MA-1 Coupling Cap upgrade

174.113.86.183

Posted on January 1, 2016 at 12:25:28

Cousin Billy
Manufacturer

Posts: 243
Location: Greater Toronto Area
Joined: September 10, 2004

Hello all
I'm on a role.

Looking to upgrade my MA-1 coupling caps.
I have V-Cap 0.1uf now. 600V.

Using V-caps online calculator, I should be using 1.0uF.

1) Is there anything wrong with going this high? It's only 450V, is that OK?

2) That little baby yellow 1uF cap. It's coming from the DC offset knob. Could it be changed?. Is it in the signal path?

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The little yellow cap

Ralph

11:12:39 01/05/16

RE: MA-1 Coupling Cap upgrade

Barry

13:36:06 01/01/16

7

CuTF ordered. Thank You

Cousin Billy

10:04:28 01/02/16

6

...

Show full thread outline!

The little yellow cap

Ralph

11:12:39 01/05/16

RE: MA-1 Coupling Cap upgrade

Barry

13:36:06 01/01/16

7

CuTF ordered. Thank You

Cousin Billy

10:04:28 01/02/16

6

Opps!, ordered wrong value

Cousin Billy

07:08:11 01/03/16

5

0.1uf is the right value.

Ralph

11:10:41 01/05/16

2

RE: 0.1uf is the right value.

Lew

05:10:47 01/08/16

timing constants

Ralph

08:42:35 01/08/16

How critical is the 1K resistor

Cousin Billy

08:46:07 01/03/16

RE: How critical is the 1K resistor

Lew

05:06:54 01/08/16

RE: MA-1 Coupling Cap upgrade, posted on January 1, 2016 at 13:36:06

Barry
Audiophile

Posts: 1003
Location: PA
Joined: November 24, 1999
Contributor
Since: January 18, 2009

Couldn't find anything quickly and am not familiar with the MA-1 circuit topology but am sure others will chime in.

I would change to the copper foil CuTf V-Caps if you are changing them. They are stock in the MA-1 Mk 3.3 and sound noticeably better than the TfTf tin foils you appear to have. I would NOT change the voltage....

CuTF ordered. Thank You, posted on January 2, 2016 at 10:04:28
Cousin Billy Manufacturer Posts: 243 Location: Greater Toronto Area Joined: September 10, 2004	I did decide to stay with the 600V version. 0.47uF, 600V, 0.5% matched quad. As far as that little yellow 1uF is concerned, I have a few Audience TO 1uF, 600V Teflon caps in my stash. I'll use those. Time to open up my MP-1 pre-amp.

Opps!, ordered wrong value, posted on January 3, 2016 at 07:08:11
Cousin Billy Manufacturer Posts: 243 Location: Greater Toronto Area Joined: September 10, 2004	Just did an extensive search on coupling cap values. It appears 0.22uF is the largest value we should go. I'd like to thank Chris from VHAudio. He put up the red flag. That's service.

How critical is the 1K resistor, posted on January 3, 2016 at 08:46:07
Cousin Billy Manufacturer Posts: 243 Location: Greater Toronto Area Joined: September 10, 2004	I've read too much. My tiny brain hurts. Some people on other websites are using 10K on the HV caps. I searched our archives, and can't find an answer. Unless otherwise advised, I'll stay with the 1K.

0.1uf is the right value., posted on January 5, 2016 at 11:10:41
Ralph Manufacturer Posts: 4769 Location: Minnesota Joined: April 24, 2002	While you do go to 1Hz with 0.22, they don't sound as good otherwise, and with the 0.1 uf units, the squarewave tilt at 20Hz is unmeasurable. This means no phase shift at 20Hz, which is how you get impact. Increasing the value will mess with the timing constants in the circuit which will increase the IMD.

The little yellow cap, posted on January 5, 2016 at 11:12:39
Ralph Manufacturer Posts: 4769 Location: Minnesota Joined: April 24, 2002	is a zener diode bypass. Its just there to knock down noise from the zener stack. However we have found that most modern zeners are a lot quieter than in the old days so you won't find a lot of effect from this part.

RE: How critical is the 1K resistor, posted on January 8, 2016 at 05:06:54
Lew Audiophile Posts: 10911 Location: Bethesda, Maryland Joined: December 11, 2000	What website? What amplifier was under discussion? Going from 1k to 10k will assuredly drop more volts across the resistor, thereby reducing the volts delivered to the circuit. (Ohm's Law). Moreover the 10k resistor will need to be re-rated to account for the increase in power across it. P= current x volts. The gain in filtering is not worth the problems it creates, imo.

RE: 0.1uf is the right value., posted on January 8, 2016 at 05:10:47
Lew Audiophile Posts: 10911 Location: Bethesda, Maryland Joined: December 11, 2000	Thanks for that insight. I once read about "slugging the bass" which amounted to using an excessively large value coupling cap. What's that all about?

timing constants, posted on January 8, 2016 at 08:42:35

Ralph
Manufacturer

Posts: 4769
Location: Minnesota
Joined: April 24, 2002

Sometimes an amplifier could do with a larger coupling cap as the timing constants in the power supplies will allow it.

The issue is that the amp should not have bandwidth that goes below that of the power supply! No power supply is truly DC (batteries are) as they all have some sort of low frequency timing constant.

If the amp has bandwidth below that of the power supply, the result will be that it has the ability to modulate the supply. If it can do that, the noise in the supply will cause intermodulations to occur.

Now our amps don't have a particularly low THD figure as modern amps go, but our IMD figures are just fine in that regard. This is because we pay attention to this rule. There is a myth that if your THD is not low neither will be the IMD. In solid state amps that are direct-coupled input to output (meaning that they by default exceed the LF timing constant of their supplies), this does occur but it does not have to be that way if the amp has well-managed timing constants.

OTL Asylum

MA-1 Coupling Cap upgrade

174.113.86.183