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Post by deepdark on Aug 11, 2015 19:26:18 GMT -6
one thing I could try but I'm a little affraid of is changing the push pull transformer for a wsm10k/600, the same one preservative sound used. I'm affraid to should b+ into a transormer which isn't specifically made for push pull operation.
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Post by deepdark on Aug 11, 2015 18:54:16 GMT -6
one thing I'm thinking is that maybe Imy threshold pot should be 1w instead of 1/2w
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Post by deepdark on Aug 11, 2015 18:52:34 GMT -6
other measurement, i got a differentieal of about 1.26v between the plates of the 6sk7. I only get a drop of 0,2v through r2 where i should probably have something like 1,2v.
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Post by deepdark on Aug 11, 2015 18:38:41 GMT -6
I tried the unit with a microphone. So far, I didn't noticed any hiss, but off course I have to large sucked out low end. Hiss is just present when I plug the output of the apogee to the input of the federal. I'm pretty sure hiss will not be a problem in a proper 600ohm environnement. I tried with unplugged input and there was no hiss, so it looks to come from the input transformer.
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Post by deepdark on Aug 11, 2015 17:52:23 GMT -6
compression help to tame the noise, the more i compress, the more noise floor is reduced. at threshold middle position, noise floor is about -55db, after is start to motorboating but i'm sure we could get to -60db. another symptom is my meter wont sit at 0 on the gr side, it sit at around -18. Imaybe not the proper vu meter, thought. I get it from hairball audio. internally rectified. I could play with parralele resistor to R2, or maybe the culprit is the 6sq7???
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Post by deepdark on Aug 11, 2015 17:35:25 GMT -6
secondary of input tranformer :263ohm and 235ohm
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Post by deepdark on Aug 11, 2015 17:32:14 GMT -6
ok. I just test 2 things. First I remove the 6sq7 and the motorboating stopped. So we could conclude it comes from the compression section, isn't it?
I measured impedance between output primary hi-center tap and Low - center tap. Weird reading here. Hi/center tap show a z of about 192,1ohm and low/center tap 175,5ohm. No really well balanced I think. Could it be our culprit here?
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Post by deepdark on Aug 11, 2015 16:06:33 GMT -6
Concerning the balanced current between 6sn7 and transfo, i guess i would have to get the exact same value at plates, coming from the output transformer and the exact same grid value, while passing audio, of course. Isn't? In case of imbalance result, what can be done to correct that?
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Post by deepdark on Aug 11, 2015 15:55:01 GMT -6
Sorry i misunderstood you.
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Post by deepdark on Aug 11, 2015 15:35:20 GMT -6
Basicaly, i should get the exact same value at each pair of pins (plate-cathode-grid)? Or the tube itself has to be balanced, or the output transformer has to be balanced between hi-center tap and low-center tap?
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Post by deepdark on Aug 11, 2015 14:37:54 GMT -6
So mine has better noise rejection than an original one, reading at those spec, isn't it? I'll move current ground to psu ground. So my trouble could be the 6SN7 tube itself, or the circuit around? I know I'm not using it as I should with load of 680ohm. Probably it doesn't help much, too.
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Post by deepdark on Aug 11, 2015 12:47:07 GMT -6
oh and by current imbalance in the output, do you mean inbalance between both 6sk7 sucking out my lows?
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Post by deepdark on Aug 11, 2015 12:45:55 GMT -6
Thanks EmRR. The current balance pot is 2W instead of 1W, so I'm pretty sure trouble isn't there.
When hooking the unit through my apogee (which has an output of 100ohm and input of 10K, so basically I load the unit at 10K), I can see on the tracking meter of my freq. analyser plugin (melda) a noise floor of about -51db, no signal, attenuator fully counterclockwise.
So my grounding would probably looks right, then? I know I could try grid stopper and other tricks, though. Maybe current control ground is better off to be strapped at the IEC bolt?? Other than that, power transformer is bolted out the chassis, psu is Inside at one extremity and the rest of the audio is at the other extremity, so a good 15inches far from the psu. Tubes have their pin 1 (shield) to ground. One thing, maybe the fact that shielding and signal ground met themselve at the same ground connection, noise and interferance flow along signal ground and pollute it? maybe if I strap these pin 1 straight to the tube socket mounting bolt it will help?
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Post by deepdark on Aug 11, 2015 11:38:12 GMT -6
Thanks. I'm thinking about C1 that could be bad??? Maybe it is Noisy and/or isn't fully passing frequencies??
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Post by deepdark on Aug 11, 2015 10:40:04 GMT -6
Hi there
I know Svart has made one (seen the thread over Groupdiy) so maybe you will be able to help me out, or anybody
I linked the schematic used. I drawn the psu I made (RC filter) and the other thing is that R3 and R4 are 47K, like the original user manual schematic instead of the 12K, appearing on teh schematic laying Under original AM864.
Input and output transformer are Edcor, as well as power transformer.
So far, it passes audio. But there is some little thing that seems to be innehrent to some build.
1. Hiss and hum. There is a little. More of hiss, thought. it don't cover the audio, but it is there. Heater is balanced and grounded at transformer center tap. There is basicaly 2 ground point: one at the IEC and taking all PT center taps and psu ground. The other one is near the main board and take R8, V1/2 pins 1-3-5, C1/R1 and R9-R13-R14. So far, I think about it and maybe V1 and V2 aren't well balanced, maybe R8 (current control) should be grounded at the IEC. I'm pretty sure I have enought filtering, I calculated around 150db of ripple reduction, which should be plenty enough. Maybe the fact that input transformer isn't shielded it could picked up some noise/parasyte?? Input and ouput xlr are shielded cable and pin 1 to case. Maybe disconnecting the output pin 1 from ground? The noise is there with no signal passing through. The more I turn the attenuation knob, the more hiss it has, but I should say it's more around the middle position through the full cw that hiss and hum is present. So, of course, we could just drive the input with a strong signal and just use the first half of the attenuation, but I really want to get it to be clean.
2. Motorboating. It appear about the 3/4 position of thershold and sometimes while I turn the current control, too. I'm pretty sure it has to do with V1 and V2, maybe they aren't well balanced so bias is not optimal??
3. The lack of low end. I mean, a real lack. Coupling caps are stock to the original (0.1uf). I really don't know where in the circuit it could be lost. A bad 6sk7 tube? Maybe I could try to pull out the 6SQ7 tube, so basically the compression side and see if my low end came back. Since I used the same Edcor transformer than other folks, it shouldN,t be the culprit.
Thanks guys Attachments:AM864 SCHEMATIC.pdf (447.94 KB)
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Post by deepdark on May 8, 2015 16:28:39 GMT -6
Thanks svart. The svhematic from which i dérives mine uses a 6x4 rectifier 2x 0A2 tube regulator. Some people claim thé 0a2 are noisy and replaced it with a zener string like m'y schematic. Si my principal concern was to know if i did dit right and the psu looks right. Maybe i'll jeep thé oa2, though. Does m'y svhematic looks Good or do i made mistake ?
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Post by deepdark on May 8, 2015 13:38:18 GMT -6
Hi there I'm about to build a Redd 47 and was looking at the psu. I first found the JBB design over groupdiy. His is build with a 6X4 and the 2* 0A2 regulators. Really simple and nice. I redraw the psu schematic with diode rectifier and I replace the 2x 0A2 with a zener string. I would like to know if I'm ok, or if I should put another filtering stage. Is the zener strings allright? By the way, I was searching how to evaluate the ripple factor within a solid state rectifier but found nothing really clear about that. I know how to determine it in a tube data sheet with the curves, but i'm not sure with the diode. Thanks Attachments:REDD47 PSU.pdf (100.08 KB)
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Post by deepdark on May 8, 2015 13:34:46 GMT -6
I thinks they re worked it entirely and they will post a new pcb on their site.
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Post by deepdark on Jan 16, 2015 5:03:11 GMT -6
Ok so input transformer Will be 600:600, as the output one. Something like cinemag should do the trick. Now i was asking myself how to evaluate the upper grid by-pass cap. Is there a general roule of thumb, or some maths i could apply?
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Post by deepdark on Jan 15, 2015 9:52:17 GMT -6
Thanks for the reply. Actually, it will be use in insert soundcard or straight after a preamp, or compressor. So my guess was to imagine the input impedance of the primary at 600ohm, then the secondary...I don'T know. But, I know I want to exit the unit with 600ohm. So there it is. I'm not sure about how to determine the secondary of the input transformer. Since it's what will load the circuit, is a 600:10K will do the tricks? And looking at the output, if the rule of thumb works, so my calculated output impedance is around 556ohm, * 10 = =/- 5 600K. I should try a 10K:600ohm. Am I right?
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Post by deepdark on Jan 15, 2015 8:00:11 GMT -6
Thanks Svart. Actually, I redraw the circuit in a mu-follower topology. There is some little thing I need help to understand, such has how to determine the right transformer ratio/impedance. Here is the new circuit and the maths on the other page. I calculated an Zout of around 556ohm. Attachments:mu-follower eqp.pdf (887.13 KB)
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Post by deepdark on Jan 14, 2015 12:24:29 GMT -6
Thanks for the reply. I'm looking at 2 topology now. The SRPP and the Mu-follower. I think I should get a try in designing a MU-follower and see what people think about the circuit.
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Post by deepdark on Jan 14, 2015 8:56:01 GMT -6
Ok, it looks like a bad idea and the tube choice isn't suited to be drive with an output transformer. Maybe a SRPP should be a better idea. Or a cascode with a 12au7?? Anyone tried it with transformers?
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Post by deepdark on Jan 12, 2015 8:43:31 GMT -6
Hi all
I'm looking to make an EQP1A but with a new amp circuit. The goal is to get rid of the interstage transformer and the feedback circuit from the output transformer. All of this in a way to save some $, simplifying the circuit and made it more diy friendly to use with a variety of transformer. I know Gyraf made a SRPP design. But I would like to make something I could show to local music store, in case they would be interested in buying some copies. Something that isn't that far from the original circuit, but not an integral copy of someone else, too.
So here it is. I looked at a Cascode design and would like to know if it's a good candidate for such an task? Assuming the filtre section will eat up around 20db, it would be nice to get back all of these and even more. Sould I consider 12AX7 or 12AU7? In know a 12AU7 will result in less overall gain but if I can get back my 20db lost, why not?
Attachments:EQP1A CASCODE.pdf (475.23 KB)
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Post by deepdark on Jan 11, 2015 7:04:39 GMT -6
Thank you john
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