Redd. 47 preamp + Redd EQ

[emi2345]

Great thank you Ian

 

[maxwall]

Edcor output type recommended , XSM(2.5w) , WSM(1.2w) 10K:600 (4:1) or 15K:600 (5:1) ?

Is there a economically friendly shielded (screen can) input (~1:7, - 1:10 ) like the Vigortronix VTX-101-003 or OEP A262A3E or similar in US ? Some say these are not the good sounding, maybe too low v gain ..... OEP A187A15C as suggested by previous forum discussions.

Input configuration :
Primary : 150ohm parallel connected or 600ohm C.T. series connected
Secondary : 6.25kohm parallel connected

 

[rock soderstrom]

For REDD47 WSM 15K:600 will work. 10K:600 will work in high impedance 10k Inputs but will loose low frequency end in low impedance 600R Inputs.

 

[maxwall]

Input : OEP A187A16C/1 1+1 : 7+10 or OEP X187B ? personal experiences ?

 

[rock soderstrom]

Input : OEP A187A16C/1 1+1 : 7+10 or OEP X187B ? personal experiences ?

No, sorry.

 

[maxwall]

Neutrik mic input Transformer
NTE10/3 1 : 3 200 : 1.8k 200 / 10 K -7 General purpose mic input step-up
-------> 1 : 10 200 : 20k 200 / 50 K -6

NTE10/3 datasheet (may need a can and potting.)

Does Haufe make anything close , they seem to be affordable , but I cannot locate a catalog for Audio Transformers.

 

[rock soderstrom]

Neutrik mic input Transformer
NTE10/3 1 : 3 200 : 1.8k 200 / 10 K -7 General purpose mic input step-up
-------> 1 : 10 200 : 20k 200 / 50 K -6

NTE10/3 datasheet (may need a can and potting.)

Does Haufe make anything close , they seem to be affordable , but I cannot locate a catalog for Audio Transformers.

Well, the Neutrik NTE 10-3 is really very small. Look at the photo, to give you an idea I put a quarter inch jack plug next to it. These IPT are not particularly level resistant and need shielding in any case.

Haufe will build you just about anything you can imagine if you have deep pockets.
But they prefer business customers and large quantities.

I'm guessing you're based in the US, which also makes shipping relatively expensive from Germany.

I would look around at Cinemag, they have great 1:7's on offer. The price is good too.

 

[maxwall]

Yes, I noticed they were small as most input types are typically small in most cases. However , I have some in line 50K : 600 types that are also small , however they sound relatively good when going from high impedance to low impedance , examples guitar and synths. I have not used them in reverse to function as a step configuration in the front end of a preamp. They seem to handle the signal quite well. Take Beyer TR BV series shielded transformers , they are very small but function well. However I think their windings designed to handle hotter low impedance signal.


Also looking for a source for ECC88 , PCC88 ? are there any subs ? the prices on these are incomprehensible from online retailers.

How are the 6N1P ( ECC88) ?

 

[ruffrecords]

6N1P is nothing like an ECC88 but the 6N23 is. Instead I use 6922 from Electro Harmonix. Available from many places at a reasonable price. e.g. Banzai Music:

6922 EH :: Electro Harmonix :: Tubes :: Banzai Music GmbH

Cheers

Ian

 

[maxwall]

thanks for the tip Ian. I was going to probably take that option since prices on those valves are out of the budget. Any preference between the EH , JJ and 6N23 ? I have had mixed experiences with EH in the past , I imagine I should find some one with selected low noise valves rather than trying my luck on a run of the mill average tube. I'm going to dig into my valve stash and see if I have some 6922's I have forgot about.

BTW who made the original iron for the R47 circuit ? Gardners , St. Ives or custom EMI

 

[ruffrecords]

I use the 6922EH because I have found them to be the most consistent. I have had a lot of parametric variation with the JJ E88CC tubes. I use cheap 6N23P Russian tube for testing purposes but replace them with 6922s when its working. They are not bad but like the JJs they are variable.

Noise in a preamp is dominated by the first stage which generally is not a 6922. For the first stage you want lots of gain and low noise so I use a 12AX7WA because I have found them to be both low noise and less susceptible to microphonics.

I have no idea who made the iron for EMI but I suspect they did it themselves.

Cheers

Ian

 

[maxwall]

Are their any quick and easy turret layouts available for the Redd47 to save time designing my own, which would be more time consuming ?

I plan to use a power supply design from a Peavey VMP-2 preamp , 290-300v B+, 6.3vdc Fila , +48vdc and fast recovery ss rectifiers.

Input Iron : OEP A187A16C/1 (1 to 7+10)
Output : Edcor 15K:600
Option : Line in , Jensen - 10K to 10K

 

[BOB42]

Hello
I would like to know if the insertion of the HPF is correct and if the 47K resistance of the filters is correct?
is it possible to replace the 9970 SAWER transformer with a UTC A11 transformer?
thank you
Bob

 

[BOB42]

Hello
Attached is my REDD47+EQ approach diagram
according to your indication Ian
I would like your opinion on the exchange of transformer at the entrance
and placement and the resistive value of the HPF
Bob

 

[ruffrecords]

Hello
Attached is my REDD47+EQ approach diagram
according to your indication Ian
I would like your opinion on the exchange of transformer at the entrance
and placement and the resistive value of the HPF
Bob

Unfortunately you schematic is very small and when it is magnified it becomes very blurred (it turns out it just takes my old computer ages to redraw it!). However, I think you asked about using a UTC transformer at the mic input, Any mic inout transformer with the correct ratio should work. However, I have never used UTC transformers so I have no experience of how godd or bad they are.

You HPF will theoretically work but it will be very prone to hum and noise pick up because it involves increasing the length of wires in a very high impedance circuit. It is good practice to minimise the length of the the connection from the input transformer secondary to the grid of the first tube.

There is no need to use a bridged T attenuator after the REDD 47. A standard 10K stepped pot will do the job. And anyway your bridged T attenuator is a 600 ohm type which the ECC88 will not drive.

Your EQ gain make up stage will not work. Its input impedance is too low. I would advise you to use an ECC88 based mu follower or SRPP stage instead as both of these options have the high input impedance necessary for the EQ to work properly. You could base the gain make up stage on a version of the attached buffer amp.

Cheers

Ian

 

[BOB42]

Thank you
if I place the HPF before the transformer the hum should be less?
I will redesign the gain compensation by integrating your expertise and your comments.
for the transformer I'll look for the report on the web (which I can't find)
thank you again Ian
I will post the modified schematic in the next few days.

 

[BOB42]

Hello and thank you Ian
attached diagrams with your suggestions for modifications
I put 1 pot of 10K on the EQ on/EQ off switch
I took your buffer.
I put R 8.2K and C 1uF on HT+
I have doubts about my calculation of the gain potentiometer
and the resistance that precedes it?
can you help me?

 

[BOB42]

Hello following the very relevant remark of IAN
I placed the HPF before the transformer and I replaced the 47k resistors with 3 K
did I do well?
does anyone know the ratio of the UTC A11 input transformer?
thank you

 

[BOB42]

Good morning all
following your advice
I redesigned the EQ selector
I would like your opinion on the choice
I am for version 1
can someone help me with the finalization of the IAN buffer?
I can't calculate the 2 resistors for the gain.

Thanks very much.

 

[ruffrecords]

The advantage of version 1 is you avoid sending the signal through the buffer amplifier when the EQ is switched out. However, it assumes the output transformer used for the buffer is also suitable for the REDD 47 output. Unfortunately the two amplifiers require different ratio output transformers so this method will not work.

Version 2 will work fine.

Ceers

Ian