IF it is the real early version such as used by Ike and Tina Turner, not the later Pantera era, back in the day "everybody copied the Twin Reverb idea" so Guitar and Bass preamps were the same (clean, no distortion), only the Guitar one added Reverb and Tremolo.

So if you find the old Guitar one, it will help you.

I have them somewhere, in some old hard disk, haven´t seen them for many years.

Quote from: franvelasco on April 10, 2025, 03:25:05 AMI have a Pathfinder 10 Bass and I'm thinking on getting the guitar one. I suspect the PB10 is the same circuit without the distortion channel, as it sounds great with a telecaster, but I don't really have a way to know because the schematic is impossible to find.

From what I've seen in the modded guitar version, removing C12 gives more clarity and the Bright switch in the bass version does something quite similar.

Anyone has a clue on what's going on? Maybe there's a way to make the LEDs work to add an overdrive channel?

Thanks!

Looking at schematics kindly posted by Tassieviking:

1) the black on white ones look reasonable, "should" work, but I can not trust the coloured Eagle/Kicad type one.

In any case, you can use the Guitar one with Bass (and a suitable speaker) by just not pushingb the Distortion button, now for the Bass one it is not practical, just use any distortion pedal up front.

Loved it, great idea 

Congratulations. 
Time well spent 

Quote from: g1 on March 16, 2025, 08:19:21 PM

Quote from: DPM309 on March 15, 2025, 11:57:50 AMThe schematic shows them as 2N5988 (PNP) and 2N5991 (NPN). The markings on the transistors are TIP42B (PNP) and TIP41B (NPN). The ones I purchased were TIP42B and TIP41B which are good replacements.

I responded to your post over at MEF forum, but will include it here for others who may be working on these amps.
The TIP41 and 42 have BCE pinout.  The original 2N5988 and 5991 have ECB pinout, so the TIP's will not work as replacements.
There are fake datasheets out there showing ON Semi 2N5988 with TO3P case and incorrect pinout, but those transistors do not exist.
The real 2N5988 and 5991 were TO-225 case with ECB pinout.

Edit:  received response that this amp had been working and came with TIP41 and TIP42 outputs.
So can only conclude there are more than one version and be sure to check where the traces of the output devices are going, as there seems to be only 1 version of schematic available, and it does not match the later version.

Guess you are right.

Back in the day Motorola salesmen were VERY active and lured many amp manufacturers to use their stuff.
One of them was Marshall and apparently Rickenbacker fell for it too.

This is a Marshall 100W SS amp made between 1975 and 1978.

This comes straight from the 1973 Motorola Power Amp design handbook.

It does not use generic transistors such as 2N3055, TIPs, etc. but specific models made only by Motorola, so end user is not tempted to switch later to cheaper suppliers.

Another dirty trick (as seen on the Rickenbacker amp) was to use non standard case sizes and pinout, so repairs HAD to be done with the original Motorola stuff.

Only Marshall "guitar" mods were to add a Presence control and a tapped autotransformer so user could have 4-8-16 ohm options, both features present in Tube amps and which Guitar players expected and were used to:



These were among the earliest Marshall SS amps, they had little to zero experience with them, so they went through with a respected suplier suggestions to play it safe.

Funny thing, I am quite certain Motorola sold them A TON of transistors, or they signed a contract to buy a ton per year for "X" years, so they ended up WAY overstocked.

So they used these anywhere, including a puny 12W amplifier: 5005/Lead 12 , where it is nonsense to use a pair Metallic TO3 10 Ampere 80V 150W transistors which eeasily power a 100W amp.
I bet they were SICK of having them for breakfast, lunch and dinner so they designed in inexpensive beginner amp to move them out fast.

I see no other explanation.

Original Pignose amp was a *cheesy* power  module, think a somewhat beefed up transistor radio power amp, bought premade at one of many Electronics suppliers.

Post original Pignose amp schematoc here and I will search and find a commercial si ila amplifier for comparison.

Pignose was 99% COOL visual design and idea, 1% Electronics.

And the right product at the right moment, there was nothi ng like it.

Today any 10W practice amp is better.

Welcome Tom 

You have just been answered, no need to repeat your question multiple times.
Do as I suggest and it should work.

QuoteBut is there anything saying you can't run the 2 sides in series (standard BTL)?  That would give full power into double the impedance.

The confusion comes from the fact that TPA3118 actually has FOUR "standard" amplifiers inside.

Two are prewired (you can´t separate them, it´s internal to the chip) as bridgedand they call that Channel 1 , other two are w1red same way and are called Channel 2.

That´s why even if you use both halves separate, as a Stereo amp, each of them requires a floating load.
 
That´s why each of the channels is already BTL, you can´t undo that.

Now if you wire both BTL amps in parallel, you can get twice the current but peak voltage does not change.

 

QuoteOne more question, in the very first sentence of the datasheet, what does TI mean by "4 ohm BTL load" ?
A load is a load is a load, isn't it?

True.
But BTL means how/where is that load connected. 

Personally, I would have callad each Channel simply "bridged amplifier", period, but somebody called them BTL and others copied it.

QuotePBTL is just 2 amplifiers working opposite to each other, one puts out a positive signal while the other one a negative and then it reverses during each sinewave.

That is plain BTL and is already happening inside each channel.

QuoteIt gets confusing in that TI still refers to the 2 'stereo' sides as BTL.  I guess that is how they are made in the chip, but if you can't access each non BTL amp seperately it is kind of pointless to call them out as such.

Each side already IS BTL.
True, you can´t access any of the FOUR amplifiers on their own, only as prewired bridged outputs.

Just thinking aloud: maybe TI does not even mention that (although it is implicit) because it wpuld be even more confusing.

Bet DIY Audio and similar sites would fillto the brim  with threads explaining how to separate each half or something.

Guess the idea is: just use them as we suggest and don´t overthink details.

It will certainly change volume, but I guess variation will not be that big, probably a few dB.

For bedroom playing we need, say, something between 20dB and 30dB or so.

Tiny Terror offers a 7W-15W switch, Mesa Boogie a 60W-100W one (cutting 2 x 6L6 out), neither as effective as it seems.
One modern Mesa offers a 50W-5W-0.5W switch ... now THAT one is useful.

Yes, that´s the truth, what is physically possible given the available voltage swing out of 24V.

Glad we are all on the same page.

Those power specs are, should we say .... too optimistic?

No way they can put out 30 Watts into 16 ohm and 60W into 8 ohms.
Not at just clipping that is.

This is what Texas Instruments say about TPA3118 ... they should know:

With a 24V supply, 60W into 4 ohm, around 33W into 8 ohm
That, at 1% distortion which is *just* clipping and the proper way to rate RMS.

The 10% distortion spec actually means a quite clipped signal.

No spec for 16 ohm but it should be about half the 8 ohm rating, some 18 W at clipping.

The video tests it with a puny 12V supply

Best case some 14-15W into 8 ohm, not even near the 30W claimed.

Oh well.

Captured the TI datasheet Power vs. Supply Voltage but found I can´t actually paste it gere.

Tomorrow will find some image site and link it here.

Quote from: Bandito on February 14, 2025, 04:41:04 PMExcellent! I am East Devon, UK. Done the cleaning. The Amp works but sounds weak and different on channels 1/2 compared to 3/4.

It should.
Channels 3-4 are Instrument (Guitar/Bass) level so  more sensitive, 1-2 are high impedance Line level, think a Grammophone with a crystal/ceramic pickup, a radio tuner or tape recorder output, etc.
Any modern pedalboard would work fine there.

If you want to convert 1-2 to 3-4 specs, replace current 1M pots and 1M mixing resistors with 50k pots and 47k rtesistors, look at inputs in the schematic kindly provided by G1

QuoteHas 3 sockets for speakers.  1 and 2 (straight parallel connection) work, but the slave (3) does not.

1 and 2 are regular speaker outs, 8 ohm impedance *total* so 16 ohm each if using both.



The 3rd one, clearly marked Slave, is NOT a speaker out but a Line out, meant to drive an extra power amp with its own speakers.

Old school design, not surprising in an early 70s amp.

QuoteIs this a "good" amp, worthy of investment?

You should ask your Financial Manager for that.

In my book, for a Musician, Amps (and Instruments and any Musical stuff) are either useful, good sounding, etc. or not.

I reserve the word "investment" for Tesla stock, gold, Bitcoin and similar stuff.

FWIW that amp is quite old style but very well made, working fine (except for some "cleaning" issues, of course) for 50 years now.

Thanks G1

Looks VERY much like an unauthorized Traynor clone, which also made a similar 4-passive-input mixer PA, YVM something.  YVM4?

Doubt anybody will "repair it for fun" though.

But maybe all it needs is some love and care: clean all pots and jacks with Deoxit or similar good quality product, (NOT WD40), check all wires are intact, etc.
Schematic apparently hints at a plug-in board.
If so, pull it, clean socket with compressed air, squirt Deoxit on contacts and wipe them with clean paper towels, etc.

It "should" work.

Do NOT start pulling parts at random "justt check them", you will needlessly damage the PCB.

A gut picture could help

That FET takes 25V with no problem, LM386 does not.

Your first video had better sound, it used a different speaker.

To my ears your amp now is unstable and jumps into oscillation, giving an ugly buzzy sound.

IF you have a scope, check that.

If not, pull board from new one and mount it in the old multimeter one and check.