Welcome, Guest. Please login or register.

March 08, 2021, 04:07:01 PM

Login with username, password and session length

Recent Posts

 

Author Topic: Hybrid  (Read 16541 times)

mensur

  • Master
  • ***
  • Posts: 94
  • Chip Points: 5
    • View Profile
Hybrid
« on: August 05, 2009, 06:33:17 AM »
Hi guys,
I made a hybrid amp. Roccaforte preamp and 100W MOSFET (TDA7294) SS amp.
I designed PCB (for the rocca and TDA):
Roccaforte Schematic & PCB.pdf
Some pics:







But I have a problem, I have noise and hum in the amp, here is sample:
Rocca Problem.mp3
and here is layout how i connected the amp,internally:
Rocca Layout.pdf

What can be the problem? Help me to solve this.

« Last Edit: August 05, 2009, 06:38:29 AM by mensur »

phatt

  • Legendary
  • ******
  • Posts: 2182
  • Chip Points: 266
    • View Profile
Re: Hybrid
« Reply #1 on: August 05, 2009, 08:00:02 AM »
Hi mensur,
              I assume you are reffering to the hum on that mp3?
From what the drawing shows it looks like you are useing AC voltage for heater supply. (from Trafo2, red and black wires)
Then Welcome to the wonderful world of Valve Amps and the manditory
*AC Heater hum* :'(

That is one good reason why you don't build Valve circuits on PCBs unless you are useing *DC heater supply*

The only way you can improve AC it is to use dedicated twisted heater wiring.
Even with DC heaters it takes a lot of know how to avoid hiss and hum when useing valves.
I can't seem to find the schematic but looks as if it uses two massive gain stages with that silly Trainwreck 10k cathode trick on V3.
Works on Trainwrecks because the guy knew about the importance of layout design. Add another gain stage like your's and it's impossible to be able to turn the knobs up.

General rule of thumb I use ; Any more than the classic Valve count and you are going to need to rethink the heaters. (ie, DC)
Even the cloners of all valve trianWreck type Amps run into trouble.

Sorry but I very much doubt that this circuit will work for you.
Maybe have a read of my comments here,, saves me saying it twice.
http://www.ssguitar.com/index.php?topic=1151.0
Phil.


phatt

  • Legendary
  • ******
  • Posts: 2182
  • Chip Points: 266
    • View Profile
Re: Hybrid
« Reply #2 on: August 05, 2009, 08:12:21 AM »
Almost forgot! 
IF That tone stack is running directly to the TDA7294 then you need a high imp buffer stage otherwise you are wasting your tone stack, it will be hardly working. Phil.
« Last Edit: August 05, 2009, 08:13:24 AM by phatt »

mensur

  • Master
  • ***
  • Posts: 94
  • Chip Points: 5
    • View Profile
Re: Hybrid
« Reply #3 on: August 05, 2009, 09:52:22 AM »
Almost forgot! 
IF That tone stack is running directly to the TDA7294 then you need a high imp buffer stage otherwise you are wasting your tone stack, it will be hardly working. Phil.
Hi phatt, it's not the trainwreck it's Roccaforte HG100 (4 gain stages preamp):
Roccaforte Project.pdf

Well, I think it's problem with ground, as I'm turning the Master pot squiling and hum become less or opposite.
Actually tone stack is very responsive

phatt

  • Legendary
  • ******
  • Posts: 2182
  • Chip Points: 266
    • View Profile
Re: Hybrid
« Reply #4 on: August 06, 2009, 08:42:39 AM »
A real one here:
Notice the shielded cable,, twisted heater wire, Shield around input socket, Coax used for tone pots, and intereconect points, large distance between sensitive components.

http://forum.metroamp.com/viewtopic.php?f=3&t=23078

Also From Roccoforte Amps own site; Click on optional extras ,,, note the $200 fee for DC heaters.   Trust me you need it.

BTW your signal without hi imp buffer will be roughly 7 times SMALLER assuming the TDA input Z is say 20/30k with a good chance of bass loss.
The preamp was built for looking into a Hi imp Not a low one.
Yes the tone still works but nowhere near as good as it should.
Just thought I would mention it and YES I did go to the trouble of simulating it before I opened my mouth.

No it's not a TW amp but the *idea* of 10k cathode R on V3 comes from TW,,
It forces half wave clipping which enhances the Power tubes as they go into compression but on it's own into a super clean SS poweramp,,, I doubt it's worth/usefulness. A preamp of triodes does not maketh the Tube sound,,
That comes from the power tubes.

Without power tubes being compressed via the big signal swing from the triodes (which I should add is comparitively clean cept for some half wave clipping) then it won't distort like an all valve amp.
My guess is a bit of half wave rattle which is way to big for the opamp/poweramp input and the power chip is just slamming into the rails which will be distorting and MAY?? sound ok I guess.
From my own experience I'd go with one Ax7 unless you have a tube power stage.

Your setup has a 300 volt supply and those triodes won't do much distorting on there own you need to use diodes if you want triodes to distort like a PP pentode output stage. Or consider the SiAB (Stack in a box) concept as it is more suited for running into SS.

Even if you fix the ground problems your board has to many tracks to close together.
If you want heater tracks pull them all down to one side of the PCB Away from everthing else.

To generalise; You can't take the front end from an All Valve Amp design and just plug it into a SSpower Amp and expect it to sound even remotely like a Roccaforte.
I respect your commitment to your idea but I'm just hinting that it might be the wrong way to do it,,,Just my say,, best of luck with it. Phil.



mensur

  • Master
  • ***
  • Posts: 94
  • Chip Points: 5
    • View Profile
Re: Hybrid
« Reply #5 on: August 09, 2009, 03:29:21 AM »
Hi,
Phil, thank you for your replays, but I fixed the problems, now, amp is quiet as dead and it's lot of rocca in the tone. I just did the hi-fi trick (that mesa do too) put 6,3VAC on diode bridge, than on a large cap, and you get 6,3VDC, it works flawless.

I'll post some clips soon.

joecool85

  • SSGuitar Admin
  • Legendary
  • ******
  • Posts: 3367
  • Chip Points: 992
  • SSG Creator
    • View Profile
    • thatraymond.com
Re: Hybrid
« Reply #6 on: August 09, 2009, 01:52:13 PM »
Hi,
Phil, thank you for your replays, but I fixed the problems, now, amp is quiet as dead and it's lot of rocca in the tone. I just did the hi-fi trick (that mesa do too) put 6,3VAC on diode bridge, than on a large cap, and you get 6,3VDC, it works flawless.

I'll post some clips soon.

I look forward to hearing your clip(s), keep us posted!
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

mensur

  • Master
  • ***
  • Posts: 94
  • Chip Points: 5
    • View Profile
Re: Hybrid
« Reply #7 on: August 16, 2009, 09:22:43 AM »
Hi guys,

I fixed the problem and here is the sample of my amp:
Ultra Sample.mp3
It was recorded with cheap PC mic.

J M Fahey

  • SSGuitar Global Mod
  • Legendary
  • ****
  • Posts: 4142
  • Chip Points: 429
    • View Profile
Re: Hybrid
« Reply #8 on: August 16, 2009, 10:06:06 AM »
Congratulations Mensur. Excellent.
┬┐What were the power amp and speakers?

Brymus

  • Elite
  • ****
  • Posts: 139
  • Chip Points: 10
  • SS amps are cool too.
    • View Profile
Re: Hybrid
« Reply #9 on: August 16, 2009, 03:49:34 PM »
If that sound clip is just the amp and no pedals then I am BLOWN AWAY :tu:
Sounds crazy, good nice heavy tone.
Is it possible to translate your PDF to English?
Sorry I only know English and little Spanish.

mensur

  • Master
  • ***
  • Posts: 94
  • Chip Points: 5
    • View Profile
Re: Hybrid
« Reply #10 on: August 16, 2009, 06:28:16 PM »
If that sound clip is just the amp and no pedals then I am BLOWN AWAY :tu:
Sounds crazy, good nice heavy tone.
Is it possible to translate your PDF to English?
Sorry I only know English and little Spanish.
Well, It was intend to be the Roccaforte preamp, but I didn't like the tone of that preamp, it was dull for my taste, and I completely redesigned it to suit my taste.
Yes, this clip is only amp, no pedals,compressor or any kind of boost,I only added slight reverb and little delay in the mix nothing else.Which thing's do I need to translate?

Brymus

  • Elite
  • ****
  • Posts: 139
  • Chip Points: 10
  • SS amps are cool too.
    • View Profile
Re: Hybrid
« Reply #11 on: August 17, 2009, 01:00:19 AM »
WOW thats a really nice sounding amp indeed then.
Very nice job.
I was thinking of trying a hybrid too.
DId you still go with 4 gain stages -2 triodes?
I have 4 stage SE amp it is a Trainwreck Francesca pre with a Marshall stage .68uf 2k7 bypass in front of that,Very high gain I was considering using that in front of my LM3886 chip but read here 12ax7s not so good for use with the SS power amp.
After hearing yours I think the tone is incredible, exactly what I am after for the dirty channel.
I was also considering using my Marshall 18 watt pre-amp all the way to include the phase inverter -
Into two 3886 chips both non-inverting BTL,wouldnt this work as well?
That way the signal is already 180 off so both chips would be non-inverting.
Or is that too much?
The normal channel is both halves of triod in parallel the other is tremelo channel.
I would just have to adjust the power rail a little to keep the V down with  the PA not being used.Or just use a different transformer.

mensur

  • Master
  • ***
  • Posts: 94
  • Chip Points: 5
    • View Profile
Re: Hybrid
« Reply #12 on: August 17, 2009, 03:50:11 AM »
WOW thats a really nice sounding amp indeed then.
Very nice job.
I was thinking of trying a hybrid too.
DId you still go with 4 gain stages -2 triodes?
I have 4 stage SE amp it is a Trainwreck Francesca pre with a Marshall stage .68uf 2k7 bypass in front of that,Very high gain I was considering using that in front of my LM3886 chip but read here 12ax7s not so good for use with the SS power amp.
After hearing yours I think the tone is incredible, exactly what I am after for the dirty channel.
I was also considering using my Marshall 18 watt pre-amp all the way to include the phase inverter -
Into two 3886 chips both non-inverting BTL,wouldnt this work as well?
That way the signal is already 180 off so both chips would be non-inverting.
Or is that too much?
The normal channel is both halves of triod in parallel the other is tremelo channel.
I would just have to adjust the power rail a little to keep the V down with  the PA not being used.Or just use a different transformer.
Thanks,
You see, you could do that, but I think you wont be happy with it.
First: your poweramp is LM3886 (super clean hi-fi powermp), I'm sure that BJT's wont give sound characteristics as MOSFET's, plus mine is little distorted in front end.
Secondly, if you put the preamp signals out of phase with each other they will cancel each other on the speakers and you'll get quiet dull sound.
Use two transformers, I wound mines by myself.
Tube trafnsformer:
Primary: 220VAC/50mA
Secondary:6.3VAC/4A

Brymus

  • Elite
  • ****
  • Posts: 139
  • Chip Points: 10
  • SS amps are cool too.
    • View Profile
Re: Hybrid
« Reply #13 on: August 17, 2009, 06:53:49 PM »
I think you misunderstood my fault.
The idea was to go from the phase inverter in the Marshall to 2 X 3886 in bridged mode.
But instead of inverting one chip to get the inverted phase for BTL mode.
I would take it from the phase inverter of the Marshall 18 watt.
This ways both chips would be non-inverting.

Maybe better to use the signal before the PI and use the 3886 X 2 in normal BTL form?

Would the 3886 chips work?

And would the signal be TOO much for use as a pre amp to the 3886s as the plates are at
high V?

mensur

  • Master
  • ***
  • Posts: 94
  • Chip Points: 5
    • View Profile
Re: Hybrid
« Reply #14 on: August 20, 2009, 11:14:09 AM »
I think you misunderstood my fault.
The idea was to go from the phase inverter in the Marshall to 2 X 3886 in bridged mode.
But instead of inverting one chip to get the inverted phase for BTL mode.
I would take it from the phase inverter of the Marshall 18 watt.
This ways both chips would be non-inverting.

Maybe better to use the signal before the PI and use the 3886 X 2 in normal BTL form?

Would the 3886 chips work?

And would the signal be TOO much for use as a pre amp to the 3886s as the plates are at
high V?
That's a different story,
try the boath ways, and see wich one suits you the best.
LM3886 will do the job, but you'll have to put voltage follower between preamp and PA, because phase inverter has hi out Z. Put 1M attenuator resistor in series with power amp input, as a  protection for your IC's.