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September 28, 2023, 08:05:46 AM

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The Newcomer's Forum / Re: MarkBass/Class D amplifier...
Last post by g1 - September 23, 2023, 12:17:37 PM
You have to deal with SMPS to get anywhere with these kind of amps.
see attached

another one here:
The Newcomer's Forum / MarkBass/Class D amplifiers
Last post by GeezerB - September 23, 2023, 10:54:53 AM
Has anyone looked at or attempted repair on these types of amps? I bought one non working for parts for a song... but now I see the complexity of such a device .   It seems that they are stingy with schematics and all roads lead to approved repair shops. This one won't even power up... no power LED, no fan, no life at all.   Just learning about class D, fascinating stuff!
The Newcomer's Forum / Re: saturated's all encompassi...
Last post by saturated - September 22, 2023, 11:22:00 PM
I was watching a video on my tv and took a pic of the screen

anybody recognize these guys  :P

You cannot view this attachment.
Schematics and Layouts / Raven RG100 Combo Schematic Wa...
Last post by willpirkle - September 22, 2023, 03:20:40 PM
schematic wanted: Raven RG100 2x12 Combo

One just came into the shop. It's a super simple setup and easy pcb access, bad filter cap... But I am looking for a schematic to add to the collection, and to look for anything else for completeness. their website is long gone but apparently they were designed in LA, not far from QSC/Quilter if my SoCal memory serves correct. it's been a while...

Thanks - will
Amplifier Discussion / Re: Modding an Ampeg SS70
Last post by joecool85 - September 22, 2023, 01:18:58 PM
This sounds like a great platform, but not something I'm very familiar with.  Care to share any pictures?  We'd love to see it!
Schematics and Layouts / Re: Looking for a schematic fo...
Last post by Tassieviking - September 22, 2023, 02:38:17 AM
I have had a good look for this schematic but i can't find one either, are you going to repair this one yourself?
I think this might be a very simple circuit as they sold very cheaply when they came out, it might not be hard to trace out.

If you can open the amp up and take photos of both sides of the PCB we might be able to trace it out for you, the more pictures the better.

I would imagine this might be a good project for people to build and also it sounds ok for a small amp, it might even be ok as a small stomp box size practice amp that you can plug into a speaker cab.

Amplifier Discussion / Modding an Ampeg SS70
Last post by FleshOnGear - September 20, 2023, 01:38:56 PM
A couple months ago I bought a solid state Ampeg SS-70. Even when it's stock the amp sounds pretty great. Channel B has a really nice clean that goes into a decent crunch at higher gain settings, and channel A does the metal thing really well. The only problems with the design are that the bass and treble controls on Ch. A are pre-distortion, Ch. A is too noisy, and the pre-distortion tone filtering takes out too much treble leaving a parked wah sounding top end (even with the treble dimed) that sounded particularly dull when rolling down the guitar's volume.

Here's the schematic:

I replaced C57 (47n) with a 4n7 cap, which opened up the top end, and replaced C20 (220n) with a 330n to extend the range of boost a bit lower. Unfortunately the extended treble caused oscillation at higher treble settings, so I wired a 10k resistor from P4's CCW tab to the wiper so that C13 drops a bit of treble at higher treble settings. Now I get oscillation only at the very highest treble and gain settings. I can probably increase C57 a little to mellow the top end a bit, but I don't run the treble very high, anyway.

I replaced IC1 and IC2 (RC4558) with very low noise LT1124 op amps. This reduced hiss significantly, even with the treble boost.

I wired a 68n cap in series with an 820 ohm resistor from the node where R19 meets R20 to ground. This drops the mids and highs relative to the bass. Before that the Ch. A tone was pretty thin, but this beefed up the overall tone a lot. I also increased C15 (560p) to 1000p, to retain a bit more presence on lower mid settings.

I'm really pleased with how this turned out. When I first played the amp I could tell it had potential, that it just needed some changes to the tone filtering before and after the distortion. I wish I could change the tone controls to be after the distortion, but it would require serious rewiring, and it's kinda cool being able to control the way the lows and highs cut through the gain. The post distortion filtering I added pretty much negates the need for post EQ, anyway. With these mods I get a distortion channel that balances well with the clean channel, and the distortion cleans up really nicely from the guitar volume.

Out of my solid state amps, this one has a unique midrange voice that I really like. My Marshall 5215 has a lot of girth to the tone, fat and corpulent; the Peavey Bandit has a smooth, creamy, but punchy midrange; this Ampeg has kind of a stiff, cutting midrange that could probably tear through any band mix. I'm a fan of all of it!
Schematics and Layouts / Looking for a schematic for th...
Last post by eidling - September 19, 2023, 02:58:41 PM
Hi - I am hoping someone can help.
Many thanks!
The Newcomer's Forum / Re: saturated's all encompassi...
Last post by saturated - September 18, 2023, 03:21:33 PM
pretty interesting
I think in my case some broken glass put the impeller in a bind and so the pump motor burned up

I tried bringing home washers and dryers for a while and fixing and selling but i guess the mentality is different these days
nobody wants a bulletproof roper or kenmore that will last forever....

oh well rant over

while I got you here I am really struggling with trying to understand how to be safe with oscilloscope grounding.
I was going to put a two prong adapter on the cord to unground it but maybe that is not a good idea.

I dont plan on working on any old tube amps or crazy vintage receivers anytime soon.

I will continue to try and learn how to keep my work safe.

thanks for your help.
Amplifier Discussion / Re: Marshall 2199 Master Lead ...
Last post by luke gibson - September 17, 2023, 09:28:41 PM
Quote from: Tassieviking on September 17, 2023, 01:29:02 PMIt might be you have a different style of PCB, possibly an earlier or later version of the same amplifier.
Marshall would release the same model but with several different layouts but basically the same circuit, they did however completely renumber all the components with several new revisions.

If you have the same circuit you should have 2 47nF capacitors in there, C14 and C15.
Can you find 2 47nF capacitors in there ?
Can you find a 25uF capacitor on the PCB ?, there should only be one.

If you can take some pictures of the top and bottom of the PCB I will see if I can trace your version out for you properly, the more pictures the better.
If I can see the top and the bottom and then compare where the traces go to what component it's fairly easy to do.


There are 2 47nf caps remaining. I traced it using the schematics and when I removed the cap it had C18 screen printed under it.  I have it buttoned up, next time I remove the chassis I will take a picture. Also noticed someone had replaced Q6 (2N3819) at some point with a different transistor.