R*E*D Forty Seven

[Winston OBoogie]

Winston,
Thanks for the input!

Can you characterize the two...

Many records (you've probably heard some of them) were done with units that had the 50-50 and no-one complained.

I wouldn't say the Hi-Nickel is clinical, it just worked nicer in some units.  Those units might also have had different type coupling caps or?

can you share what the newer one is you prefer?  is it available to the public?  You're killing me here!!       haha!

Don't kill yourself Brad, it's all good 
It'll work well with either of the Cinemags and I dare say the Sowter is a fine transformer too.

If I told you what I use now, then you'd all want them 

I will tell you that I recently used the Hi-Nickel backwards as an input for a compressor, sounded great.

John

 

[bradb]

 

[Winston OBoogie]

Brad,
Upon reflection: If you can swing it, spend the extra $30 for the Hi-N. Cinemag.  In the scheme of your total parts cost, it's a fraction.
I'd say my new transformer sounds closer to that one than it does to the 50-50

I know you're using a PCB so it's a bit more complicated but there are other things too that affect the tone of pre amps.  Power Supply topology, component choices, layout, tubes, slight tweaks in H.T. or bias, different forms of bias, Feedback (don't use too much if you can help it)... etc...


The Cinemags handle a ton on signal and, in typical level use, are very linear.  Same for the CMMI-7C input if you have a stepped attenuator before it.  You won't be hearing much iron saturation.  The differences will be tonal shifts to various degress.  I've heard as much of a difference in a pre amp by changing the brand and voltage of a cathode bypass cap.

Y.M.M.V.

John

 

[bradb]

Thanks, thats the kinda push over the top that i needed!

 

[abby normal]

John, I was just looking at the 47 spec sheet. It looks like it was designed around a 200 ohm load. Test circuit with a 200 ohm closed or built out 200 ohm. What do you think it was seeing on that secondary? Just for my own ed-ja-ba-ca-tion.  ;D

 

[Winston OBoogie]

John, I was just looking at the 47 spec sheet. It looks like it was designed around a 200 ohm load. Test circuit with a 200 ohm closed or built out 200 ohm. What do you think it was seeing on that secondary? Just for my own ed-ja-ba-ca-tion.  Grin



Dear Mr. Normal     (John Lennon called their first engineer Norman Smith "Normal"  so it's kinda, sorta apt.  )
None of the circuits in the desk operated into a 200 ohm load.  Each device 'presented' 200 ohms to the following circuit.  Except the oscillator which WAS loaded with 200.

Internal output impedance of the REDD47 (including the DCR of the original transformers) was about 50 ohms.  A 150 ohm resistor was added as 'build out' to bring it to 200 ohms.  Depended on what was following the unit as to what the actual load was.  Worst case: A following 200 ohm "T" attenuator or fader turned all the way off would load the amp with 200.  Add this 200 to the 150 build out so, worst case load was 350 ohms.  Again, this was when the amp was turned off.   Most times the amp is bridged by a higher load.


Not sure which spec sheet you're referring to, I have them all and there are quite a few but a 200 load on an original "built out" REDD47 would result in 6dB loss in gain.


Edit: which brings me back to a point earlier: measure the internal output impedance of your REDD47 and calculate backwards and you'll see that the anode source impedance to the transformer is WAY lower than 20+ K.

 

[abby normal]

Internal output impedance of the REDD47 (including the DCR of the original transformers) was about 50 ohms.  A 150 ohm resistor was added as 'build out' to bring it to 200 ohms.  Depended on what was following the unit as to what the actual load was.  Worst case: A following 200 ohm "T" attenuator or fader turned all the way off would load the amp with 200.  Add this 200 to the 150 build out so, worst case load was 350 ohms.  Again, this was when the amp was turned off.   Most times the amp is bridged by a higher load.

I understand. Very interesting, I never took that into account. You learn something everyday. Thank you for clearing that up. 

 

[hitchhiker]

My hope is to try in reverse this fairly large UTC  1 : 7.45  output from the RCA BA73 program amp. With a multi-tester the readings are just under  0.9 ohms and  31 ohms.  I've ran music through these in 7.45:1
step down into a V72 and the result was quite OK.  John, do you think they are likely to work well in this circuit?

 

[seavote]

winston i was planning on using the Gyraf G9 PSU and adjusting the B+ V. a few DIY members have done this and love their redd preamp clones. are there better topologies for the PSU? the G9 is regulated.

http://www.gyraf.dk/gy_pd/g9/g9_sch.gif
is the PSU you spoke about in a recent thread. more similar or different than the G9 PSU?

 

[Winston OBoogie]

My hope is to try in reverse this fairly large UTC  1 : 7.45  output from the RCA BA73 program amp. With a multi-tester the readings are just under  0.9 ohms and  31 ohms.  I've ran music through these in 7.45:1
step down into a V72 and the result was quite OK.  John, do you think they are likely to work well in this circuit?

The only problem I've had with using transformers backwards is when some of them are wound differently.  Sometimes there hasn't been enough coupling from the new primary to the core, but I'm splitting hairs and it generally works OK.  You need enough inductance on the new primary for low end and stuff like that too but, try it...

If it doesn't work well enough for you as an output, it's about right for a humongous input  8) 

 

[Winston OBoogie]

winston i was planning on using the Gyraf G9 PSU and adjusting the B+ V. a few DIY members have done this and love their redd preamp clones. are there better topologies for the PSU? the G9 is regulated.

http://www.gyraf.dk/gy_pd/g9/g9_sch.gif
is the PSU you spoke about in a recent thread. more similar or different than the G9 PSU?

That supply is a decent basic supply it should work in the circuit.

I do things differently when I have the budget.  Some might say more than is necessary, to which I reply: "At the end of the day, you're listening to the power supply".  As a matter of fact, I sometimes DO listen to power supplies by blocking the DC and shoving it into a power amp.  Of course, there's also scopes to see what's happening.

There are several small (in themselves) things that I do that, when added up, make fairly decent improvements I.M.O.

There's hi-freq noise on your ac, there's hi-freq. hash from your diodes.  TL783's  don't help as much at higher frequencies for eliminating this stuff.  Generally, 3 terminal, adjustable regs are about the worst sonically in my opinion.  If you have to use them, build the ouput out a few ohms or more to isolate a bit and add a good shunt cap.  The output impedance isn't as low then but it's still WAY lower than a standard CRCRC filter bank and you will notice it if you do a few other tricks as well.  By itself, on a bog-standard supply...?  Maybe.
Torroidal transformers are another thing: they may radiate less field but they're also wider bandwidth and let in more garbage from the mains.


It's all about attention to lots of details that, when added up, might get you that extra 5%.

I mean no disrespect to the Gyraf supply.  It's as good as any that are generally used in Pro gear.  I've used worse myself when budget was a consideration.  It also has a proven track record in many units that people are more than happy with 
Depends how far you want to take it really or, more realistically, how much time you want to spend learning, adapting and applying the tricks.  The learning and applying never really ends, not in my case anyway.  If it does (it won't, I'm not that smart), I'll go do something else.

My $0.02

John

 

[ethervalve]

Hi folks,
This is a little out of the scope of the current conversation...
I built a 47 using the drip board; sowter transformers; an RFT ef86 and a JJ e88cc. For the most part, I'm extremely happy with the sound.
One small question for those who've built 47s: did you find the ones you built overload gracefully? When overdriven, mine has a 'spitty' sound.

 

[bradb]

I'd swap tubes and see what happens...

 

[seavote]

thanks winston. dont understand  that but i'm off to the PSU metas and more(internet and some books) to try and rap my head around it.

 

[Winston OBoogie]

thanks winston. dont understand  that but i'm off to the PSU metas and more(internet and some books) to try and rap my head around it.

I will look for some links that give you some ideas.  It'll be a few hours or maybe later tonight as I have to go get some stuff done.

 

[ethervalve]

I'd swap tubes and see what happens...

Thanks Brad. I'll give that a go. i fear i cheaped out on the jj e88cc. Does anyone out there have any experiences with brimar e88cc's in preamps?

 

[seavote]

thanks. might have exaggerated a bit . the only part i didnt get was this:

"If you have to use them, build the ouput out a few ohms or more to isolate a bit and add a good shunt cap.  The output impedance isn't as low then but it's still WAY lower than a standard CRCRC filter bank and you will notice it if you do a few other tricks as well.  By itself, on a bog-standard supply...?  Maybe."
seems like the most important part, a solution or work around. if i  may or may not notice any difference,i may or may not try it. but i'd like to understand it and have the option.

 

[rotation]

I'd swap tubes and see what happens...

Thanks Brad. I'll give that a go. i fear i cheaped out on the jj e88cc. Does anyone out there have any experiences with brimar e88cc's in preamps?

Yes, i tried combination you had and several others:
two versions of Tesla E88CC, 6N1P, 6N23P and JJ ECC88. I could hear quite big difference between them and there was even some difference between two versions of Tesla E88CC.
Tubes i like best here are "gold" Tesla E88CC (i think those were made for Polish post) and 6N1P. First tube is very very detailed and a little agressive, the other have very open sound but not so detailed.
Preamp was a bit agressive with any ECC88. There was also some difference in dynamics, hard to explain.
I also tried several EF86 and, for example, there were big difference between two Tesla EF806. Also, both sounded different from RFT EF86 which sounded best to me.

If i was you i would try another cheap tube like 6N1P or 6N23P (watch for heather current) and leave this preamp as it is.

Miha

 

[ethervalve]

Hey thanks so much for sharing your results rotation. I was ready to try one of the Tesla varieties when I happened upon an old gold pin Siemens E88CC at a radio shop around the corner from me. It sounds wonderful to me... a huge improvement. The grid DI still doesn't overload particularly gracefully but I'm so happy about its sound as a pre that i'm willing to let that slide.

 

[bradb]

How do you hook up the CM-9661A as an output (7:1) for this circuit?  

http://cinemag.biz/output/CM-9661A_schematic.htm

i was told orange and yellow are primaries and the secondaries are brown and red/white with brown/white and red shorted... (for 7:1) but measuring the DC resistance finds 59ohms between orange and yellow and 360ohms between brown and red/white (again with brown/white and red shorted).  So that seems like 1:7...

I'm a little confused because the cinemag page doesn't have a detailed cut sheet.

correct?