Question on passive preamplifier - transformer section.

[binspaul]

Hello,

1. I think the passive preamp will require a bit more input impedance than the 200 Ohms. Can we use this transformer for the purpose : Neutrik - Audio - Transformers - NTL1 ?

2. What will be the result if we use a 1:2 transformer instead of the 1:1 model ?


Best regards,
Bins.

Originally Posted by ThorstenL

Hi,



I do not wish to be seem directly criticising another industry member and manufacturer, so I will refrain from commenting, other than noting that what this is merely the combination of a very traditional "passive pre-amplifier" with a 1:1 Line transformer.

The Line transformer has no function other than to isolate input and output. This can have benefits in systems where there is poor design with sources or amplifiers in terms of ground/earth arrangements. This subject was considerably enlarged in another thread you have already found.

Poor man's transformer volume control?



Frequency response, primary and secondary impedance and level handling. I personally also would add sound quality to the requirements.



That depends on your exact system context and your definition of "good enough".

A nominal impedance of 200 ohm means it should be driven by no more than 200 Ohm, preferably by much less than that, to attain the specified performance.

No frequency response is given, so your guess is as good as mine as to what this would be.

A level of -3dBU means around 0.5V, at which point for a 50Hz signal the transformer is practically at overload. For a 20Hz signal the transformer will overload with around 0.2V.

So you need to decide if this means your definition of "good enough".

Ciao T

[ThorstenL]

Hi,

Originally Posted by binspaul

Can we use this transformer for the purpose : Neutrik - Audio - Transformers - NTL1 ?

You can use what you like.

To be direct, a line input transformer that is suitable will cost nearly as much as a real TVC. In essence a TVC as I specify it, is nothing much different than a 1:1 line transformer at 10K nominal impedance, but with tapped secondary and a suitably changed winding structure. This was done as at the time really high performance 10K 1:1 line transformers where made by several manufacturers, so chances where good to convince at least one to make TVC modification.

FWIW, the "Ingot" uses a Magnequest transformer, quite likely the B7 10k:10k

Magnequest Products - MQ Iron Listing/Pricing

Use that with P&G 10K pot:

FS/Trade: Penny + Giles

Ciao T

[binspaul]

Hi,

The Neutrik transformers are readily available with me and that is why I had asked. I think the Neutrik NTL1 is having almost similar specifications as that of the Magnequest B7-10K:10K version.

1. What will happen if I omit the 1K fixed resistor that is added across the secondary to create an idealized constant ? Will it significantly degrade the performance ?

Best regards,
Bins.

Originally Posted by ThorstenL

Hi,



You can use what you like.

To be direct, a line input transformer that is suitable will cost nearly as much as a real TVC. In essence a TVC as I specify it, is nothing much different than a 1:1 line transformer at 10K nominal impedance, but with tapped secondary and a suitably changed winding structure. This was done as at the time really high performance 10K 1:1 line transformers where made by several manufacturers, so chances where good to convince at least one to make TVC modification.

FWIW, the "Ingot" uses a Magnequest transformer, quite likely the B7 10k:10k

Magnequest Products - MQ Iron Listing/Pricing

Use that with P&G 10K pot:

FS/Trade: Penny + Giles

Ciao T

[ThorstenL]

Hi,

Originally Posted by binspaul

The Neutrik transformers are readily available with me and that is why I had asked. I think the Neutrik NTL1 is having almost similar specifications as that of the Magnequest B7-10K:10K version.

First, non of the Neutrik transformers are very good. Second, I do not think they have the same specifications as the B7. Only in the very limited specifications given are there some parallels.

Originally Posted by binspaul

1. What will happen if I omit the 1K fixed resistor that is added across the secondary to create an idealized constant ?

What 1K resistor across the secondary? Neither does the drawing attached to your post show such nor was any such ever in any published "Ingot" drawings.

Ciao T

[binspaul]

Hi,

The 1K resistor is shown at the output end after the pot. What is the best value for the log pot (Is there any specific reason for using the 10K version) ?

Best regards,
Bins.

Originally Posted by ThorstenL

Hi,



First, non of the Neutrik transformers are very good. Second, I do not think they have the same specifications as the B7. Only in the very limited specifications given are there some parallels.



What 1K resistor across the secondary? Neither does the drawing attached to your post show such nor was any such ever in any published "Ingot" drawings.

Ciao T

[ThorstenL]

Hi,

Originally Posted by binspaul

The 1K resistor is shown at the output end after the pot.

Yes. And next to it it says "to bass amp".

So why do you claim that this resistor: " is added across the secondary to create an idealized constant ? " when it clearly is not added across the secondary first of all, never mind the rest?

Originally Posted by binspaul

What is the best value for the log pot

The value that matches the transformer of course.

Originally Posted by binspaul

(Is there any specific reason for using the 10K version) ?

The secondary winding of the transformer in your drawing is 10K impedance.

Plus, there are the usual considerations for "passive pre-amplifiers", which pretty much dictate a 1K pot to be desirable (but few sources sound good driving such a load) and a 10K as the upper end of the value range, to ensure reasonably wide system compatibility.

Please forgive, but many of your questions seem incredibly naive. Would you mind finding yourself a good book on audio electronics and actually reading it? It would inform you much better than this "q & a" game you are playing here.

Second, given your current level of knowledge I think what you are trying to do is a fools errand. If you are absolutely bent on doing it anyway, good luck.

If so, take my suggestion and use the original transformer of the device you want to copy, or look for Sy's heretical linestage and use the Jensen Transformer he used. I suspect either will be largely redundant though, depending on the rest of your system. The Neutrik Transformers may be best described as "functional, of sorts".

Second, have a look at Nelson Pass's B1 Preamplifier, this kind of buffer is a very good idea to use after a higher impedance potentiometer to overcome some of the limitations of traditional "passive pre-amplifiers".

FWIW, Steve McCormack's most recent passive preamplifier uses such a buffer potentiometers and transformers to make a device that has certainly be reviewed very well.

Ciao T