Using a left over half of a ECC83 in AB763 style amp

[finkaudio]

Hi,


now that I successfully implemented the Trem-O-mator, I have one-half ECC 83 left to play with
I would like to use it as a cold clipper gain stage, but I'm wondering what is the best place for it.

Here is how it is implemented in a Trainwreck:



Here is the schematic of my amp:



I found one video with this modification on a Bandmaster style amp.... looks he used the Trainwreck version.

What do you think is the best place to add? Just in front of the Master Volume or as a third stage in the normal channel? This channel gets never used and so I'm wondering if I can make a sort of lead channel. The nice side effect would be that I can parallel both channels. The amp with Reverb and Tremolo and MV is a lot more complex and it's not clear to me how to do it the best way.

Any advice on how to implement?

BTW, I looked at the other videos of this guy and he obviously started now designing loudspeakers. Well, I'm a speaker engineer and that is my profession and to be honest, I was shocked about how many things he said and did are not really what you would do as a speaker engineer.
If it comes down to Guitar amps with tubes, I'm more a hobby guy and I'm really scared I know as little as this guy knows about speakers. So would be nice to have some extra input   


Thanks and best regards from Germany

Karl-Heinz

[tubeswell]

FX loop recovery stage in a parallel FX loop? (with the FX send from the cathode of the tone stack recovery stage's cathode going to a tip-switching jack wired to the ground side of the cathode bypass cap, so that the bypass cap doubles as a coupling cap to the FX send when a jack is plugged in). That way you can either run an FX loop or plug a cable between the send and return and use it for a parallel gain boost.

[tubenit]

Another option is to use the triode on a mini-toggle DPDT or a relay switch as a boost.

With respect, Tubenit

[pdf64]

I would go with the 'Trainwreckise the normal channel' option. It'll put both channels in the same polarity if nothing else. Maybe put a switchable potential divider on the output to even up the gain between the 2 channels, whilst still leaving the boost option available.

[finkaudio]

Thanks to everybody for the suggestions.

I have started now adding a cold clipper to the Normal channel and it works so far. Did not really optimise the gain between the stages, but changed a coupling cap to get what I want. The cold clipper with 10k Cathode resistor does not do that much gain and it's close by the MV.

I got some ticking from the Tremolo, but that was obviously coming via the B+. Changed to a node down the line, added another RC  and the ticking was completely gone.

I can now parallel the channels and this is really fun to dial in some clean tones and mix it with the pumped up Normal channel on. I can leave the stage in and the amp looks like a standard one with no additional holes. I might do the mid potentiometer mod (25k) and maybe a TS list  via a pull-out switch.

I need to look for a program to use for schematics with defined tubes and monster components (compared to SMD parts we normally layout here). so I can post schematics as well.

Thanks again for help and advice.  I'll do a few measurements later as well. I have an Audio Precision here, but I think I can do it more simple with a soundcard and a program running a spectrum analyser. Just need to think about a protection strategy for the input to avoid frying the soundcard 

Best regards

Karl-Heinz
 

[shooter]

I was shocked about how many things he said and did are not really what you would do as a speaker engineer.

it's the web, reality doesn't count, clicks do 

[finkaudio]

it's the web, reality doesn't count, clicks do 

Yepp, normally I do not visit forums about speakers.....can not stand it. Some years ago, I tried to offer help on some DIY forums but got beaten up most of the time. They knew everything better and never wanted to listen. Just repeat BS often enough and it is getting the truth  I know this problem is everywhere and that makes it not easier for the good forums.

ATB KH

[finkaudio]

Hi,

I played with the 3rd Gain stage in the Normal channel and here is what I ended up with:



I'm not sure if my choice of voltage divider was any good (because of the mixing resistors), but so far, I could balance the level with the Vibraoro channel and have the cold clipping starting early enough.

Any idea how to make it better? Guess I need to start simulating....just time is a bit restricted for the moment.

Best regards

KH

[pdf64]

Did you tinker with the coupling cap value between 2nd and 3rd stage? Was 2nF in post #1, now 47nF..

Have you checked it with the trem running? I wonder if any oscillator signal breaks through to the other triode section? It may just be memories of bad experiences with a wonky tube that exhibited that kinda thing.

[finkaudio]

Hi,

the 2.2n is part of the Trainwreck preamp. The Guyatone always had 47n. But I might play with it, once I know what speaker I`ll use. The original Guyatone is a bit loose, the Jensen Neo tighter and my 3rd option is a JBL Alnico - but did not try it yet.

Originally, I used the same power supply node for the additional gain stage, and indeed, I had some crosstalk. I went down one node and that removed the crosstalk. In order to get the voltage on the anode below 300V, I added another resistor and a 47uF capacitor. No sign of the Tremolo - works really nicely.

Best regards

KH

[finkaudio]

Hi,

I just did a few quick measurements to check if I halfway got what I wanted.

Below you see the level of the Normal and Vibrato input, with and without bright on. The Vibrato Channel has the Tremolo switched off for some extra gain. All tone controls on 5. I'm halfway OK with the response - both channels are similar in response. Would be nice to simulate and check why the Normal channel is loosing a bit over 10kHz. Not that it is important :-)



Next one shows the signal shape of both channels. Preamp gain full, MV reduced to 7.5V Output at 1kHz at the speaker output.

Normal Channel:



The cut-off top is done by the Cold Clipper and here is the distortion spectrum:




Vibrato Channel:





Now it's time to test the amp and see if I can use the extra distortion to get some extra Crunch. And I can route the two channels in parallel as well.

Best regards

KH