Has anyone found any alternate opamps to use for Wayne's layout?
Also has anyone successfully used dual to single DIP adaptors with the OPA627s with the board?
So far I've used the AD823 and OPA2134, but both leave something to be desired. Not sure at the moment what opamps to put in my next Digikey order. Thanks for any suggestions.
-Jeff
Also has anyone successfully used dual to single DIP adaptors with the OPA627s with the board?
So far I've used the AD823 and OPA2134, but both leave something to be desired. Not sure at the moment what opamps to put in my next Digikey order. Thanks for any suggestions.
-Jeff
Is this design limited to using FET input op-amps only?
If so, you're not going to have that many options. You've already tried 2 of the better FET op-amps.
Why not try a couple of OPA627s on a adapter and see how it sounds?
Though not cheap, one of the best sounding FET op-amps is the Analog Devices ADA4627-1. Like the '627, it's only available as a single so you'll need to solder 2 of them to a SOIC to DIP adapter.
A few others you might to throw in your DigiKey cart and try are the OPA1642, OPA1652 and AD8066. All are duals and only available in a SOIC package, so you'll need a SOIC to DIP adapter for them.
If none of these sound "satisfactory", then I would question whether you have something wrong or the design in general.
I looked at Wayne's PCB in post 584 and didn't see any decoupling caps around U1.
There should be .1uF caps from pins 4 and 8 to ground.
Perhaps they're there and I'm overlooking them...I don't know.
Without them, higher BW op-amps are more likely to oscillate.
If he designed the board for lower BW op-amps, then perhaps Wayne felt they're not needed.
Good luck with your build!
Bipolar op-amps will work in the headphone amp but you may want to have C27 in place to reduce the offset if it is a problem. C27 can be shorted if you use a Fet input amplifier. I only had two bypass caps on the one I built 220 uf Panasonics. You might be better off with something smaller in film but I had no oscillation problems you can also vary R35 and R36 YMMV. Given the quantity of amps that can plug in it may take some experimentation. Mine was built with OPA2604's because we stock them for control functions and they can also run on 24 Volts.
I just did this circuit to drive my Grado 325's at work nothing special but it works and I figured other people might want to try it. I haven't been able to snag a HP1 yet
I just did this circuit to drive my Grado 325's at work nothing special but it works and I figured other people might want to try it. I haven't been able to snag a HP1 yet
Thanks for the replies everyone, and thanks again to wayne for developing and getting us the boards.
I should have provided more details in my original post, so some background info:
So far the power supplies are at +/- 16.5V, but I will drop these to +/-15V so I can swap in ADA4627s. 2SJ313/2SK2013s were used with 10 ohm source resistors. The amp has been playing on and off over the past week. Headphones used to audition the boards were Massdrop x Fostex TH-X00s, Sennheiser HD-650s and Sony MDR-CD3000s. Source components were the Resonessence Labs Concero and an iPad Air 2.
With the AD823: With no feedback capacitor the amp sounded harsh, so the default value caps were added which made the harshness go away. The amp still sounded very closed-in and VERY forward. The TH-X00s have a V-shaped frequency response, but the AD823 brought the mid-range forward so much it hardly sounded recessed. Overall the sound also lacked texture which was very evident on the TH-X00s which normally do a pretty good job of highlighting texture.
With the OPA2134: MUCH better subjective frequency response, but forward nonetheless and still closed-in. The 2134s are known to sound veiled, and they still impart this in the mid-range. Texture was back to "normal" levels, however. The amp sounded best when I hooked up the MDR-CD3000s. These are known for their cavernous soundstage, and this amp brought this out much better than any amp I've tried so far. NOW I know why some people consider the HD-650s to be $10 toys compared to CD3000s. The amp also provided much needed heft to the CD3000s bass which has never hit so hard.
What I'm looking for now is more openness and mid-range transparency, cleaner highs along with possibly more lushness and PRAT?
Overall I've heard worse headphone amps at our annual Toronto headphone audio meets, so I don't think there's anything faulty with the way the amp was built or designed. Maybe I've just become too used to auditioning very high-end gear. McIntosh MXA70s for example make any of the headphones I've used sound so amazing that it's depressing going back to my own gear.
I should have provided more details in my original post, so some background info:
So far the power supplies are at +/- 16.5V, but I will drop these to +/-15V so I can swap in ADA4627s. 2SJ313/2SK2013s were used with 10 ohm source resistors. The amp has been playing on and off over the past week. Headphones used to audition the boards were Massdrop x Fostex TH-X00s, Sennheiser HD-650s and Sony MDR-CD3000s. Source components were the Resonessence Labs Concero and an iPad Air 2.
With the AD823: With no feedback capacitor the amp sounded harsh, so the default value caps were added which made the harshness go away. The amp still sounded very closed-in and VERY forward. The TH-X00s have a V-shaped frequency response, but the AD823 brought the mid-range forward so much it hardly sounded recessed. Overall the sound also lacked texture which was very evident on the TH-X00s which normally do a pretty good job of highlighting texture.
With the OPA2134: MUCH better subjective frequency response, but forward nonetheless and still closed-in. The 2134s are known to sound veiled, and they still impart this in the mid-range. Texture was back to "normal" levels, however. The amp sounded best when I hooked up the MDR-CD3000s. These are known for their cavernous soundstage, and this amp brought this out much better than any amp I've tried so far. NOW I know why some people consider the HD-650s to be $10 toys compared to CD3000s. The amp also provided much needed heft to the CD3000s bass which has never hit so hard.
What I'm looking for now is more openness and mid-range transparency, cleaner highs along with possibly more lushness and PRAT?
Overall I've heard worse headphone amps at our annual Toronto headphone audio meets, so I don't think there's anything faulty with the way the amp was built or designed. Maybe I've just become too used to auditioning very high-end gear. McIntosh MXA70s for example make any of the headphones I've used sound so amazing that it's depressing going back to my own gear.
15 V Talema PS
Utilizing the BOM posted early in the topic I sent a parts order in to Digi-Key.
I received the PCB from Wayne ( thanks ) , which has some board parts not shown on the early BOM. I started a cart with Mouser for the additional parts.
Re-reading the topic I see the first BOM posted was for the earlier Ver 1 of the board, but current shipping is PCB Rev. 3.
When you are not going to be operating above the 15 volt Talema Power Supply should there be any changes to the PCB layout ?
Posters here have recommended changes for 15 volt operation such as deleting R10 C10 D5 ,6 and jumpering R9
or, door number 2 ......
changing R10 and R14 to 200 ohms ; R 9 and 13 to 2200 ohms ; deleting D6 and reducing C8 and C10 to 220F.
This will be my 4th diy project so any advice is definitely appreciated
thanks
Utilizing the BOM posted early in the topic I sent a parts order in to Digi-Key.
I received the PCB from Wayne ( thanks ) , which has some board parts not shown on the early BOM. I started a cart with Mouser for the additional parts.
Re-reading the topic I see the first BOM posted was for the earlier Ver 1 of the board, but current shipping is PCB Rev. 3.
When you are not going to be operating above the 15 volt Talema Power Supply should there be any changes to the PCB layout ?
Posters here have recommended changes for 15 volt operation such as deleting R10 C10 D5 ,6 and jumpering R9
or, door number 2 ......
changing R10 and R14 to 200 ohms ; R 9 and 13 to 2200 ohms ; deleting D6 and reducing C8 and C10 to 220F.
This will be my 4th diy project so any advice is definitely appreciated
thanks
I believe I was standing by door number 2. Those values work if you use the lm317 and lm337 regulators AND make several cuts and jumpers around the positive regulator. This isn't sanctioned so please proceed with caution.
I would recommend using the 7815 and 7915 regulators instead. I used the 317 and 337 only because I had them and was too cheap and lazy to order the 7815 and 7915.
Graeme
I would recommend using the 7815 and 7915 regulators instead. I used the 317 and 337 only because I had them and was too cheap and lazy to order the 7815 and 7915.
Graeme
Sad panda
Put everything together, started some basic measurements like checking all the voltages from ac socket, the regulators etc. Everything within specs and I got a nice 16.5 V on both rails.
Then I measured dc offset, that was freakin 5V on right channel and 1.5V on left channel! I found out that the right channel of the opa2604 was making a short(pin5), while the left channel was ok. I also removed the opa from the socket and there was no short.
Before I order another opa and put it in, should I check for anything else?
Put everything together, started some basic measurements like checking all the voltages from ac socket, the regulators etc. Everything within specs and I got a nice 16.5 V on both rails.
Then I measured dc offset, that was freakin 5V on right channel and 1.5V on left channel! I found out that the right channel of the opa2604 was making a short(pin5), while the left channel was ok. I also removed the opa from the socket and there was no short.
Before I order another opa and put it in, should I check for anything else?
It lives...
Got mine finished today... SuperTeddy regs at 15v (cos I had them) offset
0.1mv on both channels, very pleased with that.
brown dog OPA627...that's all I had in the parts bin.
This was never going to be used as a headphone amp in my stable....but rather as a pre-amp and at this early stage its looking/sounding very, very promising. I think the OPA627 may be a tad forward though.
Wiring needs a bit of a tidy...
as always...thanks must go Wayne and Jim...
Got mine finished today... SuperTeddy regs at 15v (cos I had them) offset
0.1mv on both channels, very pleased with that.
brown dog OPA627...that's all I had in the parts bin.
This was never going to be used as a headphone amp in my stable....but rather as a pre-amp and at this early stage its looking/sounding very, very promising. I think the OPA627 may be a tad forward though.
Wiring needs a bit of a tidy...
as always...thanks must go Wayne and Jim...
I haven't been able to snag a HP1 yet
That's the one I'm intrigued by as far as the circuit design.
If you haven't been able to get your hands on one yet, it may be a looooong time before we ever see a schematic.
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