4:1 vs 3:1 output freq response

[ruffrecords]

I see 4dB down at 20Hz with max gain

Edit:  with the Peluso that is.

Ah, now I get it. I was looking at the Jensen. This Peluso looks typical of a transformer with insufficient primary inductance. I think it would be worthwhile measuring this parameter and comparing it with the Jensen.

Cheers

Ian

 

[Winston OBoogie]

My WHOLE goal in this is to use a 3:1, 2:1, or 1:1 output TX for more output gain and less saturation on the preamp. I also want to try a lower 1:5 input TX, and switchable 1:10 or 1:20 for ribbon mics, if I can get the output level up more.

Then the easiest and least expensive way would be to loose the output transformer and go straight from the white follower to your interface.  There's no shame in an unbalanced output. 
But without resorting to some form of bass boosting compensation, I don't see how the Peluso is going to give you a flat to 20Hz response in your circuit. 

 

[Winston OBoogie]

Ah, now I get it. I was looking at the Jensen. This Peluso looks typical of a transformer with insufficient primary inductance. I think it would be worthwhile measuring this parameter and comparing it with the Jensen.

Yep

 

[BluegrassDan]

Ah, now I get it. I was looking at the Jensen. This Peluso looks typical of a transformer with insufficient primary inductance. I think it would be worthwhile measuring this parameter and comparing it with the Jensen.

Cheers

Ian

Bingo. And that makes a lot of sense, as I’ve had to increase the coupling cap from 4.7uF to 50uF just to get this amount of LF and tame the LF bump.

Thanks for all the help, guys.

 

[ruffrecords]

My WHOLE goal in this is to use a 3:1, 2:1, or 1:1 output TX for more output gain and less saturation on the preamp. I also want to try a lower 1:5 input TX, and switchable 1:10 or 1:20 for ribbon mics, if I can get the output level up more.

The problem with using a White Follower plus step down transformer output stage is that is has a gain of less than one (-12dB with a 4:1 transformer) . This means the poor preamp stage has to swing over a huge range. One solution is to use an output stage with gain. Unfortunately the 12AU7 is not the best tube for an output stage other than one with lots of NFB like a White follower and if you really need a tube with a 12V heater you are pretty much stuck with it. If you are using 6V heaters than I would suggest using a 6DJ8/ECC88 or better still the 6922 arranged as an SRPP. These have amazing drive capability without out being run super hot and also provide plenty of gain. Their downside is increased distortion so you probably need to add some NFB to reduce it to a reasonable level. You could  probably arrange one with 12dB gain which would leave about 14dB of NFB.

Edit: check out the 6922 SRPP figures in the BufferAmp folder of the DIY tab of my web site:

http://www.customtubeconsoles.com/diy

Edit2: The bonus is the 6922 SRPP works fine with a 2:1 transformer into 600 ohms.

Cheers

Ian

 

[BluegrassDan]

What about the second 12ay7 tube in the RCA BC3C? It’s arranged as a gain stage with a cathode follower.

 

[Bo Deadly]

can you go up to 500 K Hz with zero load and compare the two transformers?

I'm just curious but how does one take such a measurement without a proper analyzer? Are there converters that get anywhere near 500 KHz?

 

[Winston OBoogie]

I'm just curious but how does one take such a measurement without a proper analyzer? Are there converters that get anywhere near 500 KHz?

There is a converter you can use for measurement which goes higher than 192 (forget who makes it and how high exactly ) but not high enough for stuff in that region or higher.  I do it the old fashioned way myself with a generator and an rms meter such as the HP 3400a.  You could use a silly-scope instead of the meter with a bit more hassle involved.  It's useful for looking at poles in transistor stages etc when a compensation scheme Spice says works, doesn't in real life.
I'm stuck at 520 kHz max with my generator at the moment though so looking get something else.
Anyway, as you were...

 

[Bo Deadly]

I do it the old fashioned way myself with a generator and an rms meter such as the HP 3400a.

Ok. I see how that could work. So slowly adjust the frequency over suspect ranges, look for the meter to perk up and then zero in on the peak. But you don't get a nice plot.

 

[Winston OBoogie]

Ok. I see how that could work. So slowly adjust the frequency over suspect ranges, look for the meter to perk up and then zero in on the peak. But you don't get a nice plot.

Yep, you got it.  It's how all charts were generated back in the day (I think it was Tuesday) so you'd measure at lots of places and then join the dots on your graph.
You have to be a bit masochistic to do regular, audio range, frequency response charts that way these days.  But zeroing in on stuff in the 200k to a few MHz area is not too much trouble.  Easy if you have a good, self leveling generator so you're not having to adjust and monitor the input at the same time.

 

[ruffrecords]

What about the second 12ay7 tube in the RCA BC3C? It’s arranged as a gain stage with a cathode follower.

The problem with a cathode follower is that it is single ended. This means it needs at least twice the quiescent current that an SRPP stage will need. Also, although they have a low output impedance its drive capability is not so good so not likely to perform well into a 600 ohm load (via a transformer).

Cheers

Ian

 

[volker]

I'm just curious but how does one take such a measurement without a proper analyzer? Are there converters that get anywhere near 500 KHz?

Scope and pencil .

 

[CJ]

yes, most scopes good to 1 M Hz

3: 1 xfmr is gapped, so it will have 1/10 th the pri ind of same core ungapped

and steel is different

Jensen has about 2000 Henries at 20 Hz,  3:1 will have about 50 henries if you are lucky.

 

[abbey road d enfer]

Btw, may I ask which software and hardware you are using for measurement?

+1!

 

[BluegrassDan]

REW software. Metric Halo Lio8 interface at 192k.

 

[abbey road d enfer]

REW software. Metric Halo Lio8 interface at 192k.

Thanks!

 

[moamps]

REW software. Metric Halo Lio8 interface at 192k

Thanks!

+1!