Hey everyone,
Pete this tube amp looks great and by all reports sounds great too. I just purchased the red board from Pete a few days ago and while I await it's arrival in Australia I have been doing some research etc.
I have a question regarding the OPT, Pete mentioned that if money was not an object he would have went with the ones from Sowter, I am new to tube amps so this may be an easily answered question. What Sowter transformers would you go with, I have built many amps in the past but no tube amps so these are a little new to me ie the output winding values etc. I thought initially the Sowter 8968 This however could be overkill not really sure.
Will a gain a huge benefit from using the higher quality OPT.
Maybe I should just build the tube amp with the Edcor transformers and maybe switch them out later, that's just doubling the cost though?
Any light on this matter would be great, or perhaps recommendations for other higher quality OPT that will gain performance.
I read that another member had issues with the audible hum in the amp, as I am in Australia and our supply line is different will I experience any greater sources of line hum?
Probably all dumb questions for you tube heads but hey I am only just crossing over to the dark side.
I have found these on eBay in Australia and thought they might do the trick
1 x 5K UL PP 4/8/16 ohm 25 W Output Transformer for Valve tube Amp NEW
Thanks guys and gals
Archie
Pete this tube amp looks great and by all reports sounds great too. I just purchased the red board from Pete a few days ago and while I await it's arrival in Australia I have been doing some research etc.
I have a question regarding the OPT, Pete mentioned that if money was not an object he would have went with the ones from Sowter, I am new to tube amps so this may be an easily answered question. What Sowter transformers would you go with, I have built many amps in the past but no tube amps so these are a little new to me ie the output winding values etc. I thought initially the Sowter 8968 This however could be overkill not really sure.
Will a gain a huge benefit from using the higher quality OPT.
Maybe I should just build the tube amp with the Edcor transformers and maybe switch them out later, that's just doubling the cost though?
Any light on this matter would be great, or perhaps recommendations for other higher quality OPT that will gain performance.
I read that another member had issues with the audible hum in the amp, as I am in Australia and our supply line is different will I experience any greater sources of line hum?
Probably all dumb questions for you tube heads but hey I am only just crossing over to the dark side.
I have found these on eBay in Australia and thought they might do the trick
1 x 5K UL PP 4/8/16 ohm 25 W Output Transformer for Valve tube Amp NEW
Thanks guys and gals
Archie
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I finished mine today and connected JP1 on PCB because of Pete's and highflyin's comments. Even with the jumper I have hum with volume all the way down and hum doesn't change with higher/lower volume. All parts within whole amp are the same as required on the BOM with Hammond aluminum chassis.
I still get a very light hum in my unit even with the JP1 connected that's unnoticeable when music is playing. It's because the transformers are magnetically coupled, which is surprising given their distance on this design. The only way to get rid of it is to move them even further away on a wider chassis, which would have been too much work in my case. Since you're the third person experiencing the issue while using the Hammond chassis, it may be a good idea for Pete to take down that recommendation on his page.
The hum I get is loud enough that I can still hear it in background when music is playing at lower volumes. I'm using 64 ohm HD280's. With my 88db speakers, hum can be heard 1 feet away from woofer(at quiet times). Hum can be a big problem with >95db speakers.
I read somewhere Pete was saying that even he has hum issues. He said even with his high impedance cans, he can detect a tiny bit of hum which he reports is louder with 32 ohm Grado's.
I wonder if there is something out there; some sort of fix/dampening product to dampen the magnetic coupling. I like this amp, it plays about as detailed as my bigger amps.
I read somewhere Pete was saying that even he has hum issues. He said even with his high impedance cans, he can detect a tiny bit of hum which he reports is louder with 32 ohm Grado's.
I wonder if there is something out there; some sort of fix/dampening product to dampen the magnetic coupling. I like this amp, it plays about as detailed as my bigger amps.
Vey unfortunate day today..got one bad 13EM7; saw sparks inside tube and some smoke out from tube only.
I noticed it quickly and turned off the amp within 20 seconds..do I need to change any resistors and capacitors now? Got new tubes and amp sounds fine but hum has gotten a bit louder from that channel. R10 looks bit weird. It has kinda grey shade allover the green body now. C7's shiny metal part now has a bump and is not flat like it used to be like C8. I don't know if they were like that since assembly. Should I also change other resistors and capacitors as well??
I noticed it quickly and turned off the amp within 20 seconds..do I need to change any resistors and capacitors now? Got new tubes and amp sounds fine but hum has gotten a bit louder from that channel. R10 looks bit weird. It has kinda grey shade allover the green body now. C7's shiny metal part now has a bump and is not flat like it used to be like C8. I don't know if they were like that since assembly. Should I also change other resistors and capacitors as well??
Sounds like a plate-to-cathode short in VT2A...
The resistor is probably OK - you can verify with an ohmeter that the resistance has not changed significantly (make sure you wait until it's been powered off for a while). If the cap has a bulge, you should replace it... it may fail (sometimes spectacularly) at any time.
If the hum got louder, that may mean that the cap is leaking a lot of current, and if so it'll get hot and fail sooner or later.
Other parts are probably OK. If there were damage to something else (like the OPT) you'd probably hear it, and if there were damage in the power supply I think you'd be blowing fuses.
Pete
I'm not sure what to tell you guys with hum issues. I may not be as sensitive to the hum as others, but on reasonably efficient (~90-92dB) desktop speakers about 2 feet from my head, I hear no hum. Also not noticeable in AKG 701's or HD600s. With Grados I have to be in a quiet room to hear any hum.
I did some experiments when prototyping that showed a lot of magnetic coupling between the power transformer and OPTs. That's why I had Edcor put a flux band on the power transformer. Basically, I moved the transformers apart until I found the hum level acceptable, and that's how wide I made the chassis.
If the hum is constant, with the inputs shorted, and is also present with the volume control all the way down... the issue is most likely magnetic coupling. There is also a little bit of hum from B+ ripple, but it is not as significant (at least in my case).
Assuming that the issue is magnetic coupling (flux leakage from the power transformer), there are a couple of things that might make things worse than what I experience. If the line voltage is high (mine is 120V), the transformer will leak more flux. Same likely is true at 50Hz. The transformer looks a little small for the power output, so I do wonder if Edcor cut it a little tight, and the transformer is close to saturation. That makes it leak a lot of flux.
If any of you have access to a variac, try dropping the line voltage 20% or so, and see if the hum decreases.
Another thing to try is to rig in more B+ filter capacitance (parallel in more capacitance across C9/C10) to see if that makes a difference.
Pete
I did some experiments when prototyping that showed a lot of magnetic coupling between the power transformer and OPTs. That's why I had Edcor put a flux band on the power transformer. Basically, I moved the transformers apart until I found the hum level acceptable, and that's how wide I made the chassis.
If the hum is constant, with the inputs shorted, and is also present with the volume control all the way down... the issue is most likely magnetic coupling. There is also a little bit of hum from B+ ripple, but it is not as significant (at least in my case).
Assuming that the issue is magnetic coupling (flux leakage from the power transformer), there are a couple of things that might make things worse than what I experience. If the line voltage is high (mine is 120V), the transformer will leak more flux. Same likely is true at 50Hz. The transformer looks a little small for the power output, so I do wonder if Edcor cut it a little tight, and the transformer is close to saturation. That makes it leak a lot of flux.
If any of you have access to a variac, try dropping the line voltage 20% or so, and see if the hum decreases.
Another thing to try is to rig in more B+ filter capacitance (parallel in more capacitance across C9/C10) to see if that makes a difference.
Pete
You are correct, it should end in "KF" not "DA", like the Mouser part number (which is correct). Sorry about that...
Pete
finished my build
I decided i wanted to build an amp and after reading lots of threads here i settled on the jonokuchi to cut my teeth on. I liked the large PCB and the option that it could drive headphones or small speakers. Mr. Millett's design is very straightforward to build and other than me not paying close enough attention to the drilling pattern (i got the back panel swapped left/right) the build was quite simple. I added the 'hum' modification as shown on his web site but there is still a small amount of hum. Even with that the overall sound is quite good (currently driving with an hand me down classic ipod and using Sennheiser HD650's). Thanks Mr. Millett for answering the few questions I had. The only real modifications I made were to add Walnut panels on the ends and spray the Hammond chassis with Rustoleum Hammered Metal finish paint.
I decided i wanted to build an amp and after reading lots of threads here i settled on the jonokuchi to cut my teeth on. I liked the large PCB and the option that it could drive headphones or small speakers. Mr. Millett's design is very straightforward to build and other than me not paying close enough attention to the drilling pattern (i got the back panel swapped left/right) the build was quite simple. I added the 'hum' modification as shown on his web site but there is still a small amount of hum. Even with that the overall sound is quite good (currently driving with an hand me down classic ipod and using Sennheiser HD650's). Thanks Mr. Millett for answering the few questions I had. The only real modifications I made were to add Walnut panels on the ends and spray the Hammond chassis with Rustoleum Hammered Metal finish paint.
Attachments
Pete and others,
Just read thru' the thread and looked at the schematics etc.
It seems that some have had minor hum problems, so I ask, "Why no cap across R3?" (the bottom resistor [47K] of the heater DC elevation divider). A 10uF 63V electrolytic would help I would think, by holding the heater centre tap at AC ground.
Cheers,
Ian
Just read thru' the thread and looked at the schematics etc.
It seems that some have had minor hum problems, so I ask, "Why no cap across R3?" (the bottom resistor [47K] of the heater DC elevation divider). A 10uF 63V electrolytic would help I would think, by holding the heater centre tap at AC ground.
Cheers,
Ian
Hi,
I was tempted to try my first tube amp, following a couple of gainclones and an O2 headphone amp. But I am a bit "terrified" by the possible dangerous high voltage of tube amps (I understood more than 300V in case of Jonokuchi).
Is this a simple and reasonable safe project?
Thank you
northernsky
I was tempted to try my first tube amp, following a couple of gainclones and an O2 headphone amp. But I am a bit "terrified" by the possible dangerous high voltage of tube amps (I understood more than 300V in case of Jonokuchi).
Is this a simple and reasonable safe project?
Thank you
northernsky
not bad , I love that tube. But I think making a point to point kit would be more educational as I've seen that people struggle with tube construction techniques and I have used "the spud design" before (about 30 years ago) as a lab exercise. The low parts count makes it an excellent choice for beginner point to point.
Jonokuchi is a sutible name for something that has Edcor transformers and built on a pc board.
Jonokuchi is a sutible name for something that has Edcor transformers and built on a pc board.
I enjoy the heck out of mine. It's mostly used in a nearfield setup in my office but does occasional duty as a headphone amp as well. I did some slight tweaks to Pete's design in that I changed one of the front panel switches to switch two inputs on the back instead of a mini jack on the front. I also customized the front panel a bit and eliminated the 1/8" headphone output among other things. Since these images were taken I've replaced the stock power trafo with a shielded unit from SumR. I think it helped a little with the hum but I haven't added the resistors (yet?) and probably won't. It does what I need it to do well enough.
First Tube Amplifier Build
I've been reading all the feedback about the JONOKUCHI - 13EM7 desktop amp and I'm thinking about taking the plunge - Hopefully I won't experience much "Hum" or someone will find a fix for the problem by the time I have completed this project.
Has anyone replaced any of the parts from the BOM with better quality ones ?(if possible)
for instance replacements for the first two parts C5, C6
0.1uF 630V coupling cap Wima MKP4-0.1/630/5PCM15
(Metallized Polypropylene)
would Mojotone Dijon Coupling Capacitors (polypropylene film and foil), rated 0.1µF to a maximum of 630 volts be a better upgrade ?
I've been reading all the feedback about the JONOKUCHI - 13EM7 desktop amp and I'm thinking about taking the plunge - Hopefully I won't experience much "Hum" or someone will find a fix for the problem by the time I have completed this project.
Has anyone replaced any of the parts from the BOM with better quality ones ?(if possible)
for instance replacements for the first two parts C5, C6
0.1uF 630V coupling cap Wima MKP4-0.1/630/5PCM15
(Metallized Polypropylene)
would Mojotone Dijon Coupling Capacitors (polypropylene film and foil), rated 0.1µF to a maximum of 630 volts be a better upgrade ?
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