Redd 47 help - Drip forum taken down
« on: September 29, 2015, 06:15:51 PM »
HI All,

Since the drip forum is taken down, I thought we could get some answers to the unexplained parts of the builds.

First off, the T-Pad.  Does anyone know how to convert the 600ohm tpad to a 200ohm?

The low cut, how exactly should this be wired.  The example in the manual makes no sense.

I'm sure others have more.  I've attached the 47 manual that I have.


Re: Redd 47 help - Drip forum taken down
« Reply #1 on: September 29, 2015, 10:14:02 PM »
A lot of people are going to be screwed because some of the Drip builds have issues and not having the forums to refer to is bad news.  I did not build the 47 but I did build a V72 and have saved a bunch of things relating to both projects.  Will try to share what I can;

This shows a simplified high-pass (low-cut);
https://www.dropbox.com/s/0za1nt5jflm50p3/47-tips-and-trix.pdf?dl=0
It's an earlier board but you should be able to use that guide.

600 to 200 using a Hairball attenuator;
https://www.dropbox.com/s/9kaetqm9ep9wbjq/600to200atten.jpg?dl=0


Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #2 on: December 04, 2015, 09:06:05 PM »
Thanks a ton, Bowie.  I was looking for that info too.

I'm rather disappointed that there isn't really any documentation about the 47 Ultra build, aside from a few second-hand testimonials.  I just powered mine up for the first time and unwittingly had connected both the AC and the DC heater supplies at the same time.   Something fried (hopefully just the oa2 regulator tubes!) and now I need to figure out the extent of the damage.  I'm getting good DC heater voltage, but all my amplifier voltage test points are hovering near 0v.  If anyone has done something similar and diagnosed the issue, please let me know! 

I can't wait to actually hear this beast--I actually sprung for the Duelund output cap and all mundorf filter caps.  It should be pretty sweet.

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Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #3 on: December 10, 2015, 04:16:10 PM »
I replaced my OA2 regulators and nothing's changed.  I now believe that I blew my 6x4wa rectifier with my hookup error since I'm seeing AC plate voltages at the rectifier socket, but no plate voltages at any other tube sockets or any voltage readings at the other test points in the amp circuit.  I have a nice NOS 6x4 replacement on the way, but I want to make sure that the voltages at the rectifier pins are correct before I risk blowing my new tube.  Can anyone help me out a bit?  I'm not exactly sure how to interpret the voltage readings I just took at the rectifier socket because I'm not exactly sure how the two plates are supposed to relate to one another and to ground.

Pin 1 -- plate 1 -- 360vac referenced to ground
Pin  6 -- plate 2 -- 95vac refrenced to ground
Between the two plates, I read 630vac, which is identical to what is coming off the secondary of my PT
On the PCB, Drip has written 380v above the rectifier socket, although I'm not sure what that's supposed to mean, exactly--maybe that's the rectified DCV?

Drip seems to indicate that I should be getting between 500vac and 600vac off the PT secondary--it's unclear to me whether my voltage reading is too high, right off the bat, and that it might be causing the problem in the first place (I'm reading 630vac off the PT secondary).  For what it's worth, I'm also pulling a high reading off the secondary of my heater supply PT secondary (12vac, where it ought to be 10vac), and the heater supply seems to be working perfectly. 

In short, can anybody help me and confirm that the plate voltages at my rectifier are within an acceptable range?  Am I probably safe to just try it out when my new 6x4 arrives?  Thanks a ton!
« Last Edit: December 10, 2015, 05:09:40 PM by Shattersignal »
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moamps

Re: Redd 47 help - Drip forum taken down
« Reply #4 on: December 10, 2015, 05:43:31 PM »
I'm not familiar with the project, but maybe can help you.
Did you connected CT tap of the power transformer to the power ground?
You should get two identical voltage on the plate pins vs. ground; 250 to 300V AC RMS.
After rectifying you get PEAK DC voltage which is 1.4 times higher if the rectifier isn't loaded. If it is loaded, the voltage is lower. About 350-380V DC is OK.

Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #5 on: December 11, 2015, 02:27:29 AM »
A friend took a look and says that the circuit uses half wave rectification, which explains why the plate voltages aren't equal.  The second plate is reverse bias.  I think my voltages look correct.  I'm going to see how it goes with the new rectifier.  Thanks for the input, Moamps.  I guess I just burned up the heater in that rectifier when I fed it from both amp circuits--I'm hoping that's the case, at least.
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moamps

Re: Redd 47 help - Drip forum taken down
« Reply #6 on: December 11, 2015, 03:25:50 AM »
A friend took a look and says that the circuit uses half wave rectification, which explains why the plate voltages aren't equal.  The second plate is reverse bias.  I think my voltages look correct.

I don't think so. Please look into the similar schematic. 

Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #7 on: December 11, 2015, 12:11:06 PM »
Can anybody tell me for sure what acv I'm supposed to see on the pates of the 6x4 in the Redd47 Ultra circuit?  Has anyone who has successfully built one tell me for sure whether the power supply is supposed to run the rectifier in a full-wave or in a half-wave configuration? 

Moamps, if you're right that I should be seeing identical acv to ground from each plate pin, then what might be the cause of the discrepancy that I'm seeing?  The power transformer seems to be working fine.  Also, I'm seeing the full acv from the transformer secondary when I reference between the two plate pins, except that the acv seems to be offset toward plate 1.  Are you sure that this design doesn't use half-wave rectification, Moamps?  I would expect to see identical acv on both rectifier plates if this were a full-wave rectification design, but I'm not positive that's the case.  I can't find any specific documentation pertaining to the Drip 47 Ultra power supply design, so I'm a bit clueless at the moment. 

Thanks for your assistance, Moamps--it's very much appreciated.

PS--If the new rectifier burns out again, I might consider using a SS rectifier.  The offset avc at the two "plates" won't matter once each one is rectified through a diode, right?  I followed a build on Offset Guitars, where the builder used  UF4007 diodes from each plate location to the cathode location and he says that his built Redd 47s sound fantastic (see link):

http://www.offsetguitars.com/forums/viewtopic.php?f=27&t=70366
« Last Edit: December 11, 2015, 01:05:58 PM by Shattersignal »
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Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #8 on: December 11, 2015, 02:36:37 PM »
Update: I mistakenly did not ground the PT Sec CT.  Now that it's grounded, I see symmetrical 308 acv on both 6x4 plate pins.  When the new 6x4 arrives, I should be back in business.  I see on the 6x4 specs that it can handle 325vac on the plates, so my mistake must have burned one of them up.  I hope those filter caps are safe...

Thanks for the help, Moamps!
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moamps

Re: Redd 47 help - Drip forum taken down
« Reply #9 on: December 11, 2015, 02:52:10 PM »
Are you sure that your old 6x4 is dead?  Did you check the heater with ohmmeter?


Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #10 on: December 11, 2015, 06:02:26 PM »
I did check the heater with an ohm-meter--and it does have continuity.  But I wonder if exceeding the maximum plate voltage might have done the damage.  I'm not sure what dcr I should see on a heater, but there definitely is continuity.  The dcr seems to fluctuate.
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Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #11 on: December 12, 2015, 06:13:12 PM »
To be more specific, the 6x4 is definitely not heating up, nor is there any voltage heading downstream into the circuit.  The voltage seems to be stopping at the rectifier, which is why I suppose that it's dead.
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Deepdark

Re: Redd 47 help - Drip forum taken down
« Reply #12 on: December 14, 2015, 08:18:26 AM »
40 000uf filter bank :o

That is behond insane. I made 2 p2p redd47, made with a simple 5 stage rd filter, ss power supply, and used 6 47uf capacitor and there was no hum or noise.

Does it work now?
"I'm givin' you that money so I don't have to kill your ass."

Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #13 on: December 15, 2015, 03:01:35 PM »
I need to order filter caps with the correct rating.  It uses 3 x 22uf foil caps.  I ordered the ones in the original BOM, at 47uf, but the volatage rating is only 350v--I need to get caps that can handle at least 450vdc and then I'll fire it up.

Deepdark, what sort of filter caps did you use?  I'm curious how much one can actually hear a difference with foil PSU filter caps vs polarized caps.  I decided to just buy the best I could, since I intend this mic pre for main vocal and instrument recording.  After putting all the effort into the build, I figure I'd wish I'd used the best parts available.  I certainly saw the difference when I installed all Mundorf Supreme SGO caps in the audio path of my Pultec and my 1176 rev A builds.  I even sprung for the Duelund Cast PIO Cu for the output coupling cap position in the Redd 47  :D
« Last Edit: December 15, 2015, 04:38:02 PM by Shattersignal »
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Deepdark

Re: Redd 47 help - Drip forum taken down
« Reply #14 on: December 16, 2015, 08:17:30 AM »
Deepdark, what sort of filter caps did you use?  I'm curious how much one can actually hear a difference with foil PSU filter caps vs polarized caps.  I decided to just buy the best I could, since I intend this mic pre for main vocal and instrument recording.  After putting all the effort into the build, I figure I'd wish I'd used the best parts available.  I certainly saw the difference when I installed all Mundorf Supreme SGO caps in the audio path of my Pultec and my 1176 rev A builds.  I even sprung for the Duelund Cast PIO Cu for the output coupling cap position in the Redd 47  :D

I used Panasonic Aluminium Electrolytics. 5 stages and a first filter cap, all 47UF, 450V. I don't think you'll hear much difference between caps type in the power supply. Remember, the power supply is there to provide you clean DC to feed your tubes Anode. No audio signal pass through it. Noise Wise, I don't know if there will be some difference. I always go with Lytics in PSU for filter caps.

If you do the math, you'll see that with 6 47uf caps, I got a really clean sounding pre, no noise, no hum. It's plenty enough. That's why I was shocked to see a filter bank of 4 10 000uf caps. That's completly insane, and should cost some $$, for what benefit? Maybe there is a reason behing this, I never studied the Drip schematic. Good luck with your build  ;D
"I'm givin' you that money so I don't have to kill your ass."

Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #15 on: December 16, 2015, 11:58:52 AM »
Those 10000uf caps that you see are in the heater supply PSU.  There are two PSUs on the same PCB, giving you the option to have a separate dc heater supply circuit, or a phantom power circuit (mine is for the heaters).  The audio amp uses 3 foil caps in parallel--I'll be using 22uf caps here, since the Mundorf Evo 47uf is only rated for 350V.

I have read that foil caps do have advantages in power filtering stages.  I'll leave that point to someone who knows more that I do, though  :D

I only hope I have enough capacitance in the amp psu, now.  The pcb was designed for a bank of about 140uf, and now I'll be using a bank of only 66uf, due to the designer's mistake on the power rating of those Evo caps.   I know that electros are more cost-effective--this build was designed to be really over-the-top in build quality.  I don't know--perhaps its a bit silly.
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Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #16 on: December 16, 2015, 12:20:21 PM »
Should I terminate the output to 200 ohms after the transformer?  I used Sowter Iron (model 9988, I believe).  Will this traffo ring if run into my Lavry or another modern hi-impedance bridging device?  I'm also thinking about using a switchable T-pad on the output, for use when I want to intentionally overdrive the unit.  I'd like to be able to completely remove the pad from circuit, if no 200 ohm termination is necessary for normal operation.  If a 200 ohm term is recommended, I guess I can just leave the pad in circuit and use a modified Hairball unit ust like I used on the input.  Is a 200 ohm term needed with this iron?  I've seen conflicting opinions.
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Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #17 on: December 28, 2015, 02:01:46 PM »
Another question--the Drip Ultra PCB labels two jumpers that connect the DC heater supply to the tube filaments in the amp circuit.  The two rails are labeled +6.3V and -6.3V.  Is this a typo?  Is there actually supposed to be a negative voltage on that rail??   I have +6.3V and 0V, respectively, referenced to earth ground.  I also can't see any reason that the amp needs a differential of 12.6V, since all the tube filaments run on 6.3V.  Can any Drip 47 Ultra builders confirm that this is a typo?  Or is my heater supply messed up?

I can't test for operation until I get a new batch of Mundorf filter caps, which won't arrive in the States for a couple weeks.
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Shattersignal

Re: Redd 47 help - Drip forum taken down
« Reply #18 on: December 28, 2015, 04:02:13 PM »
Here's another useful question for builders of the Drip 47 Ultra that I'd love to have answered if there is someone who has figured it out.  If someone has the information, I think it would be enormously useful to other builders, and ought to have a place on this thread:

What are some additional resistor values that can be used in the negative feedback path, to create additional "gain" settings?  The Chandler Redd 47 has added several additional gain ranges, for instance.  It would be quite simple to modify the drip build to also include these other NFB amounts, and in doing so also create some new harmonic distortion voicings.   The three original settings (for 34dB, 40dB, and 46dB into 200 ohms) all were selected to cancel out the second order harmonic distortion in the V1 and V2 stages.  Other resistor values would provide more and less second harmonic, which I believe would be a fun way to create some new and interesting sounds from the preamp.  Has anyone experimented with values and can report on their findings?  Thanks!
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Re: Redd 47 help - Drip forum taken down
« Reply #19 on: August 07, 2017, 01:27:16 PM »
I have built the REED 47 and it is going great. I have put in a variable low pass filter. However, I get significant hum engaging more cutoff. Any ideas on how to eliminate hum in this low pass circuit?


Thanks