[Wayne1]

Occam is correct about the Teac boards. The two boards used in the TEAC A-L700P are identical. They DO NOT run one "strapped" Each board is a complete stereo amp with all parts in place. It is not very easy to reroute the traces and components to operate the TEAC boards in mono.

It would be easier to add some more holes in the chassis and put in another input jack and binding post to use the amp as a four channel.

In the A-L-700P the board for the center channel was originally designed to have the second channel power a "subwoofer". Along the design process they wisely decided that 30 watts is not enough to use for most bass drivers. so they left the channel unconnected. For a company as large as TEAC is, it is far cheaper to use one board design than spend the money it would take to design and build a second amp board for such an inexpensive product.

If you feel that you want to run the Teac as a mono-block, I would suggest that you use the L/R channel board and pull the center channel board. The L/R board is further away from the PS.

[ludavico]

Wayne, does the unconnected channel on the center channel amp board draw any power?  

If it does, is there an easy way to disconnect it, so that the power supply is used by only one channel?

Thanks,
John

[lcrim]

Having experimented quite a bit, Wayne's above post re: running in the monoblock mode and using only the L,R board has provided the best sound for me.
Removing the pots board and soldering in a jumper between an RCA input and someplace in the signal path to the amp input also provides an improvement, though not on the order of removing an amp board.
I'm not sure that power cable replacement offered very much improvement nor that shielding the amp board  w/ copper has helped much.  Perhaps the cable needs to be of higher quality or the copper needs to be thicker.
Using the L,R slot does get the amp board a bit more away from the power supply and that may be the important criteria.  
Giving the unit some time to 'burn-in" seems to offer as much improvement as anything else.  
I am using a tube preamp with 20 dB gain and this combination with my speakers, Sonus Faber  Concertino Homes, provides a load that is pretty friendly to the Teacs.  
I think its time for me to treat my listening room because thats now the area where the biggest improvements for dollar spent lie.

[Wayne1]

The Tripath chipset used in the TEAC is a 2 channel amplifier. It has one pin for power input. You cannot turn off one channel alone.

I would suggest that folks should be more concerned about the quality of power going into the TEAC. Using a balanced power or isolation transformer will improve the sound more than most "tweaks". Using a power filter that will isolate the noise on the line form the TEAC and prevent the noise the TEAC's power supply produces from "infectiing" the rest of your components will also benfit the overall sound.

Using a power cable designed around a twisted pair will improve noise rejection more than the parallel construction used in the stock TEAC cord. I do not feel that shielding a power cord helps things. Using a quality wire with a better dialectric than PVC will yield more of an improvement, IMHO

[ludavico]

Copy that, Wayne.

Thanks for the info.

John

[sluggo]

It is not very easy to reroute the traces and components to operate the TEAC boards in mono.

It's trivial.  There are no component changes, and you don't even have to modify the amp board.  The outputs of the unused channel are already brought to the main board, where they can be connected to the other channel at the 7-pin connector.  Two 1-inch wires.

It would be easier to add some more holes in the chassis and put in another input jack and binding post to use the amp as a four channel.

If you want a 4-channel amp then that's one way to go, sure.  I was describing how to make a stereo amp.

In the A-L-700P the board for the center channel was originally designed to have the second channel power a "subwoofer". Along the design process they wisely decided that 30 watts is not enough to use for most bass drivers. so they left the channel unconnected. For a company as large as TEAC is, it is far cheaper to use one board design than spend the money it would take to design and build a second amp board for such an inexpensive product.

Teac would not have to design a second amp board for a mono center channel.  They already have a board that works fine for that.  And if they wanted to make it cheap, they would depopulate the unused channel, common practice in the industry.

[Occam]

The circuit you refer to is appropriate when designing a board for paralleled outputs.  It eliminates duplicated parts and saves the manufacturer money.  For whatever reason, Teac has populated the outputs of both channels on the center channel board even though only one channel is used.  Since my comments are directed toward people who want to mod their existing Teac (as opposed to designing their own amplifier), it seems more appropriate to describe what can be done with the existing circuit.

The reason for the simplified filter scheme in the Tripath's PDF schematic for paralelling outputs of the 2050 is not the savings of monies, their methodology has sound technical rational -

Indeed, the circuit is simplified, as we only use one channel's input opamp and modulators of the 2 on the TC2000 chip and both channels of the TK2050 ouput chip. You also halve the componentry on the output filter, ect... Yes, it offers a potential savings with reduced component counts (or better components?), but more importantly, a simplified and technically superior implementation. You don't have to deal with the distortions of both input/modulator not matching. Tripath's method yeilds better distortion and noise characteristics.

If you shift from stereo to paralell as you describe you will shift the cutoff frequency of the 2nd order output filter by a factor of 1/SqRt(2), .707, as well as change the characteristics of the filter's load dependant Q and the resulting audio band phase shifts. The 2 channel's output and Zoebel caps are now in paralell. Page 8 of the TA2050 pdf -
http://www.tripath.com/data.htm

The subjective (and objective) sonic signature will be different in your modified amplifier, with a loss of 'air'. This is not 'Rocket Science', this is high school algebra. No doubt,  many might find that change in the target response utterly beguiling [some of my fondest aural memories are of listening to an 'All American 5' AM tube radio with its single ended output through a 4" speaker...]

Paralleling two fully populated outputs doesn't change the current through any particular inductor

This is true.  At bass frequencies the current through those smt inductors have its most deleterious effects. Your scheme will not exacerbate it. It will saturate at the same point in the B-H curve and suck just as much as it did previously. Give the 'challenges' as described above, one has the opportunity [admittedly more complicated your tweek] of implementing the paralelling properly and using a properly specified inductor. If your speaker cannot produce really deep bass(and presents a high impedance at low frequencies), it might not be a substantial concern.

That being said -
Your  paralell mods (as well as the others) are certailnly worth a try and quite interesting.

RTFM  
I look foward to your report on the progress of your modifications.

[ludavico]

"Monoblock" Teacs are up and running, finally.

Geesh, stone cold (in fact one of the Teacs is right out of the box) the twin little buggers kicked my mid-fi reference amp, an Amber Series 70, into the weeds.  

Dynamics, clarity, fun-factor...Nolo Contendere.  

The Amber isn't high-end, but isn't exactly chopped liver neither.  

Ta,
John  

PS - Mods include: L,R amp boards pulled, inputs pots removed. Everything else is stock (for now...  )

[sluggo]

As far as "shoot-thru" goes, remember that these currents are affected by two sets of L/C filters.  At idle, these currents are down 40dB.  At full load, more like 20dB.  There is very little energy and nearly all of it is dissipated in the inductors.

By the way, these are not SMT inductors, they are simply wound on shielded cores.

Yes, the zobels are compromised somewhat, but they are only there to damp peaking in main filter when there is no load attached.  My guess is that the readers of this august forum know enough not to turn on ANY solid-state amplifier without a load attached.  If not, you know now.

As far reporting on my progress, I can tell you that I've been running two different Tripath amps (the 1101 and an earlier version of the 2050) in this sort of paralled configuration for just over three years with no problems.

Reading the datasheet and understanding the recommended circuit is good advice, and I recommend that to anyone considering modifying their amps.  Blindly following the advice of anyone without understanding the basics of what you're doing is rarely a good idea, and I'd say this is applies especially well in this forum, where you have 137 different people telling you that they have the world's finest power cord.

And Occam, I'll read the datasheet again if you promise me you'll make a serious effort to go out and get laid.

Have a nice holiday everyone,

sluggo

[mcgsxr]

And Occam, I'll read the datasheet again if you promise me you'll make a serious effort to go out and get laid.

Sluggo - thanks for the tips on how to configure Tripath amps, and for sharing your experience with them.  As for this quote, that's not really necessary is it?

In any case, yes, happy thanksgiving to all my US friends!

[sluggo]

And Occam, I'll read the datasheet again if you promise me you'll make a serious effort to go out and get laid.

Sluggo - thanks for the tips on how to configure Tripath amps, and for sharing your experience with them.  As for this quote, that's not really necessary is it?

You are, of course, correct about that.  I overreacted to what seemed a rather preachy tone from the poster.  It was inappropriate, and I apologise to the forum for any offense taken.

Cheers,

Sluggo

[Occam]

Sluggo,

No need to apologize. I rather like the bargain.   Consider it a done deal.
(to be continued....)

[Occam]

As far as "shoot-thru" goes, remember that these currents are affected by two sets of L/C filters.  At idle, these currents are down 40dB.  At full load, more like 20dB.  There is very little energy and nearly all of it is dissipated in the inductors.

By the way, these are not SMT inductors, they are simply wound on shielded cores.

Yes, upon rereading my post, I realized that 'shoot thru' is not a large problem. This is why I edited out that comment over 3 hours prior to your responding... (You can look at the timestamp of my editing and your post for verification). If you get interrupted while composing a reply, or if it truly take you 3+ hours to write a response, I'd suggest you use the 'preview' button to view your response and see the current state of prior posts,

Yes, the zobels are compromised somewhat, but they are only there to damp peaking in main filter when there is no load attached.

I don't understand your comment that the Zoebels would be compromised. Specifically, the paralelled Zoebels, when driving a 4 ohm load are going to have the same characteristic as the unparalelled Zoebel when driving an 8 ohm loads. Likewise, the paralelled Zoebel  will exhibt twice the attenuation when driving an 8 ohm load. Tripath does an excellent job with regards to output stability. (Nor is the sole role of a Zoebel to provide stability when no load is attached)

My guess is that the readers of this august forum know enough not to turn on ANY solid-state amplifier without a load attached. If not, you know now.

Piffle... your statement is so off base that I'll go so far as to say BALDERDASH!!! I believe that very few of the 'readers of this august forum' are from the BIZZARRO dimension. I know of no commercial designs, nor any competent DIY efforts that would exhibit instability with no load attached. Didn't you just post that Zoebels addressed that issue?
 

As far reporting on my progress, I can tell you that I've been running two different Tripath amps (the 1101 and an earlier version of the 2050) in this sort of paralled configuration for just over three years with no problems.

I've no doubt that you find your mod superlative. From your perspective the increased power and drive capability might well outweigh the increased noise and distortion over that of the standard stereo implementation.

Reading the datasheet and understanding the recommended circuit is good advice, and I recommend that to anyone considering modifying their amps. Blindly following the advice of anyone without understanding the basics of what you're doing is rarely a good idea, and I'd say this is applies especially well in this forum, where you have 137 different people telling you that they have the world's finest power cord.

Indeed, understanding the datasheet is quite important, and that extends to the equations presented. If one lacks the discipline/background to do so analytically, you just need to get a calculator and work out a few examples numerically to understand the implications of various mods. But the backgrounds and experience of the posters on this board vary tremendously; nor is it a sin to not be quantitatively oriented. But if someone comes to these boards and in their first post states -
"I have some experience with the Tripath parts and can offer some advice to those interested in modding theTeac amp........"
that person is clearly stating they can 'talk the talk'. When that person goes on to make comments, suggestions, responses. etc.... It is not unreasonable for their 'product' be evaluated by whatever metric the individual reader uses to evaluate whether that person can also 'walk the walk'.

And Occam, I'll read the datasheet again if you promise me you'll make a serious effort to go out and get laid.

Sadly, I think no matter how many times you reread the datasheet, for whatever reasons, you will not apply the discipline to understand the importance and usefulness of quantitative techniques.
Nor does the character shown by saying the above from the anonymity of a keyboard surprise me. What else should I expect from someone who 'a priori' discredits all other posters with -

"...I'd say this is applies especially well in this forum, where you have 137 different people telling you that they have the world's finest power cord."

Why in heavens name are you bringing up powercords? What about powercords puts your knickers in such a twist? Has my reccomendation of the $6 Volex in other threads caused you pain and suffering? Did you actually count 137 different people discussing the worlds finest powercord? If so, I suggest that you might better spend your time relearning high school algebra.

Warmest regards.
Occam

[Occam]

In summary -

I would like to say that the mods discussed in Sluggo's first post on this thread, Page 14, are quite interesting, both his paralell mod, and his comments on the power supply as well.

Specifically, although the paralelling of 2 for the channels enabling higher power into a lower impedance is not 'ideal', it should work. Whether the higher distortion and noise of this simple mod would be subjectively different from the Tripath preferred method, I don't know.

This mod, with the implicit paralelling of the capacitors in the output filter will change (lower) the cutoff freqency of the output lowpass filter. And the Q, shape, of that filter will also change. For a 4 ohm load, the Q will lower (becoming shallower), and for an 8 ohm load, that filter will have a higher Q. and become slightly peaked, but the increased efficacy of the paralelled Zoebels, should largely compensate. I see no reason why this mod would cause instability in the Teac, either with speaker attached or unattached.
It will be difficult to discern whether whatever improvements are subjectively percieved are due to increased power or the change in the filter effect on the frequency/phase response.

But as Sluggo said, this approach to paralelling is far easier to implement on the Teac than the preferred Tripath architechture, and for those 'married' to the Teac who need that incrased drive, its worth a shot...

[albee]

You "pros" are talking about quite a few mods here.  Me, I'm a complete dunce when it comes to circuits and soldering.   The fact that I pulled the center channel board without mucking things  up is notable.  Now, I heard a "significant" postive difference after doing that.  Is there anything else I could do that doesn't require EE proficiency or sending it out to a pro?  Should I even bother?

Would pulling the volume pots be the next logical thing and will I notice a difference that makes it worthwile?

PS.  If something happens to my iin-service board, will the center channel board work properly in stereo mode when plugged in?

Thanks.

[lcrim]

Albee:
Like you, most of us are into this as a hobby (obsession).  I guess a thread about what is possible from a simple DIY perspective to improve the basic goodness of the Teac units is all I ever was looking for.
I can give you the benefit of my experimenting.
Pulling the riser board containing the volume pots and soldering jumpers from the RCA inputs to the amp board inputs does provide a gain, not on the level of pulling an amp board and is certainly not as easy and foolproof.  I corrected some clumsy soldering but I might not have been so lucky.
I am going to contact Cryotweaks about getting a sheet or two of the Stillpoints material to try and block EMI interference from the power supply.  If that works, its something anyone should be capable of as well.

[gongos]

I just picked up one of these Teac's, and I have to say I'm very impressed. I haven't quite burned it in yet, but the sound is extremely good. It's powering my 626r's, which seems to be a nice match. The 30 watts are BIG, driving my 626r's in excess 100db. I can't wait to get my Response Audio modified Ming Da preamp. The build quality on the Teac is better than I expected also. It'll be interesting to see what mods, if any, companies might offer for this dirt cheap gem.

[ludavico]

Twin TEACS have been running for 4 days.  Right out of the gate they sounded impressive, but this burn-in period has been like a roller-coaster.  At times there are bursts of sheer brilliance,  but the sound can get pretty congested on complex passages.    

Of course, part of this might be psychological; my expectations went way up (too far perhaps) when I had just one TEAC.

Time will tell....  

Albee, I agree completely with Larry.  Pulling the unused amp board made a whopping difference.  I have not addressed the power cord/AC conditioning issues yet, but I think this may be significant.  I am going to wait for another ~200 hours of run-time before I make any changes.

No question though,  the bang per buck for the TEACS is off the charts.  

John


PS - Any opinions on the Auricap mod for AC conditioning?  I was not able to read up on all that is out there for this mod,  but evidently installing two .47uF 600V Auricap caps across the AC leads can provide pretty good filtering.  Each Auricap is ~ $15.00.

[lcrim]

Could anyone comment on the relative merits of using a OneAC isolation transformer or a BPT balanced power unit with the Teac amps.
The OneAC 10 amp unit is available used on Ebay for fractions of the BPT units.   Mark, you've mentioned you have one and I'm wondering which way to go.
It seems a bit looney to spend $1200 on a BPT 2, to feed a $100 amp but the 6 Moons reviews are so ecstactic that they must be pretty damn good.

[Wayne1]

The TEAC does not draw very much current. There is not any need for an isolation or balanced transformer rated that high if it is to be used with just a Tripath amp.

I do prefer the advantages of a balanced power transformer to just an isolation transformer. Here is a FAQ that talks about the advantages of balanced power http://www.equitech.com/faq/faq.html

The BPT is a good unit that does have a VERY high current capacity and lots of other goodies that you may not need for a small system.

Transcendent Sound offers a lesser expensive, lower current balanced power transformer with just one outlet: http://www.transcendentsound.com/power_supply.htm

I am working on a smaller unit for the Teac and other digital amps.

You can check out the BOLDER Cable circle for more information on it.