[antomas]

Hi everybody!

You may find my attempt to design a pcb for the power supply of Gilmore dynamic amp here.

ExpressPCB and image files will be posted as soon as i'll build the ps (hopefully 7-10 days).

Thanks for your attention,
Massimo

 

[Voodoochile]

You have come a way with this, Massimo! Looking good, I'm anxious to hear your remarks after fabrication.

 

[Arzela]

Nice board antomas.

I have two questions:

Should all three connections for your
trimmers be connected? They should
be used as a variable resistor (from wiper to one end), no?

You don't have Ilim and V- on the 548's
connected. Will this be done above board?

 

[antomas]

Hi Arzela,
thanks very much for your comments!
Quote:

Should all three connections for your trimmers be connected? They should be used as a variable resistor (from wiper to one end), no?

I'm not sure to have correctly understood your question (apologies in case I didn't...

). I connected the pots as indicated in the KG schematics: one end and wiper to ground, the other end to the regulator. This should not leave the circuit open in case of failure of a pot (leaving maximum resistance).
Quote:

You don't have Ilim and V- on the 548's connected. Will this be done above board?

There is certainly a mistake in my pcb: the Ilim (pin 3) should be connected to V- (pin 4). This happened because I didn't put the connection in my schematic (shame on me), so ExpressPCB couldn't check it. This is very easy to correct. But pin 4 seems to me to be properly connected to V- on both chips... isn't it?

Ciao and thanks once again.
Massimo

 

[Arzela]

Quote:

... This should not leave the circuit open in case of failure of a pot (leaving maximum resistance).

Ah! Ok...sorry for my initial quibble..


Speaking of trimmers,
is this correct:

A trimmer consists of a resistive element
and a wiper. Let's say the wiper is
pin 2, and the ends are pins 1 and 3. If the resistance is R,
the and the percentage distance from
the wiper to pin 1 is X, then the resistance from pin 2
to pin 1 is xR, while the resistance from pin 2 to pin 3
is (1-X)R.

By varying the wiper (turn the screw), you
can have a "variable resistor".

Actually you have 2, one from pin 1 to 2, and the other from pins 2 to 3.


Quote:

There is certainly a mistake in my pcb: the Ilim (pin 3) should be connected to V- (pin 4). This happened because I didn't put the connection in my schematic (shame on me), so ExpressPCB couldn't check it. This is very easy to correct.

Indeed...


Quote:

But pin 4 seems to me to be properly connected to V- on both chips... isn't it?

Yes, it looks correct to me..

Let us know how it turns out.


Regards,

David

 

[antomas]

Hi David,

I realized that my (understanding of) english is worse than I could imagine... Sorry for my confused reply and thanks once again for your help.

Best regards,
Massimo

P.S. to better clarify the reason of my misunderstanding, for a while I suspected I had swapped the pins of the OPA548...

 

[Arzela]

Hi Massimo,

Your English is fine; I'm afraid my initial post
was ambiguous though. My apologies.

David

 

[antomas]

Dear David,

it's a pity we are so far away and I can't invite you for a drink (maybe, better, for having some italian food...)

My best wishes for your projects and again, thanks for the bug fix. I didn't read carefully the datasheet of the OPA548 but a kind man found the problem...

Massimo

 

[BoyElroy]

Greetings Massimo--

Now that you've got the PSU ready, I was wondering how you were going to make the amp section. Will you draw up your own custom design or use an existing amp board? Single-ended or balanced bridge?

Nelson Pass has an interesting paper on the benefits of a balanced design even when used as a single ended device you may want to check out (in case you haven't already).

Also, could you post some details of your preamp/headamp design? I'd like to hear about your solutions for the switches/volume/connectors on the unit.

My projects have been on hold for the past few months as I've had to deal with other, more pressing concerns (read: wife!) so I'm hoping your ideas will re-start the DIY bug for me!

 

[antomas]

Hi BoyElroy!

Thanks for your message and... my apologies for this very concise reply.
Quote:

Now that you've got the PSU ready, I was wondering how you were going to make the amp section. Will you draw up your own custom design or use an existing amp board? Single-ended or balanced bridge?

I just took the original KG pcb (the ExpressPCB version), then I rotated it 90° (it's easier to edit it this way), I shortened a few traces - just adding some 45° angles - to make place to my beloved grommets... hope they work!

I like a lot the smaller pcbs (like the one of Master Sjiosae), but since my enclosure shall be a lot larger than a mint can, I'd prefer to keep the transistors not too close each other, hoping to keep them fresher, too. I'm quite embarassed to post this pcb, because I just made minor changes (maybe wrong) to the KG design, but if anyone would like to see it, I'll place lots of ackowledgements around...

Quote:

Nelson Pass has an interesting paper on the benefits of a balanced design even when used as a single ended device you may want to check out (in case you haven't already).

Thanks a lot, I'll look at it ASAP.
Quote:

Also, could you post some details of your preamp/headamp design? I'd like to hear about your solutions for the switches/volume/connectors on the unit.

I'll be very happy to post details, as soon as I'll have the input pcb (in fact two, one for the selectors, the other for the pot. The ideas I'd like to implement are:
- only one Gilmore in a box (once I liked to put two with a crossbar switch inside the enclosure, but the enclosure would become too big and the wife too angry);
- make a first, single-ended version; time permitting, add the other "side" of the bridge;
- put the input section on a pcb, again mounted on grommets;
- cheap Alps Blue pot and not-so cheap italian mechanical selector; no relays; cheap-and-AFAIK-good Shark rca jacks;
- sturdy enclosure, 8mm aluminium; wherever possible, usage of some anti-vibration painting (Noise Killer, if available).
Sorry, these are just ideas and I can't say more about. the proto version will be certainly on top of a plywood panel...
Quote:

My projects have been on hold for the past few months as I've had to deal with other, more pressing concerns (read: wife!) so I'm hoping your ideas will re-start the DIY bug for me!

Next step? A power amp to drive loudspeakers! Maybe this would not be the appropriate bride for the Gilmore dynamic, but it seems a project (at least in apparence) simple enough to start with (I'm sure you know it):
http://pub134.ezboard.com/ffakeidsfr...icID=116.topic
here you may find a lot of additional inspiration on building amps, enclosures and vibration-fighting:
http://www.diyaudio.com/forums/showt...?threadid=9112

By march 2006 I hope to finish all this stuff...
Ciao,
Massimo

P.S. One more thing. Do you know this site:
http://www.tnt-audio.com ?

 

[Arzela]

Hi Massimo,

Your project sounds interesting. I am
going to build a preamp based on the Gilmore as well.
Four inputs, two outputs, and a tape loop.

I would be very interested in looking at the
layout for your unit. Please post pictures/schematics
if you can. I hope to learn a thing
or two from them.

Regards,

David

 

[antomas]

Sorry David,

I don't have very much to show for the moment, but:

I'll use a 4 pole/5-6 toggle rotary switch to switch signal and ground of both channels. One side of the switch will be connected to the (insulated) input rca jacks and the other side to the 50 kOhm Alps Blue.

No tape out, sorry.

One additional switch to select the output sink: rca jacks or Neutrik locking headphone jack (insulated, of course).

As soon as I'll have something useful to show I'll certainly post it but, as BoyElroy knows well, I'm progressing veeeeeeery slowly...

Ciao,
Massimo