Folks - I decided to sell my amp. Make me an offer!
https://www.diyaudio.com/community/threads/premium-aca-tungsten-mods-for-sale.408259/#post-7577530
https://www.diyaudio.com/community/threads/premium-aca-tungsten-mods-for-sale.408259/#post-7577530
With regards to the list of components that Rob proposed in #1419:
I have come to prefer the Vishay CMF55 series of 1/4W, 1% metal film resistors for general use in my hand made amplifiers.
Example p/n would be CMF551K2100FHEB for the 1.2k component needed at R9 to support the Vgs needed at Q1.
Another common p/n would be CMF551K0000FHEA used at a couple locations.
Fearless Amp Builders who wish to try higher supply voltages will need to find a larger chassis to house their creation.
The CCF60 or RN60 sized parts are a tight squeeze in the ACA boards. I don't normally use these unless extra power dissipation is required.
When one is starting with a new ACA build, I encourage relative novices to buy the complete Amp Camp Amp kit from the diyAudio store. This is a complete kit which, along with the excellent build guide by 6L6, makes it much easier to have a successful first build.
I have come to prefer the Vishay CMF55 series of 1/4W, 1% metal film resistors for general use in my hand made amplifiers.
Example p/n would be CMF551K2100FHEB for the 1.2k component needed at R9 to support the Vgs needed at Q1.
Another common p/n would be CMF551K0000FHEA used at a couple locations.
Fearless Amp Builders who wish to try higher supply voltages will need to find a larger chassis to house their creation.
The CCF60 or RN60 sized parts are a tight squeeze in the ACA boards. I don't normally use these unless extra power dissipation is required.
When one is starting with a new ACA build, I encourage relative novices to buy the complete Amp Camp Amp kit from the diyAudio store. This is a complete kit which, along with the excellent build guide by 6L6, makes it much easier to have a successful first build.
Hopefully I will receive a pair of ACA 1.8 (prebuilt) tomorrow. They will be used with an active horn speaker, specifically from 600Hz to 3500hz (faital HF1460 in a multicell horn) and from 3500 and up (Faital hf108 in a Karlson tube).
I will try them stock first, and if it sounds good I will try some mods.
Since it is easy to adjust the level of NFB, I think that can be a fun experiment. Compression drivers can benefit from current drive, but I fear that the gain will be excessive with no feedback resistor what so ever. Noise is a big issue with 109dB speakers, and I guess such a simple amplifier will have excessive distortion with no feedback. The crossover is DSP, so tonal changes because of low damping are easily corrected. Does anybody have experience with this type of use, and have found the magic feedback level?
I will try them stock first, and if it sounds good I will try some mods.
Since it is easy to adjust the level of NFB, I think that can be a fun experiment. Compression drivers can benefit from current drive, but I fear that the gain will be excessive with no feedback resistor what so ever. Noise is a big issue with 109dB speakers, and I guess such a simple amplifier will have excessive distortion with no feedback. The crossover is DSP, so tonal changes because of low damping are easily corrected. Does anybody have experience with this type of use, and have found the magic feedback level?
That sounds like a good explanation. I have come to prefer the IRFP140 at Q2, though others have used the now rare FQH44N10.
For Q1 I recommend the IXTQ75N10P as a readily available part. Again, the FQH44N10 works here as well if one already has a stash.
A clean linear power supply is of course very important as well. I like the Antek AS-3224 with separate CRCRC or CRCLC filtration for each channel. Final voltage at the Drain of Q2 is just under 30V; Drain voltage at Q1 is about 15.5V.
For Q1 I recommend the IXTQ75N10P as a readily available part. Again, the FQH44N10 works here as well if one already has a stash.
A clean linear power supply is of course very important as well. I like the Antek AS-3224 with separate CRCRC or CRCLC filtration for each channel. Final voltage at the Drain of Q2 is just under 30V; Drain voltage at Q1 is about 15.5V.
So glad that I ordered some extra FQH44N10 while they were still around. I think that the 140 in Q2 sounds a little clearer and more extended whilthe FQh there sounds a little fuller.
Everything is running great with dual mono 36v meanwell supplies. I am still wondering if it is worth learning how to and build a good linear power supply and putting in a bigger chassis with more heatsink. I'd also be interested in building one of the F4, F5, F6 kits but it seems those have been out of stock forever.
Everything is running great with dual mono 36v meanwell supplies. I am still wondering if it is worth learning how to and build a good linear power supply and putting in a bigger chassis with more heatsink. I'd also be interested in building one of the F4, F5, F6 kits but it seems those have been out of stock forever.
Well, the F5m may be available in the store one of these days.. 
It is certainly worthwhile to build one of the 25W class amps. They have different topologies and different sounds. I happen to really like the models with a little iron in their signal path; so M2x and F6. The Aleph J is special and worth building.
The ACA as described here is more than the low power starter amp that was originally introduced. Its sound is single-ended Class A, and bridges the gap between a starter and one of the First Watt models. It is also meant for more experienced builders.
It is certainly worthwhile to build one of the 25W class amps. They have different topologies and different sounds. I happen to really like the models with a little iron in their signal path; so M2x and F6. The Aleph J is special and worth building.
The ACA as described here is more than the low power starter amp that was originally introduced. Its sound is single-ended Class A, and bridges the gap between a starter and one of the First Watt models. It is also meant for more experienced builders.
For sure, I listen to mine with all of the mods and at 36v everyday, and it is so much different and better than the stock version, I think about building something like an Elekit Tu8600 or 8900 but with the tubes things get so expensive. The F6 kit is the one that really intrigues me and although my Forte I's run beautifully off the modified ACA I'd like to hear a desing like this with more power.
Hi,
I have two ACA kits coming the end of this week. I will be using them in bridged mono mode with a pair of ZU DW6 speakers at 95db. I am interested in the Tungsten mods. I will be using the stock 24 volts SMPS that comes with the kits for now. I have a parts order from Mouser ready to go but have questions before I place that order.
Which mosfet for Q1 and Q2 are better, the IRFP048 or IRF140's? Can either one be used without matching ?
Is the addition of r16 only for using a higher supply voltage ?
I had trouble finding a .5 ohm 3W resistor for R4. I was able to find a 2 ohm 2W 5% resistor though tp use in parallel with R4. Is that close enough tolerance ?
Seems the Nichicon KG series is now obsolete and hard to find ? I substituted with Nichicon UKA series audio grade cap ?
After all the mods are made does the bias voltage still get set at 12vdc per the guide ?
Are the heatsinks on the standard ACA kits adequate if the supply voltages are increased ?
Thanks,
Joe
I have two ACA kits coming the end of this week. I will be using them in bridged mono mode with a pair of ZU DW6 speakers at 95db. I am interested in the Tungsten mods. I will be using the stock 24 volts SMPS that comes with the kits for now. I have a parts order from Mouser ready to go but have questions before I place that order.
Which mosfet for Q1 and Q2 are better, the IRFP048 or IRF140's? Can either one be used without matching ?
Is the addition of r16 only for using a higher supply voltage ?
I had trouble finding a .5 ohm 3W resistor for R4. I was able to find a 2 ohm 2W 5% resistor though tp use in parallel with R4. Is that close enough tolerance ?
Seems the Nichicon KG series is now obsolete and hard to find ? I substituted with Nichicon UKA series audio grade cap ?
After all the mods are made does the bias voltage still get set at 12vdc per the guide ?
Are the heatsinks on the standard ACA kits adequate if the supply voltages are increased ?
Thanks,
Joe
For Q1, the best of the available parts is the IXTQ75N10P.
For Q2, I prefer the IRFP140, though the IRFP048 would also work.
R16 helps filter the voltage at the drain of Q3.
The best voltage to set at the Drain of Q1 is half the supply voltage plus 0.5V.
Each channel should have a separate power supply, whether that is a brick SMPS or separate power transformer winding + CRC(RC) filter.
Let us know how it works for you.
For Q2, I prefer the IRFP140, though the IRFP048 would also work.
R16 helps filter the voltage at the drain of Q3.
The best voltage to set at the Drain of Q1 is half the supply voltage plus 0.5V.
Each channel should have a separate power supply, whether that is a brick SMPS or separate power transformer winding + CRC(RC) filter.
Let us know how it works for you.
Tungsten, thanks so much for your quick reply !
I saw in one of your posts talking about needing additional 1 volt Vgs for the IXTQ75N10P. Do I need to make other resistor tweaks to get the IXTQ75N10P/IRFP048 combo working with the stock 24 volt SMPS supply ? Are these mosfets drop in replacements for the stock mosfets ?
Thanks,
Joe
I saw in one of your posts talking about needing additional 1 volt Vgs for the IXTQ75N10P. Do I need to make other resistor tweaks to get the IXTQ75N10P/IRFP048 combo working with the stock 24 volt SMPS supply ? Are these mosfets drop in replacements for the stock mosfets ?
Thanks,
Joe
When I switched to the IRFP140 and higher transconductance FETs (e.g. FQH44N10 or IXTQ75N10P) powered by a linear supply, I no longer found it necessary to use either of the bridged mono configurations. Each ACA is a standalone stereo amp. The 30V supply afforded by using a 300VA, 24V transformer is enough to drive moderately efficient speakers. The bias current of 1.6A is set by the 3W power resistors. This is my main recommendation. If the speakers allow for bi-amping, then it might be woth building a pair of stereo ampifiers and wiring them separately according to speaker manufacturer's recommendation.
Given a higher voltage supply and greater bias current, a larger chassis is warranted. The Mini Dissipante 3U x 300 is a good choice. That will have plenty of room inside for two sets of filter capacitors plus the power transformer.
This type of build starts to look like one of the larger 25W amps. It can be done with point-to-point wiring or a pair of smaller PCU boards. The standard ACA PCBs will handle any of the TO-3P or TO-247 style packages, so there are lots of options.
Given a higher voltage supply and greater bias current, a larger chassis is warranted. The Mini Dissipante 3U x 300 is a good choice. That will have plenty of room inside for two sets of filter capacitors plus the power transformer.
This type of build starts to look like one of the larger 25W amps. It can be done with point-to-point wiring or a pair of smaller PCU boards. The standard ACA PCBs will handle any of the TO-3P or TO-247 style packages, so there are lots of options.
I will only be using the a 24 v SMPS for now. One per amp. Depending on how they sound with your mods I will upgrade the power supplies to dual mono linear supplies. But only 24 volts to keep within the heat dissipation capability of the stock chassis.
I assume that 1.6 amp bias current at 24 volt is doable in the stock chassis ?
I have efficient speakers and really do not need to push this amp that hard.
Running 1.5 watts per channel SET tube amp now with plenty of volume.
Joe
I assume that 1.6 amp bias current at 24 volt is doable in the stock chassis ?
I have efficient speakers and really do not need to push this amp that hard.
Running 1.5 watts per channel SET tube amp now with plenty of volume.
Joe
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One 24 volt 5A SMPS power brick per monoblock. The one that came with the kit. I may try surplus linear power supplies next to see if there is any improvement in sound quality. However, these amps sound very impressive !
I've also installed a 150K 1/4 watt resistor for R13 to dim the led's. They were way too bright at night.
My system consists of a pair of Zu DW 6 floor standing speakers at 95db/m. A Wiim pro plus streamer DAC. An old Sony CD transport using optical out into the Wiim. A Schiit Skoll phono pre and a vintage B&O Beogram 1602 turntable. DIY Mogami interconnect (W2893) cables and speaker (W3103) cables.
I've also installed a 150K 1/4 watt resistor for R13 to dim the led's. They were way too bright at night.
My system consists of a pair of Zu DW 6 floor standing speakers at 95db/m. A Wiim pro plus streamer DAC. An old Sony CD transport using optical out into the Wiim. A Schiit Skoll phono pre and a vintage B&O Beogram 1602 turntable. DIY Mogami interconnect (W2893) cables and speaker (W3103) cables.
Very cool, I haven't been on this thread for a while. I am running a single stereo ACA with all the mods with FQH44n10's at Q1 and Q2, and modded to run of dual 36v Meanwell power supplies. I need to move it into a big chassis but nothing has melted... yet. It sounds really amazing and is such a huge improvement over stock that it is pretty unbelievable. It scales up really well, and I keep upgrading the equipment around it.
My system is Klipsch Forte I's, braced and damped cabinets, modded crites crossovers, Adcom GFP-750 Preamp, Hagerman Trumpet MC Tube Phono, Vinyl Nirvana/Thorens TD 125 with Sorane TA-1 Tonearm and Hana SL cart.
My system is Klipsch Forte I's, braced and damped cabinets, modded crites crossovers, Adcom GFP-750 Preamp, Hagerman Trumpet MC Tube Phono, Vinyl Nirvana/Thorens TD 125 with Sorane TA-1 Tonearm and Hana SL cart.
I built an Elekit TU 8900, have to get back to troubleshooting it as it does not work, so take this for what its worth. My motivation was in part to try a 300B amplifier, they get great hype and I had not discovered this forum. Obviously I can't address sound but in terms of build and parts I am not impressed, perhaps the thing that jumps out the most to me is the apparent quality of the PCBs used vs. those for the Pass kits. Does this translate in to better sound, don't know but the Pass boards smack of quality. The other thing that I experienced was support from Victor, it seemed pretty half hearted and no where near support members on this board have offered, some such as @rayma helped w/ my 8900 more than Victor.
In the final analysis I feel that the 8900 may be an interesting experience it is not inexpensive, build quality is decent and support poor, I wouldn't do it again.