[roman_p]

hiho,
i'm new to this forum and hope that i will find some answers here. As you can see from the subject i'm owning some old tx103. i haven't had the time to give these things some decent using time due to my work. so i think that these are still not burned in. Can someone tell me how to work this out? From the bentaudio website i see something about using female rca-connectors and  the output of a preamp. doesn't using the preamp output (which is much higher then 0,5mv from a cart) destroy the trannies?

hope someone helps.
Roman

[John Chapman]

Hello!

As you note the signal from a cart is very very small. As a result the tx103 will never really burn-in since it will not really get any 'exercise' from that small 0.5mv signal.

To burn in tx103's you can use a high level signal - It won't hurt them. The thing to watch for is making sure the load is connected to the secondary - I use about a 6K load on the secondary - this is not critical. At 1:10 ratio the source will then see a 60 ohm load - rather low.... This will drag down the voltage so it does not really 'step-up' as much as you'd expect. What it does do is put some (modest) current through them. I use either a frycleaner from Hagerman or my signal generator running a 20 hz to 1Mhz sweep every 2 seconds.  

An alternate arrangment is to connect the transformers backwards so they step down the voltage level. In this case you want a low value resistance on the output (in this case primary) side. I'd use about 10 ohms or so.

What the transformers don't want to see is DC. Over time this will magnetize the core. The output of a pre-amp will be free enough from dc (or totally free from dc if cap or tx coupled) to be used without concern.

I usually let them burn in here for about 3 or 4 days.

So:

1- Put a load on the secondary (5K to 10K Ohms).

2- Connect the primary to a source (about 2V in level) that is running some kind of varying signal - like a sweep on a sig gen, Frycleaner, tuner to station, etc.

3- Let it run for 3 days to a week.

Thansk!

John Chapman
www.bentaudio.com

[andrew]

So John, just to confirm, that its OK to connect the TX103's directly to the source @ 1:20 ratio and that its best to use say a 3K resistor?

   thanks,

[John Chapman]

Hello!

Yes you can do that - but connect the load before the source. I would use a 25K or so resistor at 1:20 - giving  a net load on the source of about  60 ohms.

Thanks!

John

[andrew]

Hi John,

I must have been having one of my specutaculary dense moments - in my defence I will say I was in a rush to go to a summer party when I posted the 3K guess.

Now I got my thinking head on rather than my drinking head I can see where you're coming from.

On a tranny, impedance is proportial to the square of the number of turns so @ 1:20 the impedance will be divided by 400 (20^2).

As you say John a 60 Ohm load is ideal then working backwards, 60 * 400 = 24K, or as you said approx 25K.

I don't have any 25K resistors handy so two 47K ones in parallel will have to do.

Using the quick product over sum rule to work out total resistance for two resistors in parallel gives (47K * 47k)/(47K + 47K) =  23.5K

which if I then divide by 400 gives a reflected load back onto the source of 58.75 Ohm.

Should be close enough to your suggested 60 Ohm, don't you think?

  thanks,

[John Chapman]

Hello!

You have a good handle on it for sure! The actual value is not at all critical so the 2 47K's in parallel are plenty close.

Thanks!

John

[roman_p]

Hi john,

ooops i didn't  expect to get an answer so soon. Thanks. If i understand you and andrew correctly, where is the difference to loading the trannies to get a wanted load? I use some 33,3 k resistors to get a load of 100 Ohm. If i just plug out the output and put the preamp (or CD) to the input will this suffice?? Or did i get something wrong? Perhaps then we should use the schematics to clear our words.
Thanks
Roman

[John Chapman]

Hello!

For 1:20 the 47K of the phono stage should work fine - although the input stage will see a HUGELY larger signal level than it will normally so don't turn it on!

For 1:10 I like to use a lower load so the 47K would be a bit high.

Thanks!

John