Unfortunately Jimmy I bought a pair of metal can OPA627BM's a few years ago to go in a DAC output, they are one grade down from those 'SM' on sale here, otherwise I certainly would.
Haven't compared to standard soic package, maybe I could send mine to you sometime for a comparison. Only thing I can think of that is better with metal cans is EMI screening etc. I honestly think you would need super ears to hear a difference and maybe some real high end reference phones.
Greg liked the 627BM's, nearly on par with the Burson.
Jimmy - when you get the Brown dog adaptor and amps, solder the tops of the pins as they are only press fit. It will improve the electrical connection if nothing else!
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I really don't think the whammy is the proper application for a metal can opamp, but it can't do harm either. The op amp represents such a small percentage of the total input side that could pick up noise, and since the power supply is linear, there is no switching noise in there anyway. Maybe I am missing something, though.
No Rich you are right in that the metal cans are possibly overkill for the whammy, it's a simple circuit with a quiet supply.
But looking at the spec sheet, the BM & SM grades are slightly better in a few parameters such as better input offset, less drift and higher PSRR. Also more importantly lower noise. I imagine that some sort of special die selection is taking place to manufacture these, hence the cost.
They are intended for medical and military applications really and we all know the army have the best sounding hi-fi!
Can this be adapted to drive a pair of fostex full range speakers that do great with less than 5w per channel? Or is another diy Amp suggested?
The speakers: Fostex P1000E DIY Kanspea 4" Full Range Speaker Kit - PAIR: Madisound Speaker Components
The speakers: Fostex P1000E DIY Kanspea 4" Full Range Speaker Kit - PAIR: Madisound Speaker Components
resistors and caps on the pcb
Hi all, I have almost finished the staffing of the PCB (I ordered the kit from DIY audio store). But there are a few things that are not clear to me:
- Do I need caps No 26 and 27? On 6L6's photos they are installed. The opamp in the kit is the rc4580 but I will try others for sure, also the burson V6. Is it bipolar?
- Do I have to install resistors No R10 and R14? They are not installed in 6L6's guide in the LED-config, but others do have them installed. I want to use the LED configuration.
- Does it make sense to use higher quality caps for C3 and C4? I've seen it in other builts.
Thanks a lot!
Hi all, I have almost finished the staffing of the PCB (I ordered the kit from DIY audio store). But there are a few things that are not clear to me:
- Do I need caps No 26 and 27? On 6L6's photos they are installed. The opamp in the kit is the rc4580 but I will try others for sure, also the burson V6. Is it bipolar?
- Do I have to install resistors No R10 and R14? They are not installed in 6L6's guide in the LED-config, but others do have them installed. I want to use the LED configuration.
- Does it make sense to use higher quality caps for C3 and C4? I've seen it in other builts.
Thanks a lot!
- Yes install C26/C27 the amp will work fine.
Not sure if the Burson is Bipolar or Jfet input but they work well in the Whammy. Make sure you get a dual version (2 channels) Is this what you mean?
- Do not install the R9/10 & R13/14 resistors around the regulator as this will increase the rails to around +/- 21V. Stick with just the LED, 220uF cap and diode initially for best operation. Check your op amp spec sheets for the maximum voltages - always read the spec sheets. Check the rail voltages to make sure all is good before installing op amp, should be around +/-16.5V with LED reference.
- Yes good quality low impedance/ESR caps are good for C3/C4. I found 47uF Nichicon KZ or Panasonic FM good here. Around 47 - 100uF will do.
You don't need C2/C7 100pF really unless the op amp oscillates, try without first.
Remember to check how much DC is on the outputs before connecting phones. Good luck!
New Build Questions
A few things are not clear on the build guide which is otherwise well done.
1) Are you supposed to solder all of the primary/secondary/points on the transformer to the corresponding points on the board? The guide simply shows the transformer mounted to the board with no mention of this.
2) Are there test point measurements that can be used to trouble shoot the power supply? I am measuring some oddly high voltages on the 35V caps (like 37VDC) which doesn't seem right but the first voltage measurements on the build guide are only done AFTER the 78/7915s are installed. For example, it would be good to see what the expected input voltages are for those.
--Tom
A few things are not clear on the build guide which is otherwise well done.
1) Are you supposed to solder all of the primary/secondary/points on the transformer to the corresponding points on the board? The guide simply shows the transformer mounted to the board with no mention of this.
2) Are there test point measurements that can be used to trouble shoot the power supply? I am measuring some oddly high voltages on the 35V caps (like 37VDC) which doesn't seem right but the first voltage measurements on the build guide are only done AFTER the 78/7915s are installed. For example, it would be good to see what the expected input voltages are for those.
--Tom
Thanks passive420 for your advice. Today I finished the PCB and did a „raw“ testing without chassis. The amp did a great job right away and sounded very good with the stock opamp rc4580. Then I tried the burson V6 vivid and again no problems. Just a very little 50 Hz hum from the mains which I am sure will dissappear when everithing is in a chassis and grounded. So was the whammy sounding very good with the rc4580, it sounds terrific with the V6. I am absolutely happy.
Just one little issue: the PSU supplied 16.9 vlts which is too much for the V6. Its spec is max. 16.5 volts. So I will change the PSU-config from LED reference to raw.
Hopefully this will solve the second issue as well (someone any idea on this?) and that is the to high power output. Even with my demanding Sennheiser HD800 the absolute max volume is reached with the pot at 11 o‘clock.
Or is there any other solution?
Just one little issue: the PSU supplied 16.9 vlts which is too much for the V6. Its spec is max. 16.5 volts. So I will change the PSU-config from LED reference to raw.
Hopefully this will solve the second issue as well (someone any idea on this?) and that is the to high power output. Even with my demanding Sennheiser HD800 the absolute max volume is reached with the pot at 11 o‘clock.
Or is there any other solution?
PSU supplies 16.9V but you are losing 1.3V on R35 (and the same for neg rail on R36). I have shorted the LEDs (as you are planning). Some people double the resistance of R35,36 which doubles the voltage drop on these. Putting aside increased dissipation in these resistors I do not know which solution is better.
Yes you can try reducing the gain - gain factor formula is R4/R1 + 1 (R8/R12+1 for other channel)
Standard gain config is 4.75K / 1K + 1 = 5.75. Use anything you have around 2 - 3K maybe for R4/R8... start there and tinker until you are happy. I haven't tried increasing R1/R12 yet so you can try that also.
So reduce R4/R8 or increase R1/R12... or both
Your hum will likely disappear when the pot is grounded to the front panel/case.
thomasnadeau -
1) Yes definitely solder all transformer pins.
2) 7815 (pos) input is pin 1 and 7915 (neg) input is pin 2 - generally you take the AC secondary voltage and x 1.41 to estimate DC output after rectification so you should see between 19 - 21 VDC on the reg inputs.
Another vote of thanks to Wayne: my WHAMMY is up and running, sounding superb as a pre-amp. In fact it's just struck me that with this and three Pass amps feeding LX-minis via the Pass crossover, everything bar the source (Bel Canto cdp) is a FW/Pass Labs/Linkwitz inspired home build. So many thanks to all concerned.
The potted transformer is very secure when held in place only by the soldered pins. Unless the board is mounted upside down in the chassis, I can't imagine a shock force that would break it loose that would not also damage things in other ways. That said, if you will be using the piece portable, banging it about a bit, a bolt would be a good idea.
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I'm a noob who's learning. Sorry for asking a question. I thought that's what this thread is for.
I really am sorry, you are very right to call me on that. I had already edited my response but it was too late.