START NEW THREAD REPLY Top of Thread LIST Read 201 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/10/2001 4:33 AM Subject: Orange 120 help I am having trouble diagnosing this Orange 120 that Im fixing 4 a freind. Please help me. Thanx :-) He just got it off of E-bay so no history. Basicaly it sounds great when playing with soft input. At loud input it make a loud non musical splat / distortin sound. Also left side (only) of the push pull runs too hot after a while they start glowing Orange :-( . I just did a DC fiter cap job and set the -B voltage bias. All the votages are dead on with the schematic, Replaced the power cord, And Retubed, all the tubes test well. And a swaping a new quartet dosent solve the problem. http://www.kbapps.com/schematics/tubeamps/orange/graphicmkII120W.html after servicing is way quite now. All the 120 sound went away. But I need to figure out were the splat is coming from. Thanx Tad START NEW THREAD REPLY PREVIOUS LIST Read 189 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/10/2001 4:41 AM Subject: 1 more detail 1 more detail It makes a pop sound or 2 when I turn it from stand-by to on. Thanx Tad START NEW THREAD REPLY PREVIOUS LIST Read 201 times From: Bruce (MissionAmp@aol.com) Date: 4/10/2001 7:58 AM Subject: Re: Orange 120 help I usually don't run those at more then about 32ma to 34ma for each power tube. Did you also replace the two 10uF/150v bias supply filter caps on the board? Sometimes the screen resistors on these are flakey and I have to replace all of them with 1K 5watt cement wire wound power resistors. Does the glowing tube problem stay in the same socket or move with the tube? Is the impedance switch soldered correctly? Make sure you use the right impedance with these amps. Does this one have a SPST standby in the back with a reverse polarity DPDT on-off switch, or is it a DPDT standby on-off switch on the front and nothing on the back? Bruce START NEW THREAD REPLY PREVIOUS LIST Read 186 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/10/2001 8:55 AM Subject: Re: Orange 120 help Bruce. I only replaced the 100uf 450v filter Caps. I suspect the screen resistors also for making half of the PP run hot. This amp came with power tubes of diferent vintage and make. And one side of the push pull power section gets hotter than the other. with brand new Svetlanas and JJ el34s. This Orange has a Stanf-by-OFF-On switch on the front panel. It is weird u go past off to turn it on. Is that right??? In your reply u mention the Power Setions current bias first; could this affect the weird splatting sound? I kinda feel like its a power suppley Cap issue since the amp sounds really good till you ask more power from it. I will look into replacing the Bias filer caps. Thanx Bruce Hope to hear frome u soon :-) TAD START NEW THREAD REPLY PREVIOUS LIST Read 179 times From: Richie{~}==::: (richhall@zoomnet.net) Date: 4/10/2001 3:50 PM Subject: Re: Orange 120 help Could be a few things might be causing this,bad OT..bad couping cap for that side. Popping sounds..i always ask this first..does it sovtek preamp tubes...?? many of them do the 2 ..3 pop thing when switched on from standby. Also bad or arc in switch..bad socket..also check the cathode resistors in preamp section and bypass caps. look for any arcing on the board when switched on,or loose solder connections.Just a few things that i can think of..whats the primary of each side of the OT read? Richie{~}==::: START NEW THREAD REPLY PREVIOUS LIST Read 185 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/10/2001 5:21 PM Subject: Re: Orange 120 help Richie I likes Bruces reply it was simple. Could u bend the laws of physics for me so life would be easy :-) This amp has new EH 12ax7s and I have a wealth of NOS and a good Eico TT. So its not that. :-) I was tapping around with my Sharpie (AKA best tool in the world)and noticed I could get the amp to make the splat sound occationally. But I could only isolate it to the AC and DC area no Pre amp or power amp splats. I'm thinking that it could be arking under hi input/output only conitions.????...hmmm,,, I guess I'm learning on this one. Thanx TAD START NEW THREAD REPLY PREVIOUS LIST Read 167 times From: Richie{~}==::: (richhall@zoomnet.net) Date: 4/10/2001 9:27 PM Subject: Re: Orange 120 help Sorry ..i tried just to add a few things to look for that might be causing the problem..I'll let others help ya. Richie{~}==::: START NEW THREAD REPLY PREVIOUS LIST Read 167 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/10/2001 9:52 PM Subject: I hope u know I was joking Richie, Please forgive me if I offened you. I was joking. I think the context and sarcastic witt of my reply was lost in the digital relm. I must have a bad DAC. LOL Once again let me say I apriciate all the help I get here. Thank you for your reply Richie :-) TAD "(Richie I likes Bruces reply it was simple. Could u bend the laws of physics for me so life would be easy :-)" START NEW THREAD REPLY PREVIOUS LIST Read 157 times From: Richie{~}==::: (richhall@zoomnet.net) Date: 4/11/2001 1:03 AM Subject: Re: I hope u know I was joking Its ok Tad..just read it wrong and too fast..just having one of those days where everything goes wrong,and messes with ya. Richie{~}==::: START NEW THREAD REPLY PREVIOUS LIST Read 155 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/11/2001 1:48 AM Subject: that happens I would like to think were all freinds here looking out for each other. I know I am. TAD START NEW THREAD REPLY PREVIOUS LIST Read 150 times From: Richie{~}==::: (richhall@zoomnet.net) Date: 4/11/2001 4:53 AM Subject: Re: that happens I agree with ya.. lots of really great people here..lets us know what ya find out with the Orange. Usually we all try and pitch in till someone comes up with an answer,or suggestion to get the amp working.. Richie{~}==::: START NEW THREAD REPLY PREVIOUS LIST Read 157 times From: Bruce (MissionAmp@aol.com) Date: 4/11/2001 5:27 AM Subject: Re: Orange 120 help OK, a few things... Sounds like yours has the DPDT on-off standby switch in the front panel. It either works or doesn't, so I think yours is OK. There is a little pinkish-tan wire that comes out of the PT in these that is really the center tap of the power transformer high voltage secondary. It is a full wave bridge rectifier and the center tap of the PT secondary is really at half the AC voltage so they stick it right between the two caps! Make sure it is soldered to the junction of the two main power supply caps.. the two 100uF 500v ones. Next, I've refurbished a bunch of these Orange amps and I don't think I've found many that didn't need at least one of the bias supply caps replaced. Since you have to lift the entire board off the stand off screws to do a proper cap job on these anyhow, do all the electrolytic caps on the board...yes all of them including the 47uF cathode bypass caps! Hopefully yours won't be one with dried up rubber grommet insulators. They'll need to be replaced if they are too stiff to give a little. Next, Don't waste a lot of time deciding to replace inexpensive easy to replace parts like 50 cent screen resistors, just put new ones in to eliminate them from being part of any problems. Make sure there are 1k5 1/2 watt grid stopper resistors on the tube sockets. Lug 6 to 5. Check to see if each side of the power tube stage is seeing the same negative bias voltage on the tube socket's lug 5. These amps really need well matched power tubes and should be setup carefully. They run pretty hot voltages to the power tubes and the trannies are large so they can swing some current and still take some serious abuse! Most of these I see will have the plates running at 510vdc to 530vdc and with current EL34 tubes, I don't like to see them idling much over about 15-17 watts in these amps. That means about 30ma to 33ma for each tube. The power tube driver is a cathodyne splitter and one side of the splitter can put more drive into it's tube(s) so it's not uncommon to find one or set of tubes wearing out faster or going into thermal run away then the other. If the tubes are old, worn out, abused or just ready to draw too much plate current and glow anyhow, this will really exagerate the tube wanting to take off all by itself. If it has been recapped and there are no tube socket shorts anywhere, splattery sounds in these probably is a bias or bad power or preamp tube thing as the amp itself is very simple. The last one I did put out a VERY clean 110 watts into a 16 ohm dummy load and an amazing 158 watts in nasty cranked up over drive distortion at 160Hz into it's 4x12 cabinet. Bruce START NEW THREAD REPLY PREVIOUS LIST Read 146 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/11/2001 6:39 AM Subject: Re: Orange 120 help Bruce, Thanks for the great detailed info. Nothing info from the experienced. Look for an update tomorrow. TAD START NEW THREAD REPLY PREVIOUS LIST Read 139 times From: MBSetzer (QualityAna@aol.com) Date: 4/11/2001 5:21 PM Subject: Re: Orange 120 help you might also check the tube socket & bases for previous arcing which makes it easier for further abrupt leakage when the signal amplitude gets up there. That really sounds like splat to me, but I haven't worked on an Orange myself. I think Bruce knows these amps thoroughly, cathode bypass caps can leak past a point and sound similar to an *arc without a spark*. Even old filter caps sound a little like that to me sometimes. Hope this helps, Mike START NEW THREAD REPLY PREVIOUS LIST Read 127 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/11/2001 8:36 PM Subject: Round 2 Ding Ding Om I'm going to Ford's Electronics in Fullerton Ca. after lunch. I'll be picking up the fallowing (if in stock hhuhhhh...). Caps: 2x 12/450v 2x 47/15v 4x .068/400 film Resistors for the PP power section 4x 2k2 4x 1k5Watt Ceramic Tad START NEW THREAD REPLY PREVIOUS LIST Read 128 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/12/2001 4:19 AM Subject: Round 2 Almost there I hope Hi all, I recapped most of the PC board minus the parts that weren't in stock (only 3 original caps left). I replaced ALL the resistors that are on the power section. So now I have solid -b DC in spec and the power tubes arn't overheaing like thay used too. and just one dull short pop on power up. Before it was makeing hars pop sound that wer longer like a whole second. Heres the problem now no sound is comming out except a slight hiss from the power section!! Doh! I guess I messed up somewere. I have checked all the votages I can and they are very close if not right on spec. I'm having trouble checking the pre amp tubes I'm not sure what pin is what on the schematic and the votages are so blurry I cant tell what I should b looking for anyway. :-\ I need help with that. I was uncertain about one caps polarity that feeds DC to the pre amp tubes. .068v400vdc Since the square green film resistor didn't have a + or a - to determin polarity. This might be the Last problem but it don't hurt to ask. I just need more experiance and reading at this point. Fill me in I'll get it :-) START NEW THREAD REPLY PREVIOUS LIST Read 127 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/12/2001 7:18 AM Subject: Re: Round 2 Almost there I hope So I'm not getting any audio thru theis Orange. I have been reveiwing all my work studing the schematic. I could have inadvertantly flip flopped the 2 blue and one red wires going to the phase inverter while replacing the caps on the PCB. I have 357dv at pin 3 ad 192 at pin 6. shouldn't the DC be at pin 1 and 6? TAD START NEW THREAD REPLY PREVIOUS LIST Read 107 times From: Bruce (MissionAmp@aol.com) Date: 4/14/2001 5:26 AM Subject: Re: Round 2 Almost there I hope Check to see if you've broken any wires off the circuit board up by that little metal shield on the FAC rotarty switch. There's a .068uF coupling cap with a wire feeding the series caps in the switch. If you flipped those leads on the tube socket...why in the world they needed to come off I don't know... ha ha ha... but anyhow, it would probably scream like spider monkey. It has to be something simple now. Bruce START NEW THREAD REPLY PREVIOUS LIST Read 124 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/12/2001 6:45 PM Subject: bump bump Please Help me... Thanx:-) TAD START NEW THREAD REPLY PREVIOUS LIST Read 119 times From: Richie{~}==::: Date: 4/13/2001 9:11 PM Subject: Re: bump Well, I'm in PA right now..be back this weekend. I have an Orange 120 at home..i could look at to see how it goes..be back home sunday eve. Richie{~}==::: START NEW THREAD REPLY PREVIOUS LIST Read 122 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/13/2001 11:40 PM Subject: Wow Wow Richie Thanx, If I could get a digital pic that would be great. I should keep a digital camera on my bench but im dead broke! Maybe Lo-Fi and get me a Polaroid. Let me know I got to get her done :-) TAD Thanx again START NEW THREAD REPLY PREVIOUS LIST Read 115 times From: Gino (giorfida@drifteramps.com) Date: 4/14/2001 12:31 AM Subject: Re: bump Where at in PA, Richie? I'm just outside of Pittsburgh (by the airport). Small world. START NEW THREAD REPLY PREVIOUS LIST Read 114 times From: Richie{~}==::: Date: 4/14/2001 1:30 AM Subject: Re: bump In Johnstown PA.. Richie{~}==::: START NEW THREAD REPLY PREVIOUS LIST Read 116 times From: Gino (giorfida@drifteramps.com) Date: 4/14/2001 6:48 AM Subject: Re: bump Ahhh not that far away. next time you are in the area, look me up! START NEW THREAD REPLY PREVIOUS LIST Read 110 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/16/2001 6:04 PM Subject: Orange PT2 Please help me I feel I'm almost there. Recapped 90% of the PCB and replaced all the resistors on the power tubes. So I'm not getting any audio thru theis Orange. I have been reveiwing all my work studing the schematic. I could have inadvertantly flip flopped the 2 blue and one red wires going to the phase inverter while replacing the caps on the PCB. I have 357dv at pin 3 ad 192 at pin 6. shouldn't the DC be at pin 1 and 6? TAD START NEW THREAD REPLY PREVIOUS LIST Read 99 times From: PeteR (valveart@one.net.au) Date: 4/17/2001 1:17 PM Subject: Re: Orange PT2 Please help me Yes Tad, What's the voltage on pin 1? PeteR START NEW THREAD REPLY PREVIOUS LIST Read 91 times From: Richie{~}==::: (richhall@zoomnet.net) Date: 4/18/2001 1:52 AM Subject: Re: Orange PT2 Please help me Tad.. when you say no sound..you mean nothing at all?? Might be in the impedence switch..might try just wiring direct to a regular jack..see if it does anything.Does yours have the send and return jacks on the front??? Richie{~}==::: START NEW THREAD REPLY PREVIOUS LIST Read 83 times From: Tad Banzuelo (ProTools4@aol.com) Date: 4/25/2001 12:43 AM Subject: Making good sounds now Richie, Bruce and others, The Ornge is sounding great now. OK so far have: -replaced the power cord -new fuses -All new caps on the PCB -reserected the -b bias voltage -replced all the Resistors on the PP Sockets -Re-tubed with new tested tubes -replaced the wires that take -bias form the PCB to the Sockets -serviced all the pots Every thing seems to be running in good order. Except the Power tubes seem to dim and then brighten as I attack the strings with a loud chord. Is this the Voltage saging then rising? its a SS rectifyer. This only happens at 90-100% volume. And that is Damm LOUD! TAD -------------------------------------------------------------------------------- START NEW THREAD REPLY Top of Thread LIST Read 180 times From: Derek (drsst53@pitt.edu) Date: 6/19/2001 1:46 PM Subject: My Orange amp Recently I blew the HT fuse in my OR120 and replaced it with a 1A 250V Fast-Acting fuse. It works now. However, when I play I hear a rattle in the amp if I bang it after i've been playing it for 10-15 minutes. It also seems the sound isn't as smooth, but that may just be me paying more attention to details. I also looked at the Mains Fuse and it has a 15A 250V Slow-Blow fuse in it but it calls for either 3A 250V Slow-Blow or a 5A 120V Slow-Blow fuse. I bought this amp used so does anyone have any ideas or recommendations for any of these things...do i need to get new fuses? Is the wrong fuse causing the rattling in what seems to be tubes? Is one of these problems what may be causing a less smooth sound? Thanks. START NEW THREAD REPLY PREVIOUS LIST Read 153 times From: tommy (tommy@thewho.com) Date: 6/19/2001 3:20 PM Subject: Re: My Orange amp The fuses did not affect the sound. Yes, replace the fuses with the correct values. 15A????? That's a fried power transformer waiting to happen, and that's expensive. If you have 120V (US voltage), put a 5A slo-blo in the mains fuse position. The rattles are probably the guts of the tubes rattling. No big deal if everything still sounds good coming out of the speaker. I put a piece of foam between my amp and the speaker cab to keep the tubes from getting vibrated to death. That will minimalize the rattling and keep your tubes alive longer. The HT fuse blowing could mean that something is wrong with the internal circuitry or a tube, so keep an eye on it if you don't want to have it checked out. If you are the worrisome type, take it to a tech for a check out and tell him the fuse blew and see if he can find anything funky. Chris START NEW THREAD REPLY PREVIOUS LIST Read 138 times From: Bruce (MissionAmp@aol.com) Date: 6/19/2001 5:01 PM Subject: Re: My Orange amp Usually a bad power tube or arced over power tube socket will blow the HT fuse on an Orange. I think there's a good chance you have a problem in the power tubes section and now you're hearing it. Rattles are normal with some tubes so I wouldn't get to upset with a mechanical rattle, however, I've heard power tubes do this if they are bad or going bad too, so you need to check those power tubes out regardless. Use a 5a slo-blo/MDL for the main as suggested and a normal 1a fuse for the HT. Set the bias so each tube is running about 15 watts for these amps to get a good tone. RED FLAG! The 15a mains fuse would scare me in terms of buying a used amp!! It frequently is an implication that the previous owner knew there was a problem and needed to put a bigger fuse in it so the amp can be quickly demo'd before it blows the main 5a-7a fuse. Bruce START NEW THREAD REPLY PREVIOUS LIST Read 96 times From: Derek (drsst53@pitt.edu) Date: 6/19/2001 10:10 PM Subject: Re: My Orange amp Would a 3A/250V suffice? Or does it need to be 5A? I couldn't find a 5A fuse for 110/120/125V at the Radio Shack. I really hope there isn't anything wrong with my amp. Thanks for the help guys. START NEW THREAD REPLY PREVIOUS LIST Read 93 times From: Bruce (MissionAmp@aol.com) Date: 6/20/2001 12:07 AM Subject: Re: My Orange amp Well you really should use a 5a in those. In a pinch, I admit to using a few stnadard or fast-blo 7a fuses. But, the fuses take a big hit from the two 100uF/500v filter caps and for that matter the rest of the amp... those El34s take a ton of juice to fire off the filaments! Plus, when cranked up, the 120s really will put out +105 to 130 clean watts, depending on what tubes and what line voltage and an amazing amount of power fully cranked up and nasty. I've seen well over 160 watts driving a 4x12 eight ohm cabinet...in classic Orange ugly distortion of course. The trannies were built for 220v and there happens to be a 120v tap so that means the PT's primary will draw more current to compensate for the lower available primary voltage in order to deliver the same output current. Bruce START NEW THREAD REPLY PREVIOUS LIST Read 81 times From: Derek (drsst53@pitt.edu) Date: 6/20/2001 2:02 AM Subject: Re: My Orange amp Would a 5A/250V Slow-Blow work? START NEW THREAD REPLY PREVIOUS LIST Read 66 times From: tommy (tommy@thewho.com) Date: 6/20/2001 4:39 AM Subject: Re: My Orange amp Yes, the 250V means it can handle anything up to 250VAC. Chris START NEW THREAD REPLY PREVIOUS LIST Read 20 times From: bart (lespaul3@aol.com) Date: 6/20/2001 4:17 PM Subject: Re: My Orange amp just to add some thoughts.. I have an orange 120 (no overdrive) from the early 70's... I bought it from plexi palace (no, not intended as a plug for them) but...mine only says 3A fuse (it doesn't tell you use a 5A for 120V). So, I was using a 3A. Of course, at a gig, between sets, the fuse blew. I called plexi palace, and they said that it should be run with a 5 at 120, but to try a 4A. The 4A has worked fine and hasn't blown, but I have some 5's on hand just in case. so, the 5's aren't a necessity, but 3's might blow just with regular operation. I imagine a 4A will make the fuse blow sooner, giving the amp a bit larger of a "safety switch" than a 5A. possibly? bart -------------------------------------------------------------------------------- START NEW THREAD REPLY Top of Thread LIST Read 121 times From: xronx (ronkra@web.de) Date: 6/14/2001 5:04 PM Subject: orange amps i´m going to buy a used orange overdrive 120 head...how can i identify 70´s models from 90´s models? i´ve heard orange reissued old models in the beginning of the 90´s...is there any difference between the old and the new ones soundwise? thanks xronx START NEW THREAD REPLY PREVIOUS LIST Read 105 times From: Brit Gear (sales@britgear.com) Date: 6/14/2001 10:05 PM Subject: Re: orange amps The early Orange amps had graphics on the front with no explanation as to what the controls did. The next ones had volume treble Low FAC control with actual writing saying what they are! The easy way to tell them apart is the Power plug. The early amps had the round Bulgin plug the later ones (90s) have the standard computer plug (rectangle). The back cover is also different with the newer ones having a perforated grill. The Data plate on the old ones say Compton Road and the newer ones say Made in England. I hope this helps START NEW THREAD REPLY PREVIOUS LIST Read 87 times From: xronx (ronkra@web.de) Date: 6/15/2001 12:21 AM Subject: Re: orange amps much thanx... START NEW THREAD REPLY Top of Thread LIST Read 130 times From: Jim Jones (boowho@mts.net) Date: 3/30/2001 6:13 PM Subject: Looking for early Orange/Matamp schem Hi guys, I've talked to several people about this and have been told that the earliest Orange amps sound a lot better than the later Graphic 120's etc. Does anyone have a schem of the real old jobbies? I'm curious to see how different they are... Thanks! Jim START NEW THREAD REPLY PREVIOUS LIST Read 137 times From: Richie{~}==::: Date: 3/30/2001 7:49 PM Subject: Re: Looking for early Orange/Matamp schem here is a link.. and i'll send ya another pic.. and you can get one of the amp from the site.. http://www.matamp.com/equipment.html Richie{~}==::: START NEW THREAD REPLY PREVIOUS LIST Read 124 times From: Jim Jones (boowho@mts.net) Date: 3/31/2001 1:38 PM Subject: Re: Looking for early Orange/Matamp schem Thanks, Richie! If anyone has a schem, please let me know. Jim START NEW THREAD REPLY PREVIOUS LIST Read 121 times From: Richie{~}==::: Date: 3/31/2001 7:38 PM Subject: Re: Looking for early Orange/Matamp schem Jim: the ones in the tube amp book are from 72 and 74..Graphic amps.. I'll see what else i can find for ya. Richie{~}==::: START NEW THREAD REPLY PREVIOUS LIST Read 125 times From: Bruce (MissionAmp@aol.com) Date: 4/1/2001 6:39 AM Subject: Re: Looking for early Orange/Matamp schem I can tell you from using my eyes that the values of caps and resistors in the "Baxandall" type tone stack are slightly different from model to model. One of these days I'm going to have to start drawing reverse engineered schematics for these things. Seems like no one has been doing that. I have two in the shop right now. One is one I've never played with before... a 50 watt (Graphics MKIII circuit board) OR115RM ... master volume and reverb...in a 2x12" combo. Bruce START NEW THREAD REPLY PREVIOUS LIST Read 136 times From: Jim Jones (boowho@mts.net) Date: 4/1/2001 5:24 PM Subject: Re: Looking for early Orange/Matamp schem Hey Bruce, If you wouldn't mind jotting down some of the tone stack values you come across, that'd be great! I have an old Garnet Pro ('66) that I've been messing around with. The preamp section of the Pro is very similar to the Orange amps that I have the schems for. It really didn't sound that great initially so I've been trying to "Orange-ize" it to see what kind of a difference it would make. I wanted to keep it as stock as possible but I figure if it doesn't sound very good there's not much point in that. (No holes being drilled - just component value swaps.) Firstly, I was amazed at the component drifts when I started measuring parts... The preamp is Orange-like in that there are two 12AX7 stages with the "Bax" and volume in between. The cathode resistors were 1.5K's that had drifted to 3K and 4K respectfully! The plate resistors were 100K's that read 105 and 110K. Changing those back to their "proper" values helped things immediately! I found it odd that the tone stack cap values were the same for both bass and treble controls... .001 on the input side of the pots and .01 from the "pin 3" to ground. The Garnet Pro schem I have has those values for the treble pot but has 470p and .0047 for the bass pot. All I had handy was a 510p and .0056, so I subbed those in on the bass pot and that made the bass pot way more useable. (Previously I couldn't turn the bass pot beyond 9 o'clock or it all turned to mud.) I don't have a lot of experience with "Baxandall" type tonestacks but I've found that they lose a lot of volume if the pots are turned "too low." What the hell is the point of this ramble - I don't really know. Just thought I'd share some of my experiences with this particular amp...hope it's of use to someone. If not, move along then. Jim --------------------------------------------------------------------------------