Hafler T2 - Anyone heard of this or had any experience??

[rnolan]

Hey RG, maybe think about it like this, tubes add gain, so do opp amps (in some ways the transistor (SS) version of a tube??). They all come in different shapes/sizes and amounts of gain they bring to a circuit. Eg you can use an opp amp to power your Fx/Aux send(s) on a desk to ensure each send gets good level when you split the input signal to them.  So from what MJMP is saying, this circuit is largely driven by SS opp amps with tubes thrown in to warm it all up (kind of hybrid circuit, not uncommon BTW). So if the tubes aren't doing that much of the distortion/tone, changing them will have less affect. (it will have some though).  Now you could change the opp amps to reduce squish, but that's not as easy as say going to lower gain tubes.  So another approach is go with high gain tubes (again the Mullards would be fine or whatever else you have around) and adjust it such that you have maximum tubes in the circuit.  Eg, my Ivory 5001 hybrid valve 4 ch preamp has SS circuits with a tube to warm them up. winding up the ch input puts more signal to the tubes and winding down the output balances it out (more tube less SS). Seems your gadget is similar...

[rabidgerry]

I mean that one tube is not enough to get a "decent sound".It has to do too much work.It's better to devide it over more tubes.

This thing would definitely sound  "decent" if it just did not squash the attack.  Everything else is good to my ears.

It sounds good if I use an external boost i.e overdrive in front  Not as squashed.  But then it doesn't have the same tone.

Hey RG, maybe think about it like this, tubes add gain, so do opp amps (in some ways the transistor (SS) version of a tube??). They all come in different shapes/sizes and amounts of gain they bring to a circuit. Eg you can use an opp amp to power your Fx/Aux send(s) on a desk to ensure each send gets good level when you split the input signal to them.  So from what MJMP is saying, this circuit is largely driven by SS opp amps with tubes thrown in to warm it all up (kind of hybrid circuit, not uncommon BTW). So if the tubes aren't doing that much of the distortion/tone, changing them will have less affect. (it will have some though).  Now you could change the opp amps to reduce squish, but that's not as easy as say going to lower gain tubes.  So another approach is go with high gain tubes (again the Mullards would be fine or whatever else you have around) and adjust it such that you have maximum tubes in the circuit.  Eg, my Ivory 5001 hybrid valve 4 ch preamp has SS circuits with a tube to warm them up. winding up the ch input puts more signal to the tubes and winding down the output balances it out (more tube less SS). Seems your gadget is similar...

Maximum tubes?  How do you mean?

Could it be that using a higher gain Tube in p1 would mean more headroom and therefore not pushed as crazily as a lower gain tube?

I could swap an op amp no problem, depends where it is and how easy to get to it.  I've done it before.  It's just like this right?

http://i.ebayimg.com/images/i/260751535896-0-1/s-l1000.jpg

Here is an internal of the Hafler


image of the whole thing
http://medias.audiofanzine.com/images/normal/hafler-t2-254403.jpg

[MarshallJMP]

Is that a pic of yours? Because I see some differences with the pic in the link? For one they removed the small tranny after the tubes and put some resistors in it's place.

[rabidgerry]

Is that a pic of yours? Because I see some differences with the pic in the link? For one they removed the small tranny after the tubes and put some resistors in it's place.

Ok perhaps this was lazy of my, but then how was I to know???? 

I did not take a photo of my own preamp.  I used one from online. 

So that leads a question wide open about this, what has the person done to the tranny and what effect has this modification done to the tone?

I recorded last night and there is definitley a range where this preamp can currently be used.  When pushed hard though it turns to squash fest.  And if you use an external boost you have other realms of possibilities.

Before I read MJMP's post I was about to say "ok so if I was an electronic wiz I would turn this preamp into a three tube preamp and lighten the load of T1 by having another tube"

and since I could never dream this up that will remain a pipe dream.  But this find that MJMP has noticed is very interesting and purely accidental on my part.  So the picture of that preamp above has had some sort of modification done to it.  But what?

[MarshallJMP]

Could be a factory mod, that at one point they decided to ditch the tranny.

[rabidgerry]

If only I could swap the op amp for a tube  :)

Haven't had time to check the tubes yet or swap, but recorded a little bit using a lighter setting and I still like the sound.  Not as much squash as well.

[Systematic Chaos]

If only I could swap the op amp for a tube  :)

Haven't had time to check the tubes yet or swap, but recorded a little bit using a lighter setting and I still like the sound.  Not as much squash as well.

Is there a TL072 dual OpAmp in the signal path before, between or after the tube stages? if so, I bet that OpAmp gets fed with too much input it can't handle (sonically) and thus results in that squashy sound. Replace that/those with a BurrBrown OPA2134. These OpAmps are the most clean and transparent sounding and can handle more input (<<this is not the scientifically correct statement....just my own and other peoples findings, e.g. in TS circuits, in the tube driven DV circuit of a preamp,...).

[Harley Hexxe]

Is there a TL072 dual OpAmp in the signal path before, between or after the tube stages? if so, I bet that OpAmp gets fed with too much input it can't handle (sonically) and thus results in that squashy sound. Replace that/those with a BurrBrown OPA2134 or 2234. These OpAmps are the most clean and transparent sounding and can handle more input (<<this is not the scientifically correct statement....just my own and other peoples findings, e.g. in TS circuits, in the tube driven DV circuit of a preamp,...).

    This is a very interesting subject to me. Are these OpAmps and sockets available through Mauser?

[Systematic Chaos]

Is there a TL072 dual OpAmp in the signal path before, between or after the tube stages? if so, I bet that OpAmp gets fed with too much input it can't handle (sonically) and thus results in that squashy sound. Replace that/those with a BurrBrown OPA2134 or 2234. These OpAmps are the most clean and transparent sounding and can handle more input (<<this is not the scientifically correct statement....just my own and other peoples findings, e.g. in TS circuits, in the tube driven DV circuit of a preamp,...).

    This is a very interesting subject to me. Are these OpAmps and sockets available through Mauser?

OPA2134, Mouser Part#: 595-OPA2134PA

8Pin IC Socket, Mouser Part#: 575-113308

[rabidgerry]

If only I could swap the op amp for a tube  :)

Haven't had time to check the tubes yet or swap, but recorded a little bit using a lighter setting and I still like the sound.  Not as much squash as well.

Is there a TL072 dual OpAmp in the signal path before, between or after the tube stages? if so, I bet that OpAmp gets fed with too much input it can't handle (sonically) and thus results in that squashy sound. Replace that/those with a BurrBrown OPA2134. These OpAmps are the most clean and transparent sounding and can handle more input (<<this is not the scientifically correct statement....just my own and other peoples findings, e.g. in TS circuits, in the tube driven DV circuit of a preamp,...).

I'm not sure if there is man, I have no idea about what kind there is (forgive my lack of knowledge).

What I will do is open it up myself and take some pics of my actual preamp.  And have a look and see what there is.

I reckon it's worth a shot trying to make some modification.  If it can't be helped well I shall sell it on.  Does the schematic tell us any of that information?

Busy recording these next few days however I will get a chance to get inside at the weekend.

[MarshallJMP]

There is a NE5532 before the tube stages (and for clean) after the tubes there is a LF347 but this is a quad opamp which can be replaced with the OPA 4134

[rabidgerry]

I've decided to try these mods

MJMP  is this the correct type of OP amp you suggest?

https://www.ebay.co.uk/itm/OPA4134PA-DIP-14-Integrated-Circuit-from-Texas-Instruments/292069205550?epid=1047485310&hash=item4400ae662e:g:n8wAAOSwax5Y2eGJ

[MarshallJMP]

That looks okay 

[rabidgerry]

OK so I bought that chip,  don't suppose you now what Characteristic's of it are?

Also can I swap out NE5532 with the op amp SC suggested? I have a BurrBrown OPA2134 you see.

[MarshallJMP]

yep the 2134 is pin compatible with the NE5532