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Messages - g1

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Amplifier Discussion / Re: Randall RM50 Channel Switching
« on: November 20, 2020, 08:07:04 PM »

page 3 Qc7 goes to:

page 1 Qc4
page 5 Qc3

the relay contact on page six goes to page 1 Qc7, which just goes to R2 - not +12VDC

unless im missing something i do not see how that gets 12V to the relay....

It has to go through a couple relays, on page 1, and page 6.
pg3 QC7 > pg1 QC4 > pg1 RL1 (above D1 lower left corner) > pg1 QC6 > pg6 QC17 > pg6 RL1 > pg6 U2.

Could have lost one of the supply rails.
Schematic attached.

Amplifier Discussion / Re: Randall RM50 Channel Switching
« on: November 18, 2020, 01:33:40 PM »
I think the source is Qc6 at top right of pg.3 ?

Amplifier Discussion / Re: Krell amplifier repair
« on: November 17, 2020, 02:28:19 PM »
Well done sticking with it.  Many would have given up on it.

Amplifier Discussion / Re: Krell amplifier repair
« on: November 09, 2020, 04:09:52 PM »
I think the results will be the same.

Can you post DC idle voltages for Q73 & Q74 bad channel, and good channel.

Ok.  This is all I have for GD2.

Amplifier Discussion / Re: Krell amplifier repair
« on: November 03, 2020, 11:13:06 PM »
Is there something a miss around Q83, 84?
All the voltages look the same on both channels.
DC voltages are all the same for both channels?  Even Q80 emitter and base?
If you don't see any differences I would maybe try swapping out Q83 and 84 with the good channel.  Those big W42 and W92 transistors seem to have their fair share of issues.

You had asked for GD1.
Is it GD1 or GD2 that you have?

Amplifier Discussion / Re: Krell amplifier repair
« on: October 28, 2020, 12:18:33 PM »
That's not the signal path but the feedback path.  It's weak there because of the low output of the power amp.
The signal path is from the collector of Q80 to the bases of Q75 and Q76.

Compare the voltage at Q75 & 76 collectors to the good side.  Also check the DC idle voltages at E,B, & C of Q75 & 76.

Guitar News / Re: More class D love - GPA-100 from Harley Benton
« on: October 02, 2020, 12:05:41 PM »
I'm not sure what the rules are regarding the power consumption labelling.
I'm not sure that 240V .6A marking is necessarily maximum.  Could be average or nominal etc.
I bet it's fused at something bigger than .6A ?
And further to the confusion, the spec sheet says 100W into 8, 190W into 4 ohms. 

The Newcomer's Forum / Re: Roland JC-120 with weak reverb
« on: September 22, 2020, 12:07:19 PM »
You can't measure DC there as it is blocked by the cap.
The volume control determines the send to the reverb IC, so if you had the volume turned down there will be no AC voltage at the tank.
Check what is getting to the input of the reverb drive IC (IC1).
From what is shown on the schematic, they have 22mVAC signal at the input jack.  Then the volume control is adjusted til there is approx. 30mV at the wiper.  Under those conditions there should be approx. 20mV at pin 10 of IC1, and 1VAC at pin 2.

Amplifier Discussion / Re: Trying To Repair a Traynor TBM 25...
« on: August 26, 2020, 01:40:29 PM »
I decided to do a quick collector voltage measurement on the two 2SC2233 trannies just like he did.  The one with the more stable resistance measurements (Q7) measures 0.528V while the one with the wandering resistance measurements (Q8) measures -28.3V...I assume they should be a little closer to the same value
Sounds like you measured the emitters, not the collectors.
There is no reason to assume they should be closer in value.  Unless D-labs was working on the same model amp (or at least configuration, quasi-complimentary), his readings have nothing to offer you as far as reference values.

Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 21, 2020, 03:11:02 PM »
g1, see my post two above your earlier one, is my explanation ffaulty?  I don't think the drawing is wrong.
No, you are correct.  I got confused expecting a positive supply requirement.  I'm not sure I've ever seen any other chips that run exclusively on neg. supply.
Now that I look at the datasheet, your explanation makes sense.

ilyaa, glad you were abe to get it fixed!

Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 20, 2020, 02:25:47 PM »

Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 20, 2020, 01:58:03 PM »
Schematic shows VDD pins of chorus chips going to ground.
Tough to say if that's the only error in the chorus part of schematic.
If schematic is wrong, that's not going to help.  :(

(edit: my error, schematic is correct)

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