I haven't tested this amp specifically, but the 55V/uS slew rate could have a role to play in this. I'll let others answer here, but I see you don't have C2/C7 caps populated on your board. With such a fast opamp, I'm pretty sure you need those to avoid oscillations!
Have you considered that the (double) OPA627 is unity-gain stable and the gain must be less than 5?
With my whammy, the gain factor 3 with the OPA627 is completely sufficient.
It's stable for me without the feedback caps, but my OPA627s are from the last millennium.
@SomekPoland Thanks for the message. Yes it is dead quiet, only when I turn the amp off does it make noise. It squeals on both channels. I triple checked my work before and after soldering. It is not dependent on volume. I have tried the Whammy with multiple sources and the same issue happens. Also it is dependent on op amp. I do not get noise from my Burson V6 Vivid for example
@Denis_O thank you very much for the reply. What feedback cap do I need? Do you have a model number?
@Roland968 thank you very much for the reply. I am not sure, how would I go about checking the gain factor? I bought mine from Cimarron Technology just recently.
@Denis_O thank you very much for the reply. What feedback cap do I need? Do you have a model number?
@Roland968 thank you very much for the reply. I am not sure, how would I go about checking the gain factor? I bought mine from Cimarron Technology just recently.
Thanks, Denis, and others. This is very clear to me know and I will post a picture before I switch it on to ensure I am doing it right.
My box of components from Digikey and Mouser is ready - I had to split my orders because of component availability and to get the minimum order size to not pay postage. Just need to buy one more cap and some screws, etc. Then I am ready to build.
Question about the space for rolling op-amps (e.g Burson V6) between caps C3 and C4 - how do I position the caps to make enough space. I read on some of the build posts that people had challenges with that?
Also, any other key things that I should be looking out for from your collective experience?
Also, any other key things that I should be looking out for from your collective experience?
Start with 1k for R4 and R8. If the gain is sufficient for you, then leave the value for the OPA627. Otherwise you can go as high as 3k, but the lower the better.
Other OPAmps might need higher values, so the 4.75k is a good starting point.
There are a lot of OPAmp gain calculators online, but always check the data sheet.
If you often want to try something out and exchange it, then solder in the sockets of precision socket strips at the points, then you can exchange resistors and capacitors just like the OPAmps.
Are you using the store kit with chassis?
If not, and depending on your choices for chassis etc., you can mount the caps or the opamp to the bottom of the board. Edited to add - forget about the opamp... probably not the best idea.
You can also leave the leads a tad longer on the caps and squish the caps over to one side... etc.
My recommendation is to plan things out ahead. Read the build guide a few times. There is a key choice re: the PSU. Read through a few more times. Decide which way you're going to build yours... take some notes... cross some things off of the schematic... circle some things.... etc. Do whatever works best for you to ensure that the right parts go in the right places... no more than necessary... and no fewer.
Have fun!
No, not the store kit - building my own chassis with plywood and steel top/bottom plates. So, I have to use an extended from the volume pot to get through the wooden case (about 2 cm thick). Also, means if have to attached the earth ground to both the bottom and top plates. So, yes, I have been planning and working through the build guide for a while now.
Thank you very much for this. I will try that out! Luckily I have some 1k spare resistors!
If you are careful and obey polarity, and there’s sufficient height below the board, you can mount those capacitors on the bottom of the PCB. That will give enough room for any discrete opamp.
I will use 20mm spacers below the circuit board to get the volume knob in the middle of the case (height-wise) and the caps are 11mm high, so there should be enough space underneath.
@Roland968 I just swapped the 4.75k resistors to 1k. I am still getting some noise when I turn it off though it is much less harsh than it was before. Do you think feedback caps would eliminate all noise?
The 35A bridge I could get at my local store is 400V - is that an overkill? Will it do the job OK?
I basically don't have headphones plugged into an HPA when I turn it on.
First switch on all other devices, then plug in the HPA and then the headphones, switch off in reverse order.
I never hear any hissing or popping...
Is there a noise when no music is playing?
If you're listening to music at a normal volume, how loud is the noise when you turn it off?
@Roland968 Ok I will do that. No noise when no music is playing, dead quiet. The noise is the same when music is on or off when I turn off the amp, it's tolerable now however, it doesn't shriek loud like before.
that's exactly what you need and will do the job perfectly well. It's not overkill since peak voltage on AC 230V is about 300V.
100pF precision film caps should work perfectly