A New SS II HPA: The glow of dark blue tubes
Hi folks,
I finally got around to ordering and building the latest Starving Student 2 HPA. First and foremost, a big thanks to Pete Millett for designing what is a very easy and fantastic sounding HPA (or preamp)! Also a big thanks on a really intuitive and easy to follow kit. I've put a couple of kits together for DIYAudio and can very much appreciate the attention to detail and effort in how this was put together. Thanks again 6L6 for another fantastic and easy to follow build guide as well. I am either getting really good at this, or Jim's guides (or both) because this kit worked the first time I turned it on.
Onto the kit, as you can see from the attached pictures, I built the stock kit without any modifications at first. This is very much a best practice for any newbies reading this. After getting it together I gave it a thorough listen using my AKG-712Pros which I've measured to around 61-62 Ohm. The tube-effect was immediately apparent. Sweet mids/highs with a very good bottom end due to the current drive from the MOSFETs. There seems to be no issue driving the AKGs with this setup. I've also used this as a preamp to drive my stock ACA 1.8s and the result was immediately pleasing even at high volumes. I've been told this is a nice preamp to drive an F4 too, which is planned for my end of December break!
I've tried the amp setup in both R and CSS modes and have come to the conclusion I prefer the CSS mode. At very low volume levels I did not detect much difference, but at higher volume levels the bass seems to roll off a bit, but I have not measured this. This is a really cool feature BTW, since previously all tube amps/preamps I've played with and listened to had only the R option. I will measure the differences later this month after I get my QuantAsylum setup working and will report back.
A few things I noticed with the stock setup. As you can see, I am running this through a custom 24vdc linear PSU based on the Sigma 22 that drives a SMSL USB DAC I've used for a dozen other projects as a stable reference point. I use Tidal master-quality as a source on the same set of tracks I use for testing (listed in the Whammy thread).
I noticed the Raytheon tubes that come with the kit were a bit microphonic. I could run my finger along the case and could clearly hear it in the headphones, as well as other induced sounds. I also noticed a high frequency "hiss". To address the microphonic issue, 6L6 recommended I try the rubber/silicone o-rings as well as the metal cans. The orings I ordered turned out to be a little too big, but I had the metal cans with springs inside too so I used those. These helped a bit but I still need to try rubber isolators on the board mounting points.
To address the high frequency hiss, I employed Mark's SMPS P089ZB filter. I've gone through extensive measurement previously on this with Mark's help as I wanted to measure how this worked before I put the kit together. It really does what it says on the tin assuming the SMPS's switching frequency is around the center Mark built this for. I put together a new one and put it into a box as shown in the pictures (the little black box). This completely eliminated the high frequency issues with the SMPS that comes with the kit, so I highly recommend its use if your DC power source is an SMPS like the stock kit comes with.
I also ordered a set of Zenith 18FX6s (the stock ones are Raytheon 18FX6As). The only differences I found were in the microphonic department, which are far less than the Raytheon tubes that came with the kit. Note that some tubes seem to be microphonic (including brand new stock like JJs) while others of the same make/model/type are not. Its seems to be a manufacturing variation, so its a trial/measure/error thing and why some tube sellers charge a little more to test for this. There seems to be no rhyme or reason in my experience as this even applies to brand new NuTubes. In any event, the stock Raytheons are fine sounding absent the microphonics.
Get soldering and enjoy!
Cheers,
--Tom
Hi folks,
I finally got around to ordering and building the latest Starving Student 2 HPA. First and foremost, a big thanks to Pete Millett for designing what is a very easy and fantastic sounding HPA (or preamp)! Also a big thanks on a really intuitive and easy to follow kit. I've put a couple of kits together for DIYAudio and can very much appreciate the attention to detail and effort in how this was put together. Thanks again 6L6 for another fantastic and easy to follow build guide as well. I am either getting really good at this, or Jim's guides (or both) because this kit worked the first time I turned it on.
Onto the kit, as you can see from the attached pictures, I built the stock kit without any modifications at first. This is very much a best practice for any newbies reading this. After getting it together I gave it a thorough listen using my AKG-712Pros which I've measured to around 61-62 Ohm. The tube-effect was immediately apparent. Sweet mids/highs with a very good bottom end due to the current drive from the MOSFETs. There seems to be no issue driving the AKGs with this setup. I've also used this as a preamp to drive my stock ACA 1.8s and the result was immediately pleasing even at high volumes. I've been told this is a nice preamp to drive an F4 too, which is planned for my end of December break!
I've tried the amp setup in both R and CSS modes and have come to the conclusion I prefer the CSS mode. At very low volume levels I did not detect much difference, but at higher volume levels the bass seems to roll off a bit, but I have not measured this. This is a really cool feature BTW, since previously all tube amps/preamps I've played with and listened to had only the R option. I will measure the differences later this month after I get my QuantAsylum setup working and will report back.
A few things I noticed with the stock setup. As you can see, I am running this through a custom 24vdc linear PSU based on the Sigma 22 that drives a SMSL USB DAC I've used for a dozen other projects as a stable reference point. I use Tidal master-quality as a source on the same set of tracks I use for testing (listed in the Whammy thread).
I noticed the Raytheon tubes that come with the kit were a bit microphonic. I could run my finger along the case and could clearly hear it in the headphones, as well as other induced sounds. I also noticed a high frequency "hiss". To address the microphonic issue, 6L6 recommended I try the rubber/silicone o-rings as well as the metal cans. The orings I ordered turned out to be a little too big, but I had the metal cans with springs inside too so I used those. These helped a bit but I still need to try rubber isolators on the board mounting points.
To address the high frequency hiss, I employed Mark's SMPS P089ZB filter. I've gone through extensive measurement previously on this with Mark's help as I wanted to measure how this worked before I put the kit together. It really does what it says on the tin assuming the SMPS's switching frequency is around the center Mark built this for. I put together a new one and put it into a box as shown in the pictures (the little black box). This completely eliminated the high frequency issues with the SMPS that comes with the kit, so I highly recommend its use if your DC power source is an SMPS like the stock kit comes with.
I also ordered a set of Zenith 18FX6s (the stock ones are Raytheon 18FX6As). The only differences I found were in the microphonic department, which are far less than the Raytheon tubes that came with the kit. Note that some tubes seem to be microphonic (including brand new stock like JJs) while others of the same make/model/type are not. Its seems to be a manufacturing variation, so its a trial/measure/error thing and why some tube sellers charge a little more to test for this. There seems to be no rhyme or reason in my experience as this even applies to brand new NuTubes. In any event, the stock Raytheons are fine sounding absent the microphonics.
Get soldering and enjoy!
Cheers,
--Tom
Attachments
Hi, I misread the instructions/photos and mounted the pushbutton power switch on the wrong side of the board. I was able to get it desoldered, but the heat damaged the part in the process. The DIY store shows the part as an E-switch P227EE1CXC. None of the vendors I would normally use have this in stock. Is there an alternative part number I can use? Thanks Brad in NM
I have some spares... PM or email me your address and I'll send one. Gotta be in the next day though as I will be out of town for a while...
Pete
I had the same issue, and nothing seemed to help. I've tried Sylvanias, RCAs, and GEs, though, and they all sound just as good without the microphonics. I haven't had time (or motivation) to compare them. I've seen mention of TungSols, which I'd love to hear, but have not found a pair I cared to buy. (I seem to remember seeing a really worn out single, but may be misremembering.)
If you set up a search on EBay for 18FX6s, you'll eventually turn up a few pairs of these others. They turn up from time to time.
I built two because it was fun to build and then it was easy to compare CCS vs Anode resistor.
I use the amp as preamp in my system.
I have no protective earth in my living room and that caused the amp to be a bit hum sensitive. The tubes picked up some hum from the environment. A hand close to the tube could really provoke this. In CCS mode it was much more sensitive than in "Anode resistor" mode. But the shields I mounted around the tubes (Yamamoto) removed the issue completely. Then it also looks good, I think.
I found the Raytheon tubes more sensitive than e.g., GE-tubes. I have collected various 18FX6 tubes. I can see prices has raised a bit on ebay and there are not as many than when SSII was just released.
I use "Anode resistor" mode in my system. Also, because this gives a bit less gain and I don't need much gain in my system (in fact I could use a bit less).
I wonder if it is possible to reduce the gain in the amp a bit?
Another issue I ran into was that one of the SMPS caused a "hissing" noise from the tubes itself (kind of mechanical noise). As it was only one of the SMPS that caused it I judged it to be defective. I upgraded the SMPS with a 48V Meanwell brick type that was medical approved etc. Then I cut the wire of the defective SMPS as I needed the connector and then I made a converter as the Meanwell used the well-known 4 pin type. I think it was a nice upgrade. It is playing very well in my system.
I use the amp as preamp in my system.
I have no protective earth in my living room and that caused the amp to be a bit hum sensitive. The tubes picked up some hum from the environment. A hand close to the tube could really provoke this. In CCS mode it was much more sensitive than in "Anode resistor" mode. But the shields I mounted around the tubes (Yamamoto) removed the issue completely. Then it also looks good, I think.
I found the Raytheon tubes more sensitive than e.g., GE-tubes. I have collected various 18FX6 tubes. I can see prices has raised a bit on ebay and there are not as many than when SSII was just released.
I use "Anode resistor" mode in my system. Also, because this gives a bit less gain and I don't need much gain in my system (in fact I could use a bit less).
I wonder if it is possible to reduce the gain in the amp a bit?
Another issue I ran into was that one of the SMPS caused a "hissing" noise from the tubes itself (kind of mechanical noise). As it was only one of the SMPS that caused it I judged it to be defective. I upgraded the SMPS with a 48V Meanwell brick type that was medical approved etc. Then I cut the wire of the defective SMPS as I needed the connector and then I made a converter as the Meanwell used the well-known 4 pin type. I think it was a nice upgrade. It is playing very well in my system.
I'm hoping someone can help me with a perplexing issue I've run into after having just built the SSII.
If I have the input RCA's plugged into my DAC when I power on the SSII, the DAC (Cambrige Audio DackMagic 200M) trips some sort of protection mode. After tripping into protect mode I can power down the DAC, then power it back up, it comes back up fine. In an attempt to "isolate" the problem, I put the Amp Camp Preamp in between the DAC and the SSII, however the problem remains, even if the ACP+ is powered down when I power up the SSII.
If I use my phone as the source (USB-C to RCA) for the SSII, there's no issue powering up the SSII. Any thoughts on what might be going on here?
Here’s another interesting piece of information. If I turn the DAC to an input that is not the computer USB input and power on the DAC, the entire computer shuts down instantly (some sort of protect mode). That means whatever “spike” is occurring, it is able to go through the RCA, through the ACP+ into the DAC, out the USB and into the back of my computer.
Additional info:
-Tried with headphone plugged in or unplugged, same result.
-If SSII is unplugged from power, power switch being pushed on has no effect (as expected and just wanted to isolate the switch).
-If the SSII is unplugged with power button on, then I push the power plug into the back, my whole computer instantly shuts down (DAC set to USB in from computer).
I put a multimeter across the RCA plug and cycled the power a few times with various voltage settings and saw no spike at all (reads 0.000 VDC), so whatever is happening is either really fast, or needs the connection to the output RCA’s on the DAC to pull current.
On the plus side, as long as I power up the SSII, then plug in the RCA inputs, it works just fine and sounds wonderful! It would be nice to know what’s going on.
If I have the input RCA's plugged into my DAC when I power on the SSII, the DAC (Cambrige Audio DackMagic 200M) trips some sort of protection mode. After tripping into protect mode I can power down the DAC, then power it back up, it comes back up fine. In an attempt to "isolate" the problem, I put the Amp Camp Preamp in between the DAC and the SSII, however the problem remains, even if the ACP+ is powered down when I power up the SSII.
If I use my phone as the source (USB-C to RCA) for the SSII, there's no issue powering up the SSII. Any thoughts on what might be going on here?
Here’s another interesting piece of information. If I turn the DAC to an input that is not the computer USB input and power on the DAC, the entire computer shuts down instantly (some sort of protect mode). That means whatever “spike” is occurring, it is able to go through the RCA, through the ACP+ into the DAC, out the USB and into the back of my computer.
Additional info:
-Tried with headphone plugged in or unplugged, same result.
-If SSII is unplugged from power, power switch being pushed on has no effect (as expected and just wanted to isolate the switch).
-If the SSII is unplugged with power button on, then I push the power plug into the back, my whole computer instantly shuts down (DAC set to USB in from computer).
I put a multimeter across the RCA plug and cycled the power a few times with various voltage settings and saw no spike at all (reads 0.000 VDC), so whatever is happening is either really fast, or needs the connection to the output RCA’s on the DAC to pull current.
On the plus side, as long as I power up the SSII, then plug in the RCA inputs, it works just fine and sounds wonderful! It would be nice to know what’s going on.
Maybe it is a question to Cambridge what can trigger this?
It is not enough to put the DAC into Standby mode and back again to get it working?
I have also used SSII with 200M. The last thing I always do when everything is powered up is to push "Standby" on DAC to release it from "Standby mode".
When just powered up it is default in "Standby mode". If it gets no input for a while it will enter "Standby mode".
I use a 3rd party 12V PSU (linear) for my DAC.
The only strange thing I have noticed is when I switch from one MQA track to another MQA track (via a Bluesound streamer) then sometimes the DAC goes into a "deadlock mode" (LED indicating "speed" turns off (normally one LED is active by default)). Then I need to set it into Standby and back again and it plays again. This happens very rarely (via the optical connection from Bluesound). I have not yet had time to ask Cambridge about this issue.
It is not enough to put the DAC into Standby mode and back again to get it working?
I have also used SSII with 200M. The last thing I always do when everything is powered up is to push "Standby" on DAC to release it from "Standby mode".
When just powered up it is default in "Standby mode". If it gets no input for a while it will enter "Standby mode".
I use a 3rd party 12V PSU (linear) for my DAC.
The only strange thing I have noticed is when I switch from one MQA track to another MQA track (via a Bluesound streamer) then sometimes the DAC goes into a "deadlock mode" (LED indicating "speed" turns off (normally one LED is active by default)). Then I need to set it into Standby and back again and it plays again. This happens very rarely (via the optical connection from Bluesound). I have not yet had time to ask Cambridge about this issue.
My guess would be that this is related to a ground transient coming from the EMI filter on one of the pieces of equipment. Often EMI filters on switching power supplies without a ground connection - those with 2-wire cords - will put a very low current AC voltage on the negative side of the output voltage. This can cause all kinds of odd behavior.
This could be originating in either the computer, DAC, or amplifier. Suspect anything that does not have a 3-wire AC plug.
You can try connecting a ground wire between all of the units separate from the audio and USB cables. Or providing a ground connection to any equipment that does not have a 3-wire cord.
Pete
This could be originating in either the computer, DAC, or amplifier. Suspect anything that does not have a 3-wire AC plug.
You can try connecting a ground wire between all of the units separate from the audio and USB cables. Or providing a ground connection to any equipment that does not have a 3-wire cord.
Pete
Pete, thank you for your thoughts on what could be going on, you are likely correct with your theory. Armed with your suggestion about EMI filter, I started by switching to an optical input into the DAC from my computer (instead of USB) and now there's no issues at all. Although I don't have a full grasp on the details of why the computer USB to DAC connection is what's shutting down audio on SSII power up, that's clearly is the connection that when removed, resolves the issue.
MEPER, also thank you for your response. If it wasn't clear in my original post, the DAC wasn't going into standby mode. What I'd see, was a "blink" on the sample rate LED (ie. MQA, 44.1, 92, ...384) when I'd power up the SSII, but other than that, there's no visual cue that anything happened. Of course, there is a clear audio cue as it would no longer play music (over RCA out or headphone jack) until I cycle it off, then on again, or, as you'll see below, just unplug and plug back in the USB with the DAC remaining on.
A few additional "tests" I tried for awareness:
1) I tried a different DAC, Lavaudio DS601 and it also had the same issue of stopping audio when SSII is powered on and connected via RCA. There was no visual cue on the DAC that anything stopped, only the audio cue when music totally cuts out. Could the computer be stopping USB output? Perhaps that's why audio stops, so I tried a few other checks.
2) I used a different USB that has what looks like a choke on it and that did had no effect on resolving the issue. The audio still dropped audio as soon as SSII was powered on.
3) After tripping the audio to stop (by powering up the SSII), instead of cycling power on the DAC, I just unplugged the USB and plugged it back in, and audio comes back. I was trying to isolate if the "spike" was shutting down audio coming out of the computer via USB, or if the DAC was going into some sort of safe mode. I'm not sure this test gave me a definitive answer to that hypothesis, however, I think it does point to the computer shutting down audio output over USB, not the DAC(s) going into any sort of safe mode.
4) If I switch to optical via the software selection in windows after the audio cuts out, it plays fine over the optical connection (no need to cycle any power or plugs). When I try to switch back to USB (via software selections) it doesn't come back. So it sure seems that the computer is taking action to shut down the USB audio out when SSII power ups. This also makes sense since the entire computer shuts down if the DAC is powered off, or set to optical, when the SSII is powered up (which I am avoiding doing again for fear of damaging a computer component with repetative rapid shutdowns).
Conclusion: I think the computer itself stops putting out audio data on the USB when it gets the "spike" from the SSII being turned on. There's clearly plenty of optional work-arounds to avoid the issue, so it's not a big deal. If there are any other troubleshooting ideas (I could try a different computer), feel free to let me know and I'll give it a try. I'd also be curious if anyone else has had this issue when using computer--USB-->DAC--RCA-->SSII.
MEPER, also thank you for your response. If it wasn't clear in my original post, the DAC wasn't going into standby mode. What I'd see, was a "blink" on the sample rate LED (ie. MQA, 44.1, 92, ...384) when I'd power up the SSII, but other than that, there's no visual cue that anything happened. Of course, there is a clear audio cue as it would no longer play music (over RCA out or headphone jack) until I cycle it off, then on again, or, as you'll see below, just unplug and plug back in the USB with the DAC remaining on.
A few additional "tests" I tried for awareness:
1) I tried a different DAC, Lavaudio DS601 and it also had the same issue of stopping audio when SSII is powered on and connected via RCA. There was no visual cue on the DAC that anything stopped, only the audio cue when music totally cuts out. Could the computer be stopping USB output? Perhaps that's why audio stops, so I tried a few other checks.
2) I used a different USB that has what looks like a choke on it and that did had no effect on resolving the issue. The audio still dropped audio as soon as SSII was powered on.
3) After tripping the audio to stop (by powering up the SSII), instead of cycling power on the DAC, I just unplugged the USB and plugged it back in, and audio comes back. I was trying to isolate if the "spike" was shutting down audio coming out of the computer via USB, or if the DAC was going into some sort of safe mode. I'm not sure this test gave me a definitive answer to that hypothesis, however, I think it does point to the computer shutting down audio output over USB, not the DAC(s) going into any sort of safe mode.
4) If I switch to optical via the software selection in windows after the audio cuts out, it plays fine over the optical connection (no need to cycle any power or plugs). When I try to switch back to USB (via software selections) it doesn't come back. So it sure seems that the computer is taking action to shut down the USB audio out when SSII power ups. This also makes sense since the entire computer shuts down if the DAC is powered off, or set to optical, when the SSII is powered up (which I am avoiding doing again for fear of damaging a computer component with repetative rapid shutdowns).
Conclusion: I think the computer itself stops putting out audio data on the USB when it gets the "spike" from the SSII being turned on. There's clearly plenty of optional work-arounds to avoid the issue, so it's not a big deal. If there are any other troubleshooting ideas (I could try a different computer), feel free to let me know and I'll give it a try. I'd also be curious if anyone else has had this issue when using computer--USB-->DAC--RCA-->SSII.
I wonder if there are any available data when SSII is used as preamp so load is like 47k or so.
The spec. for SSII shows data for 150 ohm and 30 ohm load in CCS and resistor mode.
For me it could be interesting to know max. voltage swing in 47k load and how much distortion the amp has in such a configuration.
The spec. for SSII shows data for 150 ohm and 30 ohm load in CCS and resistor mode.
For me it could be interesting to know max. voltage swing in 47k load and how much distortion the amp has in such a configuration.
I experience a similar issue as birdbox.
Setup:
Surface Laptop Studio >MS Docking Station > USB > DAC (Cambridge Audio) > SSII
When powering on the SSII the docking station triggers a signal cycle of the attached displays.
Based on Peter's explanation I will probably as a first step try replacing the DAC's power supply to a different unit with a 3-wire AC plug.
Not so happy with the idea of separate ground cabling between the devices...
Setup:
Surface Laptop Studio >MS Docking Station > USB > DAC (Cambridge Audio) > SSII
When powering on the SSII the docking station triggers a signal cycle of the attached displays.
Based on Peter's explanation I will probably as a first step try replacing the DAC's power supply to a different unit with a 3-wire AC plug.
Not so happy with the idea of separate ground cabling between the devices...
This was a great and great sounding build! Lovely to be able to combine my two hobbies; woodworking and electronics. Thanks!
/Magnus
/Magnus
Attachments
If anyone's looking for tubes, I have a bunch for sale here:
https://www.diyaudio.com/community/threads/starving-student-tubes.403690/
Selling for what I paid.
Riki
https://www.diyaudio.com/community/threads/starving-student-tubes.403690/
Selling for what I paid.
Riki