Autoformer volume control problem

discussion of magnetic volume control design for both line and speaker levels.

merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

I'm using single ended output and it's practically zero ohm to 100khz.

Felipe
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

Dave?

Strange thing, now no DC offset but still weak bass playing DSD files.
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

Dave?
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

Please support?
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

Use a DC blocking cap.

The only two things that can cause you issues with the bass are unbalanced current or an extremely high source impedance (10K+)

dave
Get Your Fix
www.hifiheroin.com
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

After a long time without using the AVC it I have put a capacitor and equally the DAC sounds badly with DSD but now also with PCM, can be that the AVC is magnetized or damaged?
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

what sized capacitor?

I thought the autoformer was on the secondary of the lundahl transformer.

dave
Get Your Fix
www.hifiheroin.com
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

I started using 1uF and ended with 51uF, AVC stacked: 1-2-3-4-3-4-3-4-3-4-3-2-1
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

Now I'm using the AVC between the DAC Twisted Pear Legato and mu-follower ECC81 used as headphone amp.
Attachments
ECC81 mu-follower schematic
ECC81 mu-follower schematic
Mufollower2.jpg (41.41 KiB) Viewed 20437 times
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

Same problem after the Lundhal using the 26 preamp.
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

Dave?
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

do the attenuation steps work as they should?

there isn't really a way to destroy them. can you measure the output DC resistance at every position of the 12 position switch?

dave
Get Your Fix
www.hifiheroin.com
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

Yes I feed 1Khz sinus as is amplifiying OK.

I will measure and let you know.

Thanks for support
Felipe
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

1 pos. 0R3
2 pos. 0R8
3 pos. 1R1
4 pos. 1R5
5 pos. 2R1
6 pos. 3R1
7 pos. 4R7
8 pos. 7R2
9 pos.11R2
10 pos. 16R7
11 pos. 25R4
12 pos. 38R7
13 pos. 57R8

1 pos. 0R3
2 pos. 0R9
3 pos. 1R1
4 pos. 1R5
5 pos. 2R2
6 pos. 3R1
7 pos. 4R7
8 pos. 7R2
9 pos.11R2
10 pos. 16R7
11 pos. 25R7
12 pos. 38R9
13 pos. 58R1
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

Can be the Chinese switch?
Attachments
WP_20160211_001[1].jpg
WP_20160211_001[1].jpg (1.48 MiB) Viewed 20392 times
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

that is all correct. measure to see if there is and resistance from the coil to the core.

Does this behavior happen in both channels?

does it happen with every source?

dave
Get Your Fix
www.hifiheroin.com
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

No resistance from the coil to the core.

Yes happen in both channels.

No only PCM & DSD files, vinyl sounds OK.

Felipe
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

I have no idea what the incompatibility could be since placing it at the output of a tube stage with a step down should completely isolate it from the source at the grid of the tube. Maybe ask on a twisted pear discussion site and point me there to discuss further.

dave
Get Your Fix
www.hifiheroin.com
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

Dave fixed the DC offset of BIII + Legato I/V, now I'm sure 100% there isn't DC goint to the AVC but still sounds distorted with DSD & now with PCM music also.

To be sure now I connected 4uF at the AVC inputs, don'0t sound distorted but the sound is too thin without body and bass.
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

With the power off please measure the resistance to ground at the input of the autoformer at a few switch settings and report back (measure at the autoformer side of the 4uf coupling cap)

dave
Get Your Fix
www.hifiheroin.com
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

1st position 0.1R
2nd 0.6R
3rd 0.8R
4th 1.3R
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

The input should remain the same at all level settings and be about 58 ohms. The output should have the measured values like you say and like the table you provided earlier.

If you have the input and output reversed that would explain your issues.

dave
Get Your Fix
www.hifiheroin.com
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

The input & output varies the same manner the impedance.
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

You are right Dave, wired wrong. Time to listen if now it's the sound OK.
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

Dave works like a charm, thanks for your patient and kind support.
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

Dave AVC still with a little bit bass but the rest of frecuencies sounds great, theres is a way to increase the inductance to get more bass?
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

you can restack them 1X1 on the laminations but you should have plenty of inductance now.

What is the output Z of the legato?

dave
Get Your Fix
www.hifiheroin.com
merlin el mago
Posts: 64
Joined: Fri Aug 15, 2014 2:48 pm

Post by merlin el mago »

merlin el mago wrote:I'm using single ended output and it's practically zero ohm to 100khz.

Felipe
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

Then changing the inductance will not appreciably change the bass.

You could try a butt gap ~20-25hy and see if that helps. (inductance will become more linear)

dave
Get Your Fix
www.hifiheroin.com
Post Reply