Thanks! Those are thoriated tungsten filaments, seen on transmitting tubes.
L0rdGwyn's DIY Audio
- Thread starter L0rdGwyn
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Thanks! Those are thoriated tungsten filaments, seen on transmitting tubes.
raindownthunda
500+ Head-Fier
What a beast! You’ve become a true artisan. Probably my favorite head-fi thread. Reading about your vision/aspirations for each build and then following the execution at such a high level is tremendously fun. Hope you have some nice days/evenings ahead to enjoy the fruits of your labor!Well, the HY69 amp is done. Here's the circuit.
Closed up.
Top without tubes.
And the finished amplifier chassis, and next to the AVC chassis.
Set up on the desk.
Only had around a half our or so with it, but it sounds amazing. However, as I expected, there is a low level hum audible on the higher impedance settings. I'll have to decide if and how far I'd like to pursue improving it, it's possible it may not be able to be gotten rid of entirely, a consequence of mixing directly heated tubes (high noise circuitry) with interstage transformer coupling (high sensitivity). I might just let it be great but flawed, as anything to lower the noise would require significantly altering the aesthetics of the amp (i.e., shielding the transformers).
Regardless, I'm very happy with the sound and the aesthetics. Off to do some yoga, then more listening tonight!
whirlwind
Headphoneus Supremus
Well, the HY69 amp is done. Here's the circuit.
Closed up.
Top without tubes.
And the finished amplifier chassis, and next to the AVC chassis.
Set up on the desk.
Only had around a half our or so with it, but it sounds amazing. However, as I expected, there is a low level hum audible on the higher impedance settings. I'll have to decide if and how far I'd like to pursue improving it, it's possible it may not be able to be gotten rid of entirely, a consequence of mixing directly heated tubes (high noise circuitry) with interstage transformer coupling (high sensitivity). I might just let it be great but flawed, as anything to lower the noise would require significantly altering the aesthetics of the amp (i.e., shielding the transformers).
Regardless, I'm very happy with the sound and the aesthetics. Off to do some yoga, then more listening tonight!
Killer Keenan!
Love the glow on those tungsten HY69's....best glow ever
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Well, the HY69 amp is done. Here's the circuit.
Closed up.
Top without tubes.
And the finished amplifier chassis, and next to the AVC chassis.
Set up on the desk.
Only had around a half our or so with it, but it sounds amazing. However, as I expected, there is a low level hum audible on the higher impedance settings. I'll have to decide if and how far I'd like to pursue improving it, it's possible it may not be able to be gotten rid of entirely, a consequence of mixing directly heated tubes (high noise circuitry) with interstage transformer coupling (high sensitivity). I might just let it be great but flawed, as anything to lower the noise would require significantly altering the aesthetics of the amp (i.e., shielding the transformers).
Regardless, I'm very happy with the sound and the aesthetics. Off to do some yoga, then more listening tonight!
That looks fantastic. I really like the different color and texture on the top plate. I wish I had thought to do that on my Aegis enclosure.
Killer Keenan!
Love the glow on those tungsten HY69's....best glow ever
Thanks guys! I appreciate it. The amp does need some work though, realistically I will need to correct that hum, it will eventually drive me crazy. Just took some measurements, bandwidth, distortion, and output impedance measurements are great. The D3a may be oscillating however, so will need to make some adjustments there as well.
It ain't ready until it's ready.
But it looks good.
But it looks good.
After spending more time with the HY69 amp, I am loving the sound. It is clear, airy, has incredible clarity and pinpoint imaging while not compromising on weight / heft.
In terms of the measured results, FR is down 1dB at 20Hz and 0.5dB at 20kHz, which is excellent.
Distortion is vanishingly low. On the 16ohm and 75ohm taps at 1mW, the harmonics are actually below some of the artifacts generated by my soundcard, so I cannot accurately measure the distortion, which is a first. I believe I measured 0.014% THD at 1mW into 300ohm on the 300ohm tap.
As for output impedance, it is 4ohms on the 16ohm tap, 13ohms on the 75ohm tap, and 55ohms on the 300ohm tap.
So I'm very happy with the measured results. Since this is my end game amplifier, it is worth getting right and I feel the noise floor needs to be improved. In the short term I'm shielding the transformers, but likely I am going to replace the EI core mains transformers with shielded toroids, which have a much lower radiated magnetic field. I am in discussion to have some custom transformers wound by Toroidy in Poland.
I did some additional work on the 2A3 amplifier today, nothing interesting just fine tuning some parts values. As such I was listening back and forth and swapping the AVC in between the two amplifiers. The difference the AVC makes is substantial, it is an improvement over a resistive potentiometer in just about every way - improved clarity, bigger staging, more precise imaging, and simply more presence of the music. Most resistive pots sound the same to me, but this is night and day. I'm very glad I decided to use one for the HY69 amp, I highly recommend it. I'll be bringing the AVC along when I drop off the 2A3 amp to Zach and see if it's something he'd be interested in down the road.
In terms of the measured results, FR is down 1dB at 20Hz and 0.5dB at 20kHz, which is excellent.
Distortion is vanishingly low. On the 16ohm and 75ohm taps at 1mW, the harmonics are actually below some of the artifacts generated by my soundcard, so I cannot accurately measure the distortion, which is a first. I believe I measured 0.014% THD at 1mW into 300ohm on the 300ohm tap.
As for output impedance, it is 4ohms on the 16ohm tap, 13ohms on the 75ohm tap, and 55ohms on the 300ohm tap.
So I'm very happy with the measured results. Since this is my end game amplifier, it is worth getting right and I feel the noise floor needs to be improved. In the short term I'm shielding the transformers, but likely I am going to replace the EI core mains transformers with shielded toroids, which have a much lower radiated magnetic field. I am in discussion to have some custom transformers wound by Toroidy in Poland.
I did some additional work on the 2A3 amplifier today, nothing interesting just fine tuning some parts values. As such I was listening back and forth and swapping the AVC in between the two amplifiers. The difference the AVC makes is substantial, it is an improvement over a resistive potentiometer in just about every way - improved clarity, bigger staging, more precise imaging, and simply more presence of the music. Most resistive pots sound the same to me, but this is night and day. I'm very glad I decided to use one for the HY69 amp, I highly recommend it. I'll be bringing the AVC along when I drop off the 2A3 amp to Zach and see if it's something he'd be interested in down the road.
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pravous
100+ Head-Fier
The avc pot is an intriguing idea. It seems like you could make one of these, set your existing potentiometers to max and use it for volume control for any amp you own? Is the the pot on the avc a wiper or a stepped pot that goes to individual windings on the transformer?
Yeah you could build one and use it with any amplifier, just turn the volume to max on the existing pot. It has to go on a stepped switch. Dave offers various options, the version I bought from him came already loaded on a 47-step attenuator made for him by Elma. They are a little over $1K. Or you can do silver wire for closer to $3K :O
Cleaning some records and getting in some listening time with the VC between cleans. While there are some tweaks coming for this design to perfect it, it's lovely to listen to as is. I threw some shields over the filament transformers to lower the noise floor as the VC is probably the most sensitive high impedance headphone in my stable.
And the outcome was...?
It's a significant improvement, but not quite where I want it to be. I have a shield on the way for the B+/heater transformer as well, but I view the shields as a stopgap. I feel confident I'm going to replace the mains transformers. They simply have too much leakage flux for a circuit that has a transformer on the output tube's cathode and grid, making it highly susceptible to noise pickup. Part of that is they are EI core, but the quality also leaves something to be desired, they're not on par with the likes of Sowter, which likely would have gotten me a better result. In retrospect, I should have made other plans when I got the heebie jeebies about the transformers, but excitement propelled me forward.
So, as of right now what I'm planning to do is replace them with toroidals made by Toroidy in Poland. They make a line of audio grade toroidals that are double insulated (magnetic shielding on the interior and potted in a steel shield), and talk a big game of their toroids being "silent" with minimized leakage. Given their symmetrical nature, toroids have significantly lower leakage flux relative to an EI core transformer. This gives me the opportunity to make some other minor changes that I think would be of benefit, namely giving each D3a its own heater winding, which will help prevent unwanted oscillations.
That's the plan, waiting to hear back on a quote from Toroidy. In the meantime, the shields lower the noise floor to an unnoticeable level on the high impedance setting, and the good news is the circuit works as intended and sounds great. It's a lot more work, time, and money to do the transformer swap, but for this build I think I need to pursue perfection, it's very close!
Toroids are often very ugly to put on an amplifier, but Toroidy offers them in these polished steel shields, seen below. I think they will actually gel well with the rest of the amplifiers aesthetics. I might need to do another pass of polishing on those brass end bells.
Right now I'm listening to another compatible input tube, the E810F, another high gm pentode with excellent linearity as a triode, very nice sounding tubes and a great alternative to the D3a which is getting very pricey.
I rented a storage unit earlier this week and put a large majority of my tubes and spare transformers in it, they were taking up too much space! Tonight I wanted to try the 6E6P in this circuit, which is also compatible as an input, and for the first time went down the basement and realized they were in the storage unit -_- it won't be the last time.
I rented a storage unit earlier this week and put a large majority of my tubes and spare transformers in it, they were taking up too much space! Tonight I wanted to try the 6E6P in this circuit, which is also compatible as an input, and for the first time went down the basement and realized they were in the storage unit -_- it won't be the last time.
I have mine around me and sometimes I can't find them anyway.....anywhere.
It is a challenge to keep them organized. Honestly it's a bit of a relief to get them out of the house. Eventually I need to sell some off, ones that I am unlikely to use again. For example, I have a huge stash of 841 triodes, including some very rare globes...
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