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Old 17th July 2006, 03:53 AM   #1
Davet is offline Davet  United States
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Default SI- Stealth Mod Problem

I have implemented the stealth mod on my disassembled SI T-Amp.

1 .Replaced the VR with the RS Alps.
2. Added a a toggle switch for power off/on.
3. Replaced the 330 electrolytic tank capacitor with a 1000 MFD Panasonic FC electrolytic.
4. Replaced speaker Jacks with binding post. Kept cap across outputs.
6. Removed resistors r01/r02.
7. Bridged Capacitors C3/C4.
8. Stealthed BG 2.2 MFD 16 volt input caps.

I am testing mod using AA batteries. Amp is breadboarded and not mounted in a chassis.

When powered on I get a squeal/buzz from the speakers. Any idea what may be causing the squeal?

Is it possible I zaped the chip?

I have two other SIs I can modify, but I would like to know what my problem may be before doing another amp. I have spent the last two days reading threads here trying to get a hint to my problem.

TIA....HELP

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Old 17th July 2006, 01:09 PM   #2
cpemma is offline cpemma  United Kingdom
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Default Re: SI- Stealth Mod Problem

Quote:
Originally posted by Davet
... Amp is breadboarded and not mounted in a chassis.

When powered on I get a squeal/buzz from the speakers. Any idea what may be causing the squeal?
(a) Is the audio signal coming through?
(b) How loud is the squeal/hum compared to the audio?

The amps are susceptible to noise pickup if you have long signal wires and no screening enclosure.
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Old 17th July 2006, 04:53 PM   #3
Davet is offline Davet  United States
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Default Trying to isolate buzz

Up until your response, I had not tried the unit with actual music input. I, initially, got a buzz through the speakers, I then disconnected the inputs. The input cables are rather long.

Today I connected the inputs and I got the buzz through one channel (speaker) only. This is only when connecting the test speaker to one channel at a time. Prior to your message I had both speakers connected and the buzz was in both channels.

I am now checking solder joints. I will keep you posted.

Thanks, for getting me pointed in the right direction.
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Old 17th July 2006, 07:00 PM   #4
Pano is offline Pano  United States
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Right, double check your wiring and connections.
It does not sound like a chip problem, more likely something in yout input wiring.

How is your grounding?
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Old 17th July 2006, 08:13 PM   #5
Davet is offline Davet  United States
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Default Grounding

My intent is to unsolder (or reheat) all inputs to the board. Then I will add a channel at a time to try to isolate the problem.

As I think about it I may have overheated the PCB when I was trying to remove the VR connector. I have to verify that there is conductivity from the pads to the various points on the PCB. I had verified that the ground on the PCB to the input ground worked. However I will be checking everything again.

Thank you for your input.
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Old 20th July 2006, 12:29 PM   #6
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My modded T-Amp squeals like a stuck pig if the PC is turned off. With no inputs connected or the PC turned on, no problems.
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Old 20th July 2006, 06:57 PM   #7
Davet is offline Davet  United States
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Default Dead Channel

After tracing everything it appears that I may hae shorted out one channel to ground at the VR. I removed all inputs. I still get a buzz through one channel. It measures the supply voltage of 11 volts DC.

So I think something is amiss. If nothing else I have a mono amplifier.

I have since modified one of the other SIs I had. This time I just removed C3, C4, R01, and R02. I bridged C3 and c4. I then cut into the wiring harness from the stock VR and inserted Blackgate 2.2 mfd caps. The SDtealth mod is working as described.

I will increase the resevoir capacitance. Test for sound. Then possibly replace the stock VR and connector harness with RS Alps and RCA connectors. Then test for sound again.

Does anyone know what the extra tab on the RS Alps VR is for?

It has often been stated that you should try only one tweak at a time; which I did not do with my first SI.

IMPLEMENT 1 (ONE) TWEAK AT A TIME.

Thanks to all that provided me with input
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Old 20th July 2006, 07:18 PM   #8
Pano is offline Pano  United States
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If you are getting 11V out it means that input is shorted after the DC blocking cap.

Check there.
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Old 20th July 2006, 08:20 PM   #9
Davet is offline Davet  United States
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Default B;pcking cap

I will check the PCB traces. With no inputs there must be a solder bridge somewhere.
Thanks.
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Old 23rd July 2006, 12:28 AM   #10
Davet is offline Davet  United States
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Talking Stealth Success

Thanks, Pano', your info was 100% accurate. Once I started checking everything again; I found that the solder bridge of c3 actually bridged onto C1. Thus shorting out to ground. Once this solder was cleaned up the amp and mod worked as stated.

Two things that I would suggest as a result of troubleshooting this mod.

1. Use a piece of wire to make the bridges. A strand from a piece of stranded hook up wire is ideal. My SMD skills were such that I lifted C3 when I tried to make the bridge. The wire is a lot simpler and for me easier to control.

2. Use a piezeoelectric speaker for testing. They are virtually indestructable and the motor boat buzz that I was experiencing is diminished considerably in volume using the piezeo.

Again thank you for all that offered input.
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