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Author Topic: Ibanez TSA30 Schematic and PCB Layout  (Read 6651 times)

phatt

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Re: Ibanez TSA30 Schematic and PCB Layout
« Reply #30 on: February 20, 2019, 06:49:27 AM »
Yes highly likely you will have to cut tracks.
As I don't have a track layout I have no idea of how easy that would be.
I've found with pcb's you often have to get inventive with solving issues. I find a week may pass sometimes before an idea comes to mind, other times it comes to me straight up.
If the tracks are wide enough you may be able to cut and drill mounting holes.
but a lot of those pcb's have very narrow tracks which makes it hard to find a spot.
If tracks are too narrow I drill beside the track and solder the pig tail along the track.

No down side to grid stop resistors that I've read about.
I think you will find it's Mandatory on nearly all good designs. 8)

As to why they omitted those resistors,, anyone's guess. xP

Be aware a lot of these amps are just whipped up in a mad frenzy with little or none R&D.
The whole amp is likely out sourced to a far off country,, read cheap labor and no QC

There was a HiWatt Amp question on here long ago that was so badly designed it was unusable because of noise due to bad PCB layout. :duh
turns out HiWatt had little to do with that Amp and hence had no records. :loco

AFAIK, Marshall still make amps that use EL34 tubes and run them at elevated voltages,, which is no problem for the plate of EL34 but the screens are then way past their max voltage limit. For most brands of EL34 the screen limit is 420volts.
They don't last very long with the screen at 470volts.
Do they care? I doubt it. :trouble
The RCA manual states quite clearly that AX7 will last for 10,000Hr's and power valves about half that.
The Valves in a well designed amp would/should last for at least 10 Years. (with heavy use)
I've witnessed Amps that are 30 plus years old and still using original Valves.
Today they just slap it together and know that the valves will last at least a year.

A chap who came to me years back had asked the local music shop,, How often do you replace the valves?
The shop owner replied,, oh every year or so. :lmao:

He was so glad he came to me for some advice. 8|

Phil.
« Last Edit: February 20, 2019, 06:53:24 AM by phatt »

Mprall00

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Re: Ibanez TSA30 Schematic and PCB Layout
« Reply #31 on: February 20, 2019, 10:08:26 AM »
I'll have to look tonight but i feel like C13 and C5 being so close to pin 5 means i could almost cut the trace and then just solder the resistor to the existing hole that the leg of C5 is already in then directly to pin 5 without modifying the board at all.  Any problem not using the board at all here?  More noise?

Mprall00

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Re: Ibanez TSA30 Schematic and PCB Layout
« Reply #32 on: February 20, 2019, 01:20:24 PM »
Another question while I am at it - V1 and V2 don't have a cathode bypass cap.  Worth adding one to pin 3 of both?  Or at least V1?  would raise gain... and depending on value, on specific frequencies?

Mprall00

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Re: Ibanez TSA30 Schematic and PCB Layout
« Reply #33 on: February 23, 2019, 12:35:37 AM »
Coming back with another question - can anyone tell me how the 2 triodes of v1 and v2 are working?  Staring at it realizing they aren't parallel.  And they aren't in series... are they?  is the signal coming from the cathode of both v1 and v2?
« Last Edit: February 23, 2019, 01:22:58 AM by Mprall00 »

phatt

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Re: Ibanez TSA30 Schematic and PCB Layout
« Reply #34 on: February 23, 2019, 06:50:50 AM »
You have 2 Cathode followers, one at V1 and another at V2.
Implementing a Cathode follower at V1 is likely just a hair brain idea by someone in design who reads too much internet gossip. probably no great advantage over a single triode. :-\

Obviously you did not google Valve wizard. :trouble
It's all there for you to learn. Hint!!! 8|

http://www.valvewizard.co.uk/dccf.html

Main Index;
http://www.valvewizard.co.uk/index.html
Phil.

Regards bypass caps at V1&V2,, yes try some values and see what happens.
Not a lot of advantage at V1 but at V2 will pull more tone change.

As it's an oddball circuit (with the SS preamp)
It's anyone's guess how much advantage adding Cathode caps will help?
Phil.

Mprall00

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Re: Ibanez TSA30 Schematic and PCB Layout
« Reply #35 on: February 23, 2019, 10:30:41 AM »
Haha. Late night dumb question. I’ve even added a cathode follower to a blues jr. Think I was thrown off because I’ve never seen one on v1 as I was looking up schematics... and it was late. Thanks for the response to the dumb question!

Mprall00

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Re: Ibanez TSA30 Schematic and PCB Layout
« Reply #36 on: March 02, 2019, 01:22:09 PM »
Any advice on adding NFB so I can add a presence control?  Tried a couple things and actually deleted a post from yesterday that didn't work.  I tried deluxe reverb style later and got a loud screeching noise.  No damage done but definitely didnt work.

For that I tried lifting the grounded side of R15 and C16 and connected them. Connected 820r resistor from the speaker output to the lifted sides of R15 and C16. Put one end of a 47r resistor to ground and the other end to the connection of the other 3.

The end goal was to add more like a bassman style with a presence control.  Just tried without to start and didnt work at all.

Edit:  Flipped primary because that sounded like positive feedback - same problem.  Hmm....  Definitely seems like I am getting positive feedback either way...  It did firm up bass and treble seems to sustain better.  It is also in phase with my blues junior when run in stereo now.  So all wins, but still NFB does work.

Edit 2: Tried the NFB of an AB165 bassman (47k in series with .1uf fed back into the phase inverter after C10).  It looks like weird compared to most NFB set ups that i tried originally.  It worked this time since it is actually negative feedback, but it reduced signal way to much.  Not sure why the much more common place NFB from other fender models squealed like positive feedback.  Research continues...
« Last Edit: March 03, 2019, 10:11:49 PM by Mprall00 »

phatt

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Re: Ibanez TSA30 Schematic and PCB Layout
« Reply #37 on: March 06, 2019, 07:11:50 AM »
well you had me wondering as I noted a posting and then it was not there. :duh
Not to worry, in one sentence;
If you want lots of distortion then don't bother with NFB. :-X

The NFB of AB165 bassman is not going to work without major mods. you need those 220k resistors from the plates of power tubes. It was not a good design. :loco
(look up Rob Robinette site for lots of clues on what works and what is a waste of time)

I'm not a big fan of presence systems as you need NFB and that will run the amp cleaner so if you want lots of OD then you have to run the amp at much higher level.
If that is what you want then go for it.
If you just want more treble then lower the coupling cap in front of the PI stage.

Look at some fender schematics for clues,, a lot of the AB763 circuits have very small value caps at the PI input.

Those big fender twins are so loud due to the 1nF cap at PI input, Change that to 22nF and they would just fart out at high volume.
Remove the NFB and they would not be so clean at high volume. xP

Regards to Bassman,,, Which one???? :loco

Old valve amp schematics might look simple but you need to build a few to realise that a couple of changed values can make a huge difference. 8|

At the heart of most of them is the Power supply resistor values, they are often very different and that has a massive impact on the sonic result.

As example;
Your Amp circuit has R3 (22k/2Watt) now go look at most Bassmans and you will see they are 1k to 5k.
That alone makes a big difference as to how early the PI distorts.
Your circuit is closer to Plexi Values which means the PI OD's early.

Most Bassman's use AT7 while nearly all marshall's use AX7. Again that changes how the amp responds.

I could go on here as the options are endless but maybe you can just print out a dozen Schematics and look closely at the Power rail values.
Meantime read up Robs pages.
https://robrobinette.com/Amp_Stuff.htm

At 750 pages you might be there for a long time ;)

HTH, Phil.

 

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