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Starving Student II Headphone Amplifier
Starving Student II Headphone Amplifier
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Old 14th August 2020, 06:10 AM   #171
robotbill is offline robotbill
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Well, I ordered the kit last week and built it tonight. The smoke test passed, I got ~19 volts on both tube sockets, but unfortunately the cables I need to hook it up and really test it out are stuck in transit. Hopefully they'll arrive soon and I can enjoy the amp.
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Old 15th August 2020, 02:26 AM   #172
robotbill is offline robotbill
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Update: It's working now and sounds great!

I had missed soldering two relay pins initially. The advice about how you should hear a click a bit after powering the amp on in Starving Student II Headphone Amplifier was super helpful for me narrowing down my search for what was wrong.
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Old 19th August 2020, 01:43 PM   #173
olen is offline olen  United States
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Starving Student II Headphone Amplifier
Quote:
Originally Posted by CrowDaddy View Post
Hello Pete ( or anyone) ...
What is the input impedance of the SS II ?
Need it to choose output caps for my phono stage.
Thanks!
Hi, the schematic shows a 50k pot in parallel with the 221k grid resistor. When the volume is at the max position the input impedance is 50k, when it’s at the minimum position it’s 40.7k (50k || 221k). For sizing your cap use the lower number.I hope this helps.
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Old 20th August 2020, 02:45 AM   #174
rikiheck is offline rikiheck
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Just finished building one of these, and it sounds terrific! Thanks to Pete for the design and to the folks at DIY Audio Store for the kit.


That said, at least with Grado SR-60s (I have not yet tried my Focal Elears), there is WAY more gain than I need. If I turn the volume knob just 45 degrees, it's already plenty loud. Is there a simple way (replacing some resistors, e.g.) to decrease the gain?
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Pronouns: they, them, etc • System: DIY Turntable, Graham 2.2, Grado Statement Master, XP15 & XP20, Schiit Yggdrasil, Logitech Transporter, Aleph 2s or VTL MB-185s, Dynaudio Contour 60s, Gotham Audio Cables • DIY Builds: Whammy, SS II, Balanced B1
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Old 20th August 2020, 03:18 AM   #175
rikiheck is offline rikiheck
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Quote:
Originally Posted by SuppersReady View Post
This will be my second iteration of the SSII. The first was a DIY store kit. This version will use Dale resistors, Panasonic FC caps and a stepped attenuated. I've been enjoying the standard version for several months now and was curious to see what impact these changes would have.
Any news on that?

I have been thinking about upgrading the pot, etc, as well. Is there an easy way to tell what pins are doing what? I guess maybe reverse engineer it from the pot specs?
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Pronouns: they, them, etc • System: DIY Turntable, Graham 2.2, Grado Statement Master, XP15 & XP20, Schiit Yggdrasil, Logitech Transporter, Aleph 2s or VTL MB-185s, Dynaudio Contour 60s, Gotham Audio Cables • DIY Builds: Whammy, SS II, Balanced B1
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Old 20th August 2020, 05:31 PM   #176
pmillett is offline pmillett  United States
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Quote:
Originally Posted by rikiheck View Post
Just finished building one of these, and it sounds terrific! Thanks to Pete for the design and to the folks at DIY Audio Store for the kit.


That said, at least with Grado SR-60s (I have not yet tried my Focal Elears), there is WAY more gain than I need. If I turn the volume knob just 45 degrees, it's already plenty loud. Is there a simple way (replacing some resistors, e.g.) to decrease the gain?
There's no easy way to lower the gain. You can attenuate the input - you could insert a resistor between the input jack and the volume control. 50k would drop it 6dB. You can also attenuate between the tube and output buffer by putting a resistor in series with the coupling caps (C4 and C7) - 100k would also get you 6dB.

Pete
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Old 20th August 2020, 05:58 PM   #177
rikiheck is offline rikiheck
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Thanks for the info. I'll see how it is with the other phones and update if I try one of these options.
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Pronouns: they, them, etc • System: DIY Turntable, Graham 2.2, Grado Statement Master, XP15 & XP20, Schiit Yggdrasil, Logitech Transporter, Aleph 2s or VTL MB-185s, Dynaudio Contour 60s, Gotham Audio Cables • DIY Builds: Whammy, SS II, Balanced B1
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Old 23rd August 2020, 08:38 AM   #178
rikiheck is offline rikiheck
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Quote:
Originally Posted by pmillett View Post
There's no easy way to lower the gain. You can attenuate the input - you could insert a resistor between the input jack and the volume control. 50k would drop it 6dB. You can also attenuate between the tube and output buffer by putting a resistor in series with the coupling caps (C4 and C7) - 100k would also get you 6dB.
Pete
So I have been puzzling a bit about how to do this, given that the board is already built, and given what the connectors are like.

Putting a resistor between the input and the pot looks complicated. There isn't anywhere sensible to do that, so far as I can see. I had been thinking about replacing the pot (stepped maybe) AND the jack AND the power switch (necessary if the pot gets replaced), but that is more than I want to do right now. Especially since I'm in the middle of building a case for the board as it is.

Putting a resistor after C4 and C7 looks easier. But that means (a) unsoldering (and replacing) the two caps (since they will then have tiny leads) and (b) somehow wedging the resistor into the circuit. I have thought about wiring the whole thing up to what would then be a "-6dB" switch, but I'm wondering if there isn't an easier option....

Would it be possible to use a shunt resistor off the input to C4 and C7? That would not require unsoldering anything but just wiring the input pads for the caps to ground, through two resistors. If so, what formula can I use to calculate attenuation from different resistor values? I'm thinking this must work like a voltage divider? Please excuse my limited knowledge of electronics. I'm trying to learn here, really!

I'm again thinking about a switch, in case different headphones do or don't want the attenuation. And something like 12dB might be better....
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Pronouns: they, them, etc • System: DIY Turntable, Graham 2.2, Grado Statement Master, XP15 & XP20, Schiit Yggdrasil, Logitech Transporter, Aleph 2s or VTL MB-185s, Dynaudio Contour 60s, Gotham Audio Cables • DIY Builds: Whammy, SS II, Balanced B1
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Old 23rd August 2020, 08:47 AM   #179
rikiheck is offline rikiheck
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Quote:
Originally Posted by pmillett View Post
There's no easy way to lower the gain. You can attenuate the input - you could insert a resistor between the input jack and the volume control. 50k would drop it 6dB. You can also attenuate between the tube and output buffer by putting a resistor in series with the coupling caps (C4 and C7) - 100k would also get you 6dB.
Pursuing a different line of inquiry....

I have been getting quite a lot of microphonics, which I've seen in other parts of the thread isn't expected. E.g., if I tap on the top plate (of my simple home-brewed case), or even tap on the headphone cable, I get ringing. It's not an issue when listening, as the external environment is quiet enough, but it makes me wonder if I've got too much gain for some other reason.

After assembly, I did the measurements suggested, and they were on the high side: Pin 3 to ground was 19.4V in one case and 19.53V in the other. Not way off, but high-ish, yes? Is there something else I should check? I measured every component before installing and measured the resistors again after installing (though some of them measured off, since there was a second path through ground for those).
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Pronouns: they, them, etc • System: DIY Turntable, Graham 2.2, Grado Statement Master, XP15 & XP20, Schiit Yggdrasil, Logitech Transporter, Aleph 2s or VTL MB-185s, Dynaudio Contour 60s, Gotham Audio Cables • DIY Builds: Whammy, SS II, Balanced B1
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Old 23rd August 2020, 11:41 PM   #180
CrowDaddy is offline CrowDaddy
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Default input impedance of SSII

Olen says :
Quote:
Originally Posted by olen View Post
Hi, the schematic shows a 50k pot in parallel with the 221k grid resistor. When the volume is at the max position the input impedance is 50k, when it’s at the minimum position it’s 40.7k (50k || 221k). For sizing your cap use the lower number.I hope this helps.
However, Pete says it's 10k, in a private message.

So ... ?
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