REDD 47 PCB

[monkeyxx]

Thanks for that.  An external power source might be what I'll do.  Any advice on a power source that could power 3 or 4 of these?  I'm a bit new to electronics so I'm still not quite sure how to design or specify a power source to a given circuit.  I guess I'd need the right voltages and enough current capability but I can't even tell how to read this off of the REDD 47 schematic.  Help? 

Are there any sonic benefits of using the original power source and voltage regulator tubes, etc?  I know some people are connoisseurs of power supply.

 

[pucho812]

Hey pucho, if you dont mind my asking.

What output transformer are you referring to?

redd 47 what this thread is about.

 

[ed rees]

John Hinson always said the voltage regulation was an important part of the sound. IIRC his amps used zener regulators instead of the OA2 diodes.

The power supplies in the Redd consoles were SS rectified. I'm far from a power supply expert, but a transformer that puts out 320v@250mA will power 3-6 amps once rectified and smoothed. Pretty sure Edcor sells one that will work.

Each amp draws 30mA@380V

 

[alexc]

My Orange 86s use around 30mA of 250Vac HV with some 320Vdc after filters and 290Vdc after regulation.
And heater is around 600ma of 6.3V depending on tube choices.

If you are going for lots of them, point-point I think 4 in a deep 2RU could be done fine with an external PSU.
Would probably make it quieter too.

I agree that regulated hv is a good idea - one of the great things about Charley's Orange 86 pcb is the simple yet very effective HV regulator. The challenge would be to make something like that for 120mA of HV. As others have said, single ended (parafeed) output stages are not the best in the world for power supply rejection ratio. A good,  quiet B+ is a must.


There are commercial regulated hv pcbs out there, but >50mA or so in a single pcb is trickier.Maybe 2 of them ?
Or you could make a 'real mans' project of it and do a pp tube regulated HV - not so hard.

Easier for some than making a pcb!

Then there's phantom power - a suitable Edcor  PSU traffo would certainly be available and with a 50V bias tap, suitable for phantom. Again, some regulation is probably required, so the challenge is to find a pcb for that.

I would probably go for ac heater - I have not seen any advantage yet in dc heaters, except maybe for vari-gm limiter GR tubes.

On the other hand,considering all the psu effort, it might be just as well to do 2x Orange 86 + PSU pcbs in a 2RU

The way Charley intended with his Orange 86 

 

[Fablab]

Someone has compared the Orange 86/REDD 47 with the G9?
I have read of persons that prefer the G9 to the Telefunken V72 (that is similar to the REDD 47)
The REDD 47 is considered a great preamplifier, but it is possible that Gyraf made a step further?

 

[alexc]

I've built both orange 86 and g9 units. 'Better' etc is very subjective and each person may have different preferences. How do you define 'better' ? Wider freq response? Lower noise floor? Lower THD or IMD ?
Or the complete opposite? Is 'better' more characterful? And so on. And on.

I found both units to be low noise floor, full freq response etc, so they are both of high enough quality for serious work.

My preference is for the Orange 86 - I found it has more 'character' than the G9. I thought this would be because the Orange 86 would have  more harmonic distortion, but I measured the opposite, using single tone tests.

I found the G9 had quite a bit more overall distortion, even though it sounds very clean. The Orange 86 had less overall distortion and quite a different mix of even/odd harmonics. But it sounded more typically 'tube like'  ie. distortion. It too was clean but driving it harder gives more character as the amount of negative feedback is reduced. (also true of the G9 - it also uses a negative feedback attenuator)

Perhaps because my Orange 86 has less gain (maybe 40dB or so max) than the G9, I tend to push it harder, giving more THD and so being more pleasing to my guitar-biased ears. But certainly under test I found the G9 had more THD. Surprisingly so.

It could be the transformer choices too - Lundahl ins, Carnhill outs on the G9 and Haufe/UTC ins and Edcor outs on the Orange 86. There is some small difference between the Carnhill and Edcor. Nothing detectable by me between the Lundahl and Haufe (except 6x price!). The UTC has less wide bandwidth but not so much.

I would expect other's experience may well differ from mine.

My opinion would be that the G9 is a fine unit but not so different in sound from solid state or discrete units. The Orange86 was much closer to what I expected a tube unit to sound like.

In other words, why go to the trouble of doing a tube unit if it sounds very similar to a cheaper, easier solid state or discrete unit? For that reason, I think the Orange86 is a must have, the G9 doesn't see so much use.

The  main thing imho is generalizations about preamps 'better', 'worse' and so on are not very useful. Much less, comparing mythical (to most people) units to diy builds.

All the options are probably very good - the best one for an individual is a combination of things, like

- price
- audio performance
- likelyhood of completing a good quality build
- usability
- character

You make a choice and go with that. Then make another choice and go with that. And so on.

Eventually you forget the original question

 

[Fablab]

Thank you alexc

 

[michal_k]

I've just done this. I should be done with routing by tomorrow. What ya think?

 

[Mike Cleaver]

Looks good, clean layout.
Are you planning a power supply card as well?

 

[michal_k]

I was planning on breadbording simplier simplistic for B+ supply:
http://www.diyaudio.com/wiki/Simplistic_Mosfet_HV_Shunt_reg_PCB_Instructions

But while I'am at it, I may as well draw a PCB.

 

[Gearsix]

Damn, the day before yesterday I have already started the p2p construction!
Anyway, thank you the same Michal

 

[buildafriend]

Alex, thanks very much for the information about the orange 86 PCB. I have two of the PCB's that I am going to start populating/building soon. I might make a nice front panel in front panel express for the pair as well. I want to rack in a 3u 8" deep chassis. for transformers i plan to use some cinemags that i was given. one is a CM9661AL and the input is a cinemag CMMI7c. Do you have any fun transformer recommendations for the other channel? I would like to experiment a little or maybe to just build them both with different transformers. i happen to have a UTC CR-725 (100ohm:600ohm) sitting next to me but im not sure if its in spec.

the squish option seems like a fun thing to play around with. I have the other PCB's too for the rotary switch and DI add ons. 

Edit* dont build two in an 8" deep chassis. use a 14" deep one. Why? because the build manual says:

2 channels will have some crosstalk; at about -105dB between 600Hz to 5KHz
-Personally, I don't mind the small amount of crosstalk especially since the test involved a
very hot sine wave, which will not be happening much unless you are running a moog
through it. However, a single channel properly encased preamp will ensure no crosstalk.
-1 channel case should be 11 inches deep
-2 channel case should be 14 inches deep

 

[buildafriend]

I was planning on breadbording simplier simplistic for B+ supply:
http://www.diyaudio.com/wiki/Simplistic_Mosfet_HV_Shunt_reg_PCB_Instructions

But while I'am at it, I may as well draw a PCB.

very cool!

 

[alexc]

Do you have any fun transformer recommendations for the other channel? I would like to experiment a little or maybe to just build them both with different transformers. i happen to have a UTC CR-725 (100ohm:600ohm) sitting next to me but im not sure if its in spec.

You could try it as an output 600:150. If it's a larger size, it should have decent amount of iron and inductance (hopefully).  Don't know what the freq response and max level is.

I did use  Carnhill ungapped Neve style as output on my G9s. That's 150:600 and I used it backwards. The freq response is ruler flat and well extended.

Only one way to find out

I have used :
- utc 08 as input, Haufe 1:4 mic as well. I like them both
- Carnhill 9600:600 ungapped, edcor xsm 10K:600, UTC a15 as output. Each of those works fine.

I would probably like to use something like an UTC A11 for mic/line and UTC A35 for output.
Both not too crazy expensive. I'm on a cheaper UTC kick at present!

Also there a some Stancor outputs WF34 or something like that - basically same as A15 or A35.
UTC A24 good also but a little expensive.

Then there's a whole raft of Sowter stuff - I like their traffos a lot but yes they can be a little pricey for some models.

And if you had real bucks, get that utc 30K:600 from emrr! 7:1 step down - a little high for me but common for this unit. Surely is the pinnacle of performance and a great price too!

Lots of possibilities - the circuit is pretty straight forward and relatively forgiving of traffo choices.

My current builds are adding a 'eq+drive' section which adds .. eq .. and .. drive!
So my output is quite a bit hotter than the stock unit. And it opens up more gain/driver stage possibilities.

The cheaper UTCs have less low end response : +/- 3db point is at 30Hz or 40Hz instead of 20Hz as these guys can take some dc current as well. I compensate for this with the eqs which can boost the low end easily by a couple of dBs and call it 'flat'

And on the subject of dual unit cross talk -105dB crosstalk is pretty low.

I find these units have a noise floor of worse than that.
I doubt I would notice it much in measurement and not at all in usage.

 

[buildafriend]

Well I'm willing to give it a shot! I'm really lucky in the sense that I have access to a shop with a whole lot of great stuff stuff in that I can usually test out and sometimes buy off of the guy. If it sounds great I'll be sure to trace the curve in RMAA for all to see. Based on what you're saying about your g9 and a similar ratio tramsformer I might get a decent result.

UTC 08 eh? I'll keep an eye out for one. I'll set the eBay account to autosearch for one. The UTC A11 and A24 are so expensive. I looked into them for my RCA BA-2A clone and it was just crazy. I don't see how they could be worth it. And they're rare now. I'm not sure where you live but I don't like paying extra and waiting longer at the same time. I feel waitlisted by the shipping time. That stuff can end up in customs for months! Though so far I don't have any real regrets about how good the Ampex 9735 iron is from them. I can't really spot the transformer differences yet outside of turns ratios, impedences, and freq response. I need to extend my understanding if transformers. Maybe I should make a thread where I can make a fool of myself and ask dumb questions. Or maybe one already exists ?

Your EQ/drive circuit sounds good. How does it work?

 

[My3gger]

I've just done this. I should be done with routing by tomorrow. What ya think?

I wouldn't place capacitors so close to tubes, ECC88 is very hot here. 8k2 resistor is pretty warm too, try to make it out of 2 resistors to divide heat between them. Think about what happens with time when you have 2 ch like this in rack; traces start to lift, caps fail, etc. Don't ask me how i know this.
Why don't you put tubes on L profile and the rest on pcb, if you really want to use it? I would also drill some holes in the lid, at least over ECC88s.
I red that people who originally used this preamps complained Redd47s were running very warm and had a lot of downtime compared to V72s. So give it a good passive ventilation.

 

[dmp]

8k2 resistor is pretty warm too,

If the current on the schematic is right (0.0185 mA) the 8k2 will be dissipating 2.8 watts.

 

[michal_k]

Thanks for the tips, I'll change ecc88 plate resistor for a 5W type. As for the capacitors near tubes, I've intended to use jj-electronics tube type caps that have a bit higher temperature tolerance. I guess I'm gonna have to build it to see how hot the caps get. For now, here's grounding scheme and full wiring. As always, I'm looking forward to your comments.

 

[alexc]

Your EQ/drive circuit sounds good. How does it work?

It's basically another Redd47 style tacked on the end!

The first time I did it, I used the Orange86 pcb using an output transformer as usual.

It fed a 'preamp' out XLR and also had a relay bypassable feed to a second Redd47 style section with both transformer in (a small easily saturated one) and a regular out.

That section used a tone stack+gain make up tube  (2 gain stages) with resistive dividers and pots 'fore nand aft'. The pentode was therefore able to be overdriven/clipped etc. I did also variable bias of the pentode and triode/pentode switching.

Line amp was standard.

Gives a wide variety of distortion and tone control from god-awful to nice-n-crunchy.

This time around, I'm not using the input transformer on the eq+drive section. I don't need it as I'm not going to include a dedicated 'preamp out'.

Apart from that, pretty similar to what I did but will have a fancier tone stack this time and each of the 2 I'm doing will have a different line amp : one an single-ended mega triode, the other a push-pull pair of triodes.

The circuit is really good fun to mess with. Take a look at Bernbrue's 'Rude Tube' and see how the 'drive' side of things can evolve from the Redd47 preamp.

 

[buildafriend]

Thanks for the tips, I'll change ecc88 plate resistor for a 5W type. As for the capacitors near tubes, I've intended to use jj-electronics tube type caps that have a bit higher temperature tolerance. I guess I'm gonna have to build it to see how hot the caps get. For now, here's grounding scheme and full wiring. As always, I'm looking forward to your comments.

Looks cool. are you planning on etching or ordering boards? I might be interested in grabbing a pair off of you if you have them made.