HDAM Bypassing

[poynton]

Hi,

In a current thread, it is suggested that bypassing the HDAM modules in a Marantz CD63 improves the sound.

( Bypassing the HDAM was also suggested in another thread for the CD6000 )

Is this a case of 'less is more'? or does the HDAM design require improving?

Looking at the HDAM circuit, the output fet's seem to be in class B.

Would a change of biasing or loading the output into class A with a ccd lead to an improvement??

Has anyone done this?

Andy

[Fidelity Audio]

The gains have only really come from putting in superior op amps and better dac psu.

It may not work bypassing on standard player (63 anyway)

[Extreme_Boky]

Approx 8 years ago i modified my CD63. One of the big improvements was HDAM bypass. 2114 was replaced with 826 coupled via AuriCaps straight from 826 output pins to RCA's. HDAM was disconnected off the power supply rails, and all tracks / components grounded to power supply ground. I did a lot of mods to this little player - an icon and object of drooling desire to many who come to me with 3-4000 AU$ CD players for modifications.

Try for yourself: lift one side of power supply feed resistors to the HDAM blocks (I think there are 4 in total of approx. 4.7 or 10 ohms each), lift one side of signal feed resistors between IC OP and HDAM, and feed this signal (out of IC OP) straight to RCA's. Install IC sockets and try different OP’s. My choice is 826, BUT ONLY if you modify the whole unit, transport section INCLUDED. If you just replace the 2114 with 826, you'll end up with sound being too bright / revealing.

Many DIY-ers hope that replacing cheap 2114, 2134 and similar with fast revealing OP's will bring benefits. It usually does not because they just emphasise the harsh sounding player that is still just the harsh sounding player with fast OP's – and that’s it.

Extreme_Boky

[Cobra2]

improving the HDAM?
Afterall, it is just a discrete buffer?
ok, there may be many versions, but it can't be that bad/impossible to wring out some performance from...?

Arne K

[poynton]

Originally posted by Cobra2
improving the HDAM?
Afterall, it is just a discrete buffer?
ok, there may be many versions, but it can't be that bad/impossible to wring out some performance from...?

Arne K

Hi.

Checking the circuits for the CD63 and CD6000 OSE, the basic HDAM is the same. There are some minor value changes and also the CD63 uses a dual fet for the input pair whereas the '6000 seems to use a 2 fets. The other major point is that the'63 is a buffer with no (0 ohm ) feedback resister, the '6000 in a differential mode with gain of 1 set by 10k resisters (in the output) and in a similar fashion in the other HDAMs.


BURSONAUDIO have produced the 'Burson HDAM module' (http://users.tpg.com.au/myfdd78/prod01.htm) as a dropin replacement for common opamp types. The circuit is, however, almost the same as the Marantz version. (They also produce a 'super-opamp' built into what looks very like a plumbing fitting!)

Presumably, the basic HDAM is effective as a buffer in isolating the preceding stages from the effects of the output until that is mods are carried out.

So, I repeat my original question?

Originally posted by poynton
............ does the HDAM design require improving?

Looking at the HDAM circuit, the output fet's seem to be in class B.

Would a change of biasing or loading the output into class A with a ccd lead to an improvement??

Has anyone done this?

Andy

[Cobra2]

Arne K

[6h5c]

Well...

I couldn't imagine that Marantz made a class-B HDAM....

so I couldn't resist taking a look at the datasheets of the FET's, and it seems that you're wrong

The FET's are of the 'normally-on' type, so with an Ugs of 0V there will be a current flowing, somewhere between 6 and 12mA (?) for the BL version, according to the datasheet. Fweew....

The CD63 and CD67 schematics indicate that there's 0.0V across the 27R resistors, but that must be a typo.

Regards,

Ray.

[poynton]

Hi.

OOPS!!

Thanks for the info. I couldn't see it either. I still think they can be tweaked!

Andy

[6h5c]

The HDAM circuit can be improved, the first thing I would do is put in 1% resistors. But the main reason I don't like it is because it has very high feedback. And I know from my tubeamp that too much feedback doesn't do much good to the sound.
So i'm going to stick to the 'less is better' approach -> out it goes

I'm hoping to get rid of the opamps too, i'm working on a tubestage.

Regards,

Ray.

[myfdd]

hi guys,

I have tried a pair of Burson HDAM module from Ebay. Much better than mine OPA627 on my Marantz CDP. Has any one else tried?