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Messages - Mprall00

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1
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« 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?

2
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« 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?

3
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« on: February 19, 2019, 11:15:40 PM »
Good advice!  Didn't notice that.  I bet it was never a problem with the original design because it was never getting loud enough to get the power amp cooking anyways.  it was so quiet stock...

I doubt I will get it cranked that loud anyways but in case I do...

Would that mean essentially cutting the trace between R14 and pin 5 of v4 and R10 and pin 5 of v5 then adding something between 1.5k and 10k where i cut the trace?  Is there any downside?  Nothing mentioned in what I am reading... did ibanez just design it without to save $.05?

4
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« on: February 17, 2019, 11:35:18 PM »
I agree... But if i toss it then i have 5 open holes in the front.  And if I keep it and break the connection as you outlined then i still have to drill a hole for the new gain pot for v2.  And if I am drilling anyways I am going to just solve it with a second input.  So my new input will bypass all of it - buffers, ts, SS, everything - and go straight to the CN3a.  And the stock input will still be there and use the stock daughter board as is.

Truth is, once we changed all that stuff (i changed a lot with your help but the biggest impact was the 12v regulator, R4, R5, R13, R72, R17 as a pot, and the tone stack caps), the SS front end actually doesnt have a bad gain tone.  So therefore I think I will drill one extra hole and have both options, even if I don't really ever use the stock option... Just turn the SS gain all the way down, plug in to the new input, and it will be like it isn't there.

Once done I will try to remember to take pictures and write up an easier to follow list of changes in a new post.  These can be fun to learn with since they are relatively cheap for 30 watts.  I got my TSA30 combo for just under $200 used...

5
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« on: February 16, 2019, 11:38:26 PM »
I just wired it as a variable resistor.  Actually just got a 1meg pot because the 500k pot at R17 was not breaking up much when cranked and even though i almost always play it clean as a pedal platform I thought having the option of more preamp gain would be nice.

I guess you could replace r13 with a pot as well to control v1 too.  Let me know if you try it!

After tweaking a lot of resistor values and replacing the tonestack, the SS front end actually doesn't sound bad either.  I got the solid state section to be switchable with the stock input jack but it doesn't sound good.  When the SS is bypassed it sounds like the impedance is way off - like something at the input needs that buffer from the SS sections.  I even tried adding a 1 meg pull down on the stock input jack...  It just sounds really flubby with no presence when the SS is bypassed but sounds perfect when i removed the whole daughter board and added my own input jack straight to CN3b.

SO... i am about to drill a hole next to the existing input for a second input direct to CN3b and a hole for the gain pot above and between the gain and bass knobs.  That way I can just plug in straight to the tube section with the new input or plug in to the TS>Boost>SS front end if i want to use it.

Side note: replacing the signal path resistors with metal film and replacing the coupling caps and tone stack made this amp a lot less noisy.  Not sure if one of those thing did more for the noise floor than any another - i just know the whole change helped.  i got mine very old and very used, so it could have been noisy due to age, but this really helped as did a proper bias.

6
Switch was good.  Rewired with a 5k and 820r.  820r was likely too low but good to hear its working.  5k is a good sweet spot.  Off now sounds like there is no negative feedback.  10k was just high enough in this circuit to be barely noticeable so stock sounded almost like no negative feedback at all.

So I may leave the switch there.  Or I may solder 5k in there and experiment with the switch at other places...  like c4.  Or maybe an off switch for the tone stack...  Or a cold clipper switch.  Wonder if this amp is high enough gain to have that be worthwhile...

7
Thanks!  Yeah it dawned on me that the 1.5k was the cathode resistor.  But when I had the 10k in there shouldnt it have read 1.3?  I guess with it being that close (and that late at night) it could easily be by own user error or mental rounding...

Also I thought higher was going to be more noticeable.  But now realize looking at it that the parallel resistor is just averaging it out to be basically no change.

Thanks - I will try 5k and see if that is noticeable.

With NFB having so little impact on this amp, is it even worth trying a presence control?  that was going to be next for me...

8
Attached is the schematic for an epiphone galaxie 10.  I have modded it heavily as a learning experience following another board's advice.  First thing I did years ago was cut the negative feedback resistor out (R15) but now thought I would like to add it back in on a switch to try values.

I wired it like the picture attached in place of R15.  I had tested the switch prior to hooking it up.  All good to go.  Attached it and fired it up - no change in sound at all between 33k, 10k, and negative feedback off.  That can't be right right?

So I took it back apart and used my multimeter to measure the switch on board and every setting (even off) measured 1.5k.

So I took the switch out entirely and measured between the pads - 1.5k.

So I wired a 33k in to r15 and measured on board - 1.5k.

Fired it up with 33k and sounded exactly like when I thought I had the negative feedback removed.

I mean it actually sounds really good after all the mods, but anyone know what is happening?  Can i not modify negative feedback loop in this amp?  Can I not even remove it?

9
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« on: February 03, 2019, 02:52:03 AM »
Thanks for all the help.

So the tube amp portion now sounds excellent and plays nicely with pedals and is much quieter now.  1meg is in place for r13.  Switched r18 to 470r.  left r25 at 15k since that is between a bassman and deluxe reverb.  May play with it someday but sounds good now.

Still pretty bass heavy.  Could play with c10 (or c54?) coupling cap but don't have any on hand rated at high voltage.  Just running bass control around 30% and it is good clean but as the new gain is turned up it distorts pretty bassy.

Now thinking about how to work the SS portion back in to the circuit on a switch.  Have an spdt on-on I am going to use maybe at the point you mentioned with r62 going to middle lug and one side going straight to cn3a and the other to C30.


10
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« on: February 02, 2019, 06:32:57 PM »
I knew i did something wrong!  Thanks.  Totally misread and thought R13 was in series in to v1 and didn't notice it was going to ground!  Stupid... i think I have it now.

11
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« on: February 01, 2019, 11:16:16 PM »
Interesting... so i bypassed all the SS by literally removing it from the chassis (unplugged the connectors for CN1a, CN2A, CN3b, and CN7a) and bolting a new input with a 1meg from input to ground just acting as a pull down resistor to the existing input hole.  Then ran that input and ground to CN3a. 

Sounds like we accomplished the same thing because i then had the input straight in to CN3b which is r13 (which I had changed it to 68k because that was what i found in other fender schematics).

But I am missing your 1meg in line before v1 right?  I don't see that in other fender schematics.  Seems very high.  Is it serving a purpose there?  Doesn't seem like it would do anything to the tone right?  68k in series with 1meg before v1...

Thanks for your help!  Learning a lot.

It sounds good without the 1meg in series, so i think I have the tube amp part solid.  Just wondering how the 1meg would effect it.

12
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« on: January 31, 2019, 05:26:18 PM »
Good advice.  Question:  I managed to bypass the u3a but I bypassed all of u3 so lost the boost too.  I pulled the leg of r33 and went to cn3a from that spot.  Can I keep the boost in place by starting somewhere else?  Not seeing where that would be.



13
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« on: January 29, 2019, 08:28:52 PM »
I went with 510k.  That with the 100k for r4 and r5 and the 250k gain pot changed the eq of the amp quite a bit.  I think i am going to up the gain pot to 500k now and thats it!  Works great with pedals.  If anything now it is too bassy and the the treble is way more tame.  I may play with values a little more but I think its a pretty happy medium now.

Here is another thing I plan on playing with - a switch to bypass the u3 solid state front end instead of using 2 inputs with a switch to select between them.  But... that will leave the buffers in place from the TS and boost so that may change the tone of having a input straight in to r13 to V1...

I'll take ideas if you have them.   :tu:

14
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« on: January 29, 2019, 12:17:09 PM »
You could replace R72 with 560k and change your new gain pot with 250k.
Also replace R4 and R5 with 100k,, that will back off the gain.
Is R13 (56k) still in circuit?

You can alter the tone stack might help back off excess treble.
Make C23 100nF and C22 22nF might work,, not sure how well but suck it and see.
Phil.


Cool thanks.  I will try it!  r13 is still there.  I have a 510k metal film on hand to replace r72 with and a 250ka pot.  So I will probably try that as well as the 2 100k changes for r4 and r5.  i already replaced those with metal film in my quest to get the noise floor down but will sub in the 100k and see how that impacts it too.  That 50k difference in your recommendation at r72 won't impact much will it?  Slightly more gain?

I already changed the tone stack to more standard fender cap values.  C23 to 100n and C24 to 250p.  Left the mid cap alone at 47n for now.  The tone is good.  A tiny bit bright but treble knob is just running lower than normal and sounds good clean.

15
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« on: January 29, 2019, 12:40:17 AM »
Sorry but
Unless you tell us Where Exactly in the circuit have you inserted the new input,,it's all meaningless?
could be  VR9?  or at R33?

Forget the presence idea,, bad for the PI stage. xP
Phil.

I just added an input jack with a 1meg resistor and went straight in to cn3b which eliminated the TS, boost, and solid state always on gain.  Actually took that whole input PCB out for now, which means the "effects loop" does nothing now. 

Replaced r17 with the 50k pot for gain.  It sounds good now.  Incredibly loud.  It was oddly quiet stock for 30 watts - quieter than my blues junior by a good bit.  But its not pedal friendly really now.  Thought I could tame some highs by cutting back the presence maybe?  Or maybe adding a tone control earlier between v1 and v2?

Just learning and experimenting with this one.  Will take any advice.  Thanks!

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