The Trace Elliot Speed Twin are a series of amps includiung a C30 (30 watt combo based around 4 x EL84) and 50 or 100 watt combo and head variations based on EL34 either pair or quad respectively. They have two channels and the usual features one would expect in a modern amp plus a few unusual features. Designed in 1996 and redesigned in 1998 to comply with EU emission standards, improved fusing and some improvements in PCB layout they have some great features and supporting information and are solidly built.
Although PCB based great care has been in the circuit layout to minimise hum and pickup typical in hand wired amps through poor lead dressing. There are two circuit boards one for the pre amp and one for the power amp – these components seem to be shared with other Trace models e.g. Bonneville according to the circuit diagram at least. I have found that the PCBs are a little cramped in places and the circuit board pads not the most resilient. However I would say that these amps are good quality and their unique features make them well worth a look.
What I like about these amps is that the bias is adjustable from the back in a safe manner (well the MkII are) meaning that anybody can do the adjustment with a cheap multimeter and a screwdriver and the supporting instructions make it very clear. Also they support different power valve types e.g. EL34 and 6L6 and power levels – I love this idea very flexible and also switched pentode / triode operation. Great for people who want to experiment with sound and for recording. Note the Mk I must be bias adjusted using bias probe as their is no measurement resistor.
I was lucky enough to take a look over a C50 speed twin combo this week. The fault was that it went bang after being left on for three days accidentally and as the owner turned it back to standby so there was a bang and a dead amp.
Upon opening up the amp which is extremely heavy and well made I immediately looked round for the source of the bang. It turned out to be a group of four diodes near to the power valves – a bridge rectifier. Not uncommon for these to burn out in response to a downstream short e.g. from a smoothing capacitor or in this case the 7824 regulator – the supply for the channel switching relays.
I had picked up a circuit diagram from a forum for this amp but kept finding inconsistancies e.g. missing fuses and different component values which made me think I was not looking at the correct diagram. However my experience contacting traceelliot / peavey for the correct diagram was a joy – see below for more on that. But first the repair details.
Replacing the four 1N4002 diodes (1A general purpose rectifying diode) was fairly straightforward apart from having to remove the smoothing capacitor nearby to get access. Although pad damage was inevitable as the plate-through holes were barely big enough to accomodate the diode leads does raise the question of layout design. I mean this amp is massive, there is no shortage of space inside yet the PCB are squashed in places. Like all things I am sure there is a good reason. Powering up the amp (without power tubes in just in case) revealed that the diodes were working ok and checking the 24 volt supply all seems good. However upon fitting the original (13 year old valves) I discovered that one was open circuit on the heater filament. So perhaps that is the cause of the issue. . . Ordered a set of Harma from Watford Valves and then we are good to go.
What was interesting in this amp was my experience in dealing with Trace Elliot or Peavey as they seemed to be owned by now. I contacted them one morning for the circuit diagram (not expecting much help) and got this fantastic response – in just two and a half hours.
Paul Stevens EngTech MIET, MAES
Product Design & Development Manager
Product Demonstrator
Trace Elliot / Peavey (Europe) Electronics Ltd
I could not believe it. I contact Trace through the web site and get a response practically from the amp’s designer. Amazing – and such a personal response I wouldn’t be surprised if he drove over to Bristol to help me carry the amp into my car for delivery to the customer. However I then queried Paul about the diodes – I wondered if they were upgraded on the MKII version of the amp and therfore should I consider modding accordingly?
Hi Mike,
I have seen a few stories on the web about diodes going on these amps so I guess that these are a bit of a weak spot. However Speed Twin Amplifier repair is straightforward and well worth doing at only about an hours labour plus a few quid for the diodes themselves. If you have one of these delightful amps and it is giving you trouble please feel free to get in touch.
hi there, i have bought a C50 first edition no working…and i would like to know if somebody can send me the shema for this first model C50.
Thank you very much !!!
Should have received by now. Good luck.
hallo guys
allthough an old post ,i ve just seen it – could somebody inform me where i could find a c30 shematic?
thank you in advance
Hi there,
I play through a Speed Twin Head MK 1 H 100 and recently purchased a MK 2 H 50 and noticed, that the MK 2 overdrive channel got less bass frequencies compared to the MK 1. The clean channel sounds the same. There is obviously no difference in the circuitry layout. Can anyone help me ?
The circuits between the pre-amp mk1 and mk2 are quite different. I guess it is that or a fault lowering the bass output.
I’ve got the schematics from 1996 (MK I) and 1998 (MK II) and there is obviously no visible difference concerning the layout of the overdrive channel and the eq controls with the only exception of two small capacitors bridging the cathode-resistor of Valve V 1 (MK1: none, MK II: 47 pf) resp. V 3 (MK 1: 1 nF, MK II: none). The eq bass control works only half way up …..at this point there’s no increase of the amount of the low frequencies ….??
Ah ok fair enough. I just took a quick scan of the schems that I have and saw a few differences around the PI so assumed more too.
Wow! I’ve been searching for the ‘96 Mk I schematics and can never find them. Where did you find it?
Hi Roger,
I don’t recall exactly as it was a ferw years ago but I just emailed Trace or Peavey and got lucky getting through to the original designer; he was very helpful. Unfortunately Peavey in the UK are no more which is such a shame as they were fantastic in supporting their users with inexpensive parts and fantastic technical advice. I think for them this will be a short term gain at the expense of long term brand loyalty.
… i recently noticed that in comparison with the the MK 1 when activating the standby switch the signal decresases very slowly (about 30 seconds)
I guess the implication is that cap discharge time is different. A less stiff power supply would account for lower bass performance – although not just on one channel?
You might want to post your query on the Music-electronics-forum. There are a lot more techs there.
I’m a speedtwin & super tramp fan & was lucky enough to be around when Trace were based in Maldon ( I live just next to the old site). The guitarist in a band I used to sing with was endorsed by Trace & swore by his speed twin ( he had a cornell & a matchless rig plus a number of high end amps & combos too but always went back to his speedtwin) so I spent a number of years hearing what it can do with an expert guitarist ( he won young guitarist of the year & was recognised as something special. I lived with him when we were in the band & he REALLY influenced my style of playing.)
When we decided that I would play 2nd guitar Trace VERY generously helped me out with the 50w head & matching cab & even tweaked the amp to suit my “throw-away” guitar style.
We were doing a show with a band called the Hoax & jesse Davies ( awesome player) amp blew during soundcheck & he used our guitarists speed twin for the gig – he LOVED it.
Their other guitarist Jon Amore was impressed with the tone & even years later I played a show with Jon when he was playing with his own band & I was in another band & he laughed as I was still rocking my speedtwin
I used to do demos for guitar mags & constantly refered to my speedtwin as the sound that I didn’t know I wanted till I looked for it .
I played most types of music with my twin as I grew older from blues to funk to metal to downright heavy metal.
It does it all……..
I still cycle past the old Trace site & remember the good times 😉
Trace even used to sort out the sound system for our town music festival & supply the engineers FOC……
Bloody awesome company & I still use my speedtwin today, nearly 20 years later.
hi there, i recently bought a mk1 of these for the princley sum of 400. i need a footpedal for it but have no idea what type i need, can you help?
You should try Peavey UK as they are very helpful and own or run the Trace brand nowadays. Number is 01536 461234
I use one of these with my Speed Twin C100: http://basschat.co.uk/uploads/monthly_10_2011/post-524-0-07805900-1319303721.jpg
Hi there. I just wanted to document my repair experience with my C50 that I had in 2012. I had found and contacted Paul Stevens about my troubles. He promptly sent me the schematics.
Yes, two of my bridge diodes burned. My repair experience told me that it was most likely the diodes themselves, although a shorted or open smoothing cap could certainly come into play. Who knows? Other things might also cause them to burn out. Paul had told me about the inadequate heat sink on the 7824 as also a possible source of trouble.
The main reason I suspected only the diodes was because I had the amp set up in our church building, which was a rented space. I knew that the building had an overvoltage condition. When I discovered that the PIV of the IN4002s were only rated for 100V, that sort of sealed the deal on that theory. I knew the building AC was running close to 130.
So, I replaced all of the bridge diodes with IN4004s, 400V PIV. I didn’t believe the 7824 was damaged, but I did address the inadequacy of the heat sink. I replaced it with a beefier TO220 convection heat sink. And new thermal grease never hurts 🙂
The amp was back in action, and has been to this day, April 25, 2014.
Great to hear of your success. I am a great fan of the music-electronics-forum site. Lots of info there too.
I have a Speed Twin 30 amp for repair on behalf of a friend. Having limited knowledge of valve amps but having a broad knowledge of transister amps in general I agreed to look at it. I went about surveying the circuit board to look for obvious signs of burning as I was told the amp started to smell of burning before it gave up. I spotted two small burned out electrolytic caps located under two of the valves , one on the pre-amp section and the other on the power side which I replaced. As a precaution I went about replacing all four EL84’s. Upon switch on the amp works great for about 5 minutes after which two of the power valves (a linked pair) start glowing hotter and hotter. At this point I turn it off, and beyond this I have been confounded by what might be causing this to happen. As these amps are self biasing this cant be the problem. The HT seems very high at 357 Volts, but upon reading the specs of the amp in the copy of the circuit diagram/service manual , this seems to be part of this type of over driven Class A design which gives it a distinctive sound. Technically EL84’s are not meant to run beyond 300 Volts, so reducing the HT might help, but how?…the only other thing that comes to mind is that the output transformer could have a partial melt down in the winding in the half of the circuit connected to the over heating valve pair. Please can anyone throw any light on the matter, I would be most grateful. Regards Chris Latham.
Hi,
Just so you know this isn’t a discussion forum where there are many techs likely to give answers; The comments feature is just a place where people with similar stories to share. Try music electronics forum which is the best place on the web for getting help on amp troubles.
Having said that, I would start by removing all tubes and re-measuring the DC voltage on all pins and the AC voltage on the heaters (unless you think these amps have DC heater, which they may do I just can’t quite recall). The HT will be high with no tubes fitted becuase there is no load. If you mentioned tubes glowinging brighter I would be concerned about the heaters as I seem to recall that Trace wired the filaments in series and perhaps if a pair go down there is some impact elsewhere. Many causes but need to start checking the basics also a dim light bulb is a good way to protect against causing further damage.
If you are unsure about draining caps and working on HT valve amps, please don’t. Instead take to an experienced amp tech.
Best,
Mike
Many thanks Mike for such a prompt and thorough reply, I will take your advice to check the heater circuits, failing that my experience is not sufficient to proceed further and I will return the amp to the owner with advice to find a technician with a lot more know how who can fix it. Regards Chris.
There is a great guide to debugging amps here. It might give you a few more ideas.
http://www.geofex.com
SAME…..I have a MKI which I got VERY cheaply from a guitar center that dumped it…..someone dropped some thing on it and busted three of the Pot on the clean channel. I got it for 250….LOL. THEN I went to the website, emailed the Trace Elliot team…and they mailed me the EXACT pots original to the unit…Same experience where one of the hands on techs there responded to my questions directly.
HERE’S why I’m posting….my diodes blew out too….charred the board only slightly.
I replaced with some from Radio Shack in a rush…but this article makes me question that decision. I really should do the right thing, and get the best diode for it
Glad to see I’m not alone in appreciating these amps…they are inspiring.
ONLY major gripe is I wish the there was a way to get the Output damper (on the back) to have separate settings for the separate channels….I LOVE the distortion channel when the Damp i up all the way (really CRISPS the low punch of the amp) but it makes the clean channel so muddy…and I am not the compromising type….so leaving it in the middle is OUT OF THE QUESTION!
Just thought you’d like to know: I own a H100 Mk 1 head, as does my friend. Both have had the 1N4002s fail. (His went in 1998!) I also repaired a C100 Mk 1 recently: 1N4002s again. All of them were 1997 vintage, and in all of them the board was a bit charred, and tracks were destroyed by the failure of the diodes.
I’ve fitted 1N4007s instead. (I had them available, and 1000V PIV doesn’t hurt.) FWIW, I reckon the unregulated rail is around 30VDC, so the PIV across the diodes could approach > 80V (2 x root-2). A bit close to the 100V rating for 4002s, I think.
None of the amps has ever failed in that area again since the 4007s were fitted.
Thanks for your comment and you are absolutely right. Higher rated diodes are the way to go – the cost difference is negligeble.