I'm familiar with the cost, I built an Orange86 a few years back, Guavatone's take on the REDD47. Decent components, tubes and transformers quickly add up. But I'd love to have the PCB in my backlog drawer, I've always wanted to build a V76.Thanks! To make some signalboards available and a bom isnt a biggie. I wont share the PSU as this is quite on the experimental side and I dont want to do a revision soon. But just to be said. Each channel is around 1k€. This isnt a cheap build.
I will meassure those values tomorrow. Thank you!Also, have you measured the actual output level on the transformer secondary when distortion starts?
Its 430 ohms. Thought it was 75. I should have a DI box in between right?What is the impedance of your source for these tests?
Cheers
Ian
Its the input tx. I tried one of Manfreds T188 and got the full spectrum. Also if I feed the audio through the direct input the spectrum response is flat.Could be worth trying a different input transformer and understand if the Sowter is causing the rolloff.
Perhaps even a more common 1:10 would give some insight.
I thought about writing him also. Will do!Brian Sowter is still replying to technical questions on behalf of Carnhill so maybe he can give some advice.
I am using 1667 15mA for the V4 and 1667 10mA for V2. They are wound on a c core with oposite windings. Like a humbucker. Lundahl says they would be really good in rejecting hum. Also I installed a mu metal shield around the power toroid. I havent jet checked the the level below -60dB FS. The left side is dead quiet. There is some hum on the right channel but I think thats a tube. I will take care of this stuff once the big issues are cleared out. I only solve one at a time.BTW I was wondering what Lundahl inductors you are using and since they are unshielded do you experience any hum pickup from the power transformers ?
I will short RN1 out and increase CN1. I have some 1:10 lying here which I will try later. If they dont do it, I will order some UTMs. Their V72 output worked great in this build here.You can remove the filters between v2 and v3 and you get 6dB more gain, and eliminate the broadcast frequency cuts.
C25/L6/C26 completely (replace L6 with a wire)
Increase CN1 to remove the low cut. Remove 80k RN1 and you eliminate the voltage divider that cuts your level in half.
You can add filters back if you want them later and your build is debugged.
Jensen transformers work great in V76 builds (JT-115k, JT-10k61-1M)
Interestingly, the Sowter tx response is in line with what I got (the graph for low Z). This confirms my suggestions that the problem is with Sowter. Another tx that you show exhibits the response close to the one I've got with 1:10 Cinemags.Here with a very small microphone transformer I had at hand
I tried feeding the input with both 0R and 50R output impedance and it didn't make any difference in my case. Curious to see if anything is different with Falk unit.I would suggest you should adjust your generator output to look like 150 ohms and repeat the tests.
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