[bassey321]

http://drachen-audio.com/dh1.4.htm

Sounds like a good starter kit, has anyone any experiance on this? Looking to take the plunge at a basic level, but kits seem few and far between. any advise??

 

[FallenAngel]

From the schematics, it looks like your average diamond buffer. Kit value may not be too bad for a 2-channel design. You could throw in a 3rd channel instead, but hey, I would just build a PPAv2

 

[ericj]

It's not clear if it gives you any gain. But i've only glanced at the schematic.

What's the deal with the to-92 transistors zip-tied together?

 

[Pars]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif It's not clear if it gives you any gain. But i've only glanced at the schematic. What's the deal with the to-92 transistors zip-tied together?

Probably thermal coupling...

 

[FallenAngel]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif It's not clear if it gives you any gain. But i've only glanced at the schematic. What's the deal with the to-92 transistors zip-tied together?

No voltage gain, just current buffer.

 

[NelsonVandal]

"Output Impedance .02 ohms". Are you sure it's not a gain stage in a closed loop with the buffers?

Drachen audio seems to be a fellow headfier "Sam9", but he has never posted anything here.

 

[kvant]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif From the schematics, it looks like your average diamond buffer. Kit value may not be too bad for a 2-channel design. You could throw in a 3rd channel instead, but hey, I would just build a PPAv2

I am certainly no expert, but to me the topology looks more like Dynalo than like a diamond buffer. Those differential pairs in the first stage are likely to give you gain.

 

[FallenAngel]

Maybe gain

I'm no techie, schematic looks close to a diamond buffer, but in comparison to a dynalo, the first part does look similar. So much for quick glances before writing an answer

 

[tyre]

I'm not that great at discrete circuits yet, but yes, I believe it does have gain. The input connects to the base of Q3 and the output is taken from Q3's collector, that means voltage gain. R13 and R14 are part of the feedback loop connected to the output and the inverting input Q4, just like in an opamp circuit. I have no idea why the second differential Q5/Q6 input is needed.

 

[jcx]

Quote:

Originally Posted by bassey321 /img/forum/go_quote.gif http://drachen-audio.com/dh1.4.htm Sounds like a good starter kit, has anyone any experiance on this? Looking to take the plunge at a basic level, but kits seem few and far between. any advise??

Stay Away, the "HA1.4 Headphone Amplifier" schematic won't work as intended, an extensive thread on DIY audio discusses the symetrical diff input and why you cannot simply use current mirrors with them feeding the balanced VAS stage as this circuit does - the VAS stage operating current is not defined by this arrangement, a separate common mode loop is needed to control the VAS operating point, or you have to give up the current mirrors to let diff pair collector R define a operating V and the VAS operating point

other diyers have fallen for the "eye candy" symmetry of the schematic, a version of which has been published in Randy Slone's amp design book but in practice the circuit will not work reliably

http://www.diyaudio.com/forums/showt...844#post521844
(and the link to the big thread in my (jcx) post)

I have simmed a fix - maybe it can help others understand the problem:
http://www.diyaudio.com/forums/showt...threadid=56860


it is possible to build Drachen's HA1.4 circuit and for global feedback to make it give some sound but the internal bias conditions are not well defined and another batch of parts may barely work at all, or sublimely well - but it is a complete crapshoot



I hate to damage a well meaning kit provider but the circuit is flawed, I have notified Drachen using their contact form:

"
sorry to have to recommend against your product in a public forum but the circuit is flawed

I welcome public debate on the head-fi or diyaudio forums on this issue

http://www.head-fi.org/forums/showpo...7&postcount=10
"

 

[dBel84]

Doesn't look to be anything basic about this amp, simple yes. It appears to be a fully discrete differential pair transistor amp with a complementary feedback pair ( David Self ) output stage and a larger output transistor for greater current. No dc servo or bias adjustment but it must be set into class A -this will make matching parts more critical for equal channels. I agree that the zip ties are for thermal coupling, I have seen this before but can't remember where. I would personally opt for the CKKIII which will be no more complicated to build and has great support on these forums..dB

ignore my ramblings, far more experienced voices have spoken