Intact Audio

it sure seems somehow pins 12 & 13 are shorted to each other. carefully retrace your wiring looking for an error. I am assuming it was functioning properly and then "broke at some point"? The fact that it is happening the same in both channels points to some external cause since it is ...

can you re-check you numbers?

the source impedance (867,2354 ohms) number does not make sense unless it rounds down to 867Ω

the measurements between steps 12 & 13 are the same which should not be the case. what is the DCR between 12&13 (at the switch and at the autoformer.

dave

it is not possible to get a balanced output from a single ended circuit but two units per channel can attenuate a balanced to balanced line.


dave

Hey, There really isn't any possibility of the AVC to become magnetized or break. The two things that come to mind are a leaky cap putting DC on the core and a possible shorted turn (two pins shorted to each other). A DVM should help diagnose the first and a visual search might point to the second. ...

this is a "loaded" question. My answer for myself is I always simply use a DVM to measure the resistance. HOWEVER! I am not going to ever suggest that to anyone else due to the small chance that something goes wrong in the process with a multi-thousand dollar cartridge. and I get blamed. T...

interesting.

My two questions on the situations:

Was the shunt resistor the same in both cases?

What was the nature of the crossover driving each autoformer?

dave

It seems odd that the change in the gap would effect the level in the measurements and it really needs to be driven from a ~1Ω source for reasonable results. My guess on the sonic results have to do with the lower inductance value of the 3X3 creating a high pass for information beyond what the speak...

The difference between 12 and 15 on the step up is only 2dB so for the most part I would consider them interchangeable.

dave

right.... and from the perspective of the SUT it is being driven from a 2Ω source or 3X the published 0.6Ω. I used to do SUT's specific to the sub 1Ω carts until I realized that the tonearm DCR has a dominant effect on the situation.
dave

The achilles heel of a 0.6Ω cartridge is the tonearm wiring is often double that value effectively turning it into a 2Ω cartridge.

I would confirm the tonearm DCR prior to committing to a design.

dave

yes...

I might still have some boards for them though. send me a private email.

dave

Hey.

The modules attenuate completely by selection of taps on the autoformers. I see adding an additional resistive attenuation as a liability rather than an asset.

dave

it simply comes down to inductance. if you have an excess then increasing the gap is worth a try.

dave

I have noticed a trend lately of people asking for high ratio SUTs for higher impedance cartridges. The current request was for a 1:50 for a 22Ω cartridge and the following is why I think that is a bad idea. There are two different places where you can get into trouble here and they both have to do ...

At this point I think it is probably best to take the unit back to stock and make sure it operates noise free when used single ended.

dave

Pins 5,7,8 go to ground.... I cannot use specific ground terminology since I did not design or build the circuit. The negative outputs that were tied to pins 5 & 7 have B+ on them so shoring them to ground is not a good move. I think we may have gotten way off point here and without me being int...

5, 7 & 8 all can tie together and go to signal ground.

the shield appears to be pin 8 from the diagram

dave

Tha autoformers and transformer secondaries should attach to the same ground as the RCA jacks and the signal tubes which appears to be "ref" for the balanced circuit. Ultimately they will all tie together at some point and the goal is to connect them in the manner that gives the least nois...

than needs to be tied to audio ground at some point.

dave

central tap???

you mean the junction of pins 1 & 3 on the 1674?

dave

did you also reference the secondary of the 1674 to ground?

It is unclear what the large cap is.... there is nothing power supply related on the output board. Only the parafeed cap and the mute circuit.

they should be interchangeable the autoformer just has a single ground wire and the TVC has two (primary and secondary) which are connected together.


dave

that depends on the preamp design and ultimately the signal levels involved. The 6H30 has a mu of 15 so call it a gain of 3.75 after the stepdown. Feed it with 2V in and you net a meax of 7.5V out which is fine for the autoformers. Feed it with 4V and you might start to run into low frequency overlo...

The pinout of the transformer appears to match the datasheet. the only difference is one is mirrored from the other 1:4 in the spec sheet and 4:1 in the schematic. It looks to me like the connections you need to change are at the input and output of the board so no traces should need to be cut. dave

ugh... slicing traces gets interesting... it looks like the 1674's are on their own boards with yellow wires to connect to the main board.

where is the 680nF 'parafeeed cap'

dave

The 1674 appears to be a 1+1:4+4 that is being used as a 4+4:1+1 so the mirror image of the spec sheet matches the schematic above.

dave

I now see the TVC's and they are early versions prior to john working with me so they may have been doing the SE>>balanced conversion at the input. To test for proper function I would put a SE signal between L+ and "ref" and groundL- to Ref. Then on the LL1674 disconnect pin 7 from L- and ...

Since John mentioned you needed 4 "TVC" units I suspect they were not TVCs but my autoformers. The original bent units used S&B TVC's which could fo bal>>SE and SE>>bal connections (albeit not very well). Your autoformers are ready to ship but I want to hold off until I am sure things ...

does it function ow SE in Se out without the TVC?

dave