Sgheadphones DIY A47 pocket amp kit

[bpribadi 0]

What volume pot is that and where did you found it?

 

ALPS RK9 from Farnell. Check page 11 for more information.

Edited November 15, 2004 by bpribadi

[tropicalrips 0]

Cool, Long time havent returned to this site. Glad to see the DIY spirit still present in Singapore. Are the schematics on the 1st post the most updated ones? And when is the expected release of the kit? Thanks!

i think the most up-to-date PCB/schematic is on page 4

there are currently 3 amps built with the first pre-production PCB, all 3 built by different people

i hav tried the one by Bpribadi, has very good separation & bass, even on a $40 "no brand" headphone

i believe the 3 amps will hav quite different sound signatures from each other when we get the chance to A-B them together.

 

for the kit, not sure when it'll be release, there's still a problem of quantity...how many can we actually make...need to wait for jason to finalise.

Edited November 15, 2004 by tropicalrips

[av98m 0]

This must be the longest running thread ever on sgheadphones. 6 months!

Hopefully the final product can be rolled out by end 2004.(edit:oops, I meant to say 2004)

Edited November 18, 2004 by av98m

[bpribadi 0]

Yes, I agree, this is a super thread

 

Hopefully Jason can meet his target, last time he said to finalized this amp by Christmas, this year, not next year

 

Yesterday I bought another OPA2228 from Farnell (previously I only have one piece) to try it in the modified Jason A47. Just rolled the OPA2134 with OPA2228, it sounds much better to my ears

 

For me, somehow the OPA2228 sounds much more musical than the OPA2134. I'm sorry Jason, I know you have bought 100 pcs of OPA2134 from Farnell But I must be honest, I favor OPA2228 more than the OPA2134, so I think it is a significant upgrade to your amp

[tropicalrips 0]

i think this amp may be "picky" when it comes to op-amps...maybe due to its design? i find it sounding quite good when in its most basic/original configuration using opa2134.

with my big alcaps on the input, the ad8620 sounds the best to me, with the 2228 sounding "weak" & 2134 sounds "muffered"

hav u tried the 8620 on your modded version bram?

[dreamie 0]

Yes, I agree, this is a super thread

 

Hopefully Jason can meet his target, last time he said to finalized this amp by Christmas, this year, not next year

 

Yesterday I bought another OPA2228 from Farnell (previously I only have one piece) to try it in the modified Jason A47. Just rolled the OPA2134 with OPA2228, it sounds much better to my ears

 

For me, somehow the OPA2228 sounds much more musical than the OPA2134. I'm sorry Jason, I know you have bought 100 pcs of OPA2134 from Farnell But I must be honest, I favor OPA2228 more than the OPA2134, so I think it is a significant upgrade to your amp

I concur. The OPA2228 does sound much more musical and warm. In fact, I'm in favor of it over the OPA637.

[tropicalrips 0]

update :

i was reading this tread...again... when i got bored and decided to try Bram's mod

i cut the track on the PCB & jumper the pins...sorry Jason i just had to try it

but instead of using the LM6171 for the ground as Bram did, i used my OPA627 which was just rolled out from my desktop Cmoy (replaced with AD8610)

now the amp has 3 of the most expensive op-amps AD8620 + AD8620 + OPA627

i left the Alcaps which were on the input side inplace, but the bass extension on this amp now is...mind blowing (with SR80) i still hav a pair of 30MFD Alcaps...wonder what effects they will hav on this amp

[bpribadi 0]

but the bass extension on this amp now is...mind blowing

 

Wow, that's cool

 

Tropical, do you mean the bass is better with the modded ground? Or it might be because of the expensive OPA627?

 

What I understand, the A47 circuit is not good for ground, since it introduce resistor in the ground channel. We know that ground should stay at 0 volt all the time, and ground also should be able to handle large current flow. So if there is resistor in the ground channel, and large current flow going through it... It is hard to keep the ground voltage to 0 volt ( I x R = V).

 

That's the reason I change the ground channel to the simple unity gain op-amp config. The LM6171 is just perfect for Jason Amp, since the goal is budget amp, and LM6171 price is less than S$ 1 more expensive than the OPA2134.

 

The OPA2228 introduce louder 'crack' sound when the headphone is pluged, and I turn the amp On>Off or the other way Off>On . With OPA2134 the 'crack' sound is soft, not as scary as the OPA2228. So with OPA2228, I have to unplug the headphone before toggle the power. I haven't check the DC offset.

 

Haven't tried with AD8620.

Edited November 19, 2004 by bpribadi

[tropicalrips 0]

Tropical, do you mean the bass is better with the modded ground? Or it might be because of the expensive OPA627?

not sure which is it...i think the 627 does not output a lot of current, so may be the mod itself

it will also work with BUF634 rite

thinking of using BUF634 on the ground channel

[bpribadi 0]

thinking of using BUF634 on the ground channel

 

That's what I did in my Pimeta clone and my brother amp But for Jason amp, I think the mod will be too much. I try to follow Jason goal which is to make budget amp, so I didn't use expensive components. I use only Op-Amp which are not so much more expensive than the OPA2134 to upgrade / mod the amp.

 

Jason when shall we meet? Tropical, what time you start working in the morning? Maybe Saturday morning is good before you start working.

 

Jason, I can pass the amp to you for testing and carefull listening at home, so you can finalized your circuit

[tropicalrips 0]

i open shop aaround 10:30am

now making an "adaptor" for the jason amp

[bpribadi 0]

i open shop aaround 10:30am

 

So if we want to have a small meeting to compare our A47 amps, we can meet around SLS on Saturday at 10 am

[jasonhanjk 0]

Hey guys, I just redesign the amp and now got the new PCB ready. This time the ground has no resistor. Will finish up by this afternoon and post some pron.

[jasonhanjk 0]

Hungry....

 

Here the pics

 

[infinitriX 0]

Very nice! Mind disclosing how much it costs to prototype a single PCB like that? And for 10 pcs? Where do you go for your prototyping?