# Modding my Traynor YBA-1



## flyswatter

Spent a pleasant afternoon getting my already decent-sounding YBA-1 (dated 1975) a little better yet. These are all modest and practical mods. I have no interest in "plexifying" the amp. I just want my Traynor to sound like a more efficient Traynor. (All these mods are reversible if you keep the old parts).

Here's the unmodded amp when I got it a few months ago:



When I got the amp, it had a 2 prong cord even though the schematic calls for 3-prong. I quickly replaced that, which made the ground polarity switch (with it's yellow "death cap" -- which you can see right at the back centre of the chassis in the top photo) redundant. First mod was to remove these and reconnect the "hot" primary wire for the PT directly to the power switch. I used a hole plug to plug up the hole left by the absent ground switch. (BTW: For those interested in adding a master volume to their YBA1 [I'm not] this hole in the back is a convenient place to stick your MV pot).



Next, I internally bridged Channel 1 and Channel II to avoid having to use a jumper wire to used both channels in tandem. One simply solders a wire to a convenient point between the wires leading to pins 2 and 7 on V1. I chose the point where the 68k grid resistors met at a point. (this mod, by the way, works on a 4-hole older Marshall as well).



Third mod: A YBA-1 has a notoriously bright Channel II (I personally found it too bright to be of any use in capturing tone with either my guitar or bass). Removing the .001 little disc shaped cap in the pre-amp takes the brighness away, and makes Channel II a rounded ballsy tone much like channel 1. With the two channels bridged, it makes the amp sound HUGE.

The bright cap is in the middle of this photo. Innocent little bugger. Some people replace it with another value to keep some of the brightness, but I didn't.



Getting rid of that little cap allows your "High Range Expander" (i.e. presence control) knob to function like a proper presence control should -- because there's now some brightness worth adding with Channel II sounding more normal.

Last mod for today, I replace the 500K volume pot for channel 2 -- which was scratchy beyond the aid of contact cleaner -- with a 1 Meg audio pot, as recommened by a lot of people who mod old Traynors. I actually might reverse this mod (adding a new 500K instead) because I find the volume on Channel 2 now jumps way too high way too soon, and kind of overwhelms channel one on a similar setting.



Last but not least will be to replace the original, very old filter caps (they're the giant brown firecrackers in the first photo above). I have new 40uF/ 450V caps on order. Will need to create some real estate to make them fit, but that's a job for another day.


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## JerS

Nice work - those seem like sensible changes to me! Post pics once you do the filter caps. Cheers!


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## traynor_garnet

Nice work! But aren't you supposed to be working on some ultra talented, handsome, and intelligent guy's YBA-2 head?


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## flyswatter

traynor_garnet said:


> Nice work! But aren't you supposed to be working on some ultra talented, handsome, and intelligent guy's YBA-2 head?


Ha, ha. As the great Tom Petty once sang, "The waiting for parts is hardest part". %h(*&


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## Brett Pearson

Very nice amp! I used to have one just like it with the buggy bumpers. I even had the original Traynor cover for it too. Wish I could have kept it but I prefer my YSR-1 and just don't have the room for everything I want..lol, but I managed to keep a few of my old Traynors.


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## mhammer

If you're wondering what else you might do with the hole created by the elimination of the polarity switch, consider a boost function.

The tonestack has a similar configuration to the traditional Fender tonestack. Some 35 years back, someone posted a mod in _Polyphony_ (which became _Electronic Musician_) for a boost that simply lifted the ground connection of the midrange pot (which, in this amp is largely what the Bass Expander pot is, or at least it occupies the same position). When you do that, the passive signal loss normally introduced by the tonestack is essentially eliminated, and you get a boost, which overdrives the subsequent stage. The treble control is still reasonably functional, but the bass and midrange pots are not and the normal midscoop is also lifted.

The degree of boost is noticeable but not excessive. I.E., one is not running to turn the amp down. Of course, degrees of tonestack-lift and boost can be achieved by inserting some fixed resistor between the ground leg of the mids/expander pot and ground, so that the change goes from the value of the pot to , say 100k/220k/470k rather than from pot-value to infinite resistance.

The best part is that all it requires is a standard mono jack and a SPST switch to close the hot and ground connection on the jack. Connect the ground leg of the pot to the hot lug on the jack, and leave the switch open for boost, and closed for normal. I don't know that footswitchable boost gets any easier than that. I did it to an old blackface Tremolux head I used to own, and found it a very useful mod.


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## nonreverb

Another great mod is the JCM800. Totally reversable and sounds spectacular! Did this one for a customer a while back.












__ https://www.facebook.com/video.php?v=230875810581780


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## sammyr

These yba-1s are too much fun to tweak. I sold my yba-4 combo which I had modded from the late 70s specs to the earlier 60s specs. With my yba-1 head I ended up going to town on it. cascaded inputs jcm style on a push pull switch. PPIMV and some component tweaks to get it more pleasing to my ear and its become my favourite amp. It outrocks all my marshalls and my bassman. With the master volume off it's paint peelingly loud but with the master and cascade and I can dial in huge amounts of low end girth and dirty grind. I fucking love playing with traynor bassmasters.


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## nonreverb

Personally, I think the YBA-1 JCM800 mod sounds better than the real thing. I've done this mod on a YBA-1A as well however, it was mind numbingly LOUD!!!


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## sammyr

I agree with you 100%. I play my 50 watt modded yba-1 way more than my unmodded 83 100watt jcm 800. It just creams up way nicer, has the girth and is never brittle. I've been playing it with an lp jr dropped down to c. It's vicious... I even got really gratuitous and added an extra gain stage bainzy mod style.


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## traynor_garnet

nonreverb said:


> Personally, I think the YBA-1 JCM800 mod sounds better than the real thing. I've done this mod on a YBA-1A as well however, it was mind numbingly LOUD!!!


How invasive were the mods? What is involved?

TG


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## sammyr

I can't speak to nonreverb's method but it can be done pretty easily. its a little more involved with later era bassmasters as they have a plate driven tone stack rather than the cathode follower. With a later yba-1 you would rewire v2 as a cathode follower using the marshall specs and remove the mid filters in the tone stack. Bypass the v1 cathode with the jcm values. I have my inputs cascaded but with a switch to flip between cascaded inputs and non cascaded. It's a lot easier to not have it on a switch. but it depends on what you're going for. Add a ppimv in the back panel and you're pretty much off to the races. then season to taste.

*this isn't exactly to jcm specs. i use a ppimv master and use the switchable one wire mod for the cascade. if you want to do it faithful to jcm specs just wire up the preamp vol and master as per marshalls layout.


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## danielSunn0)))

Where can I go to learn the in depth description to doing the jcm800 mod? I have a '72 yba-1a that I bought already modded down to about 60watts.


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## sammyr

I don't know of anywhere that has an in dept explanation for modding to jcm specs but looking at a layout of the jcm and yba-1a schematic we can break it down. LAyout for jcm 800 2204 
traynor yba-1a schematic 

Starting at the input side of the preamp. you need to rewire the 4 inputs and 2 volume controls as per the jcm layout. Make sure to mount the 68k grid resistor on the tube socket. Cathode resistors and bypass cap configuration changes to 2k7/0.68uf and 10k/no bypass cap. 

Also you may be able to omit the 100pf plate bypass cap thats mounted between 5 and 8 on the jcm layout. If after modding there's too much hiss/high gain hash install that bypass cap. 

Onto v2... the mixer resistors in the yba-1a are 100k going to the grid of v2 (pin7) the jcm spec calls for 470k mixer resistors with a 500pf bypass cap. Next is the tone stack which is configured the same just with slightly different component values. yba-1a 0.001uf 0.1uf 0.02uf I believe. For the jcm specs change tone stack caps to 500pf and 0.022uf x2 and change the slope resistor from 47k i believe to 33k. 

then the phase inverter has a similar layout so again it comes down to component tweaks. Change the outside legs of the PI from 47k to 1Meg (there may be an additional 47k in there you can keep or remove). Change the 6.8k tail of the PI to 10k. In terms of cap values they're pretty much the same but check and if not season to taste. I would leave the power amp section the way it is if its working.


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## nonreverb

There is some room to play with the tone stack. The OEM values aren't bad but it's to personal taste. JCM values sound great too. On one unit I did, the I installed a push/pull pot for the .001 bypass cap on the preamp control. It takes some of the high frequency out at lower preamp settings.


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## mhammer

mhammer said:


> If you're wondering what else you might do with the hole created by the elimination of the polarity switch, consider a boost function.
> 
> The tonestack has a similar configuration to the traditional Fender tonestack. Some 35 years back, someone posted a mod in _Polyphony_ (which became _Electronic Musician_) for a boost that simply lifted the ground connection of the midrange pot (which, in this amp is largely what the Bass Expander pot is, or at least it occupies the same position). When you do that, the passive signal loss normally introduced by the tonestack is essentially eliminated, and you get a boost, which overdrives the subsequent stage. The treble control is still reasonably functional, but the bass and midrange pots are not and the normal midscoop is also lifted.
> 
> The degree of boost is noticeable but not excessive. I.E., one is not running to turn the amp down. Of course, degrees of tonestack-lift and boost can be achieved by inserting some fixed resistor between the ground leg of the mids/expander pot and ground, so that the change goes from the value of the pot to , say 100k/220k/470k rather than from pot-value to infinite resistance.
> 
> The best part is that all it requires is a standard mono jack and a SPST switch to close the hot and ground connection on the jack. Connect the ground leg of the pot to the hot lug on the jack, and leave the switch open for boost, and closed for normal. I don't know that footswitchable boost gets any easier than that. I did it to an old blackface Tremolux head I used to own, and found it a very useful mod.


I was reading a review of the Allen Amplification Hot Blonde ( Allen Amplification - Hot Blond ) in the new issue of _Vintage Guitar_ I got last week, and they have a "Raw" control. From the description of what it does, it sounds like they've turned the mod I'm describing above into a continuous control. In other words, it sounds like it adds more resistance to the ground path of the Middle pot (or if you have a blackface Treble/Bass amp, the 6k8 fixed resistor). Smart!


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## danielSunn0)))

sammyr said:


> I don't know of anywhere that has an in dept explanation for modding to jcm specs but looking at a layout of the jcm and yba-1a schematic we can break it down. LAyout for jcm 800 2204
> traynor yba-1a schematic
> 
> Starting at the input side of the preamp. you need to rewire the 4 inputs and 2 volume controls as per the jcm layout. Make sure to mount the 68k grid resistor on the tube socket. Cathode resistors and bypass cap configuration changes to 2k7/0.68uf and 10k/no bypass cap.
> 
> Also you may be able to omit the 100pf plate bypass cap thats mounted between 5 and 8 on the jcm layout. If after modding there's too much hiss/high gain hash install that bypass cap.
> 
> Onto v2... the mixer resistors in the yba-1a are 100k going to the grid of v2 (pin7) the jcm spec calls for 470k mixer resistors with a 500pf bypass cap. Next is the tone stack which is configured the same just with slightly different component values. yba-1a 0.001uf 0.1uf 0.02uf I believe. For the jcm specs change tone stack caps to 500pf and 0.022uf x2 and change the slope resistor from 47k i believe to 33k.
> 
> then the phase inverter has a similar layout so again it comes down to component tweaks. Change the outside legs of the PI from 47k to 1Meg (there may be an additional 47k in there you can keep or remove). Change the 6.8k tail of the PI to 10k. In terms of cap values they're pretty much the same but check and if not season to taste. I would leave the power amp section the way it is if its working.




Okay Sammy, I'm very interested in doing this now. All I've left to ask is if you (or anyone else) know a good website/store in the GTA to get the components. I'm trying to save cost by getting everything in one place if it's going to be online. Tried the websites linked from Sozo page, mojotone, tube depot, etc... but every website I go to is missing this or that. Biggest problem is finding most of those resistors at a 2W rating. Tons of 1/4 or 1/2 watt rated ones.. Only website that had the 500pf cap at all was Mojotone.. Thanks for any help and sorry for jacking the post!


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## sammyr

you should be able to find almost everything at a1 electronic surplus in the west end of the gta. its a bit of the pain in the ass to go through the place and find everything but they have a good selection of components. as well, in terms of finding the right resistors and caps you may be able to find them at college and spadina home hardware in the basement.


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## danielSunn0)))

I found all the right resistors that were suggested (assuming every resistor I needed was 2W rated) at the Home Hardware as you suggested, but not the caps. None of the caps there were axial with the leads at opposite ends though. More like what you would need in a pedal, as opposed to an amp. Thanks for the advice regardless; that much closer!!


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## copperhead

Get probably everything you need here 
Capacitors - Silver Mica | Antique Electronic Supply


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## copperhead

Great thread ..Sounds like were looking to do the same thing .


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## PTWamps

copperhead said:


> Get probably everything you need here
> Capacitors - Silver Mica | Antique Electronic Supply


Avoid US if you can. You'll pay extra costs on exchange and shipping + duty on larger orders. Those silver micas (and other caps for Traynors) can be found at TubeStore.com in Hamilton, Ontario and you'll get them within a few days. 

Best of luck!


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## danielSunn0)))

sammyr said:


> Make sure to mount the 68k grid resistor on the tube socket.


Looking at the schematic it seems to me that the 68k grid resistors are already on the tube, as it shows the first inputs going to pin 7 grid, and the other two going to pin 2 grid. Does that mean if I bridge them together, as Flyswatter showed in the original post, then it's good to go? Will that also connect the volumes in the same fashion as the jcm800?


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## copperhead

Updated pic after the Traynor tweaks


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## danielSunn0)))

What eletrolytics did you use for the swap, copperhead?


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## copperhead

All JJ's ,3 80ufs inside the chassis & went with 50/50uf in the first can ,secoud can was 32/32uf
originally this thing had 3 80's & 2 40/40's 450v
all new caps are 500v


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## danielSunn0)))

Okay cool, mine also has the old dynamite sticks in them so I think I should also do the swap.


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## copperhead

It's the safe thing to do , as for old caps going out of spec .all of my old caps were all close to spec as the new ones ,except one which one of the old fire crackers which were 80uf was reading about 103uf just a little out of spec 
. Im sure that 40+ year old caps ? get em changed.
this amp was in mint condition & sounded great .I did not notice any difference before or after the cap replacement ..but this not the case always . My latest YBA 1 Iwill replace the caps as well ,i have a JJ 50/50 can here .


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## copperhead

sammyr said:


> I don't know of anywhere that has an in dept explanation for modding to jcm specs but looking at a layout of the jcm and yba-1a schematic we can break it down. LAyout for jcm 800 2204
> traynor yba-1a schematic
> 
> Starting at the input side of the preamp. you need to rewire the 4 inputs and 2 volume controls as per the jcm layout. Make sure to mount the 68k grid resistor on the tube socket. Cathode resistors and bypass cap configuration changes to 2k7/0.68uf and 10k/no bypass cap.
> 
> Also you may be able to omit the 100pf plate bypass cap thats mounted between 5 and 8 on the jcm layout. If after modding there's too much hiss/high gain hash install that bypass cap.
> 
> Onto v2... the mixer resistors in the yba-1a are 100k going to the grid of v2 (pin7) the jcm spec calls for 470k mixer resistors with a 500pf bypass cap. Next is the tone stack which is configured the same just with slightly different component values. yba-1a 0.001uf 0.1uf 0.02uf I believe. For the jcm specs change tone stack caps to 500pf and 0.022uf x2 and change the slope resistor from 47k i believe to 33k.
> 
> then the phase inverter has a similar layout so again it comes down to component tweaks. Change the outside legs of the PI from 47k to 1Meg (there may be an additional 47k in there you can keep or remove). Change the 6.8k tail of the PI to 10k. In terms of cap values they're pretty much the same but check and if not season to taste. I would leave the power amp section the way it is if its working.


I've been going over you suggestions to mod to jcm specs ,great job i think i want to do the same thing with my Mark II


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## copperhead

sammyr said:


> I don't know of anywhere that has an in dept explanation for modding to jcm specs but looking at a layout of the jcm and yba-1a schematic we can break it down. LAyout for jcm 800 2204
> traynor yba-1a schematic
> 
> Starting at the input side of the preamp. you need to rewire the 4 inputs and 2 volume controls as per the jcm layout. Make sure to mount the 68k grid resistor on the tube socket. Cathode resistors and bypass cap configuration changes to 2k7/0.68uf and 10k/no bypass cap.
> 
> Also you may be able to omit the 100pf plate bypass cap thats mounted between 5 and 8 on the jcm layout. If after modding there's too much hiss/high gain hash install that bypass cap.
> 
> Onto v2... the mixer resistors in the yba-1a are 100k going to the grid of v2 (pin7) the jcm spec calls for 470k mixer resistors with a 500pf bypass cap. Next is the tone stack which is configured the same just with slightly different component values. yba-1a 0.001uf 0.1uf 0.02uf I believe. For the jcm specs change tone stack caps to 500pf and 0.022uf x2 and change the slope resistor from 47k i believe to 33k.
> 
> then the phase inverter has a similar layout so again it comes down to component tweaks. Change the outside legs of the PI from 47k to 1Meg (there may be an additional 47k in there you can keep or remove). Change the 6.8k tail of the PI to 10k. In terms of cap values they're pretty much the same but check and if not season to taste. I would leave the power amp section the way it is if its working.


So these changes should be the changes for to change basically the preamp to jcm specs ? i guess this would be what they refer to the cascaded gain stage ? i'm getting ready to order the parts for this for my yba1a JUST making sure im not going to miss anything .


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## sammyr

Yep, the cascaded gain stage is referring to how the inputs and first gain stages are laid out. In a standard 4 input marshall or similar amp there is a bright channel and a normal channel. V1 is split into two gain stages and each channel would get one gain stage that passes the signal on to v2. In a jcm or cascaded preamp instead of having the channels separate, the input goes to the first channel gain stage but instead of passing it on to v2 it sends the amplified signal to the second channels half v1 before passing it on to the tone stack.


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## copperhead

sammyr said:


> I don't know of anywhere that has an in dept explanation for modding to jcm specs but looking at a layout of the jcm and yba-1a schematic we can break it down. LAyout for jcm 800 2204
> traynor yba-1a schematic
> 
> Starting at the input side of the preamp. you need to rewire the 4 inputs and 2 volume controls as per the jcm layout.


 from the jcm800 layout I'm find the cliff jack layout a little confusing when trying to relate it to the traditional switchcraft style jacks found in the Traynor .
ALSO in the same layout the yellow line that goes across back of all the pots ? must be a ground bus wire ?


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## PTWamps

copperhead said:


> from the jcm800 layout I'm find the cliff jack layout a little confusing when trying to relate it to the traditional switchcraft style jacks found in the Traynor .
> ALSO in the same layout the yellow line that goes across back of all the pots ? must be a ground bus wire ?


This might help:
http://el34world.com/charts/images/cliffjacks.gif

You can use the 68k and 1 Meg to get your bearings. So when holding the cliff jack lugs up with the input to the right, bottom left lug would be your "tip" connections, the 1 meg bridges across to the top left lug on Low jack, and all the other lugs link to ground, in same way as your sleeves and switches do on the Traynor/ Fender type jacks.

And, yeah, on that Ceritatone layout the wire across the backs of pots is a ground bus. Ceritone practices star-grounding, where all the grounds head to a common point.


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## copperhead

how do the volumes work after the jcm mod ? is one volume a master & the other gain ?
cause I do have the PPIMV installed on the back of this thing ?


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## copperhead

I'm getting ready to rewire my YBA 1A to the jcm style today what should i do with the jacks ? as this has 4 inputs & the jcm has 2 inputs ,


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## copperhead

sammyr said:


> I don't know of anywhere that has an in dept explanation for modding to jcm specs but looking at a layout of the jcm and yba-1a schematic we can break it down. LAyout for jcm 800 2204
> traynor yba-1a schematic
> 
> Starting at the input side of the preamp. you need to rewire the 4 inputs and 2 volume controls as per the jcm layout. Make sure to mount the 68k grid resistor on the tube socket. Cathode resistors and bypass cap configuration changes to 2k7/0.68uf and 10k/no bypass cap.
> 
> Also you may be able to omit the 100pf plate bypass cap thats mounted between 5 and 8 on the jcm layout. If after modding there's too much hiss/high gain hash install that bypass cap.
> 
> Onto v2... the mixer resistors in the yba-1a are 100k going to the grid of v2 (pin7) the jcm spec calls for 470k mixer resistors with a 500pf bypass cap. Next is the tone stack which is configured the same just with slightly different component values. yba-1a 0.001uf 0.1uf 0.02uf I believe. For the jcm specs change tone stack caps to 500pf and 0.022uf x2 and change the slope resistor from 47k i believe to 33k.
> 
> then the phase inverter has a similar layout so again it comes down to component tweaks. Change the outside legs of the PI from 47k to 1Meg (there may be an additional 47k in there you can keep or remove). Change the 6.8k tail of the PI to 10k. In terms of cap values they're pretty much the same but check and if not season to taste. I would leave the power amp section the way it is if its working.


trying to follow what you have done here & the cathode resistors & bypass cap change configuration to 2k77/0.68uf & 10k with no cap ? thats off pin 3 on v1 right ? what about the YBA1a i might be wrong but it has 2 sets of cathode resistor & cap , a set from pin 3 & a set from pin 8


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## sammyr

both amps use a split cathode arrangement so each cathode has its own resistor/cap connected to it. The cathodes are pin 3 and 8. In this ceriatone layout the cathode layout is shown (yellow wires pin 3 and 8).


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## copperhead

I have a question ? wiring the master & using the Ceritone layout you see they have E which goes to the return of the fx loop ,we got no loop so wouldn't it go to the speaker inputs ?


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## copperhead

this layout makes more sense.


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## copperhead

Modded to the JCM specs now ,Still got a little work but I must say this thing sounds killer .my ears are ringing .it has lots of gain now .not really much hiss but so i will possibly be adding 100pf cap on v1 few things i need to check out , my PPIMV now turned all the way down is fairly loud ,if you turn it up it gets louder .that's something i will look into .a few minor details .


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