Schematic for Peavey Bandit 112

johnheath · Sep 3, 2017

Hi all...

I have a Peavey Bandit 112 on my bench for a friend. The clean channel is dead and the lead channel is just fuzzy and my friend want me to have a look at it. But I cannot find the proper schematic so I ask kindly if there is someone here who have this schematic available?

Best regards

/John

panman · Sep 3, 2017

Which model you have? There are many models and I don`t know how differend they are. I have schematics for "silverline" Bandit transtube 112 with the Sheffield-speaker. Many years ago a friend gave this amp to me, because it gave no sound. The problem was the effect loop jacks.

panman · Sep 3, 2017

This is it:

PRR · Sep 3, 2017

https://www.manualslib.com/manual/903864/Peavey-Bandit-112.html

Top-left, click green DownLoad button. You have to pass a test to see if you are a robot (I failed the first time). Then you get a page to Download or View in browser, you probably wanna download.

I would start by looking at the + and - 15V supplies. Also VB+ and VB++, which appear to be something under 50V.

johnheath · Sep 3, 2017

panman said:
Which model you have? There are many models and I don`t know how differend they are. I have schematics for "silverline" Bandit transtube 112 with the Sheffield-speaker. Many years ago a friend gave this amp to me, because it gave no sound. The problem was the effect loop jacks.

Thank you sir.

The amp have no other names or logos than the "Bandit 112"... My friend is a guitar teacher at the community music school and the amp belongs to this school... the speaker is an unmarked 12" something so basically I do not know what model it is.

Best regards

/John

johnheath · Sep 3, 2017

PRR said:
https://www.manualslib.com/manual/903864/Peavey-Bandit-112.html

Top-left, click green DownLoad button. You have to pass a test to see if you are a robot (I failed the first time). Then you get a page to Download or View in browser, you probably wanna download.

I would start by looking at the + and - 15V supplies. Also VB+ and VB++, which appear to be something under 50V.

"blip-blip" thank you sir... I had to transform into human flesh first but it worked well.

I'll have thorough look at it after I have printed the schematic and I can sit down write down some measurements... +15V and -15V supplies... thanks.

Best regards

/John

JohnRoberts · Sep 4, 2017

panman said:
Which model you have? There are many models and I don`t know how differend they are. I have schematics for "silverline" Bandit transtube 112 with the Sheffield-speaker. Many years ago a friend gave this amp to me, because it gave no sound. The problem was the effect loop jacks.

The transtube model will be different mainly in the preamp... Transtube was Peavey's solid state tube emulation that would introduce tube like distortion, and IIRC they also played with synthesized higher output impedance from the amp section to increase loudspeaker/cabinet interaction (also like with a tube amp).

There were many versions of bandit over the years, but I expect transtube versions to have significant differences in pre and power amp sections. (Note: I am not a guitar amp guy but I did drink beer with a few of them over the years).

JR

CJ · Sep 5, 2017

if you email or call PV and give them the ser # they will send you the schematic for that particular amp and their service is fast.

yes try a patch cord in the send/return loop

ask owner if he uses loop, 99% of the time they don't

if not, solder jumper wire across return jack at the appropriate terminals, hot and sw, not ground.

this can be easily removed if selling the amp later.

johnheath · Sep 5, 2017

JohnRoberts said:
The transtube model will be different mainly in the preamp... Transtube was Peavey's solid state tube emulation that would introduce tube like distortion, and IIRC they also played with synthesized higher output impedance from the amp section to increase loudspeaker/cabinet interaction (also like with a tube amp).

There were many versions of bandit over the years, but I expect transtube versions to have significant differences in pre and power amp sections. (Note: I am not a guitar amp guy but I did drink beer with a few of them over the years).

JR

Thank you sir

Yes, I have heard that there are different models over the years but the specific one that I now have on the bench is pretty musch unmarked except the "Bandit 112". I will have a cup of coffee right now and then I will sit down and have a look at it

(Night job day rhythm)

Best regards

/John

johnheath · Sep 5, 2017

CJ said:
if you email or call PV and give them the ser # they will send you the schematic for that particular amp and their service is fast.

yes try a patch cord in the send/return loop

ask owner if he uses loop, 99% of the time they don't

if not, solder jumper wire across return jack at the appropriate terminals, hot and sw, not ground.

this can be easily removed if selling the amp later.

Thank you sir

I have thought of the possibility to e-mail Peavy for the correct schematic but as mentioned before this particular amp is pretty much unmarked. Perhaps Peavey could trace it by the S/N but all I can find is a small sticker with five numbers... hard to tell if that is the S7N or not.

And for sure I will try the patch cord thing.

I have found that someone else has been in there and replaced a 250k pcb pot to a 100k pot with short leads but this pot was too big and shorted the entire clean channel. This due to the fact that the housing of the new pot touched the new solder joint... eh... and shorted it all.

The clean channel is way too fuzzy for a clean channel but the lead channel seem to work better at this moment as well.

Best regards

/John

PRR · Sep 5, 2017

> Perhaps Peavey could trace it by the S/N but all I can find is a small sticker with five numbers...

Tell them all you can see.

Maybe they come back "No, look behind the glovebox bracket" or some odd place you have not found.

Or maybe it really is 5 digit early production.

CJ · Sep 6, 2017

the Bandit has been around a while, here is a thread on the history and timeline,

somebody might have took off the sticker , you can get the date off the speaker hopefully,

normally any schematic would be enuff, but there have been so many versions,

https://peavey.com/forum/viewtopic.php?t=14177

johnheath · Sep 6, 2017

PRR said:
> Perhaps Peavey could trace it by the S/N but all I can find is a small sticker with five numbers...

Tell them all you can see.

Maybe they come back "No, look behind the glovebox bracket" or some odd place you have not found.

Or maybe it really is 5 digit early production.

Thank you sir

It seems that the schematic you showed me is the correct one...

Best regards

/John

johnheath · Sep 6, 2017

CJ said:
the Bandit has been around a while, here is a thread on the history and timeline,

somebody might have took off the sticker , you can get the date off the speaker hopefully,

normally any schematic would be enuff, but there have been so many versions,

https://peavey.com/forum/viewtopic.php?t=14177

Thank you sir

It seems that I have the correct schematic ... I have some info here but I guess the thread will take another turn if I start explaining the things that I have found but I will do any way

Best regards

/John

johnheath · Sep 6, 2017

I have found that R17 (22R/1W) was burned and replaced and checked all the groundings I tried to fire it up but this resistor started smoking after a second or so. I turned it off straight away but did not have time to measure any voltages along the way.

So what I have is a resistor in the power section that gets too hot.

For the curious one I attach a screen shot of the schematic since it is too big for posting in original.

Best regards

/John

JohnRoberts · Sep 6, 2017

Driven rail amp design... R22 is in series with the driver stage so check all the driver and output transistors.

JR

johnheath · Sep 6, 2017

Thank you sir

I am far from an expert on transistors but I figured that there must be a too big current draw over the R17 (22R). Correct me if I am way out on this but is it correct to have a look at Q2 and Q4 (driver stage)?

Also what about the effect transistor Q3?

C15 (220uF/63V) was also faulty so I changed that one for a 220uF/ 100V.

Best regards

/John

JohnRoberts · Sep 6, 2017

johnheath said:
Thank you sir

I am far from an expert on transistors but I figured that there must be a too big current draw over the R17 (22R). Correct me if I am way out on this but is it correct to have a look at Q2 and Q4 (driver stage)?

The schematic is chopped off but a driven rail design output stage looks just like a typical class A/B output stage but instead of the emitters driving the speaker, the emitters are grounded and the speaker is driven from the junction of the power supply caps that are driven by the power transistor collectors.

Also what about the effect transistor Q3?

Q3 is the NPN power transistor pulling down the top of the + supply cap. R17 does not feed Q3, but if Q3 is dead Q2 may be trying to do all the work... That said typical failure modes for power transistors is shorted C-E. I have seen open bases before but less common. If Q3 was shorted R17 probably wouldn't smoke... One obscure possibility is a bad connection open circuit collector of Q3 (just a guess). The Q2 driver is driving hard into Q3 base but no output from Q3 collector.

C15 (220uF/63V) was also faulty so I changed that one for a 220uF/ 100V.

Best regards

/John

The faulty C15 could smoke the resistor all by itself (if shorted). Does the resistor still smoke after you replaced the cap?

There should be a symmetrical negative drive circuit , cut off in your schematic. If you can power up without smoke, you can compare voltages between + and - driver circuitry

Check the Q3 collector is making a good connection to +PS cap?

JR

johnheath · Sep 6, 2017

JohnRoberts said:
The schematic is chopped off but a driven rail design output stage looks just like a typical class A/B output stage but instead of the emitters driving the speaker, the emitters are grounded and the speaker is driven from the junction of the power supply caps that are driven by the power transistor collectors.

Q3 is the NPN power transistor pulling down the top of the + supply cap. R17 does not feed Q3, but if Q3 is dead Q2 may be trying to do all the work... That said typical failure modes for power transistors is shorted C-E. I have seen open bases before but less common. If Q3 was shorted R17 probably wouldn't smoke... One obscure possibility is a bad connection open circuit collector of Q3 (just a guess). The Q2 driver is driving hard into Q3 base but no output from Q3 collector. The faulty C15 could smoke the resistor all by itself (if shorted). Does the resistor still smoke after you replaced the cap?

There should be a symmetrical negative drive circuit , cut off in your schematic. If you can power up without smoke, you can compare voltages between + and - driver circuitry

Check the Q3 collector is making a good connection to +PS cap?

JR

Thank you sir.

Yes, the schematic is chopped due to the large document in original... but as you imply there is a symmetrical negative drive circuit and I was hoping to be able to compare the two. After the C15 change and also replacing the burned R17 again I have not been brave enough to fire the amp up again... so therefore no comparison of the two driver circuits.

I could try though because I have no knowledge to check the transistors as they are (not powered up)

I was also thinking that the C15 if shorted could perhaps smoke R17 so I will give it a try and get back here for the result.

Best regards
/John

JohnRoberts · Sep 6, 2017

many VOM have a diode checker function.... back in the day we had to use ohms scale but ASSuming you have a vom with diode checker, you should measure a diode junction from both base to emitter and base to collector (+ lead on base for both measurements of NPN transistor). Collector emitter should measure open circuit. Reverse polarity for checking PNP. Note; do not measure diode junctions with power applied, and other connected local circuitry can affect these measurements.

JR

Schematic for Peavey Bandit 112

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