Reduction into TVC issue

[undertowogt]

Hello everyone.

I have a weird issue here. Not exactly pertaining to only the REDUCTION
I have finished my Reduction and it runs / sounds great.

First I will explain my system.

TURNTABLE  INTO REDUCTION PHONO

REDUCTION PHONO OUT/ INTO  PROMITHEUS TVC (transformer volume control Preamp)

OUT TVC INTO AMPS.

******I have test other sources and all cables, gear is working perfectly*************

****** When I run the REDUCTION PHONO directly into my amps bypassing the TVC everything is working correctly.*************

HERE IS THE ISSUE: When using the same tested cables I run the REDUCTION into the TVC then to the AMPS. The system does not work correctly. 1 interconnect (that worked fine before) does not work. The channel sounds thin, with no bass being reproduced.

The strange thing is another interconnect (exactly the same cable as faulty interconnect) works perfectly. I have tested the cables and channels separately as well as together to rule out any

 

[Doc B]

Going balanced XLR to single ended RCA can be tricky. The logical thing to do is figure what is different about that one cable that has bass. My hunch would be that there might be an open between the cold leg and ground that might be connected in a typical balanced to SE cable. Check continuity with your meter, comparing the one cable that seems to work right against the other cables.

 

[undertowogt]

thanks for the quick reply.

I am  now at a point that I realize it is an interconnect issue and not a Reduction/tvc issue. I just hooked up my old (very low fi inexpensive) phono preamp to test again.

Seems to me I have actually been having this issue for a very long time and have NOT noticed it  :-\. The Reduction has much more bass and must be way more revealing. With the old phono is is tough to tell, with the REDUCTION in line it is right in my face wrong.

Should I try wiring single ended cables? My TVC has Balanced in /outs. Wouldnt I be sacrificesing cable/signal quality?

 

[Doc B]

It is a very common misconception that balanced cabling is arbitrarily better. It is technically better for one specific usage, that being very long runs of cable where a single ended cable might be more prone to pick up noise. Other than that, my experience has been that at line level and at sane cable lengths the wire and dielectric used in a cable seem to have a lot more impact than a balanced configuration.

 

[undertowogt]

wait a second............. I am still not on track. I have tested manufactured, working, balanced RCA to XLR cables and they sound very thin as well.  I have inspected the soldering of those manufactured cables and they look great. I also tested my DIY RCA to XLR direct from the reduction to the AMPS and they work perfectly. I am still very confused...............

I am going to rewire some unbalanced rca to xlr and try them.

The Reduction should work the same as with a balanced cable and an unbalanced right?

So to restate: I have 1 nice sounding RCA to XLR Balanced cable. the other three I have tested, work, are soldered correctly are professional Audio Cables but sound VERY VERY THIN, So thin they sound broken?
any other thoughts?

 

[Doc B]

A balanced to single ended cable is sort of a band-aid. They can be internally connected different ways, based upon what you assume the user is connecting to what and which end is source and which end is load. The connections inside each device can influence the way the cable works too. For example the TVC may have a center tapped primary, or it may have a non CT primary. That might change the way the signal cold is connected with respect to the chassis/shield ground, and that could affect the sound. If the "bad" cable is floating because of a broken shield/ground connection to the signal cold, that might actually be helping the situation. You would need to examine how the cable is wired and how the input of the TVC is wired to figure out exactly what might be going on.  Do you have a single ended RCA input on your TVC? If so, try RCA to RCA single ended connections, as that may bypass the entire issue.

If you don't want to attempt to sort this out by pulling things apart the next best step would be to check with the manufacturer of the TVC and ask if there are any potential issues with connection of a single ended to balanced cable to the TVC's balanced input.

 

[undertowogt]

Hi Doc,

I appreciate your reply very much. I re wired 2 silver cable UNBALANCED RCA to XLR interconnects. I attached them to the REDUCTION/TVC/AMPS. The sound is extremely thin with much lower volume with both cables.

I then when direct REDUCTION/AMP with the same cables. the sound is correct. Full, bass, highs...its all there.

So I took the working (possibly bad) cable out of the equation. SO IT IS THE TVC.

If the TVC is wired differently on the input/output would it create this THIN low volume sound, or would it not work at all? I would have to think that there would be no sound at all. the next step is opening up the TVC to see how the inputs and outputs are wired.

To answer your question, NO I dont have rca jacks on the TVC on XLR in/out

 

[Doc B]

If the TVC has a center tap on the primary and it goes to chassis ground internally, that in combination with a cable that ties shield to signal cold could cut in half the expected signal coming in to the TVC, which would reduce the signal level coming out of the TVC. If this is the case it could also affect the tonal balance.

But this is pure speculation, you will need to trace the actual connections in the TVC or talk to the manufacturer to know for sure what is going on. We have seen some very squirrely behavior in systems that have had single ended to quasi-balanced connections and such. You really need to know how it is actually wired to be able to take steps to correct any issues.

 

[undertowogt]

Thank so much for your help. I will open the tvc tomorrow to take a look how it is wired. I will also be sending the manufacturer an email asking them how they wire the XLR jacks.

 

[Doc B]

I just want to clarify that I'm not saying the TVC manufacturer is doing anything wrong. They simply may not be expecting that someone would connect a single ended to balanced cable to their balanced input control. Without that constraint there are more possible ways to wire things.

 

[undertowogt]

So I have done some more test.

cassette Player - through TVC = lower volume, reduced bass
cassette Player - Direct = Higher volume, Full bass, sounds nice

Laptop/FLAC through TVC = lower volume, reduced bass
Laptop/FLAC - Direct = Higher volume, Full bass, sounds nice

correction

Reduction Phono through TVC = lower volume, reduced bass
Reduction Phono Direct= Higher Volume, Full bass Sounds nice.

I am now use re wired UNBALANCE RCA to XLR to go to the TVC and to go DIRECT

I opened up the TVC and it is balanced IN/OUTS

here is my Question- If I rewire the TVC IN/OUT jacks to be UNBALACED will this fix my issue. Will i have more volume, more bass and a more full sound?

I have not contacted the manufacturer. They are in Malaysia and are known for not responding to emails.

any advice is appreciated.

 

[Doc B]

What is the amp you are using?

 

[undertowogt]

I am using studio near field monitors with XLR or Quarter inch inputs.

 

[Doc B]

What is the input impedance of the monitors?

 

[undertowogt]

i though you were going to say that.........................

YSM1p Specifications


Program Power (Watts) 115
Nominal Impedance (Ohms) 8
Sensitivity (dB @1Watt/1m) 90
Frequency Response (Hz +/- 3db) 40-20,000
Crossover Frequency (Hz) 2,500
Input Sensitivity (Vrms Sine) 1

 

[Doc B]

Yeow, I just wrote a big long conjectural reply and then saw that you corrected your post! That'll teach me to skip steps...

OK the issue is the same with all sources. I looked at the schematic of the active speaker. The input is differential (push-pull) - which is often mistakenly called balanced.  Obviously it is happy with all of your sources plugged into it directly so the issue seems to be the TVC not liking something ahead of it. The common "thread" is that SE to BAL cable.

So you probably need to adjust the wiring of the TVC. Once again, note that this is not my product and I am being asked to fix a circuit I haven't even seen. If you can't get an answer from the manufacturer the only alternative is to open the sucker up and figure out how it is wired. If it's point to point you might be able to take a really sharp close up photo and we might be able to figure out the input to primary connections. I'll also throw out that a replacing the TVC with a Quickie or even a Submissive could be a viable solution to the issue.

Possibly, getting inside the cable and disconnecting the shield from the RCA outer shell could solve the issue, but it might add noise. One possibility regarding the one cabel that seemed to work is that you might have had in intermittent shield connection that, when open, allowed the TVC to function as designed.

 

[undertowogt]

ok, this seems like it is worth a shot, if re wiring the TVC doesn't work I can easily put it back the way it was.

I am basically going to re wire the TVC INPUT and OUTPUTS to UNBALANCED JACKS correct?

I am not totally convinced that this will work but it is worth a try. I am thinking that it is an impedance issue, My TVC is not matched with my amp................ I might just have to buy a foreplay and some of your monoblocks    ;D. but then I would need passive speakers.
attached is a pic of the inside of the tvc. 1 INPUT 2 OUTPUT:

Do I need to ground PIN 1 as well as jump it to PIN 3........................... or just jump PIN 1 to PIN 3?

thanks again for your VIP service, this is amazing

 

[undertowogt]

Just looking into the IMPEDANCE of my gear.

These numbers are quoted straight from the bottle head site the Yorkville site and the Promitheus site.

Bottle head - "The Reduction is designed to operate into line stages with 50K or higher input impedance "

Yorkville Sound - "Input Impedance 10k ohms , Input Sensitivity 1 Vrms"

Promitheus - "A TVC output impedance is always calculate from the equipment source, and is always lower than the source output impedance."

I am no where near an Impedance expert (obviously), but with my current reading seems to me this is why my sound is thin, and lacking bass.

The original cable that sounded great, full and loud still boggles my mind. If I could duplicate that result I would and be happy.  So with this information, do you still think it is a BALACED/UNBALANCEED issue?

 

[Doc B]

I had hoped that maybe the transformers had labels that indicated the lead connections. You have mentioned two distinct issues. One is the lack of bass. This could be due to some impedance matching issue that seems to be related to having the TVC between your amp and any source you connect. The other issue you mentioned is low signal level from some combination of cables and gear that I am afraid I have lost track of. Low signal level could be due to the single ended to balanced cable grounding out half of the signal in certain conditions. The mystery cable that seems to work correctly has not been described in enough detail to tell us what is different about it. I have offered about all the advice that i can based upon knowledge of our phono preamp and the schematic of your amp, which seem to work properly with each other. We would need to see what the actual design and connections are on the transformer, the cables, etc. to be able to make any truly informed suggestions about why the transformer is changing the sound.

Asking the manufacturer of the TVC for guidance in using the TVC with single ended sources seems to be the most direct course of action at this point.

 

[Paul Joppa]

Doc B was posting at the same time, so some of the following is repeating his words in a slightly different way. Nevertheless, here are my comments:

There are two completely separate issues here:

1) As Doc B has said, but perhaps to clarify, a balanced cable has three wires (+. -. and Shield, sometimes called ground). A single ended cable has two (+ and ground). This leave a number of possible ways to interconnect with a cable. Balanced cables are wires with the Shield grounded at one end, or the other end, or both. The Shield may or may not be connected to the ground or the chassis or both, at one end or the other or both, in a SE-to-balanced connection. The Shield may be (at the balanced end) connected to the chassis shield, or the centertap (which may or may not exist). Each of these has different issues, so it is critical to determine how the cable is wired. Furthermore, a balanced input to the TVC might have the Shield connected to the chassis or the centertap of the transformer or to nothing at all. Again it is critical to determine how it is wired. I will further add that since two "identical" cables behave differently, they are not in fact identical.

2) The Reduction is optimal with a 50K load, but it can drive a load as low as 15K. 15K at 20Hz is 120 henries inductance. I can't find an inductance rating for the Promitheus TVC, so I can't usefully interpret the "10K impedance" specification - but if loss of deep bass is the source of "thinness" then a larger output capacitor will help. I would not go above 1.0uF because the distortion will increase and the gain will decrease, but that should take you below 10kOhms without other trouble.