[scootsit]

Quote:

Gidday lordearl, have you managed to pop a pair of the AD825s in the amp yet? The OPA627's also sound fine, though need more grunt from the power supply to work as well as the AD825s do even with the stock supply. Very open and sweet, they do seem to overload in the bass quite easily, not sure if that's anyone else's experience, would love to hear more feedback on that one. Cheers all

Sorry, I haven't been keeping up. I replaced the regulator with just a jumper. I really should have used a resistor and then decoupled the opamp with a large-ish cap. Anyway, it worked with a TS922 which is a CMOS based chip and doesn't really sound all that great (sibilant). But, it works and with a bit more tinkering, I should be able to do even better. The Millet Hybrid originally had a chip supplied by the same V+ as the tube, they were just separated by a 1k resistor with big decoupling caps to ground before and after said resistor, I'm thinking something like that should offer plenty of power to both the chip and the tubes. The 5V regulator likely does minimize drain on the batteries, so battery life is anyone's guess.
 
There are other super low power chips that work well as buffers. The OPA2835/2836 used in the pupDAC come to mind.

 

[sennsay]

This little amp continues to amaze me! I bought a new set of Sony MDR-1Rs a few weeks ago and they work such a treat with this amp that the Denons are now relegated to occasional use elsewhere, the Sony's leave them for dead as an overall musical experience and it's very easy to hear the difference! Even swapped around the output op-amps again to see if there might be an even better match with the Sony cans, nope! The AD825s still easily rule the roost, the OPA627s are definitely not suitable with this amp (they really need a higher voltage supply), the OPA2134 I find is still bland and flat - nice enough but emotionally uninspiring. I haven't found any of the OPA3825s yet, anything new now will have to be absolutely outstanding to remove the AD825s from their home
 I am going to purchase a couple more of these kits and find a supply of quality plastic film pots to replace the carbon units I'm currently using. The amp deserves it, being more than capable of showing minor changes in the system anywhere, the Black Gate caps and the Nichicon Muse output caps being very transparent, as are the AD825s. I really don't find the 1Mohm pots are needed, as the 500Kohm pots provide for a more subtle adjustment range, both the Denon AH-D1000 and Sony MDR-1R headphones are very efficient, though strangely, my UE IEMs will not work at all. I haven't tried them with the stock op-amps though.
 I believe the power supply diodes can be simply bypassed with small value caps for lower noise, but I will go and check this out and report back.

 

[sennsay]

Ok, well after nearly three years of listening to this great little amp with the AD825 op-amps on board, this morning I realised that I had never actually heard this amp with the original supplied PT2308 op-amp, having moved straight into the more expensive options. So I popped one in, gave it moments to get a bit of voltage flowing while I made a coffee and slid the cable plug on the end of the Sony MDR-1R headphones into the jack and selected the first CD of the Dave Matthews/Tim Reynolds Live at Radio City concert. iTunes with the MIDI output set at 24/96kHz. I'm genuinely surprised at the result and especially considering I'm running the output through a brand new op-amp. No grain, no sandy, sharp and edgy vocals - which is pretty standard for many new and cold electronic items - smooooth. Now, at this moment of writing, the first CD has been played all the way through, with not a trace of fatigue or a touch of edge and it sounds, well ..... like a good valve amp! A touch on the warm side of neutral, definitely not upper mid forward or bright. I say smooth, yet it's in no way dull ... unless you are used to bright and sharp hot sounding electronics/sources, in which case it will be likely lacking some spark for you. I imagine this op-amp will take little more to be run in, as it's signature has changed little in the last hour and more, there is plenty of transient details in the two guitars, each with their particular sonic signature, the vocals are expressive if a little lacking in sheer 3D space around them. This is something the AD825s do with aplomb and are also more detailed and open, with more sharply defined focus. They are also less forgiving of compressed and hot recordings, yet at the same time will give you an open window into what really is on the album. The PT2308 blurs those details somewhat, yet remains delightful to listen to for hours. 
 Popping on the latest from Muse, The 2nd Law, the worst excesses of compression and sharp vocals are smoothed over to leave the album easy to listen too, but loses some edge and impact at the same time, not really a bad thing, in this case. Going back to the 16bit/44.1 Integer setting on iTunes Midi and the sound moves back a bit from centre and becomes messy and sharper, not that nice really, losing focus and blurring detail, not the fault of the op-amp! Back to the 24/96 setting, a much cleaner and weightier version of Survival returns, the backing vocals of the choir are really quite good and easily discernible, if not to the more explicit and open degree of the AD825s. Actually, the PT2308 makes this highly compressed (mostly) album rather listenable, without the need to throw off the headphones and run away holding your ears
All credit to the Sony MDR-1Rs here too, they will not accentuate bright and edgy recordings unless they are truly horrible .... like the Franz Ferdinand album Tonight, crikey, Bro!  This album may well be more suited to the PT2308's soothing balance.
 All in all, so far, the PT2308 is quite a pleasant surprise, will make many of todays rather hotly recorded albums incredibly listenable and for some listeners at least, without them sounding dull. It's use would actually suit slightly brighter cans than the Sonys and in fact, on popping my Denon AH-D1000s on my head, there is a small lift in higher treble, though the soundstage compresses here too and vocals lose the open clarity of the Sonys. The PT2308 op-amp can easily show the differences between the headphones. 
Trying some female vocals, Emili Sande's Heaven, from Our Version Of Events, is punchy, clean and dynamic, and allowing the hot mids to be at least tolerable. Eva Cassidy's beautiful soaring vocals on Bridge Over Troubled Waters (Live At Blues Alley) is simply gorgeous, no edge here, the bass digs deep and the cymbals are explicit without being at all bright. Overall though, well balanced. This album is really very good with the PT2308, with a fine musical flow, it's easy to just sit back and listen to the whole set with no fatigue at all. 
 While it's true, I'm using $1000 worth of very fine silver Interconnect, MusicStreamer II+ DAC and Kimber Kable USB cable here, I believe they are really showing the true worth of this remarkable little amp. Also, I have the amp connected to a much higher capacity 12V sealed battery, which allows for an effortless dynamic flow. I am now able to have a genuine choice between the sheer detailed openness, speed and dynamism of the AD825s, or relax with the more liquid and slightly darker rendition (though equally as musical in many ways) of the PT2308 op-amp. 
 I have seen that there is a new version of this amp on Oatley's website, which looks like it has a higher voltage supply, I shall be investigating and building a couple of versions The price is significantly higher too, at a whopping $40AU No wurries. 
 
Sennsay.

 

[nofacemonster]

Ok, well after nearly three years of listening to this great little amp with the AD825 op-amps on board, this morning I realised that I had never actually heard this amp with the original supplied PT2308 op-amp, having moved straight into the more expensive options. So I popped one in, gave it moments to get a bit of voltage flowing while I made a coffee and slid the cable plug on the end of the Sony MDR-1R headphones into the jack and selected the first CD of the Dave Matthews/Tim Reynolds Live at Radio City concert. iTunes with the MIDI output set at 24/96kHz. I'm genuinely surprised at the result and especially considering I'm running the output through a brand new op-amp. No grain, no sandy, sharp and edgy vocals - which is pretty standard for many new and cold electronic items - smooooth. Now, at this moment of writing, the first CD has been played all the way through, with not a trace of fatigue or a touch of edge and it sounds, well ..... like a good valve amp! A touch on the warm side of neutral, definitely not upper mid forward or bright. I say smooth, yet it's in no way dull ... unless you are used to bright and sharp hot sounding electronics/sources, in which case it will be likely lacking some spark for you. I imagine this op-amp will take little more to be run in, as it's signature has changed little in the last hour and more, there is plenty of transient details in the two guitars, each with their particular sonic signature, the vocals are expressive if a little lacking in sheer 3D space around them. This is something the AD825s do with aplomb and are also more detailed and open, with more sharply defined focus. They are also less forgiving of compressed and hot recordings, yet at the same time will give you an open window into what really is on the album. The PT2308 blurs those details somewhat, yet remains delightful to listen to for hours.
Popping on the latest from Muse, The 2nd Law, the worst excesses of compression and sharp vocals are smoothed over to leave the album easy to listen too, but loses some edge and impact at the same time, not really a bad thing, in this case. Going back to the 16bit/44.1 Integer setting on iTunes Midi and the sound moves back a bit from centre and becomes messy and sharper, not that nice really, losing focus and blurring detail, not the fault of the op-amp! Back to the 24/96 setting, a much cleaner and weightier version of Survival returns, the backing vocals of the choir are really quite good and easily discernible, if not to the more explicit and open degree of the AD825s. Actually, the PT2308 makes this highly compressed (mostly) album rather listenable, without the need to throw off the headphones and run away holding your ears
All credit to the Sony MDR-1Rs here too, they will not accentuate bright and edgy recordings unless they are truly horrible .... like the Franz Ferdinand album Tonight, crikey, Bro! This album may well be more suited to the PT2308's soothing balance.
All in all, so far, the PT2308 is quite a pleasant surprise, will make many of todays rather hotly recorded albums incredibly listenable and for some listeners at least, without them sounding dull. It's use would actually suit slightly brighter cans than the Sonys and in fact, on popping my Denon AH-D1000s on my head, there is a small lift in higher treble, though the soundstage compresses here too and vocals lose the open clarity of the Sonys. The PT2308 op-amp can easily show the differences between the headphones.
Trying some female vocals, Emili Sande's Heaven, from Our Version Of Events, is punchy, clean and dynamic, and allowing the hot mids to be at least tolerable. Eva Cassidy's beautiful soaring vocals on Bridge Over Troubled Waters (Live At Blues Alley) is simply gorgeous, no edge here, the bass digs deep and the cymbals are explicit without being at all bright. Overall though, well balanced. This album is really very good with the PT2308, with a fine musical flow, it's easy to just sit back and listen to the whole set with no fatigue at all.
While it's true, I'm using $1000 worth of very fine silver Interconnect, MusicStreamer II+ DAC and Kimber Kable USB cable here, I believe they are really showing the true worth of this remarkable little amp. Also, I have the amp connected to a much higher capacity 12V sealed battery, which allows for an effortless dynamic flow. I am now able to have a genuine choice between the sheer detailed openness, speed and dynamism of the AD825s, or relax with the more liquid and slightly darker rendition (though equally as musical in many ways) of the PT2308 op-amp.
I have seen that there is a new version of this amp on Oatley's website, which looks like it has a higher voltage supply, I shall be investigating and building a couple of versions The price is significantly higher too, at a whopping $40AU No wurries.

Sennsay.

Thanks for this review. I was looking for sound signature information about PT2308 OP amp which is in my little bear b5 headphone amplifier.

 

[sennsay]

Thanks for this review. I was looking for sound signature information about PT2308 OP amp which is in my little bear b5 headphone amplifier.

Glad to have been of some help, even if some years later! That's the beauty of Head-Fi, there's a wealth of information stored in this great web site. The AD825s are quite a bit more expensive than the PT2308 .. relatively speaking ... but well worth it if your circuit will drive them, the AD825 I used come as two mono units on a double sided board, one op-amp per channel per side, one up and one down between the pins. Some op-amps don't work in this circuit, as there is not enough drive voltage to run them, such as the excellent OPA627BP. The OPA 2134 will run just fine in this circuit, though. You could try a number of them, depending on the headphones you're running. All the best with your little amp.

 

[sennsay]

Glad to have been of some help, even if some years later! That's the beauty of Head-Fi, there's a wealth of information stored in this great web site. The AD825s are quite a bit more expensive than the PT2308 .. relatively speaking ... but well worth it if your circuit will drive them, the AD825 I used come as two mono units on a double sided board, one op-amp per channel per side, one up and one down between the pins. Some op-amps don't work in this circuit, as there is not enough drive voltage to run them, such as the excellent OPA627BP. The OPA 2134 will run just fine in this circuit, though. You could try a number of them, depending on the headphones you're running. All the best with your little amp.

In fact, last night I even ran the little tacker into my HifiMAN HE400S and it worked a treat, much to my surprise! I even used the Modi Multibit DAC via pure silver wire into it, probably a bit extreme for many, I know, but it still gave me the goods with rather good instrument separation and bouncy fairly taut bass. The soundstage wasn't quite as wide or large as I'm used to with the Magni 3 and Ref 1 HD540 Senns, but still remarkably good.