Matamp GTO Schematic

[Diablo]

I found this schematic on the web for the Matamp GTO. I don't know if it's 100% correct - I spot some question marks. Would anyone care to check it out and see if there are any obvious mistakes. I don't fully understand what's going on at the phase inverter. I've been searching for a schematic for the Matamp Series 2000, and I think this is the closest I've seen.

http://www.nicosonic.com/schems/Mata...0%20recent.jpg

[Nyqusit5]

Hey Diablo, I am glad you are interested in my schematic.

Yes, it is the most complete you'll find on the web. But I have already posted its link here looking for input and got no reply. Maybe your post will be more succesful?

Let me know what you don't understand in the phase inverter. It is equivalent to a 1974 Orange Graphic PI. Not the most hi-fi of designs, but who wants hi-fi for guitars?

[J M Fahey]

The ?uF filter cap can be 22uFx450V.
The 690? plate resistor in the phase inverter is way too high; 100K to 150K there will do nicely.
This amp will put out around 30W tops, maybe even around 20W, but probably have very good sound.
The switched gain control has almost nil effect (at least with those values), I would not use it; the "depth" control, really a bass cut one, may be very useful as a "mud cutter" when overdriving the amp.
Copy the classic Orange one for greater flexibility.

[Nyqusit5]

Thanks JM, but although your comments are perfectly valid, I am not looking for guessed values, I can guess values that will work myself.

I don't mean to be harsh when I say that my point here (and I believe Diablo's) is to produce an accurate Matamp GTO schematic. Wether the control work as you wish they would probably isn't.

As a side note, the switched gain control is the correct one implemented in the amp and I believe it has a very audible effect.

[J M Fahey]

Do you have a Matamp?
Where did you get those values from?

[ThermionicScott]

That direct-coupling between the last gain stage and PI is unconventional, but it should work. I think there ought to be a ground reference on the PI grid though, a 5 meg would do the job. The 690k (probably a 680k) plate resistor on the previous gain stage actually makes sense, to squeeze a lot of gain out of that stage and keep down the voltage on the PI grid.

There are more ways to skin a cat than are found in Fender/Marshall/Vox designs!

- Scott

[Diablo]

If the above schematic is accurate, please let me know. However, the reason I asked in the first place is because some things don't make sense to me. I am not all that experienced in amp-building, as I've only built 4 amps and am still learning.

1. A tube rectifier with a 100 mfd filter cap. Aren't tube rectifiers limited to around 40 mfd max for the caps? Is this a 5U4GB or GZ34 rectifier? I could understand if it's 50 mfd filters before and after the choke. Maybe those caps are totem poled so it's only 50 mfd (4 - 100 mfd caps total) on each side of the choke?

2. The cathodyne phase inverter looks highly unusual compared to what I found looking at the "Valve wizard" website. I don't know the purpose of the 47 pf cap in parallel with the 690K resistor on the anode of the previous gain stage triode. The 690K resistor also looks like a high value compared to "typical" anode plate resistors and also high compared to other Orange schematics (100K or 390K). On the cathodyne PI triode, I don't see a cathode bias resistor or a source of bias voltage, or a grid leak resistor - I see these on other Orange schematics.

Any info on power tube plate voltage or transformer spec voltage?

[ThermionicScott]

If the above schematic is accurate, please let me know. However, the reason I asked in the first place is because some things don't make sense to me. I am not all that experienced in amp-building, as I've only built 4 amps and am still learning.

Beats me if the schematic is accurate, but we're all learning.

1. A tube rectifier with a 100 mfd filter cap. Aren't tube rectifiers limited to around 40 mfd max for the caps? Is this a 5U4GB or GZ34 rectifier? I could understand if it's 50 mfd filters before and after the choke. Maybe those caps are totem poled so it's only 50 mfd (4 - 100 mfd caps total) on each side of the choke?

5AR4/GZ34 is spec'd at 60uF max, but some designs exceeded that with the robust tubes of the day and got away with it. The fact that it's shown as a directly-heated rectifier narrows it down. Doesn't look like the person who made this schematic bothered to write down any tube types apart from the EL34s.

2. The cathodyne phase inverter looks highly unusual compared to what I found looking at the "Valve wizard" website. I don't know the purpose of the 47 pf cap in parallel with the 690K resistor on the anode of the previous gain stage triode. The 690K resistor also looks like a high value compared to "typical" anode plate resistors and also high compared to other Orange schematics (100K or 390K). On the cathodyne PI triode, I don't see a cathode bias resistor or a source of bias voltage, or a grid leak resistor - I see these on other Orange schematics.

My guess is that the 47pF is to remove any "fizz" in that gain stage. As you increase the plate resistor and gain, the low-order harmonics decrease, but the high-order harmonics increase. It may also be for anti-oscillation purposes.

A cathode-bias resistor isn't always needed for cathodyne invertors. The "grid leak" resistor is what I was alluding to with the "ground reference". Some high-value resistor just to help stability (but without shunting too much of the plate voltage to ground) would be a good thing, I think.

- Scott

[Diablo]

Thanks all for your thoughts.

[Ghandi]

MADAMP Series 2000

Guys, look what I found:
Picasa Web Albums - james hadfield - MATAMP

I have started a hand drawn schematic from what I can make out of the pics at home that I can scan this afternoon.

cheers
Ghandi

[Ghandi]

here it is,
the schematic of the Matamp 2006 Reissue :shock:


Cheers
Ghandi