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April 07, 2020, 01:59:09 AM

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21
Amplifier Discussion / Re: Ampeg Vh140c power transformer replacement
« Last post by joecool85 on March 31, 2020, 09:52:30 AM »
Hi guys,

I’ve had a Vh140c running through an external step down transformer for years (I’m in the UK, and the amp is a US model)and would really like to be rid of it. But I’m having a very hard time finding a suitable 230v PT.

Any help would be massively appreciated.

Any reason you want to get rid of the step down transformer?  If it is just to make it all simple and plug straight to wall, I would consider installing the step down transformer permanently in the amp rather than replacing the original transformer.  The reason being, unless you have the specs for the stock transformer, finding a replacement will be difficult.
22
Amplifier Discussion / Re: Customized Kustom 12 Gauge
« Last post by phatt on March 31, 2020, 09:10:46 AM »
Regards Speakers.
 Years ago i read an article in a El magazine, I can't recall details now of course but the writer made the observation that it is better to design from the speaker back to amplifier.
He was referring to hifi but over the years I've come to understand why he made that observation.

The reality of this Amp/speaker thing is complex.
FWIW,
Many pages on guitar forums are filled with Spk debates and observations.
I can tell you that even though many amp circuits might look similar one only has to alter a 20cent passive in a circuit and it can have big impact on the outcome.

Much like Valve shootouts, they always give me a giggle.
Someone swaps a whole lot of valves in a particular amp circuit and gives an observation of which one is best.
Even some educated folks entertain this stuff.
Yes in one particular amp circuit Valve X might work better than Valve Y.
But that does not mean that valve X is better for every circuit. In another circuit design the opposite might be the case.
Same goes for speakers.
I may have told this little story before but years back a mate brought me his Trademark 60 combo.
He said do whatever you can but if it does not work I'll dump it. It's way wrong, too harsh, brittle. Dist ch is not usable.
After a few days of pondering what could be done I decided to try a few old speakers I had laying around.
OK the Hot rod Eminence special design speaker that was in the trademark might have higher SPL and make the amp sound a lot louder than another similar 50 watt chip amp design but those big name fancy pants drivers that promise so much will often peak at higher freq and hence sound Louder. (they know the kids will often buy the loudest unit) ;)
Problem with that is they are excessively bright when using heavy distortion, All sweetness is lost when you do that.
To overcome that issue one would have to dig deep into the circuit and change a lot of stuff.
As Trademark goop all the circuitry that I would need to change,, well it's just not worth all the fuss when all that was needed was a more balanced (Flatter SPL freq response driver)
My mate could not believe the huge difference.
the speaker was a $10 junk sale purchase. 8|

Just my observations,, Phil.
23
Amplifier Discussion / Ampeg Vh140c power transformer replacement
« Last post by Ratsapprentice on March 30, 2020, 06:55:17 PM »
Hi guys,

I’ve had a Vh140c running through an external step down transformer for years (I’m in the UK, and the amp is a US model)and would really like to be rid of it. But I’m having a very hard time finding a suitable 230v PT.

Any help would be massively appreciated.
24
Schematics and Layouts / Re: 5th Gear Overdrive v3.0
« Last post by joecool85 on March 30, 2020, 08:20:02 AM »
Thanks for posting that. Looks cool, might try it.

Which diode is the LED and which is the 4148?

Can two general purpose NPN transistors be configured as the darlington, or does the sound depend on the characteristics of that particular transistor?

Phil in gorgeous Young Harris, Georgia, USA

It doesn't matter which diode is which as long as you have them facing opposing directions.  I haven't built it with general NPNs as a darlington, but others have on diystompboxes, and it seems that it works fine.  That said, I had another person build it and try a bunch of trannies and couldn't get the exact same sound as MPSA13 with anything else - close enough to work, but not quite the same.  Take that for what it's worth!
25
Schematics and Layouts / Re: 5th Gear Overdrive v3.0
« Last post by paelgin on March 29, 2020, 09:38:42 PM »
Thanks for posting that. Looks cool, might try it.

Which diode is the LED and which is the 4148?

Can two general purpose NPN transistors be configured as the darlington, or does the sound depend on the characteristics of that particular transistor?

Phil in gorgeous Young Harris, Georgia, USA
26
Amplifier Discussion / Re: Customized Kustom 12 Gauge
« Last post by Unique Amps on March 29, 2020, 08:12:43 PM »
Thanks for the welcome and speaker vote!  Duly noted.

 :tu:
27
Schematics and Layouts / Re: Teisco CheckMate 22 schematic
« Last post by galaxiex on March 29, 2020, 05:40:02 PM »
Got the coil wound and installed.  :)

4760 turns and 662 ohms.

It's alive!
We have reverb!
(albeit not very good reverb, but I expected that  ::))

Now I'll disassemble the tank and clean it up some,
just to get rid of some of the corrosion.

Edit: This is the output coil that I just wound at 662 ohms.
No idea what it was originally, or what it's supposed to be.
Seems to be working fine.

The input coil measures 1K6 ohms DCR and both coils were/are wrapped with blue tape.
I don't know if the tape color indicates coil impedance/DC resistance like the Accutronics tanks.
28
Schematics and Layouts / Re: Teisco CheckMate 22 schematic
« Last post by galaxiex on March 29, 2020, 03:27:00 PM »
Ok, the reverb coil winding has started....  :)

First pic is the bobbin mounted to the winder with the old wire still on it.

Second pic is the new wind started.

Wow this thing is tiny!

Winding going really sloooow cuz I don't want to break the wire and hafta start over...

The new wire is thicker than the old, so I'll over-wind it somewhat.

Old wire measures .015"
New is .025"

I was able to find the end wrap and paid attention to the direction of wind.

New wind is going on the same direction, don't know if it would matter (phase issue, maybe?).


29
Schematics and Layouts / Re: Teisco CheckMate 22 schematic
« Last post by galaxiex on March 29, 2020, 12:16:14 PM »
Here's some modifications to the little CM-22.  :)

Pics show the added stuff.

The input buffer is just hung on some stiff wires, right on the input jack.

The added C24 and R39 (see schematic) give a large gain boost,
very "crunchy" germanium transistor distortion, almost Fuzz Face territory.  8)

I tried with just the 100uF cap and it was too much gain, squealing feedback.
The 1K resistor tames it just right.
Thinking to maybe put the C24, R39 "gain boost" on a switch...

Last pic is a size comparison of the power Tx.
The bridge rectifier setup is temporary, I'll make a little board for it.

Can you tell I'm bored with being stuck at home?  ;)

Edit; still haven't fixed the reverb tank, I'll get to that later today... maybe...

Edit 2; schematic removed, mistakes were made, corrected schematic with all modifications in post below.


30
Software / Re: Zoom G5 software
« Last post by flester on March 29, 2020, 08:50:17 AM »
Or any other way to get acoustic instruments talking to a computer.

Sent from my SM-A505FN using Tapatalk

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