So having already having cases for it to go into things moved along quickly after the initial testing revealed everything to be functioning within reasonable tollerances.
This is the case and then with the buffer, regulated power supply and transformer fittted.
This is the case and then with the buffer, regulated power supply and transformer fittted.
Attachments
So once it was in the case I tested it again with a Denon mini system (as this has a volume controlled input that I could test behaviour at switch on and switch off with a level of safety for the speakers) before it got moved downstairs to be trialled in the main system where it will live. As I am the nervous type I swapped out my Monitor Audio floor standers for an old pair of Missions... I need not have worried as it all worked fine. So I reconnected the MAs and gave India Arie a spin and was greated with beautful music (as opposed to hiss, crackle or the sound of speaker drivers hitting the back wall).
It has definately improved, what I thought was already impressive, bass control of the chip amp driving the speakers. The snap of drums and the pluck of bass guitar strings is just amazing. I am now very excited about trying the 627's!
It has definately improved, what I thought was already impressive, bass control of the chip amp driving the speakers. The snap of drums and the pluck of bass guitar strings is just amazing. I am now very excited about trying the 627's!
Well it has been a while since I have updated this thread. I finsihed off my Amish and had those connected whilst running the OPA134s, which I enjoyed and after a good period of getting used to the system I finally swapped in the OPA627s.
What was the result? Well, thankfully it all worked, which was a bonus. As for the sound, there was not much in it really, I believe the 627 has better control over the bass, but only by a small margin (perhaps it is a little leaner too). I have run the system with the 627 for about a month and have now had an itch and the whole thing has gone Analogue Devices in the form of the new ADA4627 which come in an SMD package, so needed a DIP8 adapter. These have now been soldered and last night I dropped them into the system... initially I didn't really notice much difference, but then the more I listened the more I started to notice. Bass regained a bit of weight, but is unbelievably tight and controlled and the treble has cleaned up a lot, particularly noticable on the Foo Fighters Skin and Bones live album.
So, this has proved to be really interesting and I think I may consider trialling the ADA4627 in my Tag Maclaren DAC20 and seeing what improvements that brings. Also I am keen to try discretes and valves in my pre-amp, just so I feel I have given most things a try.
What was the result? Well, thankfully it all worked, which was a bonus. As for the sound, there was not much in it really, I believe the 627 has better control over the bass, but only by a small margin (perhaps it is a little leaner too). I have run the system with the 627 for about a month and have now had an itch and the whole thing has gone Analogue Devices in the form of the new ADA4627 which come in an SMD package, so needed a DIP8 adapter. These have now been soldered and last night I dropped them into the system... initially I didn't really notice much difference, but then the more I listened the more I started to notice. Bass regained a bit of weight, but is unbelievably tight and controlled and the treble has cleaned up a lot, particularly noticable on the Foo Fighters Skin and Bones live album.
So, this has proved to be really interesting and I think I may consider trialling the ADA4627 in my Tag Maclaren DAC20 and seeing what improvements that brings. Also I am keen to try discretes and valves in my pre-amp, just so I feel I have given most things a try.
Using HF Opamps in General
I have designed several circuits using 627 or similar high speed opamps. It is particularly important to minimize the impedance between the power rails and ground. This rule also applies to a lesser degree to the load. The proto board photos did not indicate whether the reverse side was a ground plane or not. I suggest that you incorporate a ground plane in the layout. This can be done with copper foil tape, thin copper sheet, or with the second PCB layer.
Surface mount ceramic capacitors are better than thru hole devices since their package and lead capacitance is lower. It is also good to parallel several devices of different capacitance (such as 1.0, 0.1 and 0.01 uF). That way the resonance peak of any given capacitor is bypassed with another device whose resonance frequency is different.
I have designed several circuits using 627 or similar high speed opamps. It is particularly important to minimize the impedance between the power rails and ground. This rule also applies to a lesser degree to the load. The proto board photos did not indicate whether the reverse side was a ground plane or not. I suggest that you incorporate a ground plane in the layout. This can be done with copper foil tape, thin copper sheet, or with the second PCB layer.
Surface mount ceramic capacitors are better than thru hole devices since their package and lead capacitance is lower. It is also good to parallel several devices of different capacitance (such as 1.0, 0.1 and 0.01 uF). That way the resonance peak of any given capacitor is bypassed with another device whose resonance frequency is different.
Of course they are. Inside the Kemet multilayer ceramics I use are small 0805 SMD capacitors connected to the leads
I don't agree with the suggestion on using ceramic caps for decoupling the IC pins. Polypropylenes are probably the best type for that application. But they do not have to be large, of course.
There several small types from Panasonic or Wima or Siemens that might do the job quite well. You don't need more than 50v types, 0.1 or .22 values.
The gainchooser page you mention is inaccurate when they say "The 15V rails are a little too high for the amp, which is built for 12V operation". The 627 can take up to +/- 18v, and +/-15v should be perfect for it. In fact all specs in the Application page are taken @ 15v.
You didn't mention the supply you are using, which is as important as the chip itself. Use quality regulators and parts, if possible avoiding 78XX/79XX types.
There several small types from Panasonic or Wima or Siemens that might do the job quite well. You don't need more than 50v types, 0.1 or .22 values.
The gainchooser page you mention is inaccurate when they say "The 15V rails are a little too high for the amp, which is built for 12V operation". The 627 can take up to +/- 18v, and +/-15v should be perfect for it. In fact all specs in the Application page are taken @ 15v.
You didn't mention the supply you are using, which is as important as the chip itself. Use quality regulators and parts, if possible avoiding 78XX/79XX types.
I am using a fairly identical power supply to the one used on the website I put the link to, I think it was for his phonoclone project. It does make use of the 7815 and 7915 voltage regulators. I understand that these are not the best, but given the PSRR figures for both the 627 and the ADA4627 they should be adequate, however, i am open to suggestions for my next build. From my listening tests there is no discernable noise when the volume is turned all the way up with no source playing.
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