thx for your report. Funny how I was just looking at the design/gerber data yesterday.
6, failed components?
this design is dc coupled/servo'd, it could be something else other than U203,204!
consisting of per board, 2x LME49870(U203,204)
spec on these say 46V abs max, suggest +/-22V max. It is 250mW power unless you have a low z load.
good luck.
6, failed components?
this design is dc coupled/servo'd, it could be something else other than U203,204!
consisting of per board, 2x LME49870(U203,204)
spec on these say 46V abs max, suggest +/-22V max. It is 250mW power unless you have a low z load.
good luck.
Fault or Feature?!
Hi,
I’ve been using my HPS5.1 for some time now, with the input load set to 100 Ohms, gain at high, and have had no issues. I recently purchased a very low o/p MC cart which needs an SUT. The input load is 47K and the gain is set to low .when this is used.
If I now switch on the phono amp with the inputs disconnected or remove them when powered up, the DC servo will not stabilize continually swinging’s both positive and negative. It sometime stays a few volts negative which results in the feedback resistors getting too hot (which has damaged them and the pcb). It does this in both high and low gain settings and with the input load set to or above 1KOhm; settings lower than this are still OK. Both channels act in the same manner. Normally the DC servo stabilizes within a few second with the Head Amp output then < 2mVDC.
Realising now that it would be best practice to switch off the amp when changing input connections, is the behaviour I’m seeing a feature of the design with its low resistance feedback loop/high current/DC servo, coupled with the high input impedance I’m setting (noisier?) or do you think I have a fault?
Regards,
Hi,
I’ve been using my HPS5.1 for some time now, with the input load set to 100 Ohms, gain at high, and have had no issues. I recently purchased a very low o/p MC cart which needs an SUT. The input load is 47K and the gain is set to low .when this is used.
If I now switch on the phono amp with the inputs disconnected or remove them when powered up, the DC servo will not stabilize continually swinging’s both positive and negative. It sometime stays a few volts negative which results in the feedback resistors getting too hot (which has damaged them and the pcb). It does this in both high and low gain settings and with the input load set to or above 1KOhm; settings lower than this are still OK. Both channels act in the same manner. Normally the DC servo stabilizes within a few second with the Head Amp output then < 2mVDC.
Realising now that it would be best practice to switch off the amp when changing input connections, is the behaviour I’m seeing a feature of the design with its low resistance feedback loop/high current/DC servo, coupled with the high input impedance I’m setting (noisier?) or do you think I have a fault?
Regards,
Hi Karl,
I am still subscribed to this thread, not sure how many are keeping track, certainly not the creator it seems.
My first guess is that the circuit is oscillating with the transformer when it is being loaded with higher R? throwing the servo out of wack, need to check with a scope.
I guess lowering the SUT load damps out any oscillations.
So why not just use the lower R loading on the SUT?
What load does the SUT require per its spec?
What effects does having the SUT with lower input R do?
If you go back to the original setup
"I’ve been using my HPS5.1 for some time now, with the input load set to 100 Ohms, gain at high, and have had no issues"
Does it operate correctly?
Does HPS5.1 work okay with the new lower o/p MC cartridge used, without using the SUT? I assume that you used the SUT because the level is too low for you? Can you not make up the gain elsewhere?
Rick
I am still subscribed to this thread, not sure how many are keeping track, certainly not the creator it seems.
My first guess is that the circuit is oscillating with the transformer when it is being loaded with higher R? throwing the servo out of wack, need to check with a scope.
I guess lowering the SUT load damps out any oscillations.
So why not just use the lower R loading on the SUT?
What load does the SUT require per its spec?
What effects does having the SUT with lower input R do?
If you go back to the original setup
"I’ve been using my HPS5.1 for some time now, with the input load set to 100 Ohms, gain at high, and have had no issues"
Does it operate correctly?
Does HPS5.1 work okay with the new lower o/p MC cartridge used, without using the SUT? I assume that you used the SUT because the level is too low for you? Can you not make up the gain elsewhere?
Rick
Rick,
Thanks for taking the time to reply.
Yes, the amp still works correctly once the i/p load is lowered to 100 Ohm. It also does so if you select the lower load whilst the amp is on and unstable, the servo quickly does its job.
The SUT is designed for 47K load. It has a turns ratio of 1:70 which gives about 9.6 Ohm at the cartridge input.
Yes, I did initial use the cartridge without the SUT as the set up was giving horrendous hum issues - the SQ was rather lack luster though. Once cured (screened interconnect) I have kept the SUT in situ as the cartridge now performs as it should. The cartridge only gives 0.05mV o/p so the SUT is important.
Just to clarify, this instability only occurs when there is no input connected and the load is at or above 1K Ohm.
All the DC rails look OK on a DVM but I shall check them and a few other things on a scope.
Thanks for taking the time to reply.
Yes, the amp still works correctly once the i/p load is lowered to 100 Ohm. It also does so if you select the lower load whilst the amp is on and unstable, the servo quickly does its job.
The SUT is designed for 47K load. It has a turns ratio of 1:70 which gives about 9.6 Ohm at the cartridge input.
Yes, I did initial use the cartridge without the SUT as the set up was giving horrendous hum issues - the SQ was rather lack luster though. Once cured (screened interconnect) I have kept the SUT in situ as the cartridge now performs as it should. The cartridge only gives 0.05mV o/p so the SUT is important.
Just to clarify, this instability only occurs when there is no input connected and the load is at or above 1K Ohm.
All the DC rails look OK on a DVM but I shall check them and a few other things on a scope.
HPS 5.1 builders, how do you like sound quality reproduction of that phono preamp? I collected parts to build one.
need to check with a scope to see what is going on.
Thus it will not work with a normal MM cartridge using a std 47K load?
Did you test it initially under all input loads and gain?
So it has nothing to do with your new cartridge and transformer then!!
Thus it will not work with a normal MM cartridge using a std 47K load?
Did you test it initially under all input loads and gain?
Correct, it's the first time I have used the 47K i/p load and it seems likely that I did not test it with this load when first built (hindsight - how wonderful!) I did check and record certain voltages as well as the RIAA filter accuracy when first built but as it all appeared to work OK, with the load I'd set, was keen to get using it!
I don't own a MM cartridge, the reason I built the HPS5.1 was because of it performance with the MC type (although it performance the low gain mode is no less impressive).
I assume from your answers that your amp works correctly, so I am likely to have something wrong with mine.
Sorry Karl, I do not have one. Just following an interesting design and thread.
That is a possibility. It could be a marginal design. It could be the parts you used. it could be assembly errors replicated on both assemblies. I can not say which one it is.
It is not like it does not work, but it does not work for all that it was intended for or at least your version does not.
Would be nice to hear from others that have working units to compare against. The documentation is limited from what I saw, no BOM, no silkscreen/assembly drawings. I do wonder how folks manged to figure it all out.
I know the designer did not spare any expense. He could have Idss matched all the jfets, made no note of it. No history.
How well was it tested by the designer = who knows?
It is stated that the design is prone to oscillations, that is why he used all those input inductors!
I guess you are going to have to do some debugging.
Could verify a few things like can you measure the input load R setting, is it actually what it is supposed to be? supposed to be 47K by default, R208.
Figure out if it is oscillating first. maybe focus on the comp cap, C201
Are the comp caps the right ones, values,type. C201. R206/C206 are interesting.
He shows in his sim drawing, that C201 is 47p, i'd try that, put another 22p on top of the other one,22p?
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Hello.
I can confirm this behavior when the amp's input impedance is high.In this mode, after power-on or at any gain change the outputs will swing violently from one power rail to the other for a few seconds until they will begin to sort of stabilize to swings of only a few hundred milivolt amplitudes. So the amp will always oscillate at low frequencies, somewhere below 15Hz. This is a consequence of the DC-coupling and DC- servo. I am currently moving the amp from one small enclosure to a bigger one because of temperature dissipation problems so after rebuilding it i plan on doing some phase margin measurements. I also plan on building a microcontroller PCB that disconnects the input at power-on or gain change. I will post progress here.
If this amp's behavior is a problem to you, you should make sure you use the HFP filter to protect your speakers and if you want you could try to add a few uF of film decoupling capacitor between the first linear amp stage and the filter stage.
Another question that was posted by a member was about the amp's sound quality. I have never heard a more detailed phono amp. Sound is crystal clear, no comparison to those muddy op-amp based amps.
I can confirm this behavior when the amp's input impedance is high.In this mode, after power-on or at any gain change the outputs will swing violently from one power rail to the other for a few seconds until they will begin to sort of stabilize to swings of only a few hundred milivolt amplitudes. So the amp will always oscillate at low frequencies, somewhere below 15Hz. This is a consequence of the DC-coupling and DC- servo. I am currently moving the amp from one small enclosure to a bigger one because of temperature dissipation problems so after rebuilding it i plan on doing some phase margin measurements. I also plan on building a microcontroller PCB that disconnects the input at power-on or gain change. I will post progress here.
If this amp's behavior is a problem to you, you should make sure you use the HFP filter to protect your speakers and if you want you could try to add a few uF of film decoupling capacitor between the first linear amp stage and the filter stage.
Another question that was posted by a member was about the amp's sound quality. I have never heard a more detailed phono amp. Sound is crystal clear, no comparison to those muddy op-amp based amps.
RIAA part of this phono preamp is standard op-amp based circuit powered by humble IC regulators.Not high-end approach.No discrete circuit, no shunt or super regulators here. Headamp part is more exotic and can be used in combination with RIAA stages of others preamps, like Xono,Borbely etc.
OP134 has a slew rate of 20V/us while the OPA211 is around 27V/uS. I believe the DC servo op-amp should be faster than the other op-amp.
Read the explanation on Low Noise Design Schematics on the reasoning why such a regulator implementation was used.
Yes the supplies are 'basic' (LM317/337) although there is a need to deliver upto .8 amp into the headamp whilst it stabilizes and if this is limited the DC loop will keep hunting (and damage the feedback resistors - don't ask!)
I have actually removed the IC Regulators from the pcb and built two Pre Tracking Regulator modules (one for each channel) with a capacitor multiplier on the i/p. The info/inspiration for the design came from here - Using 3-pin regulators off-piste: part 4.
I believe earlier designs in the HPS series did use more sophisticated regulators (Jung and shunt) but there requirements were different to the 5.1
Yes, designer thinks that with high PSRR op-amps, using the highest performance regulators is a luxury.Walt Jung would not agree.
I am building my version at the moment and I have no OP 827. Is OPA 134 or TL 071 suitable for servo? It seems that this is not fully developed project.
I am building my version at the moment and I have no OP 827. Is OPA 134 or TL 071 suitable for servo? It seems that this is not fully developed project.