tcpip said:
The single bolt works fine for me for the LM1875. The chips are only a bit warm after 1 hour's play (3 of them mounted on a single heatsink with thermal paste) and sound great, although I've got a fairly small room (11ft x 12ft x 10ft) and I don't play at ear splitting levels 😀. IMO you'd need a really BAD contact to get the chip so hot that its protection kicks in.
On the other hand, the LM3886 is wider than the LM1875, so maybe you have a point there ...
- Ashwin
You're right... a lot depends on the listening levels and (most important) the speaker efficiency. And even there, the LM1875 is a nice little chip, perhaps half as wide as the LM3875/3876/3886. And if you're getting loud enough volumes with the power output of the LM1875, I guess you will not face any heat transfer problems. 😀ashwin said:
My point is more about those who complain about how the sound of these chips worsens at high volumes; such users' amps need good heat dissipation, I feel. If this angle is addressed, I think these chips will really sound very good. Let's hope when I actually build one of these, I won't be disappointed. 🙂 How do you compare the sound of your LM1875 amp to other discrete amps you like?
Gainclone
Hi Ashwin
Not having heard a a gainclone I dont know how it sounds, though various users indicate it's quite good. How do you rate yours, in comparison with other amps that you have heard? I've always believed that what you pay is what you get, though technology changes have resulted in lot of price bars being lowered.
I'm tempted though by the low entry price of this deal-$55..Problem with spouse is that with three amps at home and three speaker systems how do I justify one more toy?? Prior to this I was focussed on some upgrades and spares for my existing system-extra tubes, a good Noble/Alps pot for a preamp, and completion of existing projects etc.. some of which were planned to be brought back on my next trip.
George
Hi Ashwin
Not having heard a a gainclone I dont know how it sounds, though various users indicate it's quite good. How do you rate yours, in comparison with other amps that you have heard? I've always believed that what you pay is what you get, though technology changes have resulted in lot of price bars being lowered.
I'm tempted though by the low entry price of this deal-$55..Problem with spouse is that with three amps at home and three speaker systems how do I justify one more toy?? Prior to this I was focussed on some upgrades and spares for my existing system-extra tubes, a good Noble/Alps pot for a preamp, and completion of existing projects etc.. some of which were planned to be brought back on my next trip.
George
tcpip said:
Unfortunately, I haven't heard any other amps. I kid you not 😀 So all I can say is, I like mine! The obvious shortcomings are all due to the speakers, and that being the weakest link (along with the room) IMO, I won't be experimenting with different amps until I get my speakers to be anywhere near good.
FYI, my system is a 3 way active x-overed thingy, with bolton drivers. Well, actually the midrange is a bolton knock off called Hilton 😀 I found the Bolton midrange had a pathetic build quality, and if I screwed it too tight to the baffle, the cone seemed to get misshapen and the sound got horribly distorted
- Ashwin
Just saw your mail. Maybe sometime that is convenient we can do a comparison with my speakers and my amp(s), along with some other local friends who may want to come along. I have two ways using Scanspeaks, and another using Focals and Raven tweeters, so good speakers won't be an issue. We can also have some good test tracks played. I use a preamp, but if you want we can bypass that if your amp has a volume control.
George
George
lm1875
George,
I'm game! You'll have to tolerate an amp with no enclosure and volume control, though. I'll bring enough for two channels. There are 6 amps, and each amp is on its own PCB, so pulling out two for testing should not be a problem if a few wires hanging out are not a problem for you.
- Ashwin
gjo said:
George,
I'm game! You'll have to tolerate an amp with no enclosure and volume control, though. I'll bring enough for two channels. There are 6 amps, and each amp is on its own PCB, so pulling out two for testing should not be a problem if a few wires hanging out are not a problem for you.
- Ashwin
Ashwin,
Can u please let me know the source of the LM3875/3876/3886 or LM1875 in bangalore. And how much u paid for them. The chips that u have got, are these the electrically isolated ones or not..?
Thanks
ajju.
Can u please let me know the source of the LM3875/3876/3886 or LM1875 in bangalore. And how much u paid for them. The chips that u have got, are these the electrically isolated ones or not..?
Thanks
ajju.
Ashwin
It has RCA line out connectors I hope?
Just for info-what did two channels cost you, just the basic stuff-pcb/components/transformers/input-output connectors etc? And how much more do you estimate it will cost to complete?
George
It has RCA line out connectors I hope?
Just for info-what did two channels cost you, just the basic stuff-pcb/components/transformers/input-output connectors etc? And how much more do you estimate it will cost to complete?
George
ajju said:
Ajju, I got 3 LM1875s them from Om electronics(his last pieces) and 3 more from Ankit electronics (his last pieces as well 😀) They cost Rs 100+ each, IIRC. They're probably so rare because most people will be happy with the TDA devices. TDA2030 is only Rs. 30
Actually, comparing the TDAs to the LMs should be an interesting excercise
Mine are not electrically isolated.
gjo said:
Yes, RCA inputs hanging on for dear life to the PCBs 😉 Outputs and power are via screw type terminals mounted on the PCB.
Cost per amp: lets see...
Amp : LM1875 = Rs100+ (don't remember exactly how much), passives negligible
Power supply : Rs. 350 for a xformer (15-0-15, 5A for 3 amps, single amp should be much less), Rs 190 each for two 10,000uF 70V caps
Heatsink : Al extrusion was very expensive, don't tremember exactly how much, but a 1ft long heatsink cost a couple of hundreds.
So for 1 channel, about Rs1500 including switches, jacks, terminals etc. Two channels will double the cost if you want a dual mono setup, or about Rs150+ extra if you share the power supply.
Of course, the actual cost was more because I had several iterations of PCB layouts to get rid of hum, and many attempts for a good heatsink.
Edit : add Rs 100 for turn on speaker protection relays. The 1875s have a nasty turn on thump.
The amp is complete as of now, it only needs a nice enclosure. Right now it's sitting in an open-top MDF box I hacked up
- Ashwin
Heatsinking chassis
Tarun
With an amp of this power rating, a separate Al extrusion heatsink may not be needed. If you have a chassis which is black aluminium, powder-coated, you can mount the chips on the side walls or floor of the chassis. You can go upto about 100W Class B amps (total rating across all channels) this way, for domestic use, according to one rule of thumb.ashwin said:
Tarun
Well i can tell u my experiences about the TDA20xx
2030 cant deliver any power, so u need a high sensitivity speaker to go with it.( i guess it delivers around 12W rms into 8ohms)
2040 can deliver upt0 around 21W into 8ohms.
THD is within limits on both the chips..!
These devices look descent for low power applications, especially pc speakers and all...but dont use them for anything bigger, unless as the mid or high section amplifiers in an active xo. They have huge dissipations and localised heat takes its toll if a good heatsink is not employed....The amp has a nasty protection circuit, which actually generates weird crackles due to clipping when it justs gets active. The transition from safe operating to protect mode is not smooth.Hence there is a huge restriction on playing high dynamic range content. The chip has reliability problems. Oscillates badly. Drives 4 ohm loads with great difficulty. The sound is OK at low levels, but starts getting mushy as the level is increased, The refinement goes off, i guess it is something to do with the current delivering capability..which is restrictied to a mere 3-4amps peak, which once crossed yeilds nasty results.
I would rather reccomend the TDA1514 in place of these devices, They are much more controlled, but i am a bit skeptic about the output impedence of the device. I get a feeling that its a bit higher, resulting in a low damping factor.
(Probably some one experienced can throw some light on this..!)
But the chip is good, well designed/built and the in built protection mechanisms are also good. I think the performance is fractionally improved if u get rid of the bootstrap circuit, at the expense of available power, which drops marginally.
ajju
Re: Heatsinking chassis
Actually, my original idea was to put it in a nice retro looking wooden enclosure, that's why the separate heatsink. Now it seems to be too much trouble for a measly gainclone 😉
- Ashwin
tcpip said:
Actually, my original idea was to put it in a nice retro looking wooden enclosure, that's why the separate heatsink. Now it seems to be too much trouble for a measly gainclone 😉
- Ashwin
Isn't this too large a pair of caps for the Gainclones? I thought NatSemi suggests something like 1000uF per rail for even their bigger amp chips. Just curious... specially considering that these caps are some of the most expensive components in your amp. 🙂ashwin said:... Power supply : Rs. 350 for a xformer (15-0-15, 5A for 3 amps, single amp should be much less), Rs 190 each for two 10,000uF 70V caps
tcpip said:
Sorry Tarun, but there was no reason whatsoever for my doing this 😀 I just wanted to take no chances, what with some of the guys on the chip amps forum putting humungous caps on the supply. I did try with and without these big caps, but it was really hard to tell the difference because I couldn't tell whether the sound was really better or whether it was something psychological. So since I'd already bought them, I let them stay. But I do suspect that the difference, if any, would be inaudible to my ears.
- Ashwin
🙂
true..Its called "Experimenter Expectancy syndrome" 😀
I would recomend good quality bulky caps for the power rails.
just enough to produce acceptable ripple on the power rails...Laws of dimnishing returns sets in soon after...! And from then on all that governs the size of the cap is its price tag.😉
Also along with these bulky caps it would be a nice idea to parallel caps approximately 10% , 1%, .1% there values. This is recomended to reduce the parasitics and to lower the effective ESR of huge caps. Huge electrolytes have parasitic inductance associated with it. The bulkier the cap the more prominent the value of the parasitic. This has the effect of producing higher supply impedence at higher frequencies. Hence the small capacitors tend to nullify the effect. Even a low value non eleoctrylitic cap should be sufficient...say 1uf paralleling the Rails..!
ajju
For about six months, my main listening rig was based off of a bridged TDA2030 setup, 4 chips total. Only one volume pot (linear, not The assembly was P2P using off-the-shelf MFRs, polyester caps and each channel had a dedicated rectifier bridge and filter cap assembly (2200 uF/ch - yes, 2200). Lots of PS decoupling and a lenient Zobel (100 ohm/0.1 cap). A simple EI 12V which was jury rigged to get a higher rail and 21 volts DC is what I finally settled at. The limit is 22 volts, but each chip is 18 bucks so what the hey. The project was not meant as a piece of quality audio gear, but to sharpen my soldering skills and revive the DIY enthu.
Well, it revived it so well I did not build anything at all in the next six months and I managed to accumulate a collection of chipamps (not th 3875, did not attract me). I was using a NAD c521i as the source and my Jamo E470 (91dB+) as speakers. I was pleasantly surprised at the sound quality. Yes at its limits it did start getting nasty, but provided you were reasonable about it, it sounded infinitely better than my NEC receiver (itself no slouch) and a little bit better than my Harman Kardon 665. In the end I had to move back to the Harman because it could not keep up with my demands - I like a very high volume on clasical and jazz, and the 2030 wasn't able to keep pace with the transients.
In short, the top end was very detailed, without even the slightest trace of harshness and sibilance. The midbass was a little weak, but accurate (again, I think our preference for fluffed-up midbass comes from years of listening to minicompos), and the low end was just fantastic, tasty, tight and accurate! Again, I was pushing these puppies to the limit with very hot rails and into a terrible load (the E470s are 4 ohms, so 2 ohms per amplifier) so that may have something to do with it. But yes, after about 80-85% volume it was getting a little edgy, and was unlistenable after 90%.
I am now starting on LM4780 chipamp build for my monitoring system. Will not have the 2030 on hand, but I remember their sound pretty well. Comparison will not be fair as the 4780 is 60 w/ch, different circuity, different supply, etc. Also I will not be pushing it too hard, the monitors will be fairly sensitive and used in nearfield, so will not need too much volume. I understand the 4780s also sound pretty good and have a litle headroom over the 3875s et al. Thermal management may be an issue, not something that can't be worked within.
Well, it revived it so well I did not build anything at all in the next six months and I managed to accumulate a collection of chipamps (not th 3875, did not attract me). I was using a NAD c521i as the source and my Jamo E470 (91dB+) as speakers. I was pleasantly surprised at the sound quality. Yes at its limits it did start getting nasty, but provided you were reasonable about it, it sounded infinitely better than my NEC receiver (itself no slouch) and a little bit better than my Harman Kardon 665. In the end I had to move back to the Harman because it could not keep up with my demands - I like a very high volume on clasical and jazz, and the 2030 wasn't able to keep pace with the transients.
In short, the top end was very detailed, without even the slightest trace of harshness and sibilance. The midbass was a little weak, but accurate (again, I think our preference for fluffed-up midbass comes from years of listening to minicompos), and the low end was just fantastic, tasty, tight and accurate! Again, I was pushing these puppies to the limit with very hot rails and into a terrible load (the E470s are 4 ohms, so 2 ohms per amplifier) so that may have something to do with it. But yes, after about 80-85% volume it was getting a little edgy, and was unlistenable after 90%.
I am now starting on LM4780 chipamp build for my monitoring system. Will not have the 2030 on hand, but I remember their sound pretty well. Comparison will not be fair as the 4780 is 60 w/ch, different circuity, different supply, etc. Also I will not be pushing it too hard, the monitors will be fairly sensitive and used in nearfield, so will not need too much volume. I understand the 4780s also sound pretty good and have a litle headroom over the 3875s et al. Thermal management may be an issue, not something that can't be worked within.
ajju said:
Great Job!
Tarun
Excellent work there with your PCB and the amp Heatsink. Is your P03 amp also getting the same treatment?
Just a small nitpick. You have mentioned drilling and taping the Heatsink to tie down the output devices. But I think the tap holes will become loose over a period of time because constant expansion and contraction of the heat sink. I don't know though how much heat your amp dissipates. Is it a Class A design?
You already have most of your amp chassis. You now only need a Faceplate and a back plate. Of-course top and bottom covers too. Currently, I'm building a new tube pre-amp. I'm departing from wood to an all aluminium enclosure. Even the tubes will be inside the chassis. I have give lot of thought. Using shaft couplings for volume/input selectors and completely shielded section within the chassis. The side panels will be 15mm AL and the front will be 3mm AL. Brushed finished and cadmium plated. Bronze feet. Idea is to solid, well-damped chassis (it will also have a phono section) with soft materials.
Roadkill:
I doubt your grandpa's radio will have 2 x EL34. In that config you are looking at around 35 watts out of the radio.
Secondly, BEL never made any octal valves. So if they have 8 pins then probably you are having a 6V6 (quite possible in a radio). Also, is it a stereo radio? Philips Maestro was a stereo radio with EL84 Class A output stage. One hell of a stunner! If you can lay your hands one then you are looking at a quick and easy Valve amp for your self. Old radio shops may have some.
On RS India.
Must thank Tarun for showing us this one. What he has posted earlier in the thread quite right. You must order intelligently to benefit from their mindbogling range. I've just rcvd my first lot of goods from them. Rifa caps, MFR's, lap cable, RCA jacks and Sockets, Panasonic low ESR elco, Ampohm coupling caps, silver alloy solder, Greyhil rotary switch, Alps pot and many more. All for around 12k. Worth it.
They have some really nice things at very cost effective prices. Small things like cable ties, spacers, clips, etc. SSM is around 1 box or so. Maybe we can do a group buy cause one box of such small items will last more than one lifetime for a guy like me 🙂
Tarun
Excellent work there with your PCB and the amp Heatsink. Is your P03 amp also getting the same treatment?
Just a small nitpick. You have mentioned drilling and taping the Heatsink to tie down the output devices. But I think the tap holes will become loose over a period of time because constant expansion and contraction of the heat sink. I don't know though how much heat your amp dissipates. Is it a Class A design?
You already have most of your amp chassis. You now only need a Faceplate and a back plate. Of-course top and bottom covers too. Currently, I'm building a new tube pre-amp. I'm departing from wood to an all aluminium enclosure. Even the tubes will be inside the chassis. I have give lot of thought. Using shaft couplings for volume/input selectors and completely shielded section within the chassis. The side panels will be 15mm AL and the front will be 3mm AL. Brushed finished and cadmium plated. Bronze feet. Idea is to solid, well-damped chassis (it will also have a phono section) with soft materials.
Roadkill:
I doubt your grandpa's radio will have 2 x EL34. In that config you are looking at around 35 watts out of the radio.
Secondly, BEL never made any octal valves. So if they have 8 pins then probably you are having a 6V6 (quite possible in a radio). Also, is it a stereo radio? Philips Maestro was a stereo radio with EL84 Class A output stage. One hell of a stunner! If you can lay your hands one then you are looking at a quick and easy Valve amp for your self. Old radio shops may have some.
On RS India.
Must thank Tarun for showing us this one. What he has posted earlier in the thread quite right. You must order intelligently to benefit from their mindbogling range. I've just rcvd my first lot of goods from them. Rifa caps, MFR's, lap cable, RCA jacks and Sockets, Panasonic low ESR elco, Ampohm coupling caps, silver alloy solder, Greyhil rotary switch, Alps pot and many more. All for around 12k. Worth it.
They have some really nice things at very cost effective prices. Small things like cable ties, spacers, clips, etc. SSM is around 1 box or so. Maybe we can do a group buy cause one box of such small items will last more than one lifetime for a guy like me 🙂
Hi Ashok
FYI my new Transcendent tube preamp has a brushed aluminium body and front face plate, with the 12AUs being inside the enclosure. The gauge is quite thin, but its adequately rigid. I will send you details after I check the specs, if they have specd the enclsoure panel out.
There are enough ventilation vents on either side as well as on top. The bottom, front and rear are part of one sheet, bent ina "U " shape to form the rear and front, while the top and sides are another"U" shaped piece. There is an additional face plate with the lettering which is screwed to the front.
I have been doing some limited listening these past few days after I got it up and running and I find that the top gets a little warm after some time. The small 12AU7 tubes dont glow very much-unlike my EL 34s.
What did the Alps pot cost-is it a stepped one?
Rgds
George
FYI my new Transcendent tube preamp has a brushed aluminium body and front face plate, with the 12AUs being inside the enclosure. The gauge is quite thin, but its adequately rigid. I will send you details after I check the specs, if they have specd the enclsoure panel out.
There are enough ventilation vents on either side as well as on top. The bottom, front and rear are part of one sheet, bent ina "U " shape to form the rear and front, while the top and sides are another"U" shaped piece. There is an additional face plate with the lettering which is screwed to the front.
I have been doing some limited listening these past few days after I got it up and running and I find that the top gets a little warm after some time. The small 12AU7 tubes dont glow very much-unlike my EL 34s.
What did the Alps pot cost-is it a stepped one?
Rgds
George
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