Krell KSA 100mkII Clone

[RKH]

Originally posted by LuckyLyndy

if someone could get hold of John at Victoria Magnetics, he also might be willing to wind us a set of these.
This has been a major block to the start of my building process.

Lyndon
Salt Lake City

I sent John an e-mail a month or so ago but didn't get a reply. If I get a spare moment, in the next week, I'll give him a call. What sort of numbers can I quote in terms of volume. Would 'we' be able to get quantity 20?

Are we satisfied with 39 x 2 at 1 kVA?

Ryan

[AndrewT]

Hi,
39Vac is a bit high.
37Vac seems to be the original.
Remember most manufacturers quote the resistive loaded secondary voltage with specified input voltage.

120+120:37+37 is the spec we should be aiming for.

If we want flexibility then the primary could be 110,115,120 + 110,115,120 and the secondary could also have the extra windings for the regulated front end and something to feed relays etc.

[Flodstroem]

Regarding the transformer:
Anyone company who make toroidal transformers could also make custom design.
But its not that winding issue that is the point here. Its the possibility to make transformers that is SILENT under heavy load(=high bias). Most of the companies who make toroidal transformers dont bother if looking at this variable, sadly to say.

This has been stated several times before in this thread and in other threads too, for that matter. To get a transformer to be dead silent when feeding the amp to full bias (2-300W) most commercial and industry model transformer has a hum and buzzes when loading them. Some of this humming could be filtered away by a DC-trap (DC-filter) but for the most of the time, this is not enough due to loose parts in the simple/cheap core (for commercial transformers) or/and loose windings (vibrating magnetic wire).

To get a dead silent transformer for Hi-Fi use the maker must choose such transformer parts that is higher quality/and silent (glued/impregnated and potted cores) and the winding process is not as simple as for the commercial transformers (bifilar windings etc...).

Also there is often some sort of electrostatic shielding implemented in the transformer (between the prim. and sec. windings). Krell also potted the whole transformer in a steel-can and this made the transformer looking very nice together with that extra shielding.

All of those extra quality specs cost a lot of money and thats why we had to pay a little bit more for the custom made Hi-Fi transformer.

You are putting in a lot of effort and money to this amp, then you would like to buy a simple transformer (for $50-100) which probably is humming and buzzing. That does not make any sense for me?

Regards

[AndrewT]

Hi Flod,
you hit the nail on the head.
If one wants the best then one has to pay.

If I or anyone else want to be a cheapskate then I/us will have to face the consequence. But, at least take the informed decision.
Listen to Flod and be warned.

[Mark A. Gulbrandsen]

Building this amp is a huge undertaking and I want the best... so I'm sticking with Flod on this one. Victoria Magnetics would be my 2nd cjhoice though... They always provided extremely high quality and he could do an electrostatic shield too although potting in a steel can probably not....

Mark

[TomWaits]

I've been thinking about my build attempt at this amp and I really think the pre/driver board from Watts/Gulbrandsen should have a regulated supply for optimum performance. I'm not certain I can draw up a good performance circuit for this task. I'm not even certain of the power consumption of the driver board on its own?

So I'm wondering if there is someone out there that has a schematic up to the task. Also, is there trouble if the pre/driver board circuit has a separate power supply including a separate transformer? Any advice to would be great!

Cheers,

Shawn.

[PWatts]

I'm actually going to experiment with three regulator stages: 1) LTP 2) frontend excl. LTP 3) driver. Designing a rather nice one, already built and tested the prototype with great promise but would first like to test it in the intended application before making sweeping statements. However I'll probably end up using a separate transformer to feed the drivers unregulated and the LTP tapped from that and downregulated.

[AndrewT]

Hi Pwatts,
are you planning to post details of your regulation schemes?
Have you a timetable/calendar for releasing this info?
Are you intending to keep the LTP Zeners or replace them with the 39Vdc regulated rails? or is that part of the experiment?

For those that can't wait:
LTP + DC offset stage requires 15mA.
VAS + prior to driver requires 21mA.
Drivers varies with load current. Quiescent about 100mA (50+50 for the pair) but can go to 500mApk for a 10A to 15Apk output to the load. 500mA is adequate for a 4r0 load, anything less than 4r0 and more driver current will be drawn.

If any of the component values or supply voltages are changed then all the preceeding current values must be re-calculated.

[AndrewT]

Hi,
has anyone reached the stage of measuring voltages on a completed set-up yet?

I am still hoping someone can tell me the voltages that exist either side (D&S) of the FETs.
I think the drains are sitting at 1.5V below the supply rails, but the source voltages depend on the Vgs of installed devices.

[Flodstroem]

Originally posted by PWatts
I'm actually going to experiment with three regulator stages: 1) LTP 2) frontend excl. LTP 3) driver. Designing a rather nice one, already built and tested the prototype with great promise but would first like to test it in the intended application before making sweeping statements. However I'll probably end up using a separate transformer to feed the drivers unregulated and the LTP tapped from that and downregulated.

Excellent PWatts. We will wait for it.

Originally posted by AndrewT
Hi,
has anyone reached the stage of measuring voltages on a completed set-up yet?

I am still hoping someone can tell me the voltages that exist either side (D&S) of the FETs.
I think the drains are sitting at 1.5V below the supply rails, but the source voltages depend on the Vgs of installed devices.

Andrew, when measuring/matching those FETs´I got the following results:
a span of Vgs from 1.093 to 1.356V (for the N-ch) and Vgs from 1.791 to 2.027V (for the P-ch) FETs´are the ZVV/ZVP 2110G (SOT-223)

Then its "only" to calculate the Vcollector for the Q1-Q4 and then you will get the results of the Vg for the FETs´, but if this is the same as when measuring in a working amp, I dont know?

Regards