chris
Thanks for the info.
You did not mention whether you have an oscilloscope or not.
I was also asking, is the hum still present with the B+ disabled (rectifier tube removed)?
[Oh, I see you just posted the answer to this.]
If that is the case, without plate voltages present, about the only plausible explanation I can think of is that the power transformer is electromagnetically coupling with the output transformers to produce the hum. I notice in your photo that you did not twist the two sets of power transformer wires going to the the filament supply plate. Those wires run in close proximity to the output transformers and it is certainly possible they could induce current in them. The photo of the SV built product shows all of the wire groups of the power transformer twisted, even the main AC input. You might want to try desoldering the two 3-wire groups from the filament supply plate lugs, twisting them, and reconnecting them.
[It still would not hurt anything to try this. Maybe twist the main AC input wires also.]
-Chris
Chris,
I do have an oscilloscope and I do see the noise on the scope. It's not a clean 60hz signal but more like noise with a leading 60hz component to it.
I twisted the leads for both filament supplies which did not change anything. Initially I did not as the documentation does not show these as twisted. Tomorrow I will go over all solder joins again focusing on the grounding in hope that redoing the solder will help.
Thanks,
Ron
I do have an oscilloscope and I do see the noise on the scope. It's not a clean 60hz signal but more like noise with a leading 60hz component to it.
I twisted the leads for both filament supplies which did not change anything. Initially I did not as the documentation does not show these as twisted. Tomorrow I will go over all solder joins again focusing on the grounding in hope that redoing the solder will help.
Thanks,
Ron
Thanks for the new info.
Good to hear you have an o-scope. For electronics work, that is as essential as a ratchet wrench is for a mechanic. It sounds like you are seeing more of a buzz than a hum, due to it having multiple harmonics. That tends to point to bad grounding or ground loops rather than power supply ripple coupling.
Do you hear it (or see it on the scope) immediately after you power up the amp, or does it take a little while to build up, coinciding with filament warm-up? Knowing this would help rule out electromagnetic coupling. Although, since disabling B+ eliminates it altogether, we can mostly rule that out anyway. Since it exists in both channels, it really makes the B+ supply and the 12AT7 input tube the most suspect. Do you have the ability to roll in a different 12AT7 tube for a quick comparison?
It would be worth a try to build up the SS rectifier provided with the kit and swap that in for the tube rectifier. If the buzz ceases or reduces significantly, it could point to a bad 5AR4 tube. A really simple A/B test to produce another data point.
Regarding the B+ supply, carefully check all the dropping resistors and RC filters in the plate supply path all the way back to where it ties into the center tap for the AC filament supply. Use the scope to measure what kind of AC component is present on the DC B+ path at every connection point. This might reveal a bad solder connection or a bad component.
With no input connected, turn the volume all the way down, essentially shorting the input to ground. Then take a look at the AC component on the grid of each tube for each channel. Note what the waveforms looks like and how the amplitudes compare. This may help you find the origin. Each stage will amplify the buzz if it is already present at a prior stage.
Another thing to try might be to disconnect the negative feedback and see what changes. Something there might be making the amp unstable. Again, it is hard to imagine both channels exhibiting the same problem without there being something in common with both, i.e. the B+ supply.
Let us know if anything changes after you re-check and/or re-flow your solder joints. There is definitely no reason this amp should have this level of buzz at the output. What you are measuring is an order of magnitude higher than expected and something is not right. I think it will really make the amp sing when you get this resolved. An unnecessarily high S/N ratio directly deprives the dynamic range.
-Chris
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Chris,
Problem solved. Your insights have been super helpful. I traced the voltages and in doing so noticed that the two in series filter caps after the choke were not connected in series as the solder was not making good contact. Once that problem has been rectified all is good.
Thanks again for your assistance. I owe you a cold one if you ever land in the west CT area.
Cheers,
Ron
Problem solved. Your insights have been super helpful. I traced the voltages and in doing so noticed that the two in series filter caps after the choke were not connected in series as the solder was not making good contact. Once that problem has been rectified all is good.
Thanks again for your assistance. I owe you a cold one if you ever land in the west CT area.
Cheers,
Ron
That is excellent news my friend! Glad you persevered and ran the problem to ground (so to speak). 🙂 It always seems like a simple thing once you find it, but sometimes very daunting to track down. I bet the amp has a new voice now that the B+ is being filtered properly.
-Chris
The amp sounds absolutely great. Still have a hard time deciding if I prefer the Sunvalley or the Elekit TU-8900. The Elekit is more accurate and has a lower noise floor but the Sunvalley has more "soul" for lack of better word. I played with rectifiers today and they make a big difference. The Gold Lion has more articulate bass but when I switched to a Matsushita 5AR4 (Mullard like) I got a bigger and airier sound stage while losing some definition in the bass.
Overall these DIY projects are a lot of fun!
Overall these DIY projects are a lot of fun!
From Mr Ohashi's blog about the coming shipment of SV1616-300B (by Google translator )
The inspection of products for export at the end of this month is reaching its climax.
I am in charge of the SV-S1616D / 300B model (115V, Hashimoto version).
A standard tube is determined for measurement, and each unit is checked to see if there are any abnormalities in its characteristics, whether the variation is within the standard value, whether there is any audible noise, whether the gain and maximum output are OK, whether there are any gang errors in the input volume...a variety of inspection items must be cleared before the unit is considered OK for shipment.
The coupling capacitor is a customer-specified V-Cap . It is a luxury item that costs over 10,000 yen each, and in terms of tone, it is a masterpiece that combines modern clarity with a vintage scent.
While performing the shipping test, I always have a strong feeling that if I miss some problem here, I will not be able to meet the expectations of the dealer who visited me from Canada six years ago, who said, "I want Made in Japan quality."
The inspection of products for export at the end of this month is reaching its climax.
I am in charge of the SV-S1616D / 300B model (115V, Hashimoto version).
A standard tube is determined for measurement, and each unit is checked to see if there are any abnormalities in its characteristics, whether the variation is within the standard value, whether there is any audible noise, whether the gain and maximum output are OK, whether there are any gang errors in the input volume...a variety of inspection items must be cleared before the unit is considered OK for shipment.
The coupling capacitor is a customer-specified V-Cap . It is a luxury item that costs over 10,000 yen each, and in terms of tone, it is a masterpiece that combines modern clarity with a vintage scent.
While performing the shipping test, I always have a strong feeling that if I miss some problem here, I will not be able to meet the expectations of the dealer who visited me from Canada six years ago, who said, "I want Made in Japan quality."
