russ this component setup is great. now, how many of your output lm3886 boards do you think can be strung along before the input devices need tweeking. would the control and power units handle 8 lm3886 chips in a mono configuration without overloading the control and power supplies. that would yield about 400 watts to the speaker. ie, 4x4 parallel then bridge for a total of eight. i currently run two line arrays with 20 3.5 inch drivers in each. as i add power, to a limit, the overall sound is improved dramatically. are boards ready to ship currently. anxiously waiting to get this project in high gear.
tryonziess said:
The TXD could easily drive 8 LM3886s at 100K input impedance each. The TXD should be good down to a load of around 600ohms easy. So you could theoretically drive something like 50-60 of them
Not that you ever would... You actually should be able to do more than 400W with just three in parallel for each half channel. So 6 LM3886(TPM modules) per channel. Assuming your PS is capable of supply the current.
The TXSPS would work just fine(one per channel) but you would need to calculate the trafo accordingly. Cheers!
Russ
ok, monday morning i am going to order these toys and have some growup fun. i assume every available configuration is easily spelled out. will 625 va at 25-0-25 work for the 300 plus. i have a few on hand. national does not specify more than 30 volts for multiple parallel or bpa. is there a land line number for asking detailed questions or just email and the forum. thanks
Javin5 said:
Actually I think thats an incorrect artifact. The TXPS takes the place of the LCPS in the TXO as it has a built in regulator for the TXD (that was what the LCPS was for).
We will get that straightened out.
The difference is that the dual mono has two TXPS and the stereo just one.
Cheers!
Russ
I have the stereo pair with the power supply that I had built for me and haven't even hooked up. Going different direction. Cost$126. If somebody wants them for $100 shipped email me.
drptpcpe@gmail.com
drptpcpe@gmail.com
Digesting your post, but, small bites:
TPM BOM shows a 220pF FKP2 cap for C7
Schematic in the user manual is out of date, we will get it updated ASAP. The schematic on the page is accurate. R6 is always 3.32K, no 221R alternate value.
TPM BOM shows a 220pF FKP2 cap for C7
Schematic in the user manual is out of date, we will get it updated ASAP. The schematic on the page is accurate. R6 is always 3.32K, no 221R alternate value.
Brian
Thank you for quick response.
On the new schematic it staes that R1 could be reduced, not by much though as G= (1+R1/R2) as it stands G=(1 +10/1)=11
R1 could be 9k0 to yeld 10
Lm3886 gain per data sheet should be 10 or more.
BTW I had sent some of the same questions to Russ a few days back through the DIY email. There was no answer. I have noticed a few posts about this. There may be something wrong.
Regards
Thank you for quick response.
On the new schematic it staes that R1 could be reduced, not by much though as G= (1+R1/R2) as it stands G=(1 +10/1)=11
R1 could be 9k0 to yeld 10
Lm3886 gain per data sheet should be 10 or more.
BTW I had sent some of the same questions to Russ a few days back through the DIY email. There was no answer. I have noticed a few posts about this. There may be something wrong.
Regards
Re: Brian
HI Sheldon, I am sorry for my Tardy answer, I started a reply and some how sent it to drafts instead of sending it on. I was in the midst of finishing up Opus (our new DAC) etc and have been quite busy.
Which schematic are you looking at?
I am not sure why you are computing gain like that. This is like an inverting amp for calculating gain. So 10K RF and 1K RG = 10X voltage gain.
Cheers!
Russ
SheldonD said:
HI Sheldon, I am sorry for my Tardy answer, I started a reply and some how sent it to drafts instead of sending it on. I was in the midst of finishing up Opus (our new DAC) etc and have been quite busy.
Which schematic are you looking at?
I am not sure why you are computing gain like that. This is like an inverting amp for calculating gain. So 10K RF and 1K RG = 10X voltage gain.
Cheers!
Russ
Look at page three of this document:
http://www.twistedpearaudio.com/docs/txd/txd-doc.pdf
It should answer you questions. If it does not then please post again.
Remember that with the TXO the gain of the TXD module sets the gain of the entire amp. The gain for the TPMs should stay at 11 (10K + 1K) as that has produced very good results. The gain of the TPMs only effects the voltage that the TXD has to swing (which will not be much) along with the bandwidth for the power stage, too high a gain and you loose some bandwidth.
http://www.twistedpearaudio.com/docs/txd/txd-doc.pdf
It should answer you questions. If it does not then please post again.
Remember that with the TXO the gain of the TXD module sets the gain of the entire amp. The gain for the TPMs should stay at 11 (10K + 1K) as that has produced very good results. The gain of the TPMs only effects the voltage that the TXD has to swing (which will not be much) along with the bandwidth for the power stage, too high a gain and you loose some bandwidth.
Re: Brian
Oh yes, I think i understand your post better now. That note on the schematic was made prior to me change the feedback resistor to 10K. It had bee 22.1K which also worked fine, but the 10K seems better to me.
10 is indeed the minimum gain, but the LM3886 seems quite happy with its little loop at a gain of 11. Perfectly stable.
I should have deleted the note.
I just got in from mowing the lawn so it took me a bit to recover from the heat stroke.
Cheers!
Russ
SheldonD said:
Oh yes, I think i understand your post better now. That note on the schematic was made prior to me change the feedback resistor to 10K. It had bee 22.1K which also worked fine, but the 10K seems better to me.
10 is indeed the minimum gain, but the LM3886 seems quite happy with its little loop at a gain of 11.
Perfectly stable.I should have deleted the note.
I just got in from mowing the lawn so it took me a bit to recover from the heat stroke.
Cheers!
Russ
The value of C7 and C8(TXD) are computed to give a high pass filter with RF of the TXD. 220pf is as low as I would ever go. 280pf is fine as is 330pf. The higher the value the lower the filter and the more phase shift at higher frequencies.
C6 on the TPM also forms a low pass, but you should never use it with the TXO.
The rule for the servo resistor is that it should be "at least" 10X the FB resistor. It is absolutely fine for it to be more, at least with the op amps I am using.
This is not a BPA200 so while some of the info in that document will apply, a lot of it will not.
If you use the same parts Brian supplies with the kit (adjusted for the gain you want) you will be golden.
I would not touch the TPM, leave it at G=11, just modify the TXD.
Also, while the 3.3K resistor is fine on the non-inverting input but is optional, it does not hurt to have it there, but it can be replaced by a jumper or lower value resistor. The non-inverting input of the LM3886 has a very high impedance. The TPM standalone(not TXO) is more like a regular chipamp, where you want that 3K3 to work with C7 to form a low pass to reject high freq noise etc. In TXO that low pass would cause instability and is omitted.
Let me know if there is more you need.
Cheers!
Russ
C6 on the TPM also forms a low pass, but you should never use it with the TXO.
The rule for the servo resistor is that it should be "at least" 10X the FB resistor. It is absolutely fine for it to be more, at least with the op amps I am using.
This is not a BPA200 so while some of the info in that document will apply, a lot of it will not.
If you use the same parts Brian supplies with the kit (adjusted for the gain you want) you will be golden.
I would not touch the TPM, leave it at G=11, just modify the TXD.
Also, while the 3.3K resistor is fine on the non-inverting input but is optional, it does not hurt to have it there, but it can be replaced by a jumper or lower value resistor. The non-inverting input of the LM3886 has a very high impedance. The TPM standalone(not TXO) is more like a regular chipamp, where you want that 3K3 to work with C7 to form a low pass to reject high freq noise etc. In TXO that low pass would cause instability and is omitted.
Let me know if there is more you need.
Cheers!
Russ
Brian/Russ
Thanks guys.
Things are starting to clear up.
As I see it to compensate for SE (not balanced) I have a choice to increase gain at TXD and/or TPM.
Going along with your original design you had balanced the gain
across both modules to provide the least distortion. I am inclined to maintain the ratio across both.
So again: I propose to share the gain increase across both TXD and TPM. One advantage is that in general one should have circuits running near the centre of their "happy" range. Not at the boundarieswhere things like change/stolerance on components and line voltage and loads could affect things..
What I am still concerned about is the relative values of resisters as per National Semi BPA-200. Your values are out of line but I
realize the TPM is inot in Isolation but is part of a greater loop
with ths4131.
I also realize you both have a successful build but balanced.
One thought is for me to build a SE to balanced in my preamp,
And then I could just follow your successful values.
I am working on a passive premp with only a Pearl phono with external PS. I could use 4562 with unity gain. but I would brefer not to.
Thanks guys.
Things are starting to clear up.
As I see it to compensate for SE (not balanced) I have a choice to increase gain at TXD and/or TPM.
Going along with your original design you had balanced the gain
across both modules to provide the least distortion. I am inclined to maintain the ratio across both.
So again: I propose to share the gain increase across both TXD and TPM. One advantage is that in general one should have circuits running near the centre of their "happy" range. Not at the boundarieswhere things like change/stolerance on components and line voltage and loads could affect things..
What I am still concerned about is the relative values of resisters as per National Semi BPA-200. Your values are out of line but I
realize the TPM is inot in Isolation but is part of a greater loop
with ths4131.
I also realize you both have a successful build but balanced.
One thought is for me to build a SE to balanced in my preamp,
And then I could just follow your successful values.
I am working on a passive premp with only a Pearl phono with external PS. I could use 4562 with unity gain. but I would brefer not to.
BRIAN/RUSS
my last post crossed yours.
I am hanging fire on parts orders because of my confusion,
One thing I can't find is the phoenix terminal posts you are using there are plent at Digikey and mouser but not exactmatch to yours (at least I can't match).
I have spent too long on this alone.
my last post crossed yours.
I am hanging fire on parts orders because of my confusion,
One thing I can't find is the phoenix terminal posts you are using there are plent at Digikey and mouser but not exactmatch to yours (at least I can't match).
I have spent too long on this alone.
Digikey:
277-1667-ND
277-1578-ND
I would leave the tPM at our standard gain (11) and use the following on TXD:
Rg = 1.1K (matched to 0.1%)
Rf = 22.1K (matched to 0.1%)
That will give you 20X gain in the TXD and you will be very happy. These are standard values in our TXO kit (for TXO 20x). My balanced TXO is running at 10X (Rg = 2.21K).
277-1667-ND
277-1578-ND
I would leave the tPM at our standard gain (11) and use the following on TXD:
Rg = 1.1K (matched to 0.1%)
Rf = 22.1K (matched to 0.1%)
That will give you 20X gain in the TXD and you will be very happy. These are standard values in our TXO kit (for TXO 20x). My balanced TXO is running at 10X (Rg = 2.21K).
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