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October 27, 2021, 12:09:21 AM

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11
Amplifier Discussion / 1970 Standel SB30 troubleshooting/ death cap identification
« Last post by Ethernaut on October 23, 2021, 01:30:39 PM »
     Hello, all. Hoping someone here could assist w/ issues concerning a 1970 Standel Studio Bass 30. Some background: amp powered up and functioned upon purchase 3 mos. ago w/ two JBL K130s (non original, but 8 ohms ea., wired parallel so showing 4 Ohms). Has original 2 prong cord. I swapped two 8 Ohm Madison branded 15” in (JBls went to another rig), and powered it up via a lamp limiter which was plugged into a Variac at 120v. Bottom speaker sounded out, but not top. After about 15 seconds, it sputtered, produced no sound, power light flickered & died. I looked up to see that the bulb was bright & shut it down. Then I discovered a potential culprit:

-The top speaker was not connected

     I spoke w/ Danny McKinney, current owner of the Standel line, who is quite familiar w/ this amp and owns one himself. We sorted out that either:

A) Old caps finally gave way and it’s coincidental that this occurred w/ speaker change
B) The unattached speaker wires toutched & fried output transistors

I got the chassis out & without measuring any values (which I don’t know how to do- I have not progressed past basic safety, buying a variac, building a limiter and the ability to swap capacitors & upgrade to a 3 prong in an old Fender), I immediately saw a cap which appears shrunken & has white residue on it, which I’m hoping indicates that it has failed or is in the process of doing so, and that’s the true culprit. It is teal blue & connected to two tabs directly behind the power indicator bulb (I’d include a pic but can’t get one to upload). If I’m reading the schematic correctly (pdf link below), it’s a C14 .02 600V. Can anyone ID this component as the death cap? If it is, can I simply snip it out, remove the two pronger, solder in the leads of a grounded cord, ground to chassis & test again?

Another clue is that someone, at some point, wrote “short PC” on the side of the chassis- maybe this problem was known by a previous owner?

That was a large amount of words to pose a short question. All thoughts & advice greatly appreciated.

http://www.standelamps.com/support/schematics/documents/1970/custandstudiobass_service.pdf

Be good,
-Pete
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Amplifier Discussion / Re: Remote channel/FX switch
« Last post by Enzo on October 22, 2021, 10:52:14 AM »
Switching is simple, it was his desire to have a remote reverb level control that was a challenge.
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Amplifier Discussion / Re: Remote channel/FX switch
« Last post by phatt on October 22, 2021, 08:43:05 AM »
It  baffles me why people go chasing the most complex way around simple problems.
I'm old enough to remember all the old amps that came with 2 "Separate independent" channels. Often one Ch had Trem/Rev.
One only needs a 2 way splitter,, guitar in with 2 cables out to the 2 channels.
No convoluted switching systems needed. :-X
If you want much more than that it's likely far better to build a simple Amp setup and use use a pedal board for all the tricks. 8|
Just my 2 cents worth.
Phil.
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Amplifier Discussion / Re: Remote channel/FX switch
« Last post by ampetrosillo on October 22, 2021, 05:12:29 AM »
A digital pot would also require digital circuitry (a microcontroller, even a simple PIC chip, etc.), if I could do without digital circuitry it would probably be better (easier to shield, no interference, etc. mine is just a hobby project), but with some help on best practices I suppose it could be done.
15
The Newcomer's Forum / Re: Busking Amp for Bass & Vocals
« Last post by Puguglybonehead on October 21, 2021, 02:20:24 PM »
Thanks for the advice on the TPA3116D2 and the TPA3122D2N. I will definitely look into those. If I use it with a trimpot controlling output I should be able to conserve battery life and avoid ugly clipping as well, no? I will probably use the TDA2003 module I have here for just a guitar amp. 4 watts with a good speaker and a good preamp should be enough for guitar alone.
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Amplifier Discussion / Re: Remote channel/FX switch
« Last post by Enzo on October 20, 2021, 10:05:11 PM »
RElays are clean, and can switch signal at 40mv or 40 volts  Relays let you control completely isolated from the signal path.  I have found them darn reliable over my decades.  I have replaced a few, but that is in thousands of amps. 

But I expect relays to be here a long long time.  DG419?   And when they stop making them?  Remember the useful TL604 that were used in large numbers in the 1980s?  GOne now.

Don't get me wrong, if you have a useful design based on them, go ahead.   I just didn't buy the backup argument

A common approach to using a FS and panel switch is to run them in series.  The FS jack between panel switch and ground, with its normal shunt completing the circuit when no FS is used.

A remote level control?  I'd hate to run the signal path outside the amp and back.  If you want to run a control voltage, you'd have to have a supply out to the FS, and make up a control circuit there.  VCA?  Would work, I don't know what is current in VCA chips.  On th other hand a simple digital pot would likely work too.
17
Amplifier Discussion / Remote channel/FX switch
« Last post by ampetrosillo on October 20, 2021, 10:51:02 AM »
I'd like to implement a clean/dirty channel switch for my design, and also a vibrato/reverb on-off switch. I'm using DG419 parts (nice and reliable, clean if a bit fast, etc.) for switching, although I could use simple relays as well (but the cost and complexity is basically the same, with the added bonus that the DG part is solid state, therefore potentially more reliable) and I'd like to be able to both operate the switch from the panel and via a footswitch. Are there any schematics you could point me to? Secondly, I'd actually like to have a remote reverb mixer (as well as the panel-mounted one), this screams VCA of course, but what would you suggest?
18
The Newcomer's Forum / Re: Busking Amp for Bass & Vocals
« Last post by joecool85 on October 19, 2021, 12:01:23 PM »
I just looked at the TDA2003 spec sheet, it looks like you would get 4 watts at 12 volts, not enough for bass in my opinion, but I am not an expert.
If you have the kit, build it and run your send/line out/ to effects output of your amp into it, and run the output to a separate cab and see what it sounds like.
Or get the signal from your stereo/phone/MP3 player and try it, see how loud the music sounds.
If its not enough the just get another amp module, like I mentioned before, the TPA3116D2 has 15 watts at 12v on the spec sheet at 4 ohm speaker.
You will not us a lot of extra power with a TPA3116D2 if you keep the volume down.
Class D power amps are very efficient and only use a bit more then what you use, if you use a 100w class D amp and only turn it up to 10Watt you will only use about 12-13 watts of power, at least that's my understanding.
Check the spec sheets of the power amp you are thinking off using and find the power rating for the voltage you intend to use, that's what I would do.
Class D amps don't need big heatsinks as well which saves money and weight.

This is correct.  One thing to note though is the TPA3116D2 is an SMD component and difficult to solder.  TPA3122D2N is a through-hole component and much easier to work with.  There are several kits available with this chip, or you could do something on your own.
19
Amplifier Discussion / Re: Sunn SL260 Help Needed With Pot Orientation
« Last post by Tassieviking on October 15, 2021, 06:16:01 AM »
Thanks for all that info Phatt.
I definitely live in Tassie, where the Devils roam free. ( I have had them under the bedroom, makes you jump when they scream at night. )
I was born in Sweden but moved to Australia when I was 12, I still remember climbing on Viking rune-stones as a kid, they were all around the area where I lived.
I went back to Sweden in 1976 when I was 16 for a holiday, but it was still too bloody cold, stayed down under since then.

I am interested in solid state guitar amps off all kinds, I am going to order PCB's for Marshall Mosfet 3310 and Sunn Beta very soon and I just wanted another type of preamp for the order.
I order my PCB's from JLCPCB and find it better if I have a lot of different boards in one order, postage is the killer, but does not increase too much for more boards.

I like to stick circuits into KiCad and making circuit boards up for myself, I find it relaxing, I will have to learn the simulation bit soon in KiCad or some other software.
I don't have much experience in audio circuits, but been a sparky since 1980, mainly industrial maintenance repairing DC and AC drives and any other electronic boards that needed it to keep machinery running. My only tube experience was with high voltage spark testers checking insulation in cable manufacturing.

I have never seen a Sunn SL160 or SL260 in my life, but I might just have the preamp made by Xmas. (Just for fun)
I do love Rod's circuits and have looked at nearly all of them, I have read up on the reverb circuits on his page, but I will stick to what was original on the Sunn SL260 circuit.

Again, thank you for your help, I' gonna start reading up on what you mentioned now.
Michael
20
Amplifier Discussion / Re: Sunn SL260 Help Needed With Pot Orientation
« Last post by phatt on October 13, 2021, 04:06:48 AM »
Hi Michael,
for info on the Sweep mid section just search for Parametic circuits.
Yours is a mid sweep circuit with a set low Q.
(Q is the width of the boost or cut)
For Q control you need an extra pot.
It looks like it sweeps form ~200hZ up to about 1,200hZ.

Info here; http://www.geofex.com/article_folders/eqs/paramet.htm

I just did a quick simulation of the tone section you posted and it's about a +/- 5~7db boost/cut at whatever freq is set.

Can I ask if you have used this Amp?
If not be aware there are a lot of pitfalls when one just goes straight into a build without at first Bread board testing to see if it actually does what it claims.

OK I'm no teck geek but I've spent 30 plus years building many amps/circuits and I can tell you the short cuts are the most painful learning curves. :'(

I bread board everything now which takes longer but you learn so much more and end up with a far better design. 8|

I have a bottom draw full of pcbs that seemed like a great idea at the time but ultimately ended up as land fill. but better to keep as spare parts. :tu:

If I find a circuit that looks promising then i break out the breadboard and test if it actually works ""Looong"" before I heat up the solder. ;)

Having just simmed the tone of the sun I'd be reluctant to go ahead as I question if it works as well as other circuits which may well prove far better. My best tone circuit design does a 30dB cut at 400hZ, while many parametric circuits can only achieve 15dB max.

Of course if this Sun circuit is *Exactly* what you want then disregard my ramblings. :dbtu:

Oh yeah I doubt the reverb is going to be stunning as it looks like the drive section will be too weak to give a strong reverb. I maybe wrong but I've built many reverb circuits and a lot of them are crap. :trouble :grr

If you want to get a better handle on Spring rev circuits it's hard to beat this page,
info here; https://sound-au.com/articles/reverb.htm
I use the Transformer circuit down the page,, I came up with this idea and Rod kindly perfected the Drive circuit.
Unlike a lot of rev circuits found on the net Rods basic Rev/mixer circuit worked as claimed.
hope it helps,, Phil.
ps judging by your handle I take you are in Tassie Au?
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