Dug my Yamamoto headphone amp and transferred it into the bedroom system a couple of days ago and was reminded once again for the main reason I dont use it a lot. My problem is with the volume control, or rather lack of.  I have used it with the Oppo PM1, PM3 and Audio Technica ATHW1000X phones over the weekend and at no time could I use it above 8.30 on the volume knob, most times below that. Getting to around 9 would blow my ear drums out.  I find this basic on/of control very frustrating, especially coming from the lovely, fine stepped control on my Violectric V200.
Question is, how difficult would it be to have some sort of resistor added to give me finer control and does such a thing effect the sound quality. I had my big Meier amp dialed back X manufacturer to better suit the AT and Grado phones I was using at the time and that worked fine although I didn't have a chance to hear it without the resistor fitted.
Being an empty vessel when it comes to technical questions I'm a little puzzled about the volume thing as the amp only puts out 300mW into 50ohm and at the time of release the defauly position at HeadFi was that it lacked power but I'm guessing here that output and gain (9.5db) are separate issues.
I've held onto the Yammy a long time and dont want to sell it but if I can't get this sorted it may find its self on TM.

HA-02 specifications Use vacuum tube: Only WE408A 2 tubes / Sircuit system: Single stage amplification, pentode connection, and non-feedback system / Maximum output :300mW (at the time of 50ohm load) of headphone terminals,240mW (at the time of 8-ohm load) of speaker terminals/ Frequency characteristic:30-21,000Hz (headphone terminal) 45-17,000Hz (speaker terminal) / Gain : Headphone output power 9.5dB (at the time of 50-ohm load) Speaker output power: 1.5dB (at time of 8-ohm load) / Remains noise: 100 microvolts of headphone output power 70 microvolts of speaker output power / Outside dimension: 150 (W) 325 (D) 125 (H) / Weight: 3.5kg




userweb.117.ne.jp/y-s/HA-02-new-e.html
 

Yes, it's more a question of (input/overall) sensitivity I think.

I believe the simplest way might be to fit a voltage divider (simply 2 Rs in ea ch), probably at the output (to maintain signal-to-noise) - I've heard Clarry (Schollum of 34 Audio) talk about this sort of common problem with audio gear. I would ship it to him, if it was me.

Other methods, might be to wire the pentode to 'quasi-triode' mode - this would lower gain but however also alter the sound character somewhat I'd expect.

Shame not to have this lovely piece not matching up & more usable.

DarkLantern blog - darklanternforowen.wordpress.com

Thanks for your reply Owen. I'll get in touch with Clarry in the next week or so. He did my Mapletree headphone amp a year or so back and tidied up a few things on it. Shame I went and sold it, still we all do things that we regret down the line.

I actually had a similar issue with a fender deluxe guitar amp that went from off to loud to REALLY LOUD in the space of 3 markings of the volume knob. Turned out it had a linear volume pot instead of the usual log pot, so changed that together with changing the input valves from 12ax7 to 12au7 (IIRC). Anyway might turn out to be a simple fix.

I'm wondering now if the volume isn't directly related to the source. I swapped the Yamamoto out last night for the Oppo HA-1 amp into the bedroom system and noted straight away a change in levels from using the same amp in my room, mainly with vinyl. Out in the man cave the Oppo was generally in high gain mode and around half volume, in the bedroom back to std gain and around quarter volume.
Also,at a guess I'd say that the Project Phono RS in the MC is out putting a little less level that the Dynavector P75 was in Dr T mode as well. Must give the Yamamoto a try with vinyl later and see where it ends up.

Lemme try understand what you are saying, cooksferry...
The Yamamoto has too high gain (in your Brm system), so you think that the Brm source is putting out high volts.

OK, try moving Yama to another system.

Q:
What is the Brm source device?

DarkLantern blog - darklanternforowen.wordpress.com

Hi Owen. The Yam amp usually lives out in the music room and the very few times I've used it has been via lp playback. I really noticed the volume issue in the bedroom using a Rega Saturn. I'm guessing the the disparity in output between the two sources could be to blame.

The Hana SL (0.5mV) + Project Phono RS (60dB gain) => 0.5V output.
Whereas the Saturn CDP will output around 2V - ie. 4 times.

So, unless you have a linestage to get the phono output up to "line-level", the phono source will be only around 25% of the CDP signal level.

However your Melody main amp I think has input sensitivity of around 0.38V (for full power), so will happily run from the ProJect Phono RS's 0.5V output.

DarkLantern blog - darklanternforowen.wordpress.com

Dynavector XX2 output 0.28mV, means I get the volume of the Melody occasionally around 11.00 a bit higher than I ever went with the P75/DV20XL.

anyone tried these.
www.rothwellaudioproducts.co.uk/html/attenuators.html
look like a simple way to cut back the gain.

Hi cooksferry - yes, these are the same in principle, a Voltage Divider as above, with the 2 Rs built inside RCA plugs (instead of soldered inside the amp).
The advantage is that they can be inserted or removed & could be used on other devices.
A disadvantage is that there is an additional mechanical socket connection.

DarkLantern blog - darklanternforowen.wordpress.com

Hi Cooksferry, I'd first examine the volume pot to see if it's a linear one or not, as guitardude mentioned. Volume controls generally have a logarithmic taper to suit the ear's perception of volume. You could also cut back the sensitivity with a small resistor divider network on the input rca's, as others have suggested. It sounds like the gain of the headphone amp is very high with the tube's pentode connection.

AMR-iFi R&D