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October 27, 2021, 12:04:47 AM

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91
Amplifier Discussion / Re: Fender London Reverb
« Last post by Jazz P Bass on September 09, 2021, 12:22:57 AM »
What does the supply read for the power amp stage?
+33Vdc & -33Vdc is stated.

 The 15 Vdc supply is for the opamps.
A 3 volt drop will not hurt.
As long as they are both the same. (+ & -)

 The 18 Vdc supply is for the reverb & effects.
Again. No biggy as long as they are both the same.

 Have you checked for Vac ripple?

92
Amplifier Discussion / Fender London Reverb
« Last post by GOR3 on September 08, 2021, 06:01:36 PM »
I'm re-hab'ing a Fender London Reverb. The schematic states ±18VDC and ±15VDC from the low-voltage power supply. I’m measuring around ±15 and ±12, respectively, unloaded, so 3V low on all the rails. (The high-voltage supply matches the schematic at ±33). The secondary of the transformer for the low-voltage supply measures about 12-0-12VACrms, again unloaded. I don't see how that makes it to ±18VDC.
I’m wondering if ±15 and ±12 actually is normal.  That is, that after the schematic was drawn and published, Fender decided to drop the low-voltage supplies by 3 volts and just didn't update the schematic (or at least the schematic I have).  I contacted Fender for the service manual, but they demurred. I also searched the web; no joy. If you’ve been inside one of these things, I’d be curious what voltages you found.
Thanks,
George
93
Honey Amp / Re: Just got the kit this weekend
« Last post by Amdthedestroyer on September 06, 2021, 09:44:29 PM »
Ok, it's been a long time. I kinda burnt out some parts trying out a laptop charger without thinking. So, yeah, check the specs on your power supply a before trying it xP

Any dang way, I put a socket in and I've tried several different caps to boost gain. I would NOT recommend bridging that connection as I got some really bad sounding distortion (like damaging my speaker type)

After fixing it and fixing my pc, I should be able to record some tracks now.
94
The Newcomer's Forum / Re: Greetings from a new member
« Last post by Jazz P Bass on September 04, 2021, 01:34:16 AM »
Hello, Andre.
Welcome to the Forum.
95
The Newcomer's Forum / Greetings from a new member
« Last post by Andre Rock on September 03, 2021, 07:24:55 AM »
Hi, everyone. I am very glad to join this forum. My name is Andre, 54, from France. When I started, I used a Peavey Bandit 65, then a Fender Stage Lead. I loved both amps very much. Later, I owned a Marshall 30th anniversary combo, and a Hiwatt 100W head. Now that I live in Mongolia, my needs are more reasonable. I have a small Marshall MG15DFX, which performs quite honorably. Willing to start an instro/surf band, I was looking for a decent solid state stage amp in a 2X12 configuration. I just bought a Roland JC120 from Japan at a very good price ($369). And I think I will need a lot of advice in order to make it work...again.  :cheesy: Andre
96
The Newcomer's Forum / Re: How to use a Multimeter video
« Last post by Andre Rock on September 03, 2021, 06:46:57 AM »
Thank you for these videos: very informative! Will help me a lot in my first steps.
97
The Newcomer's Forum / Re: books on amp building
« Last post by Andre Rock on September 03, 2021, 02:10:25 AM »
Hello everyone. As a new member, I would like to thank you for the list of reference books on amps and electronics. Here are some new direct download PDF links to Op Amps for Everyone, respectively as first, second and third editions:

https://web.mit.edu/6.101/www/reference/op_amps_everyone.pdf

https://www.pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/Texas_Instruments/Op_Amps_for_Everyone_TI.pdf

http://index-of.es/z0ro-Repository-2/Cyber/02%20-%20Electronic%20Engineering/Op%20Amps%20For%20Everyone,%20third%20edition%202009%20(Texas%20Instrument).pdf



98
Amplifier Discussion / Re: Marshall 3005/Lead 12 Power Trans Question
« Last post by pinkjimiphoton on September 01, 2021, 11:53:15 AM »
i build guitar effects for a living. the 1458 is my favorite chip in many distortions, it really sounds different from a lot of the others, i mean for all intents its a dual 741, but to my ear, it sounds great. so i tend to keep a couple hundred kicking around in the semi conductor junk drawer.
i DID socket it, so i could mess around with it if i wanted to, but i always go back to the 1458 in all of my own personal circuits. i figure if it was good enough for the guv'nor, its good enough for me ;)
i've tried just about every dual opamp available in distortion circuits. most folks prefer the jfet based ones, but to me, the '58 is the only way to fly.
proper transformer arrives tomorrow, so i'll install that and button it up.
thanks for the support!
99
Amplifier Discussion / Re: Marshall 3005/Lead 12 Power Trans Question
« Last post by Enzo on August 31, 2021, 09:42:28 PM »
Glad you got it.   Good you had a 1458.

Just a note.   Most times a 4558 will work fine in place of a 1458.   But in the Marshall preamps of that era, it won't.  a 4558 might function, but becomes unstable and you get squeals and can't turn it up past whatever without howls.   Oh not every time, but I always stocked old 1458s in my shop just to have them for Marshall repairs.

And yes, I saved good pulls from working equipment
100
Amplifier Discussion / Re: Marshall 3005/Lead 12 Power Trans Question
« Last post by pinkjimiphoton on August 31, 2021, 06:04:06 PM »
gotcha. my bad. and my apologies to the forum.  :dbtu: :dbtu:

well to finish up, yeah the 1458 was the issue, but not the one i thought it was.
previous owner had tried to replace the chip apparently, and killed the pad for pin one of the opamp.
so i desoldered it, replaced with a socket and ran a piece of wire from pin 1 of the socket to r7/8.
took some voltages, now i was reading a lower voltage than i expected, +/- 5vdc.
close enough for rocknroll to not fry the chip. replaced it. dead. put in a fresh 1458n out of my junk drawer and fired right up.
thanks for the support and patience.
rock on!
PjP
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