Mezmerize DCB1 Building Thread

[cfishbowl]

Hot Rod Mezmerize Level 2 transformer help

Hi All-

I've spent a fair bit of time reading and researching this thread and others so I apologize if this is redundant. I'm planning a build of a Hot Rodded Mezmerize DCB1. This is what I've figured I need to do to reach the 600mA level (level 2)

1. Switch to Mur-820 diodes with a small heat sink
2. Heat sink on the mosfets capable of dissipating 6w/mosfet or 12w per rail
3. I think the PS caps at 35V are ok, but would increase if you though I needed to
4. Transformer--this is where I am really stuck. I don't want to spend a ton of money (around 30$ US or less would be good) and I've found the Triad F-187U as a candidate. Center tapped, 28V, 112VA. I'd love some confirmation that this is right though. Data sheet here. https://system.netsuite.com/core/media/media.nl?id=5841&c=ACCT126831&h=8dbf43d15ce63188d8f9&_xt=.pdf

Sound right? Thanks!

 

[Salas]

1-3 are alright steps. 4 could be 80VA EI but more won't hurt if having the box space. So your pick is alright and then some.

 

[cfishbowl]

1-3 are alright steps. 4 could be 80VA EI but more won't hurt if having the box space

Gracias Salas.

 

[Stixx]

Didn't know our good Salas was a Spaniard...

Sorry, no pun intended, just kiddin...

 

[pidesd]

Hi salas,

Did you tried B1 with bs129?

I remember you told me once you had a few to try out when you had the time...

i had a pretty good experience myself with them myself, except that for either noise or distortion in some particular case ( i dont have a scope).

Anyway, it sounded pretty good driving a f4 directtly to 96db bookshelves...

 

[Salas]

The high input capacitance when considering a pot between it and the source put me off and I got into another project so I postponed. But I have it in the back of my mind.

 

[AndrewT]

The Follower plus current sink of the B1 is just two transistors.
One could very easily make both into cascodes and thus end up with a 4 transistor Buffer.

Some of the other Forum Buffers are already cascoded to get the benefits that ensue.

 

[Salas]

I know Andrew. But then its not a DCB1 when Jfets will become Mosfets and then cascoded. Its a classic with its own character and we will retire it only when no longer can find proper Jfets even from Linear Systems. For other differentiated design on its own there are many good ways of course.

 

[AndrewT]

The talk seemed to be moving to input capacitance.
Cascoding is a way to reduce input capacitance.

 

[Salas]

Cascoding is a way to to stop multiplication of Cdg i.e. Miller in gain circuits. How it will reduce Ciss?

 

[AndrewT]

Does it not work for a follower?

 

[Salas]

It will increase bandwidth and PSRR due to it will make the HF impedance higher but it won't reduce the circa 100pF Cgs non linear gate to source capacitance of that Infineon part.

 

[pidesd]

I'm not exactly sure how the distortion mechanism work for the dcb1 (i'm no audio expert)...

but isn't 2sk170 and bsp129 Ciss curves pretty similar in their non-linearity?

...though Cgs is not Ciss.

Also, i'm not sure if it's of any help, but....

from my experience, soldering the drain to a small copper interface that i can screw to a heatsink,

2W didn't do any difference to case temp,
2,5W made the device a bit warm to touch
3W was probably a bit too much

So running 25V at 100mA with 2 Ohm or so source resistor is possible.

 

[Salas]

They are similar in nonlinearity but that MOSFET has three times more. Statically any device's input capacitance reduces bandwidth the higher the source impedance. Dynamically it increases HF distortion & IMD. Although this can be still moderate for a purpose and the high bias drive can be a reward. Good thing in a follower is that no Miller is reflected to add up.

 

[helfred]

I would like to hot-rod my Blue Mezmerize to 200mA. I have the following trafo's on hand (2x12V/50VA and 2x15V/30VA). Will any of these do the job or do I have to order a 2x15V/50VA?

 

[Salas]

2X15VAC 30VA will suffice for 200mA

 

[dodog]

Life got in the way and I never built my DCB1 but things are stable again and I'm looking to finally getting this thing built! I have a question about internal wiring, and please be kind as I've searched this thread and others and seen many different recommendations.

For the Mez board, there are two signals (L & R) with one return. On the RCA jacks, I'd connect both signals to center, two separate returns and connect those two together on the single return pad on the PCB? If I'm measuring correctly, that's only about a 22-24 AWG hole, no?

For the wires, has anyone just used cat5, twisted pair? The tight twisting should be good for noise rejection, but are they good enough? Would I be better off with some shielded cable? I see many iterations (twisted pair, shielded, single core shielded, etc.) but given the small size of the hole on the PCB, I can't jam too much in there. Would cat5 be OK (assuming things are tightly twisted and the loop between signal and return on the RCA jack is minimal)?

 

[Eric]

For the return, you can just connect the outer barrel of the RCA jacks together and bring a single wire back to the PCB. I've seen some built where three wires come back from each RCA pair, I've seen other builds where ALL returns are joined together at the chassis and a single wire connects these to the PCB.

A twisted pair from CAT5 wire is PERFECT for signal wiring. I've never used shielded wire for an internal signal run and have never had a problem because of it.

 

[42001]

I used CAT7 and it is perfect! Just braid the three wires as tight as you can. No hum whatsoever.

 

[AndrewT]

Cat5 seems to be quite hard. I wonder if it is deliberately work hardened as part of the specification? Be careful you don't fatigue crack them.
The existing twist and wire size makes it very good for line level connections.