ODS #183 Build

[martin manning]

I don't know how you could get power supply caps any closer together than putting them in the same can ;^)

[talbany]

I don't know how you could get power supply caps any closer together than putting them in the same can ;^)

I am not aware of different compositions of electrolytics being significant to sound quality,

[pompeiisneaks]

I don't know how you could get power supply caps any closer together than putting them in the same can ;^)

I am not aware of different compositions of electrolytics being significant to sound quality,

These two statements are so clear the pretty much tell the story themselves. Especially after your last statement that you had some kind of problem with smaller caps vs cap cans. The non can style were physically 'not as close' to one another as the muti-section style could be. I can totally see how some specific arrangements of PCB and/or specific brands that have an unexpected design flaw may cause problems that were not expected. I'm not sure I understand your point here and would love you to clarify, or were you just saying 'yes this hits the nail on the head' type thing?

~Phil

[talbany]

I don't know how you could get power supply caps any closer together than putting them in the same can ;^)

I am not aware of different compositions of electrolytics being significant to sound quality,

These two statements are so clear the pretty much tell the story themselves. Especially after your last statement that you had some kind of problem with smaller caps vs cap cans. The non can style were physically 'not as close' to one another as the muti-section style could be. I can totally see how some specific arrangements of PCB and/or specific brands that have an unexpected design flaw may cause problems that were not expected. I'm not sure I understand your point here and would love you to clarify, or were you just saying 'yes this hits the nail on the head' type thing?

~Phil

Sorry Phil I'll clarify
I took Martins quote literally (which is why I posted it again). I was thinking of these as two separate issues that can on there own affect the sound of the amplifier. I was addressing the composition (2) comment only? and that the composition of an electrolytic cap can sound different.
Here Dumble even mentions the two,(but doesn't say they are related)

2) The caps that were in there were ok, but Howard wanted a different cap composition than the regular Sprague caps. Turned out an Illinois capacitor had the construction he wanted.

3) Then there was the spacing of the caps from each other. He insisted that EMSR or ESR (???) was restricting the tone because they were too close together. A new board spaced them the distance he wanted to see.

Sorry for the confusion!

Tony

[pfarrell]

This is all pretty fascinating (I read the whole thread that was referenced)... I'm not sure I have any empirical evidence regarding guitar amps... but certainly depending on the circuit design and where caps come in the circuit in the hi-fi amp/preamp world—caps and their makeup can make a huge difference sonically—good and bad—I lean firmly in the direction of less editorialization is good—but guitar amps are a different animal entirely.

I was looking at Martin's relay supply board versions (while making the FET pre and bias boards just now)—here's a noob question. Do I need a separate pair of 6.3 VAC windings for the 6.3 VAC doubler version? ... or can this be run off the heater windings, dual duty as it were, and thereby skipping the (extra) internal 12V trafo? Sure seems simpler, if so. I did something similar in a tube audio preamp one time—tapped off the heaters into a weeny switching converter to make 15VDC+/- to power a Muses volume control.

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[martin manning]

You can power the relays from the heater winding, but you can only have one ground reference. To minimize the possibility of 60 Hz hum it's typical to ground the center tap of the heater winding or to use a faux center tap consisting of two 100 ohm resistors. Either way the AC heater voltage is centered around chassis ground. If the relay circuit is also powered from the heater winding it must be floating, with no chassis connection of its own. That will work, but you have to avoid letting any part of the relay and foot switch wiring connect to ground. It's also possible that rectifier switching noise could find its way into the audio. Personally I prefer to use a separate transformer, and ground the relay circuit to the chassis at a single point like Dumble did.

[pfarrell]

You can power the relays from the heater winding, but you can only have one ground reference. To minimize the possibility of 60 Hz hum it's typical to ground the center tap of the heater winding or to use a faux center tap consisting of two 100 ohm resistors. Either way the AC heater voltage is centered around chassis ground. If the relay circuit is also powered from the heater winding it must be floating, with no chassis connection of its own. That will work, but you have to avoid letting any part of the relay and foot switch wiring connect to ground. It's also possible that rectifier switching noise could find its way into the audio. Personally I prefer to use a separate transformer, and ground the relay circuit to the chassis at a single point like Dumble did.

Perfect, makes sense.

[pfarrell]

...Project isn't dead! ... Had to do some other work, ongoing for another week.. been stuffing stuff here and there kinda working everything at once. Not much soldering, still making sure it's all "correct". I've been reading the FET bias thread...and have started with the value's on Martin's drawings/pdfs/eyelet maps—also his biasing PDF—wow thanks again Martin, guess I'll be prepared to swap some parts if needed...
No iron in hand yet. Hopefully soon. Some progress anyway...

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[Guy77]

...Project isn't dead! ... Had to do some other work, ongoing for another week.. been stuffing stuff here and there kinda working everything at once. Not much soldering, still making sure it's all "correct". I've been reading the FET bias thread...and have started with the value's on Martin's drawings/pdfs/eyelet maps—also his biasing PDF—wow thanks again Martin, guess I'll be prepared to swap some parts if needed...
No iron in hand yet. Hopefully soon. Some progress anyway...


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Looking great! Were did you get that multiple arms device with the orange base?

Cheers
G

[martin manning]

The small boards are looking good! You probably read that you can set the FET up as a clean boost to drive V1 harder, or as more of a distortion generator. For the relay supply, are you going with an auxiliary transformer? 5V or 12V for the relays?

[pfarrell]

Multi arm base. (I really do quite object to Amazon reliance...but...)

Yes, Martin I did read that. I'm going to lean on the clean side—I do intend to use it with an acoustic, but the pickup in that is active, so it should be interesting. Open to suggestions of course.
You can see the 12V trafo in the pic actually, center back, per your suggestion of separate trafo... 12V relays.

[martin manning]

I'm going to lean on the clean side—I do intend to use it with an acoustic, but the pickup in that is active, so it should be interesting. Open to suggestions of course.

I have not tested the low voltage off-center bias on the FET in hardware yet. That information came to light fairly recently with the SSS schematics and the measurements obtained by Charlie W.

You can see the 12V trafo in the pic actually, center back, per your suggestion of separate trafo... 12V relays.

Sounds good. I'm a fan of build and test as you go, starting with the power supplies.

[pfarrell]

Slowly... Still waiting on iron... Cut all the panel holes, mounted inner side boards—will make the relay boards next. Amp board is about 50% wired... I'll post a pic later. Oh, and tested the FET board per Martin's pdf. Looks good! Vdd/Vd=2.08—really needed a 3K resistor, but had 3R3K on hand, seems like this will be a fine starting point based on the chart in the PDF?

PF-183_10.jpg

[martin manning]

Slowly... Still waiting on iron... Cut all the panel holes, mounted inner side boards—will make the relay boards next. Amp board is about 50% wired... I'll post a pic later. Oh, and tested the FET board per Martin's pdf. Looks good! Vdd/Vd=2.08—really needed a 3K resistor, but had 3R3K on hand, seems like this will be a fine starting point based on the chart in the PDF?

That should be close enough. You could also parallel a 27k and 3k3 and get 2k94. What's you plan for machining the top of chassis cut-outs?

[pfarrell]

Cool! Good to know..

Drilling holes, I have the all the bits etc.... pretty straight forward.. I just don’t want to cut anything until I have iron in hand… No idea if they match what’s on the drill plan… which is a luxury (drill plan)! Usually i’m just doing my own layout…(I did cut all the front and back panel holes/IEC etc., you just can’t tell from that shot really.) Also the rivnuts and case registration is done..