[Guile]

Cloners!
I'm in desperate need of help to save my SLO50 clone project. I don't speak enough German, so I hope English is okay.

I bought a SLO100 clone a while back that is based on the Tube Town pcb and transformers set. It sounds AWESOME. Downside is that it was put together very poorly. It failed on me several times. But still, it sounds BRUTAL \m/ I absolutely LOVE it.

So I decided to build a SLO50 and bought the pcb's from [ADMIN]Werbung entfernt[/ADMIN] and bought the 50 watts transformers [ADMIN]Links entfernt[/ADMIN]

I'm fairly new to making cloned amps (only made a Fender Reverb Deluxe) so it took a long time to make it work. It works now but it sounds bad: flat, shrill, harsh and unforgiving. Not at all like the badly made SLO100 which sounds radically different: very transparent, sparkly with tons of bass without being shrill but with great bite. It sound already great with all the pots at noon. I can't dial in ANY acceptable sound with the newly build SLO.. The middle pot is the most useful for more body, but still no match for the poorly built SLO100.

I checked all the parts and their values and all voltages but can't find an error.
Swapped tubes many times and always biased correctly.
I also compared everying with the SLO100.

Could it be the difference in transformers?

Would love to hear suggestions
Thanks

https://www.flickr.com/photos/115176149@N03/

[Stone]

Hi Guile

Sad to hear about your build … :-(

I am using InMadOut transformers, too, and never ever had any trouble with them and also in my opinion the OTs are sounding pretty good. And at least I think Dirks transformers are also IMO or based on them.

The only thing I get in mind is about the colour code of wiring of the transformers, which change in the past as I had to notice on a MA100 set.

It is hard to guess, what you mean by "harsh" and "shrill" - is there no bottom end (bass) at all? Have you checked the amp by plugging the guitar directly into the FX return? How is it sounding then?

If the sound has kind of "crackles" I would assume there is a broken or bad soldering point; also the VTL are a source of problems - have you checked their resistance within the different channel switching positions? Maybe you have crossover distortion and something is out of phase which will lead to a harsh sound (think of out of phase pickups in a guitar e.g.)?

I know about the C3 boards (I have bought one in the past) but I do not have a scheme for the C3 board - maybe you can post the scheme here? I am not sure, but I can imagine, the numbering of the different parts does not match the scheme of Joachim (which the TT pcbs are based on).

Can you post some more detailed pictures? I had a look to them on Flickr, but some more in higher resolution would be nice.

Regards, Stone

[Guile]

Thanks for your reply Stone.
I will do my best to give you information.

The amp has almost no bottom end and is very trebly and midrangy, not smooth, unfriendly to the ears..

I put a guitar in 'return' and got weak sound (not loud) with humm.

Please explain how I could test the octocouplers.

I used several sources to build the amp (see attached). This led to confusion, but I compared it to the poorly build TT SLO.

I will take more closeups and post them on flickr asap

[Guile]

I added more pictures to: https://www.flickr.com/photos/115176149@N03/?

I also attached the colourcodes of the transformers. Could I have made a mistake? Please check if you can.
Thank you!


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[Stone]

Hi

I am not sure, if the schemes match the C3 board, but I know them all - more or less by heart Especially the one drawn by Joachim, which is the basis for the TT boards (as I said before).

If you plugin the guitar to the fx return you should have low volume, but I think it should not produce any hum. If it does and it sounds like mains voltage hum (50 or 60 Hz) then I think there is a wrong ground connection on the fx return - you could check the preamp by connecting fx send to a separate power amp (or connect it to fx return of the SLO100 you got); how does the preamp sound?

The optocouplers can be checked pretty easy with a multimeter - if you refer to the layout the connectors on the "tube" side of the board are the resistance part of the couplers as the opposite side of them is the voltage connection.

If you switch to clean then VR1 (according to SLO 0.7 scheme of Joachim) and VR4 should measure only a few ohms (I do not have the data sheet at hand, but Vactec should measure around less then 100 ohms), VR2 and VR3 should be around 50 meg ohms I think.

If you switch to lead the other way round: VR1 and VR4 are of high resistance as V2 and VR3 are of low resistance.

Everything around a few kilo ohms when switched will be too much (also check the voltages at the optos … not sure about the Vactec, but they need 1,5 to 2,0 volts in order to switch correctly I think).

If the preamp is working correctly (as mentioned you could check this by using fx send) the power amp may be wired wrong - how is it sounding if you adjust presence and (if installed) depth?

I still assume that there is a mismatch in the parts labeling of the C3 board and the schemes you used - I will check it tomorrow as I have got a board, too (as mentioned).

I will have a look at the pictures

Regards, Stone

[Stone]

Hi

First guess as it is hard to follow the traces / wires in the pictures: you did not set up a PE wire from the mains connector to chassis, but you connected "black" (CT of the secondary side of the power transformer) to the mains connectors "middle" eye?

If so ...

You need to / must set up PE connection (!) - a green/yellow wire from "middle eye" of the mains connector to chassis and to connect "black" (CT) to chassis ground connection (you set up a lug with several ground wire connection near the plastic clamp).

Not sure, but I think I misunderstood the use of the C3 board - you have used the TT boards and transformers for your 50 watt model? If so, the scheme of Joachim (SLO 0.7) is valid.

Regards, Stone

[Stone]

Hi

Hard to follow the wires of PT … do me a favor and check them again.

As far as I can see there is a brown wire running from PE tap of mains connector to chassis star ground next to plastic clamp, right? Should be green/yellow wire and must be placed with a separate screw and lug near mains connector to chassis (afaik).

CT (Black) of heater connection goes to? Is it connected to ground / chassis?

What about BIAS voltage?

Hm …

I would recommend to clean it up a little bit concerning wire layout, length and wire color code (PE is a must in green/yellow with separate connection).

After that I would try to run the preamp by using FX send of the SLO50 into the power amp by using FX return of the SLO100 and have a "look" if it is still not sounding.

If it does sound the right way there must be a fault from FX return into power amp section of the SLO50.

Regards, Stone

[Guile]

Thanks Stone.
I added a new picture: https://www.flickr.com/photos/115176149@N03/?
I believe the PE is wired correctly? If not tell me.

You are right about the colourcodes
Bias voltage= 45
CT (Black) heater connection is connected to ground / chassis. could you please check TASLO5.pdf and TUSLO50.pdf I have doubts if I have interpreted the different wires/colours correctly!

[Athlord]

Hi,
at a first glance your cable laying is horrible! 
Most cables are too long: especially the red cables - which go to the pre-stage tubes.
As a beginner you should use different colors for the cables, which makes the error search considerably easier.

Please remember, this is a high voltage device!
There is no room for interpretation:

CT (Black) heater connection is connected to ground / chassis. could you please check TASLO5.pdf and TUSLO50.pdf I have doubts if I have interpreted the different wires/colours correctly!

You have to know what you are doing!

It's better if you rebuild the AMP step by step.
Ask before you do something that you do not know if it is right.
This is the best solution.
At the end you will have a functioning AMP which is also great to watch. 

Regards
Jürgen

[Stone]

Hi Guile

PE must be connected to a separate screw on chassis; it will work this way, but afaik it is not allowed to connect PE to ground lug together with other ground wires any longer.

The wiring seem to be ok - the new photo clears it up a bit to me.

According the datasheet you should have purple-grey-black-purple as 0,5 mm² wires which is HT and BIAS tap, wires with 1,5 mm² and brown-black-brown which is heater with 6 amperes and pink-black-pink for heater number 2 (with 3 amperes).

Primary side is white-blue-grey-brown - I think with 0,5 mm².

Heater centre taps (black) can be connected to ground directly.

According the last pictures it looks connected in the right way (I can guess from the other pictures where the black ones are connected to).

I went through your posts: the 50 one has been build with the C3 boards. I would recommend to check the preamp the way I described (connect fx send of the 50 one to another fx return, e.g. of the 100 SLO) in order to see if it is a power amp related problem.

Also it would be interesting to check voltages before and after anode resistors of the preamp tubes; same to cathode resistors - I remember mixing up resistor two or three years ago and my amp had nearly no volume at all (mixed up 2M2 with 2k2 ...).

Again, how is the amp sound if you turn presence and depth controls?

Regards, Stone

[Stone]

Hi,
at a first glance your cable laying is horrible! 
Most cables are too long: especially the red cables - which go to the pre-stage tubes.
As a beginner you should use different colors for the cables, which makes the error search considerably easier.

Please remember, this is a high voltage device!
There is no room for interpretation:You have to know what you are doing!

It's better if you rebuild the AMP step by step.
Ask before you do something that you do not know if it is right.
This is the best solution.
At the end you will have a functioning AMP which is also great to watch. 

Regards
Jürgen

+1

Jürgen is right - a re-wiring of the power transformer stage would clean up a lot ... and most of the times the fault is erased, too.

Regards, Stone

[Stone]

by the way ... are those boards the actual ones of C3? I have got a green silked one and it is about 2,4 mm thick with a very accurate labeling of the parts on it

[Guile]

Hi, many thanks for taking interest in my project.

Have to admit that I did not expect this amp to be so complicated. I took great care in sourcing the parts and took my time to put it all together..
In my defense, the wiring looks messy but since it sounds so bad I did not yet tidy things up. I like it to look good too (within reason, electrons don't care if they wear a tie).

I ran the SLO50 (+ guitar) send into return of the SLO100. I have to open up the master and preamp of the SLO100 to have audible sound. Volume is very weak and thin with a hum.

Can you see from the picture if Send/Return is correctly wired? Jacks are well isolated from the chassis btw.

The pcb's are 100% C3 amps.

I will take care of the PE wire (separate screw on chassis).

The presence and depth controls work, but presence gives even more highs and depth does almost nothing.

Rebuilding the amp sounds like a good idea. Please tell me how to proceed  re-wiring the power transformer stage.

[Guile]

I compared the voltages of the two amplifiers on both PA and TS and I see no major abnormalities. What I did notice is that the new SLO has +/- structurally 10% lower voltages. I also noticed that the standby switch of the SLO50 is 470V and 375Von the SLO 100.

[Guile]

I made a couple of quick samples of the the two Slo's. The first riff is the SlO100, the second is the SLO50.
All pots are dialed in at 12:00.

https://soundcloud.com/guilese/comparison-slo-clones

To my ears the SLO50 sounds like a Behringer amp...